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lil-jinx
Samba Member
Joined: August 14, 2013
Posts: 1565
Location: New Brunswick,Canada
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 Posted: Sun Mar 30, 2025 2:15 pm Post subject: Re: Brakes heating up and seizing after replacing calipers |
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Bentley says the MC internals are the same on both brake types,
your brake line nuts appear to be bottoming out on the nut heads ,may be just the angle ,but make sure they are not .
the brake line ports in a early MC are bigger than a booster MC ,they are made a for a residual valve ,a brake line fitting would be sloppy or very loose,( I don't know how much bigger the ports are,)so check the fittings on the mc,maybe Skilz is correct and the bigger ports are causing the line nut to bottom,if they are not bottoming out ,and not leaking,you should be good.
others will know more on this then me.
if you had residual valves they would be between the brake line fitting and the MC port ,they look like a extra fitting/ adaptor
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1974 Bay Westfalia. she likes to be called Ethel.
1968 Dune Buggy sold dec 2024
1974 parts bus
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 23104
Location: Oklahoma City
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| Posted: Sun Mar 30, 2025 2:42 pm Post subject: Re: Brakes heating up and seizing after replacing calipers |
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| jtauxe wrote: |
| Abscate wrote: |
| I bet that wrong part has a residual pressure setup that is killing you here |
What wrong part, specifically?
Now - Here's where I am:
• no "shims" on the MC. It is firmly bolted to the booster.
• without the shims, the front calipers are locked tight
• this is all with the clevis in a neutral state: no forces fore or aft |
So....let's be super clear:
1. No shims....check!
2. Pushrod/clevis adjusted neutral...no tension anywhere right? Check!
3. And....the calipers are locked??????
Questions:
1. did the calipers lock just because you pulled out the shims and tightened down the nuts.....or.....did you get in after tightening down the nuts and then pump up the brakes?
If they locked up just because you removed the shims and locked the nuts....we have seen you do this a few pages back.
2. Is the pedal pulled back with the bungee cord?
What I would like to see/be sure of.....is that the pedal is pulled back with the bungee cord + the clevis adjusted neutral like you have already stated + the shims removed and the MC bolted up tight and normal + release residual fluid pressure with the bleeder valve at a caliper +.......get in and pump up the brakes.
If the calipers lock up again with all of this done......it will tell you that the pedal return spring has nothing (at least nothing significant) to do with the issue.
The problem will be the booster or MC. Ray |
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lil-jinx
Samba Member
Joined: August 14, 2013
Posts: 1565
Location: New Brunswick,Canada
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| Posted: Sun Mar 30, 2025 2:59 pm Post subject: Re: Brakes heating up and seizing after replacing calipers |
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front rod adjusted , check
mc bolted on ,check
brakes locked,check
back off the mc install 1 mm spacer,
brakes still locked
install 2 mm spacer
repeat untill the brakes don,t lock,
then measure the shim pack and adjust the rod between the booster and the mc to match the shim pack thickness,
you may only need a mm or two
_________________
https://www.thesamba.com/vw/forum/viewtopic.php?t=620186
https://www.thesamba.com/vw/forum/viewtopic.php?t=668799
1974 Bay Westfalia. she likes to be called Ethel.
1968 Dune Buggy sold dec 2024
1974 parts bus
A smart man learns from his mistakes,a very smart man learns from other's mistakes. |
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jtauxe 
Samba Member
Joined: September 30, 2004
Posts: 5967
Location: Los Alamos, New Mexico, USA
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| Posted: Sun Mar 30, 2025 3:12 pm Post subject: Re: Brakes heating up and seizing after replacing calipers |
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| lil-jinx wrote: |
Bentley says the MC internals are the same on both brake types,
your brake line nuts appear to be bottoming out on the nut heads ,may be just the angle ,but make sure they are not .
the brake line ports in a early MC are bigger than a booster MC ,they are made a for a residual valve ,a brake line fitting would be sloppy or very loose,( I don't know how much bigger the ports are,)so check the fittings on the mc,maybe Skilz is correct and the bigger ports are causing the line nut to bottom,if they are not bottoming out ,and not leaking,you should be good.
others will know more on this then me.
if you had residual valves they would be between the brake line fitting and the MC port ,they look like a extra fitting/ adaptor |
The brake line fittings are snug and no sign of trouble there. As is typical, I had to get the nuts aligned "just so" to get them to go in. No "bottoming out" that I can tell.
| raygreenwood wrote: |
| jtauxe wrote: |
Now - Here's where I am:
• no "shims" on the MC. It is firmly bolted to the booster.
• without the shims, the front calipers are locked tight
• this is all with the clevis in a neutral state: no forces fore or aft |
So....let's be super clear:
1. No shims....check!
2. Pushrod/clevis adjusted neutral...no tension anywhere right? Check!
3. And....the calipers are locked??????
Questions:
1. did the calipers lock just because you pulled out the shims and tightened down the nuts.....or.....did you get in after tightening down the nuts and then pump up the brakes?
If they locked up just because you removed the shims and locked the nuts....we have seen you do this a few pages back.
2. Is the pedal pulled back with the bungee cord?
What I would like to see/be sure of.....is that the pedal is pulled back with the bungee cord + the clevis adjusted neutral like you have already stated + the shims removed and the MC bolted up tight and normal + release residual fluid pressure with the bleeder valve at a caliper +.......get in and pump up the brakes.
If the calipers lock up again with all of this done......it will tell you that the pedal return spring has nothing (at least nothing significant) to do with the issue.
The problem will be the booster or MC. Ray |
Answers:
1. Yes, the calipers lock just because I pulled out the shims and tightened down the nuts.
2. The pedal is pulled up with the bungee cord in the cab.
With the pedal pulled up by the bungee cord + the clevis adjusted neutral + the shims removed and the MC bolted up tight and normal, I released residual fluid pressure with the bleeder valve at a caliper
[After relieving fluid pressure now the wheels rotate freely.]
+ got in and pumped up the brakes (careful to allow the pedal to return to its full up position between pumps) ... and...
After 10 pedal pumps I could feel the front wheels start to resist.
After 20, they resisted more.
| lil-jinx wrote: |
front rod adjusted , check
mc bolted on ,check
brakes locked,check
back off the mc install 1 mm spacer,
brakes still locked
install 2 mm spacer
repeat untill the brakes don,t lock,
then measure the shim pack and adjust the rod between the booster and the mc to match the shim pack thickness,
you may only need a mm or two |
Done, and the resulting magic thickness is 3 mm (1/8 inch) as seen in the photo.
_________________
John
"Travelling in a fried-out Kombi, on a hippie trail, head full of zombie..." - Colin Hay and Ron Strykert
http://vw.tauxe.net
1969 Transporter, 1971 Westfalia, 1976, 1977, 1976, 1977, 1971, 1973, 1977 Westfalias,
1979 Champagne Sunroof, 1974 Westfalia Automatic, 1979 Transporter, 1972 Sportsmobile, 1973 Transporter Wild Westerner, 1974 Westfalia parts bus, 1975 Mexican single cab *FOR SALE*, 1978 Irish 4-door double cab RHD
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SGKent
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Joined: October 30, 2007
Posts: 42412
Location: at the beach
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| Posted: Sun Mar 30, 2025 3:29 pm Post subject: Re: Brakes heating up and seizing after replacing calipers |
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John - if you need a 3mm shim on the master one of two things is happening - either the booster is fubar or your adjustment is fubar. The bar gets adjusted so that the master has zero pressure on it. If you need to add a 3 mm shim then the rod has 3mm of preload in your adjustment, or the booster is broken inside and not releasing to the neutral position.
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lil-jinx
Samba Member
Joined: August 14, 2013
Posts: 1565
Location: New Brunswick,Canada
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| Posted: Sun Mar 30, 2025 4:41 pm Post subject: Re: Brakes heating up and seizing after replacing calipers |
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3 mm you may be able to reduce that by a mm or two at the rod ,by removing the spacers under the tip ,has was shown earlier in this thread,
if you can,t shorten the rod ,a 3 mm spacer would not be a concern ,
I would not condemn the booster for this just yet,if i was concerned about the booster,I would test fit the old mc and see if it also is tight,if yes then i would look toward the booster.
a comparison of the 2 MC rod socket depth to flange,they should be the same,my bet is that the new one is shorter
in a link that i posted i think they had a measure of how far the rod poked out of the booster ,
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https://www.thesamba.com/vw/forum/viewtopic.php?t=620186
https://www.thesamba.com/vw/forum/viewtopic.php?t=668799
1974 Bay Westfalia. she likes to be called Ethel.
1968 Dune Buggy sold dec 2024
1974 parts bus
A smart man learns from his mistakes,a very smart man learns from other's mistakes. |
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lil-jinx
Samba Member
Joined: August 14, 2013
Posts: 1565
Location: New Brunswick,Canada
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 23104
Location: Oklahoma City
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| Posted: Sun Mar 30, 2025 5:33 pm Post subject: Re: Brakes heating up and seizing after replacing calipers |
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| jtauxe wrote: |
| lil-jinx wrote: |
Bentley says the MC internals are the same on both brake types,
your brake line nuts appear to be bottoming out on the nut heads ,may be just the angle ,but make sure they are not .
the brake line ports in a early MC are bigger than a booster MC ,they are made a for a residual valve ,a brake line fitting would be sloppy or very loose,( I don't know how much bigger the ports are,)so check the fittings on the mc,maybe Skilz is correct and the bigger ports are causing the line nut to bottom,if they are not bottoming out ,and not leaking,you should be good.
others will know more on this then me.
if you had residual valves they would be between the brake line fitting and the MC port ,they look like a extra fitting/ adaptor |
The brake line fittings are snug and no sign of trouble there. As is typical, I had to get the nuts aligned "just so" to get them to go in. No "bottoming out" that I can tell.
| raygreenwood wrote: |
| jtauxe wrote: |
Now - Here's where I am:
• no "shims" on the MC. It is firmly bolted to the booster.
• without the shims, the front calipers are locked tight
• this is all with the clevis in a neutral state: no forces fore or aft |
So....let's be super clear:
1. No shims....check!
2. Pushrod/clevis adjusted neutral...no tension anywhere right? Check!
3. And....the calipers are locked??????
Questions:
1. did the calipers lock just because you pulled out the shims and tightened down the nuts.....or.....did you get in after tightening down the nuts and then pump up the brakes?
If they locked up just because you removed the shims and locked the nuts....we have seen you do this a few pages back.
2. Is the pedal pulled back with the bungee cord?
What I would like to see/be sure of.....is that the pedal is pulled back with the bungee cord + the clevis adjusted neutral like you have already stated + the shims removed and the MC bolted up tight and normal + release residual fluid pressure with the bleeder valve at a caliper +.......get in and pump up the brakes.
If the calipers lock up again with all of this done......it will tell you that the pedal return spring has nothing (at least nothing significant) to do with the issue.
The problem will be the booster or MC. Ray |
Answers:
1. Yes, the calipers lock just because I pulled out the shims and tightened down the nuts.
2. The pedal is pulled up with the bungee cord in the cab.
With the pedal pulled up by the bungee cord + the clevis adjusted neutral + the shims removed and the MC bolted up tight and normal, I released residual fluid pressure with the bleeder valve at a caliper
[After relieving fluid pressure now the wheels rotate freely.]
+ got in and pumped up the brakes (careful to allow the pedal to return to its full up position between pumps) ... and...
After 10 pedal pumps I could feel the front wheels start to resist.
After 20, they resisted more.
| lil-jinx wrote: |
front rod adjusted , check
mc bolted on ,check
brakes locked,check
back off the mc install 1 mm spacer,
brakes still locked
install 2 mm spacer
repeat untill the brakes don,t lock,
then measure the shim pack and adjust the rod between the booster and the mc to match the shim pack thickness,
you may only need a mm or two |
Done, and the resulting magic thickness is 3 mm (1/8 inch) as seen in the photo. |
So.....to be 100% clear.....after setting everything to normal (no shims and clevis adjusted with bungee cord installed and residual pressure relieved)...........after 20 pumps of the brakes...........your calipers started locking up again?
Did I sum that up correctly?
So, for the last 2-3 pages:
Lil-jinx thinks it could have been the bad pedal spring. I think that was a good hypothesis
Nitramrebrab72 thinks it's a good hypothesis and agrees that it could have been part of the problem all along.
SGKent agrees that it's not right and needs to be fixed and I agree and we both said it pages ago that the pedal needs to be up against the stop with some force.
But as I noted, I did not think that was the issue.....but the only way to be sure is to test it and get it out of the picture with a definite yes or no.
So.....I think you just did that. While you need a new spring.....that spring is NOT the issue.
You also have proven that with everything else normal (pedal against the stop, clevis and pedal pushrod adjusted properly).....you appear to have 3mm too much pushrod pressure on the master cylinder from the booster.
That's still a shit-ton.
Honing in on either the wrong master cylinder (or at the very least a master cylinder machined wrong....but two in a row....I doubt it).....or as SGKENT noted....your booster is fubar.
Ray |
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SGKent
Samba Member
Joined: October 30, 2007
Posts: 42412
Location: at the beach
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| Posted: Sun Mar 30, 2025 6:05 pm Post subject: Re: Brakes heating up and seizing after replacing calipers |
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John - bolt the mc down and pull the clevis pin. Hang the bar with a piece of wire or something. Are the brakes still locked? If yes, pull the bar forward 3/8" to a half inch and check again. If no, you are somehow missing the adjustment.
I will warn you that if you have any air in the brake lines, you may not be able to feel when the master cylinder engages.
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kreemoweet
Samba Member
Joined: March 13, 2008
Posts: 4089
Location: Seattle, WA
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| Posted: Sun Mar 30, 2025 6:24 pm Post subject: Re: Brakes heating up and seizing after replacing calipers |
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That new master cylinder that jtauxe is showing is what ATE is now providing for 71-79 bus, at least in some markets. It is what you get from many US parts ventdors
when you order m/c for 71-79 bus. It is made in China. It is certainly different from the original ATE m/c as VW provided. The Brazilian Varga m/c for 71-79 bus is also
different in many details from the original ATE one.
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Last edited by kreemoweet on Sun Mar 30, 2025 6:40 pm; edited 1 time in total |
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kreemoweet
Samba Member
Joined: March 13, 2008
Posts: 4089
Location: Seattle, WA
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| Posted: Sun Mar 30, 2025 6:39 pm Post subject: Re: Brakes heating up and seizing after replacing calipers |
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The front booster rod that connects to the pedal linkage has nothing to do with the m/c-booster interface.
They are NOT connected.
There is an intermediate "pushrod" internal to the booster, that has gaps at each end. It is only when pushing down the brake pedal and those 2 gaps close up, and then the gap between the rear booster pushrod and m/c closes up, that the brake pedal begins to activate the brakes.
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kreemoweet
Samba Member
Joined: March 13, 2008
Posts: 4089
Location: Seattle, WA
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| Posted: Sun Mar 30, 2025 6:45 pm Post subject: Re: Brakes heating up and seizing after replacing calipers |
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| SGKent wrote: |
| John - bolt the mc down and pull the clevis pin. Hang the bar with a piece of wire or something. Are the brakes still locked? If yes, pull the bar forward 3/8" to a half inch and check again. |
There is no "pull the bar forward", unless the booster is seriously broken. When not being pressed by the brake pedal/linkage, the whole booster internals should be as far forward as they ever get, and be on a hard stop of some sort.
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SGKent
Samba Member
Joined: October 30, 2007
Posts: 42412
Location: at the beach
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| Posted: Mon Mar 31, 2025 12:11 am Post subject: Re: Brakes heating up and seizing after replacing calipers |
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there is only one thing that John has to do to move this along. John I hope you are listening. With your bungee solution, step on the brakes until you feel pressure and drag, then disconnect the clevis and bar. Hang it with a wire or string etc., move it towards the front of the bus just a tiny bit - you don't want to pull it apart or tug on it, just make 100% sure that there is NO PRELOAD back towards the master cylinder. Then check the brakes to see if they are free.
If yes > then you need to carefully adjust the bar so it is not preloading the master cylinder. If you have air in the lines it will be hard to feel when the master is being pushed by the bar and rod.
If no > and there still is pressure and drag - then the master and booster are not compatible, or one is defective or machined differently than the originals. When the booster is at rest it should absolutely not put pressure on the master cylinder. VW designed it so the master and servo could be swapped without a hassle.
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lil-jinx
Samba Member
Joined: August 14, 2013
Posts: 1565
Location: New Brunswick,Canada
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| Posted: Mon Mar 31, 2025 5:41 am Post subject: Re: Brakes heating up and seizing after replacing calipers |
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raygreenwood ,where are you getting the idea of two faulty MC ,I said it often and you just seem to ignore it,so for the last time,
the problem started and was probably caused by a weak return spring.nothing to do with the orginal MC ,it was working fine,when jtauxe replace the mc he replaced a perfectly good mc with one that has a rod that is too long.a very common problem ,there are several threads of people having issues with replacement mc and a rod adjustment or shimming the mc solved there problem,heck even the great Tcash spoke of the need to shim them.
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https://www.thesamba.com/vw/forum/viewtopic.php?t=620186
https://www.thesamba.com/vw/forum/viewtopic.php?t=668799
1974 Bay Westfalia. she likes to be called Ethel.
1968 Dune Buggy sold dec 2024
1974 parts bus
A smart man learns from his mistakes,a very smart man learns from other's mistakes. |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 23104
Location: Oklahoma City
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| Posted: Mon Mar 31, 2025 5:59 am Post subject: Re: Brakes heating up and seizing after replacing calipers |
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| lil-jinx wrote: |
raygreenwood ,where are you getting the idea of two faulty MC ,I said it often and you just seem to ignore it,so for the last time,
the problem started and was probably caused by a weak return spring.nothing to do with the orginal MC ,it was working fine,when jtauxe replace the mc he replaced a perfectly good mc with one that has a rod that is too long.a very common problem ,there are several threads of people having issues with replacement mc and a rod adjustment or shimming the mc solved there problem,heck even the great Tcash spoke of the need to shim them. |
Where....in the fuck....did I ....ever.....say................there were two faulty master cylinders?
COPY IT ....POST IT....AND QUOTE IT.
I have not said once....in this entire thread.....that there are TWO faulty master cylinders. I do not even believe there is ONE faulty master cylinder.
Where are you getting this crap?
Read more carefully!
I have not even insinuated that!
I have SIMPLY SAID THAT......... THE PROBLEM HE IS HAVING.....WAS PRESENT WITH BOTH MASTER CYLINDERS.
If it's the master cylinder.....at all......is anyone here.....LEAST OF ALL ME!!!!!!.....suggesting that both of the master cylinders are broken ........EVEN THOUGH.....the first master cylinder has been on the bus for quite a while.....AND......was not causing this problem BEFORE the calipers we're changed.
Ray |
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lil-jinx
Samba Member
Joined: August 14, 2013
Posts: 1565
Location: New Brunswick,Canada
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| Posted: Mon Mar 31, 2025 6:10 am Post subject: Re: Brakes heating up and seizing after replacing calipers |
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| raygreenwood wrote: |
| jtauxe wrote: |
| lil-jinx wrote: |
Bentley says the MC internals are the same on both brake types,
your brake line nuts appear to be bottoming out on the nut heads ,may be just the angle ,but make sure they are not .
the brake line ports in a early MC are bigger than a booster MC ,they are made a for a residual valve ,a brake line fitting would be sloppy or very loose,( I don't know how much bigger the ports are,)so check the fittings on the mc,maybe Skilz is correct and the bigger ports are causing the line nut to bottom,if they are not bottoming out ,and not leaking,you should be good.
others will know more on this then me.
if you had residual valves they would be between the brake line fitting and the MC port ,they look like a extra fitting/ adaptor |
The brake line fittings are snug and no sign of trouble there. As is typical, I had to get the nuts aligned "just so" to get them to go in. No "bottoming out" that I can tell.
| raygreenwood wrote: |
| jtauxe wrote: |
Now - Here's where I am:
• no "shims" on the MC. It is firmly bolted to the booster.
• without the shims, the front calipers are locked tight
• this is all with the clevis in a neutral state: no forces fore or aft |
So....let's be super clear:
1. No shims....check!
2. Pushrod/clevis adjusted neutral...no tension anywhere right? Check!
3. And....the calipers are locked??????
Questions:
1. did the calipers lock just because you pulled out the shims and tightened down the nuts.....or.....did you get in after tightening down the nuts and then pump up the brakes?
If they locked up just because you removed the shims and locked the nuts....we have seen you do this a few pages back.
2. Is the pedal pulled back with the bungee cord?
What I would like to see/be sure of.....is that the pedal is pulled back with the bungee cord + the clevis adjusted neutral like you have already stated + the shims removed and the MC bolted up tight and normal + release residual fluid pressure with the bleeder valve at a caliper +.......get in and pump up the brakes.
If the calipers lock up again with all of this done......it will tell you that the pedal return spring has nothing (at least nothing significant) to do with the issue.
The problem will be the booster or MC. Ray |
Answers:
1. Yes, the calipers lock just because I pulled out the shims and tightened down the nuts.
2. The pedal is pulled up with the bungee cord in the cab.
With the pedal pulled up by the bungee cord + the clevis adjusted neutral + the shims removed and the MC bolted up tight and normal, I released residual fluid pressure with the bleeder valve at a caliper
[After relieving fluid pressure now the wheels rotate freely.]
+ got in and pumped up the brakes (careful to allow the pedal to return to its full up position between pumps) ... and...
After 10 pedal pumps I could feel the front wheels start to resist.
After 20, they resisted more.
| lil-jinx wrote: |
front rod adjusted , check
mc bolted on ,check
brakes locked,check
back off the mc install 1 mm spacer,
brakes still locked
install 2 mm spacer
repeat untill the brakes don,t lock,
then measure the shim pack and adjust the rod between the booster and the mc to match the shim pack thickness,
you may only need a mm or two |
Done, and the resulting magic thickness is 3 mm (1/8 inch) as seen in the photo. |
So.....to be 100% clear.....after setting everything to normal (no shims and clevis adjusted with bungee cord installed and residual pressure relieved)...........after 20 pumps of the brakes...........your calipers started locking up again?
Did I sum that up correctly?
So, for the last 2-3 pages:
Lil-jinx thinks it could have been the bad pedal spring. I think that was a good hypothesis
Nitramrebrab72 thinks it's a good hypothesis and agrees that it could have been part of the problem all along.
SGKent agrees that it's not right and needs to be fixed and I agree and we both said it pages ago that the pedal needs to be up against the stop with some force.
But as I noted, I did not think that was the issue.....but the only way to be sure is to test it and get it out of the picture with a definite yes or no.
So.....I think you just did that. While you need a new spring.....that spring is NOT the issue.
You also have proven that with everything else normal (pedal against the stop, clevis and pedal pushrod adjusted properly).....you appear to have 3mm too much pushrod pressure on the master cylinder from the booster.
That's still a shit-ton.
Honing in on either the wrong master cylinder (or at the very least a master cylinder machined wrong....but two in a row....I doubt it).....or as SGKENT noted....your booster is fubar.
Ray |
you dismiss the idea of the MC being the cause ,because it happened with both MCs,and after repairing the brake spring problem,the brakes still drag with the second mc just as they did with the first mc ,so you are saying that shows that the second mc is also good and the problem must be elsewhere because the return spring didn't fix it .you said it has to be the booster ,and and it unlikely
that both MC are faulty ,I,m saying that the first mc is good ,and the return spring would have fixed the problem at the start if he had not replace a perfectly good MC with a MC that has a too long push rod,which many has corrected by shimming it
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1974 Bay Westfalia. she likes to be called Ethel.
1968 Dune Buggy sold dec 2024
1974 parts bus
A smart man learns from his mistakes,a very smart man learns from other's mistakes. |
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lil-jinx
Samba Member
Joined: August 14, 2013
Posts: 1565
Location: New Brunswick,Canada
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| Posted: Mon Mar 31, 2025 6:47 am Post subject: Re: Brakes heating up and seizing after replacing calipers |
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he don't have the same problem,he has the same symptom different causes,
first problem to cause dragging ,return spring
second problem to cause drag ,cause unknown at this time,imo caused by a replacement part ,the MC a very common problem that many addressed by stimming out the MC.
I also suggested that he test fit the old MC if it fit properly that would prove that the replacement is faulty,and if it also stands off ,then we suspect the booster,
I also suggested that he measure both mc push rods to verify that they are the same ,both are very simple tests that would resolve the issue one way or the other.
https://www.amazon.ca/Adjustment-Cylinder-Measurin...d_source=1
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https://www.thesamba.com/vw/forum/viewtopic.php?t=620186
https://www.thesamba.com/vw/forum/viewtopic.php?t=668799
1974 Bay Westfalia. she likes to be called Ethel.
1968 Dune Buggy sold dec 2024
1974 parts bus
A smart man learns from his mistakes,a very smart man learns from other's mistakes. |
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wagen19
Samba Member
Joined: November 16, 2007
Posts: 651
Location: germany
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| Posted: Mon Mar 31, 2025 7:13 am Post subject: Re: Brakes heating up and seizing after replacing calipers |
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| lil-jinx wrote: |
| raygreenwood wrote: |
| jtauxe wrote: |
| lil-jinx wrote: |
Bentley says the MC internals are the same on both brake types,
your brake line nuts appear to be bottoming out on the nut heads ,may be just the angle ,but make sure they are not .
the brake line ports in a early MC are bigger than a booster MC ,they are made a for a residual valve ,a brake line fitting would be sloppy or very loose,( I don't know how much bigger the ports are,)so check the fittings on the mc,maybe Skilz is correct and the bigger ports are causing the line nut to bottom,if they are not bottoming out ,and not leaking,you should be good.
others will know more on this then me.
if you had residual valves they would be between the brake line fitting and the MC port ,they look like a extra fitting/ adaptor |
The brake line fittings are snug and no sign of trouble there. As is typical, I had to get the nuts aligned "just so" to get them to go in. No "bottoming out" that I can tell.
| raygreenwood wrote: |
| jtauxe wrote: |
Now - Here's where I am:
• no "shims" on the MC. It is firmly bolted to the booster.
• without the shims, the front calipers are locked tight
• this is all with the clevis in a neutral state: no forces fore or aft |
So....let's be super clear:
1. No shims....check!
2. Pushrod/clevis adjusted neutral...no tension anywhere right? Check!
3. And....the calipers are locked??????
Questions:
1. did the calipers lock just because you pulled out the shims and tightened down the nuts.....or.....did you get in after tightening down the nuts and then pump up the brakes?
If they locked up just because you removed the shims and locked the nuts....we have seen you do this a few pages back.
2. Is the pedal pulled back with the bungee cord?
What I would like to see/be sure of.....is that the pedal is pulled back with the bungee cord + the clevis adjusted neutral like you have already stated + the shims removed and the MC bolted up tight and normal + release residual fluid pressure with the bleeder valve at a caliper +.......get in and pump up the brakes.
If the calipers lock up again with all of this done......it will tell you that the pedal return spring has nothing (at least nothing significant) to do with the issue.
The problem will be the booster or MC. Ray |
Answers:
1. Yes, the calipers lock just because I pulled out the shims and tightened down the nuts.
2. The pedal is pulled up with the bungee cord in the cab.
With the pedal pulled up by the bungee cord + the clevis adjusted neutral + the shims removed and the MC bolted up tight and normal, I released residual fluid pressure with the bleeder valve at a caliper
[After relieving fluid pressure now the wheels rotate freely.]
+ got in and pumped up the brakes (careful to allow the pedal to return to its full up position between pumps) ... and...
After 10 pedal pumps I could feel the front wheels start to resist.
After 20, they resisted more.
| lil-jinx wrote: |
front rod adjusted , check
mc bolted on ,check
brakes locked,check
back off the mc install 1 mm spacer,
brakes still locked
install 2 mm spacer
repeat untill the brakes don,t lock,
then measure the shim pack and adjust the rod between the booster and the mc to match the shim pack thickness,
you may only need a mm or two |
Done, and the resulting magic thickness is 3 mm (1/8 inch) as seen in the photo. |
So.....to be 100% clear.....after setting everything to normal (no shims and clevis adjusted with bungee cord installed and residual pressure relieved)...........after 20 pumps of the brakes...........your calipers started locking up again?
Did I sum that up correctly?
So, for the last 2-3 pages:
Lil-jinx thinks it could have been the bad pedal spring. I think that was a good hypothesis
Nitramrebrab72 thinks it's a good hypothesis and agrees that it could have been part of the problem all along.
SGKent agrees that it's not right and needs to be fixed and I agree and we both said it pages ago that the pedal needs to be up against the stop with some force.
But as I noted, I did not think that was the issue.....but the only way to be sure is to test it and get it out of the picture with a definite yes or no.
So.....I think you just did that. While you need a new spring.....that spring is NOT the issue.
You also have proven that with everything else normal (pedal against the stop, clevis and pedal pushrod adjusted properly).....you appear to have 3mm too much pushrod pressure on the master cylinder from the booster.
That's still a shit-ton.
Honing in on either the wrong master cylinder (or at the very least a master cylinder machined wrong....but two in a row....I doubt it).....or as SGKENT noted....your booster is fubar.
Ray |
you dismiss the idea of the MC being the cause ,because it happened with both MCs,and after repairing the brake spring problem,the brakes still drag with the second mc just as they did with the first mc ,so you are saying that shows that the second mc is also good and the problem must be elsewhere because the return spring didn't fix it .you said it has to be the booster ,and and it unlikely
that both MC are faulty ,I,m saying that the first mc is good ,and the return spring would have fixed the problem at the start if he had not replace a perfectly good MC with a MC that has a too long push rod,which many has corrected by shimming it |
=> lil-jinx, I´m afraid, you are wrong!!!
The MC has no push rod. The push rod you are talking from, is part of the booster!!!
If the lengh of that inner push rod of just that booster in question is adjustable or not, is still unclear! Shimming it makes no sense, because it´s too long and not too short!
If you think the first MC is OK, then measure the distance between of surface and inner cup for push rod.
Then remove the actually installed MC and compare. Are there given specs?
Due to wear, any push rod does not get longer, only shorter!
If the end of that push rod is too near the MC, has come out too far, out of which reason ever, the booster is the culprit! (when outer push rod from pedal coming is disconnected!)
maybe the position of the cup inside MC piston is on wrong position, due to an issue, failure while fabrication.
It´s not clear, if we have one single cause, or more!
I can only repeat, inside that combination, unit MC-booster, there is the problem. Maybe one or even both parts are out of tolerance and not adjustable.
REGARDING THE INDIVIDUAL PARTS:
MC: is nearly new, makes pressure, holds it, works great, makes no pressure as long piston is not pushed. So far OK. Only question: is the cup for push rod out of correct position, or not?
Booster: unclear, it works when pedal is engaged, but the rest is unclear. (going back to rest position, condition and lengh of push rod (bent?), maybe vacuum issues)
Return spring: unclear, if also a culprit, but as long bungy helps, the rest of parts can be tested!
=> Replace the return spring and do measuring the MC, if problems are going on, your HOLY COW, the BOOSTER is the main culpit!
So far!!! |
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lil-jinx
Samba Member
Joined: August 14, 2013
Posts: 1565
Location: New Brunswick,Canada
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| Posted: Mon Mar 31, 2025 7:55 am Post subject: Re: Brakes heating up and seizing after replacing calipers |
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yes push rod in the mc may be the wrong term ,it's a socket ,plunger is the term is see in diagrams,that receives the push rod from the booster ,and the socket,on the new mc is not deep enough for the booster push rod,so either deepen the socket ,not a diy job without the proper tools,shorten the booster push rod if provision is built into the rod or hasn't,t already been shortened to it max or shim out the MC.and as I said many have gone the route of shimming to correct a rod clearance issue.
i think you are thinking of the shims going on the push rod which would make it longer or removing shim/spacers from the push rod would do the opposite and make it shorter,the tip can be removed,( not in all cases but I think this is correct for an ATE booster) to change the shim/spacer altering it length and distance that in protrudes into the mc plunger socket,
shim makes no sense? if the rod in the booster and the plunger in the MC are making contact when the mc and booster is bolted together,put a shim between the mc and booster will move the two parts way from each other creating a non contact fit between the rod and the plunger,make sense to me,
i also suggested measuring the plunger and comparing both mc, i also suggested test fitting the old mc to check if it also make contact,and if it does then the booster is suspect, I,m saying that befor the return spring was fixed it was putting pressure on the booster and the MC causing the brakes to alloy lightly ,fixing the spring fixed that problem ,and the new mc is the cause of this new problem.
_________________
https://www.thesamba.com/vw/forum/viewtopic.php?t=620186
https://www.thesamba.com/vw/forum/viewtopic.php?t=668799
1974 Bay Westfalia. she likes to be called Ethel.
1968 Dune Buggy sold dec 2024
1974 parts bus
A smart man learns from his mistakes,a very smart man learns from other's mistakes. |
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wagen19
Samba Member
Joined: November 16, 2007
Posts: 651
Location: germany
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| Posted: Mon Mar 31, 2025 10:12 am Post subject: Re: Brakes heating up and seizing after replacing calipers |
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| lil-jinx wrote: |
yes push rod in the mc may be the wrong term ,it's a socket ,plunger is the term is see in diagrams,that receives the push rod from the booster ,and the socket,on the new mc is not deep enough for the booster push rod,so either deepen the socket ,not a diy job without the proper tools,shorten the booster push rod if provision is built into the rod or hasn't,t already been shortened to it max or shim out the MC.and as I said many have gone the route of shimming to correct a rod clearance issue.
i think you are thinking of the shims going on the push rod which would make it longer or removing shim/spacers from the push rod would do the opposite and make it shorter,the tip can be removed,( not in all cases but I think this is correct for an ATE booster) to change the shim/spacer altering it length and distance that in protrudes into the mc plunger socket,
shim makes no sense? if the rod in the booster and the plunger in the MC are making contact when the mc and booster is bolted together,put a shim between the mc and booster will move the two parts way from each other creating a non contact fit between the rod and the plunger,make sense to me,
i also suggested measuring the plunger and comparing both mc, i also suggested test fitting the old mc to check if it also make contact,and if it does then the booster is suspect, I,m saying that befor the return spring was fixed it was putting pressure on the booster and the MC causing the brakes to alloy lightly ,fixing the spring fixed that problem ,and the new mc is the cause of this new problem. |
You are not reading carefully!
It was about "shimming the push rod" to MC. In some cases this is possible.
Shimming the MC body is a theoretic possible option, but at least not a solution proposed by factory. Imo, the very last way.
On page 1 already the booster was recognized to be suspect, but I don´t want to repeat this unbelievable poor dilemma here.
Any quality part of the system has to fulfill it´s own technical specs and if not, it has to be adjusted, repaired or replaced. That´s the normal way, to drive safe. |
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