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Tcash
Samba Member
Joined: July 20, 2011
Posts: 12844
Location: San Jose, California, USA
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 Posted: Fri Jun 29, 2018 8:45 am Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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Sure looks like the pistons are not collapsed all the way.
Yours
One from the Gallery.
Another thing to look at is the Rubbing blocks on the backing plate. This is where the brake shoe rubs against the backing plate. They can get grooved and not allow the shoes to fully collapse.
They are the four rectangular blocks in this picture. File them flat and apply anti seize to them.
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 50332
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| Posted: Fri Jun 29, 2018 12:48 pm Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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Do the shoes pull in when you open the bleeder on the slave cylinder? |
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SGKent 
Samba Member
Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Fri Jun 29, 2018 1:44 pm Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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that cylinder is expanded. I concur that there is pressure in it holding it out.
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Abscate
Samba Member
Joined: October 05, 2014
Posts: 22633
Location: NYC/Upstate/ROW
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| Posted: Fri Jun 29, 2018 6:42 pm Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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That parking brake bar is hung up and holding the shoes out. I’m guessing it isn’t in right
Remove it, temporarily, and see if your hang ups improve.
Your Bus hang ups, I mean.
The spring should be resting in full compressed position.
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Ben Middleton
Samba Member
Joined: April 11, 2016
Posts: 219
Location: England, UK
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| Posted: Mon Jul 02, 2018 4:30 am Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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Well chaps, looks like the handbrake cable was causing the problem in the right rear drum. I disconnected it and the cylinder closed up fully.
I’m glad I didn’t spot that earlier because I have replaced a somewhat blocked rubber brake hose and refurbished the rear brake pressure regulator in the process of trying to isolate the cause of the problem, problems which I may not have noticed otherwise.
I am a bit confused by the handbrake cable. The Bentley manual tells me to unbolt the cable from the backing plate - I can’t find a bolt anywhere. Is the ‘72 different?
Also, the left rear brake drum has had its handbrake cable replaced at some point. It appears to be functional, but the spring doesn’t fully close up when disconnected. It looks different from the original style spring on the other drum.
The handbrake cable in the right drum doesn’t move freely. Should I just remove it and grease it, or does it need to be replaced?
PS - Today I intend to use an air compressor to blow through the brake lines, just to be sure they’re not blocked at all. |
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 50332
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| Posted: Mon Jul 02, 2018 8:00 am Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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| Ben Middleton wrote: |
Well chaps, looks like the handbrake cable was causing the problem in the right rear drum. I disconnected it and the cylinder closed up fully.
I’m glad I didn’t spot that earlier because I have replaced a somewhat blocked rubber brake hose and refurbished the rear brake pressure regulator in the process of trying to isolate the cause of the problem, problems which I may not have noticed otherwise.
I am a bit confused by the handbrake cable. The Bentley manual tells me to unbolt the cable from the backing plate - I can’t find a bolt anywhere. Is the ‘72 different?
Also, the left rear brake drum has had its handbrake cable replaced at some point. It appears to be functional, but the spring doesn’t fully close up when disconnected. It looks different from the original style spring on the other drum.
The handbrake cable in the right drum doesn’t move freely. Should I just remove it and grease it, or does it need to be replaced?
PS - Today I intend to use an air compressor to blow through the brake lines, just to be sure they’re not blocked at all. |
For later Transporters the cables are not particularly expensive, can't say for your one year set up.
Your picture doesn't make it look like the cable is at fault though??? |
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Abscate
Samba Member
Joined: October 05, 2014
Posts: 22633
Location: NYC/Upstate/ROW
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| Posted: Mon Jul 02, 2018 9:20 am Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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| Quote: |
| functional, but the spring doesn’t fully close up when disconnected. |
Pretty much nails it
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Ben Middleton
Samba Member
Joined: April 11, 2016
Posts: 219
Location: England, UK
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| Posted: Mon Jul 02, 2018 2:46 pm Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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Well, here’s another depressing update.
I removed the handbrake cables. Only the right one was broken and the pic I sent was of the left one, that’s why it looks OK.
Firstly, I blew compressed air through the rear brake circuit and confirmed there are no blockages.
After removing the handbrake cables and bleeding the brakes again, the problem persisted. I bled the pressure regulator first, then the right rear and left rear brakes.
Initially, after bleeding, the brake cylinders closed up and the drums were free (indicating to me that the shoes aren’t catching on the backing plate). I pressed the brake pedal and it went low and soft. The brake drums didn’t lock up after releasing. However, after more presses of the pedal, the pedal got harder and higher. Eventually it felt like a good brake pedal but the rear brakes were now locked on. I re-bled the pressure regulator and the brakes freed up again. Once again, after multiple pedal presses, the shoes locked on.
It’s like the pressure is building up and forcing the cylinders out after repeatedly pressing the brake pedal.
I have also double checked the servo pushrod clearance. I can rattle the connecting rod back and forth about 1-2mm without any considerable pressure while the brakes are locked on, which makes me assume that the pushrod clearance is correct and no pressure is being applied to the servo when the brake pedal is released.
The Bentley manual mentions that locked brakes could be caused by a blocked compensating port. Could it be blocked with anything other than the servo pushrod?
I am starting to think that I haven’t managed to refurbish the pressure regulator correctly. I didn’t apply any grease inside because I assumed that only brake fluid was required. Does anyone know if that’s correct? I know they apparently fail but the seals were good and the ball moved freely, so I can’t see what the issue is, if it is indeed not functioning correctly.
There is a possibility that some brake fluid is leaking from either the tube connecting the upper reservoir to the lower reservoir, or from the master cylinder bungs (or both). Would this cause this problem with the brakes locking on?
Otherwise, I’m stumped! |
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raygreenwood
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Joined: November 24, 2008
Posts: 21507
Location: Oklahoma City
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| Posted: Mon Jul 02, 2018 3:43 pm Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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| Ben Middleton wrote: |
Well, here’s another depressing update.
I removed the handbrake cables. Only the right one was broken and the pic I sent was of the left one, that’s why it looks OK.
Firstly, I blew compressed air through the rear brake circuit and confirmed there are no blockages.
After removing the handbrake cables and bleeding the brakes again, the problem persisted. I bled the pressure regulator first, then the right rear and left rear brakes.
Initially, after bleeding, the brake cylinders closed up and the drums were free (indicating to me that the shoes aren’t catching on the backing plate). I pressed the brake pedal and it went low and soft. The brake drums didn’t lock up after releasing. However, after more presses of the pedal, the pedal got harder and higher. Eventually it felt like a good brake pedal but the rear brakes were now locked on. I re-bled the pressure regulator and the brakes freed up again. Once again, after multiple pedal presses, the shoes locked on.
It’s like the pressure is building up and forcing the cylinders out after repeatedly pressing the brake pedal.
I have also double checked the servo pushrod clearance. I can rattle the connecting rod back and forth about 1-2mm without any considerable pressure while the brakes are locked on, which makes me assume that the pushrod clearance is correct and no pressure is being applied to the servo when the brake pedal is released.
The Bentley manual mentions that locked brakes could be caused by a blocked compensating port. Could it be blocked with anything other than the servo pushrod?
I am starting to think that I haven’t managed to refurbish the pressure regulator correctly. I didn’t apply any grease inside because I assumed that only brake fluid was required. Does anyone know if that’s correct? I know they apparently fail but the seals were good and the ball moved freely, so I can’t see what the issue is, if it is indeed not functioning correctly.
There is a possibility that some brake fluid is leaking from either the tube connecting the upper reservoir to the lower reservoir, or from the master cylinder bungs (or both). Would this cause this problem with the brakes locking on?
Otherwise, I’m stumped! |
Yes....this sounds like a compensation port. Some things that can cause this:
1. You noted its a NEW master cylinder. Is it NEW...or NOS (new old stock)?
On new old stock cylinders it is VERY common that the brass flap valves which are the compensation port flap valves....are stuck to teh pistons and not opening due to moisture and age corroding them to the piston faces.
Even on some new MC's I have found stubborn dried assembly lube gluing the flap valves down or clogging the ports in the piston.
2. As you already know....the pedal push rod must have free play between it and the piston so that the piston does not move down the bore and cover fluid inlet ports from the reservoir. Since you have a power brake booster....make sure that the free play between brake pedal and booster...also is allowing actual gap between the booster pushrod and the MC piston like in the picture below.
3. Another way this can happen...and is also really common with brakes that pump up and then will not release is that the plastic elbow in the brake fluid feed line from the reservoir...on some master cylinders...where it sticks through the rubber grommet in the top of the master cylinder...can be pushed slightly too far in. This can cause the flood of the recess to close off teh flow of replenishment fluid during a brake movement...as well as the back flow of fluid into the reservoir when you let off the pedal.
This can also happen if the grommets in the top of teh MC are installed upside down.
This is not actually a blocked compensation port...but acts just like one. You can see this effect in this link if you scroll down to the very bottom of the post.
https://www.thesamba.com/vw/forum/viewtopic.php?t=...highlight=
Ray |
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Ben Middleton
Samba Member
Joined: April 11, 2016
Posts: 219
Location: England, UK
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| Posted: Mon Jul 02, 2018 4:39 pm Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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Thank you for that in-depth reply Ray, I really appreciate your advice.
The master cylinder I bought is a Varga/TRW one, presumedly Brazilian-made. Do you think I should dismantle it and rebuild it as you describe in your other post? The servo is also Brazilian-made.
I think I should get some new seals for the lower reservoir because I reused the old ones as they seemed a tight fit, but they are possibly leaking. I will probably also install a new reservoir-to-reservoir hose.
Do you know of a good method for measuring the clearance between the servo push rod and the master cylinder?
Finally, when I rebuilt the pressure regulator, I initially used an alcohol spray but then used brake cleaner to remove the debris, as I thought it would be more appropriate. Was that the wrong decision?
Again, thanks for your help. It looks like it’ll be many more hours before I can stop my camper. |
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 50332
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| Posted: Mon Jul 02, 2018 5:27 pm Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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| When removing an old master cylinder and installing a replacement, it is possible from crap to break loose in the outlet and end up blocking the outlet on the new cylinder. This blockage may act like a check valve. |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 21507
Location: Oklahoma City
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| Posted: Mon Jul 02, 2018 6:31 pm Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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| Ben Middleton wrote: |
Thank you for that in-depth reply Ray, I really appreciate your advice.
The master cylinder I bought is a Varga/TRW one, presumedly Brazilian-made. Do you think I should dismantle it and rebuild it as you describe in your other post? The servo is also Brazilian-made.
I think I should get some new seals for the lower reservoir because I reused the old ones as they seemed a tight fit, but they are possibly leaking. I will probably also install a new reservoir-to-reservoir hose.
Do you know of a good method for measuring the clearance between the servo push rod and the master cylinder?
Finally, when I rebuilt the pressure regulator, I initially used an alcohol spray but then used brake cleaner to remove the debris, as I thought it would be more appropriate. Was that the wrong decision?
Again, thanks for your help. It looks like it’ll be many more hours before I can stop my camper. |
Personally.....I started many years ago ....cleaning out all brand new brake cylinders. Simply disassemble and clean with high quality denatured alcohol. What I mean by that.....is check the SDS for whatever brand you buy. Make sure its not a blend of the wrong stuff like I noted in that MC rebuild thread.
As for brake cleaner.....I never use it.....but....it is for external components ONLY. All internal seals of brake parts are made of EPDM. This rubber type breaks down with contact of any VOC.
Seals like the caliper external dust boots are actually viton to work with exposure to high heat, oils, foad salts etc. Brake cleaner is fine for those.
As long as you do not get brake cleaner inside of components you should be fine. Ray |
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Tcash
Samba Member
Joined: July 20, 2011
Posts: 12844
Location: San Jose, California, USA
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| Posted: Mon Jul 02, 2018 8:58 pm Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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The Bentley manual mentions that locked brakes could be caused by a blocked compensating port. Could it be blocked with anything other than the servo pushrod?
Yes, by debris in the Master cylinder.
You should be able to see fluid return to the Brake fluid fill reservoir upon releasing the brake pedal.
I assumed that only brake fluid was required. Does anyone know if that’s correct? I know they apparently fail but the seals were good and the ball moved freely, so I can’t see what the issue is, if it is indeed not functioning correctly.
Only brake fluid is required.
You need to start cracking brake line fitting starting at the master cylinder. Crack the fitting, brakes don't release move toward the wheel until it does release. Then therefore your problem lies in the section between that fitting and the master cylinder.
Make sense
Tcash |
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OB Bus
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Joined: February 09, 2003
Posts: 2535
Location: Ocean Beach in Beautiful BLUE California
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| Posted: Tue Jul 03, 2018 6:15 am Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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I'm not nearly as adept as most of you here, but an idea. Early on I remember the OP saying that he backed the adjusters way off. Did he ever properly readjust them? Could the slave cylinders be over extending and then not return?
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69 Westfalia and 2002 Eurovan Camper. |
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CarlosZ
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Joined: April 23, 2016
Posts: 319
Location: Los Angeles
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| Posted: Tue Jul 03, 2018 6:38 am Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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| OB Bus wrote: |
| I'm not nearly as adept as most of you here, but an idea. Early on I remember the OP saying that he backed the adjusters way off. Did he ever properly readjust them? Could the slave cylinders be over extending and then not return? |
Interesting theory. I just did my rear brakes on my ‘72. I hit the brake to see if the brake cylinder worked and the pistons (not sure the correct term) in the brake cylinder popped out all the way. I had to disassemble and push back in.
OP - Maybe too much slack due to the stars being loosened up all the way? I think by tightening the stars you’ll reduce the travel of the pistons. Does the locking still occur with both brake cables completely disconnected? |
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Ben Middleton
Samba Member
Joined: April 11, 2016
Posts: 219
Location: England, UK
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| Posted: Tue Jul 10, 2018 5:31 pm Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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Thanks for the suggestions guys. The star adjusters are still completely loosened off. I don’t believe this is causing the issue because when I opened the bleeder valve on the pressure regulator, the wheel cylinders closed up nicely.
I have decided to remove, dismantle and clean the master cylinder. Ray, I noticed in your article that you say there are different rubbers of similar appearance used inside your example master cylinder, and these may be installed incorrectly. Could this be the case for a T2 servo master cylinder?
Also, you recommend denatured alcohol for cleaning of the master cylinders, should I just use brake fluid to rebuild it or some sort of assembly paste?
I am also replacing the bungs for the top of the master cylinder. I have noticed that the rubber insert at the bottom of the reservoir-to-reservoir pipe is perished. This rubber has broken up so maybe particles of it have blocked the master cylinder. Are these inserts available to purchase?
Thanks,
Ben |
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busdaddy
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Joined: February 12, 2004
Posts: 51112
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Tue Jul 10, 2018 5:52 pm Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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Yes the master cylinder reservoir grommets are available from most vendors.
Silicone grease or brake assembly paste is best for lubing everything when putting it back together, alcohol or brake kleen for washing it out if you are drying everything right away.
They will always be grabby if you don't tighten up the adjusters, loose shoes are hard to regulate.
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Tcash
Samba Member
Joined: July 20, 2011
Posts: 12844
Location: San Jose, California, USA
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| Posted: Tue Jul 10, 2018 8:03 pm Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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After the pressure reg, loosen the brake line at the master cylinder.
Wheel cylinder does not close up. Line between the pressure reg and master is plugged.
If the hose between the fill reservoir and the master reservoir where plugged, both front and rear brakes would be locking up. |
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 50332
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| Posted: Tue Jul 10, 2018 8:25 pm Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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| Ben Middleton wrote: |
| Thanks for the suggestions guys. The star adjusters are still completely loosened off. I don’t believe this is causing the issue because when I opened the bleeder valve on the pressure regulator, the wheel cylinders closed up nicely. |
Try cracking the line for the rear brake circuit at the master cylinder and see what happens. |
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Ben Middleton
Samba Member
Joined: April 11, 2016
Posts: 219
Location: England, UK
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| Posted: Wed Jul 11, 2018 2:08 am Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) |
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I’ve already removed the master cylinder and pressure regulator again. I forgot to crack the line at the master cylinder and check if the brakes free up, but I know I want to clean out the master cylinder and replace the rubbers anyway now. I’d already refurbished the pressure regulator, and blown compressed air through the line between the regulator and the MC so I knew that wasn’t blocked.
I’ll take a photo of the perished rubber that I need to replace, just to show bad it looks. Part number 211-611-833/C. |
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