Brakes heating up and seizing after replacing calipers - SOLVED!

[jtauxe]

I don't think that the calipers are sticking. Remember that when the pressure is let off by backing the MC off of the booster, the wheels turn freely. That would indicate that the pressure relief translates to the pistons backing off, too, and that the calipers are working as intended.

And I also believe that the MCs, the previous Varga and the current ATE, are probably working correctly, although I did not run such a thorough batch of tests on the Varga one. Its evidence is that it worked for years until this incident. That said, I have yet to pull out the new ATE MC to see if there is anything in the throat contributing to the preloading. I can't reinstall the Varga one until I get the seals to the lower reservoir, which are on order.

That leaves me with the booster. The history on this is that it was original to the truck, as far as I could tell (it did not come with repair records) and that I had it rebuilt by Brake Materials and Parts 8 years ago -- I found the receipt!

I have sourced a 1975 booster that needs a rebuild (thanks to SGKent for finding that) and will use it to experiment with. At that point, I will have 2 1975 boosters that probably both need rebuilding, to the tune of ~$300 each either by the same folks or by Karps in California. I'll probably rebuild just one of them now, because my other truck does not even use a booster.

I will also have in my hands soon another set of original calipers for rebuilding, so I will have all the brake parts I need for awhile.

So, bear with me while I get some more parts together.
_________________
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

[SGKent]

good job John on a quite unusual situation. I would buy a lottery ticket at this point.
_________________
"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[raygreenwood]

[SGKent]

Jeff (owner) at Karps called. He said that sometimes, especially if the diaphragm has gotten brake fluid on it, it can distort when over extended and cause the issue, plus sometimes other things can cause it. He said that when the front of the servo is at rest, the MC side should be at rest too, and not extended. He also said that deep inside the unit there are a couple shims that can change the pushrod length but it is extremely hard to change them because they will fall out inside the unit requiring disassembly to get at them. He said those shims are good for only a couple thousands of an inch change but when it is like 2 or 3 mm, 1/4" etc out then something is goofy in the booster, most likely the diaphragm warped. If it was working before then over stressing the diaphragm may have distorted it.

Karp's price is $295 plus shipping, and his general warranty is 1 year unless a master leaks or something like that. The service includes glass beading the shell during service, and painting it engine bay black when done unless the owner wants it back unpainted. If Eastwood engine black powder coating is desired as an additional service, it is $45 extra. They are on Mills in Chino now. For what it is worth, they did my 1982 CJ7 when the booster (GM made) went out about 70,000 miles. It was still going strong when I sold it with close to 650,000 miles on the Jeep. Lots of other things wore out multiple times but the booster they rebuilt was rock solid. I like Karps and will use them for mine because after close to 50 years old, it is time to have it gone thru.
_________________
"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[jtauxe]

I got that estimate from Karps, and a very similar estimate from Brake Materials and Parts in Indiana. They rebuilt this one 8 years ago. I found the receipt. Another option is to go through Scott at GermanSupply. He also has a rebuilder that he trusts, and stocks rebuilt boosters for your core. It's cheaper because it's in Canadian $.

But I don't want to get ahead of myself. First off, I will substitute the used booster that I am getting from troutbus in Fort Collins, Colorado.

It would be really interesting to do an autopsy on one of these, having never seen inside one. But it would probably be a destructive process, and I would not want to make a booster unsalvageable.
_________________
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

[SGKent]

[jtauxe]

I have answers! TLDR: It's the booster (tentatively).

Today I removed the brake booster and master cylinder from the pickup and compared the parts to other units. I had to remove the pedal pivot bolt to get the pedal-booster rod to clear the pedal, but that's OK since I have to do that to replace the pedal spring anyway. Which I will do on reassembly.

Here are photos showing the length of the "sleeve" on each of 2 master cylinders:

The Varga (which served for years on the truck) has a sleeve length of 29.5 mm:

On the new ATE MC, the sleeve length is 31.0 mm:

I believe the discrepancy to be irrelevant, since the end of the sleeve does not contact anything.

More important is the nature of the inside of the sleeve, where the booster rod contacts. The depth from the edge of the sleeve to the contact point inside is 48 mm on the Varga and 49 mm on the ATE. Both look clean:

Varga:

ATE:

I got another 1975 ATE booster, believed original, from JH in Fort Collins. Mine is on the left, and the JH booster is on the right:

The insides of both my (rebuilt in 2013) original booster and the JH booster both look clean:

JH booster:

My original rebuilt booster:

So far, so good. Now for the important stuff. The protrusion of the rod from the booster that fits into the MC sleeve and makes contact with the booster should be 0, meaning that the tip of the rod should be just even with the rim of the booster. That is the case with the JH booster (which also needs are rebuild, but apparently for other reasons):

On my original (2013 rebuild) booster, the rod protrudes a good 5 to 6 mm:

And it does not want to move back into the booster at all. If I had known what to look for when I replaced the Varga MC with the ATE MC, I would have noticed that this is off. That completely explains why backing off the MC by 5 mm allowed the brakes to release.

With that evidence, I don't think there is any point in reassembling anything until the booster gets rebuilt, or trying out the rear brake pressure regulator that was kindly sent to me on approval.

So, anyone who was betting on the booster is likely to get paid off, but before I claim victory, I am going to get my original booster rebuilt again (unless anyone thinks that rebuilding the JH booster would be a better choice). Karps said they could do in in under a week. Then we will have our answer and you can settle your bets. And I hope to go out for a drive!

Fingers crossed!
_________________
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

[raygreenwood]

Let whoever rebuilds your current booster....what is happening. This way they can be on the lookout for something odd inside like something bent.

Ray

[lil-jinx]

did you test the fit of the old mc on the booster,maybe send your MC to the rebuilder with the booster and have them match it up with the proper clearance
_________________
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.

[jtauxe]

I have informed the rebuilder (Karps, in Chino, California) about the issue.

I did not do a test fit of the MC to the booster, since it was obvious (to me now) what the problem is.
_________________
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

[wagen19]

[SGKent]

I'll be happy when John is all back together and going down the road again.
_________________
"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[jtauxe]

[jtauxe]

Today was a Good Day. In short, this problem is now

SOLVED!


Yay! And the answer is...

It was the vacuum booster (servo) all along. Those of you who had placed bets may now collect or pay up, depending.

The rebuilder, Karps Power Brake of Chino, CA, told me that the diaphragm was ruptured and that there was fluid in the booster.

<aside>
Inexplicably, they returned the rebuilt unit without the bellows, cup, spring, and circlip. They got a bit defensive when I asked them to please send these parts, and accused me of sending it to them that way. As if. It was directly off the vehicle.

So, Karps is on probation until that gets resolved, but I managed to cannibalize another booster and put this together. Still need the parts, of course, to resupply the cannibalized one.
</aside>

But I've taken the truck out for test drives, and today did about 100 miles. The brakes squeaked a bit until we got back down to metal on the disc, but never got warm, never resisted a gentle rolling...

So, I can finally say that this truck now has all its GO parts working as well as all its STOP parts.

It was a sometimes painful process, but certainly engaging and educational.

And I now have
• new calipers
• new pads
• new brake hoses all around
• new master cylinder and lower reservoir
• new vacuum hoses on booster
• rebuilt brake booster
• new brake pedal return spring

And while it was out of commission, I repainted the bumpers and wheels, and put on new rubber, Hankook Vantra LT RA-18s. So,
• new tires, too!
_________________
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

[SGKent]

They are good people. I am sure it was just an oversight. I haven't forgotten you and are working towards getting the engine back in before the heart surgery. Just came in to check my e-mails. Put the clutch on a few minutes ago. Love that sound, pop, when the disc alignment tool comes out. The only thing I hate about the clutch is one book says 18 ft lbs and one says 14 ft lbs. I used 18 and blue loctite.
_________________
"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[germansupplyscott]

There is a tolerance to the removeable nipple on the servo actuating shaft. Every factory original booster will have different length nipples and different thickness of shims to set the working length of the actuating shaft. I believe the spec is for the nipple to protrude about .5mm (or just past flush) past the mounting plane of the master. If the shaft/nipple protrudes too far past the mounting plane of the servo the front circuit of the master will never fully close and just driving along the servo will be applying the brakes (without driver touching the pedal). What can compound this issue is remanufactured brake servos so the setting gets lost, and as well different master cylinders can have different depth to the bore that contacts the actuating rod of the servo. This depth should be exactly the same on any master but it probably isn't perfectly consistent across manufacturers, and once the servo is rebuilt, or an aftermarket servo is used, all bets are off. All the parts came from stock Bay Bus servos (one nipple is shortened as noted)

Two different length nipples and both have shims of different sizes:

The one on the left was shaved down in an installation where the nipple was projecting too far:

In my experience if you set up the servo/master so there is zero preload on the master, or maybe just a tiny bit of preload, the hanging brakes won't be an issue. Worst case is the pedal is a but longer but the front brakes will always release.
_________________
SL

[jtauxe]

Good to know, Scott.

At any rate, the brakes are working fine now.

Karps sent me some jury-rigged nonsense as a replacement for what they lost, but I'll see if they can pony up to cover a proper replacement sourced from someone like BustedBus.
_________________
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

[SGKent]

I accidentally came across this video on a late bay with an adjustable master and thought of this thread. Apparently some adjustable masters do exist, perhaps as replacements. View of it is about half way thru, maybe 2:50 or so. Looking at the video at that point, someone could use a little soft modeling clay to set the actual clearance. That is what we used to use to check piston to valve clearances on racing engines.
Link

_________________
"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[Wildthings]