1978 Pickup: Brakes redone, but now pedal two-step behavior

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jtauxe
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1978 Pickup: Brakes redone, but now pedal two-step behavior

Post by jtauxe » Sat Mar 20, 2010 8:26 am

Along with a lot of other wheel work, I had a mechanic completely go over the brakes on the '78 pickup. I know, I know, I should have done this work myself, but I've been too busy and I liked the idea of getting a lot of work done at once in a couple of days. Luxurious, I know. And everything is great except this brake issue:

Problem: The brake pedal stops at the normal place, down a few centimeters, and the bus begins to stop. Then, every time, after a few seconds, the brake pedal drops another few centimeters, to a second position. The bus continues to stop normally.

What is causing this two-step behavior?

Is it dangerous (should I stop driving)?

Background:

The brake system on this bus has no vacuum booster and never did, FWIW.

The brake work done by the mechanic includes:
- new hoses all around
- new cylinders and pads on the rear drums
- new rotors and pads on the front discs
- adjustment of emergency brake
- replace fluid and bleed, or course
John
"The bus came by and I got on. That's when it all began..." - Garcia/Weir/Kreutzman
http://vw.tauxe.net

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Re: 1978 Pickup: Brakes redone, but now pedal two-step behav

Post by Amskeptic » Sat Mar 20, 2010 8:47 am

jtauxe wrote:Along with a lot of other wheel work, I had a mechanic completely go over the brakes on the '78 pickup. I know, I know, I should have done this work myself, but I've been too busy and I liked the idea of getting a lot of work done at once in a couple of days. Luxurious, I know. And everything is great except this brake issue:

Problem: The brake pedal stops at the normal place, down a few centimeters, and the bus begins to stop. Then, every time, after a few seconds, the brake pedal drops another few centimeters, to a second position. The bus continues to stop normally.

What is causing this two-step behavior?

Is it dangerous (should I stop driving)?

Background:

The brake system on this bus has no vacuum booster and never did, FWIW.

The brake work done by the mechanic includes:
- new hoses all around
- new cylinders and SHOES on the rear drums
- new rotors and pads on the front discs
- adjustment of emergency brake
- replace fluid and bleed, or course
Master cylinder . . . the one thing he did not do.
Oy, baby. Oy veigh.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Post by jtauxe » Sat Mar 20, 2010 10:13 am

Well, in fairness, I had not asked him to do that, either.

Master cylinder R&R... After searching and reading, it seems that it is probably best to simply replace this part. All the ones I find, like this one,
http://busdepot.com/details.jsp?partnumber=211611021AA
assume that you have a vacuum servo. I do not. Do I need a completely different part?

Back to one of the original questions... Is it unsafe to drive in this condition?
Is that a stupid question?
John
"The bus came by and I got on. That's when it all began..." - Garcia/Weir/Kreutzman
http://vw.tauxe.net

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Post by jtauxe » Sun Mar 21, 2010 2:45 pm

OK. More research, including a site visit under the vehicle.

This '78 RHD Irish pickup is odd in many ways... and I believe that the brake system is one of those ways. It has no vacuum servo, but looks much more like this system shown on the VW Heritage site:
http://www.vwheritage.com/vwh/VW-Camper ... lateID=vwh

Although the inset says "reservoir assembly >7/72", my setup looks more like the one in the main diagram, with the twin-reservoir hooked up to the refill reservoir to the REAR, not toward the front. There is also only one brake light switch, not two. The rear one has an electrical connector, but the front one is simply plugged.

My master cylinder looks like 12 in the diagram. It also looks a lot like the photo in the Bentley, Chapter 8 (Brakes and Wheels) Figure 3-3, except that the twin reservoir is reversed. Perhaps this does not matter, as it would just go into the top connections one way or the other. The funny thing is that the Bentley implies that this is for earlier years. But perhaps this pickup uses the old system, just as it came originally with a 1600 upright engine.

Looking below on the VW Heritage page in the list of parts for various years, it seems to match up to this one:
Master cyl. 1.6, 8/70-79 ATE
[211-611-021/AE/ATE]
RHD/LHD German master cylinder, NOT SERVO 8/70> (includes end boot)

Is this then the same master cylinder as the early buses? Could one of those work with my system, which does have disc brakes up front...

I'd appreciate any input from folks with a similar setup. To my knowledge, this would include Wooly Dave, but I know of no one else. Anyone?
John
"The bus came by and I got on. That's when it all began..." - Garcia/Weir/Kreutzman
http://vw.tauxe.net

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Post by Amskeptic » Sun Mar 21, 2010 3:07 pm

jtauxe wrote:OK. But perhaps this pickup uses the old system, just as it came originally with a 1600 upright engine.

Looking below on the VW Heritage page in the list of parts for various years, it seems to match up to this one:
Master cyl. 1.6, 8/70-79 ATE
[211-611-021/AE/ATE]
RHD/LHD German master cylinder, NOT SERVO 8/70> (includes end boot)

I'd appreciate any input from folks with a similar setup. To my knowledge, this would include Wooly Dave, but I know of no one else. Anyone?
You do have disk brakes? Pre 08/70 buses had drum brakes. Now I do not know what the actual circuit volume /piston diameter variations exist between the drum front circuit and the disk front circuit, but I think you want to know. If there are variations both between circuit volume and piston diameter, you need to specify disk brakes without booster. It may be that the master cylinder is identical between booster/non-booster buses. A aprt numbers investigation may help.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Post by jtauxe » Sun Mar 21, 2010 3:32 pm

Yes, disc brakes. (I edited the post to mention that after it occurred to me as well that it may be important.)

It seems clear from the VW Heritage description that they know it's for discs (>8/70) and also no servo. So this looks like the part...

Indeed... such an odd beastie this pickup. And the current master cylinder has no numbers on it...
John
"The bus came by and I got on. That's when it all began..." - Garcia/Weir/Kreutzman
http://vw.tauxe.net

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