Another Hot Rear Brake

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vwlover77
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Another Hot Rear Brake

Post by vwlover77 » Sun Dec 02, 2012 11:57 am

I've been gradually working on my rear brakes trying to figure out why my Bus slews left from the rear under hard braking (viewtopic.php?f=44&t=10988 .

To that end, the wheel cylinder that was originally on the passenger side is now on the driver's side. Yesterday after driving the Bus I noticed that the driver's drum was significantly hotter than the passenger side - too hot for such a short drive. I immediately jacked up the Bus and found excessive drag on the driver's side rear wheel, although there was none after I adjusted the brakes when I installed the wheel cylinder a few weeks ago.

Thinking that the parking brake cable might be hanging up, I grabbed the cable under the spring plate and moved and flexxed it all around. No effect. I then got in the Bus and worked the parking brake lever back and forth 5 or 6 times. No effect.

Finally, I depressed the brake pedal firmly and released it one time. This released the brakes and the drag disappeared.

Strange.... Then, to rule out the parking brake cable, I drove the Bus again with the now-freed brakes, came home, and without touching the parking brake, immediately jacked up the rear wheels. The drag was back on the left rear wheel. Once again, a single firm application and release of the brake pedal freed the wheel.

Is there something happening mechanically to "jam" the shoes to the drums from the rotational force of braking, or is the wheel cylinder sticking?
Don

---------------------------
78 Westy
71 Super Beetle Convertible Autostick

"When we let our compassion go, we let go of whatever claim we have to the divine." - Bruce Springsteen

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Re: Another Hot Rear Brake

Post by Amskeptic » Sun Dec 02, 2012 10:25 pm

vwlover77 wrote:I've been gradually working on my rear brakes trying to figure out why my Bus slews left from the rear under hard braking (viewtopic.php?f=44&t=10988 .

To that end, the wheel cylinder that was originally on the passenger side is now on the driver's side. Yesterday after driving the Bus I noticed that the driver's drum was significantly hotter than the passenger side - too hot for such a short drive. I immediately jacked up the Bus and found excessive drag on the driver's side rear wheel, although there was none after I adjusted the brakes when I installed the wheel cylinder a few weeks ago.

Thinking that the parking brake cable might be hanging up, I grabbed the cable under the spring plate and moved and flexxed it all around. No effect. I then got in the Bus and worked the parking brake lever back and forth 5 or 6 times. No effect.

Finally, I depressed the brake pedal firmly and released it one time. This released the brakes and the drag disappeared.

Strange.... Then, to rule out the parking brake cable, I drove the Bus again with the now-freed brakes, came home, and without touching the parking brake, immediately jacked up the rear wheels. The drag was back on the left rear wheel. Once again, a single firm application and release of the brake pedal freed the wheel.

Is there something happening mechanically to "jam" the shoes to the drums from the rotational force of braking, or is the wheel cylinder sticking?
If it is not a mechanical issue with the ebrake or return springs, then we are veering towards another look at brake hose and *master cylinder push-rod free play*.
Get the drag to occur on the left rear wheel.
Release the 7mm bleeder screw. Does drag go away? Then it is a proven hydraulic issue. Re-tighten bleeder.
A) Make sure that the pushrod has at least 1mm free play before you feel it contact the master cylinder. Do not mistake slop at the clevis pin for free play, we are talking actual back-and-forth click of the rod as it passes through the booster. If and once that play is guaranteed, try to replicate drag.
B) If it comes back, replace the left rear brake hose. If it does not come back, well, the push rod was not allowing the compensating port for the rear circuit to release residual brake fluid pressure.

This has been a vexing and subtle issue. Kudos for your persistence . . .
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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vwlover77
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Re: Another Hot Rear Brake

Post by vwlover77 » Sun Dec 09, 2012 8:05 pm

Latest update:

Just to be sure, I pulled out the driver's side parking brake cable for inspection and lube. The cable looked fine and now sports a nice fresh coat of grease.

Since I had the drum and shoes out and replacement wheel cylinders are cheap, I went ahead and replaced the driver's side cylinder too. Now driver and passenger side cylinders are both new and match.

The driver's side drum was showing much more wear than the passenger side and had some ridges too so I replaced it with a new German one (found a good deal on TheSamba).

Finally, I checked out the master cylinder pushrod. By slowly and gently pulling down on the brake pedal lever, I encountered two "clicks". The first was the free-play at the clevis pin being taken up, with no connecting rod movement. Then, the connecting rod moved a short distance (looked to be about 1mm but tough to measure) and the second click occured. I'm assuming this is the connecting rod to master cylinder free play, and it seemed to be OK.

Unfortunately, I have not had the opportunity to drive it yet!!! :-(
Don

---------------------------
78 Westy
71 Super Beetle Convertible Autostick

"When we let our compassion go, we let go of whatever claim we have to the divine." - Bruce Springsteen

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Amskeptic
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Re: Another Hot Rear Brake

Post by Amskeptic » Mon Dec 10, 2012 4:52 pm

vwlover77 wrote: Unfortunately, I have not had the opportunity to drive it yet!!! :-(
What a tease . . . Good Luck!
Colin
(when are you going to drive it??)
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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drober23
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Re: Another Hot Rear Brake

Post by drober23 » Mon Dec 10, 2012 5:19 pm

Getting a little chilly for busses in Ohio nowadays. He may make you wait till spring!
DJ

'75 Westfalia, '79 Deluxe
(plus more busses than sense)

In a time of chimpanzees I was a monkey

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Re: Another Hot Rear Brake

Post by Amskeptic » Mon Dec 10, 2012 6:48 pm

drober23 wrote:Getting a little chilly for busses in Ohio nowadays. He may make you wait till spring!
It is not too chilly for you get out into your treasure trove and start restoring your sixtymillion thousand Volkswagens languishing piteously.
Colin :sunny:
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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vwlover77
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Re: Another Hot Rear Brake

Post by vwlover77 » Mon Dec 10, 2012 7:58 pm

Well, it's pretty clean right now and I didn't want to take it out in the pouring rain! :geek:

No way can I wait for Spring, though. I need to know!!!

Hopefully I will drive it tomorrow evening. I don't mind the cold, but when the road salt comes out, the season is over.
Don

---------------------------
78 Westy
71 Super Beetle Convertible Autostick

"When we let our compassion go, we let go of whatever claim we have to the divine." - Bruce Springsteen

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Re: Another Hot Rear Brake

Post by Amskeptic » Tue Dec 11, 2012 2:34 pm

vwlover77 wrote:Well, it's pretty clean right now and I didn't want to take it out in the pouring rain! :geek:
Except when it helps . . . :
Image
(blizzard of '91 cross-country in Vanagon)
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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vwlover77
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Re: Another Hot Rear Brake

Post by vwlover77 » Tue Dec 11, 2012 7:19 pm

That was one dirty Vanagon! Poor thing....(I want one!)

I drove the Bus tonight and am declaring victory!

- No drag or excessive heat from the left rear brake after a 20 minute drive
- No significant slewing under hard braking (still a slight slew to the left, but significantly better)
- Under panic braking, both rear wheels lock at the same time
- Brake pedal feels more responsive

I think it was the wheel cylinder.
Don

---------------------------
78 Westy
71 Super Beetle Convertible Autostick

"When we let our compassion go, we let go of whatever claim we have to the divine." - Bruce Springsteen

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Re: Another Hot Rear Brake

Post by Amskeptic » Wed Dec 12, 2012 8:49 am

vwlover77 wrote: am declaring victory!
I think it was the wheel cylinder.
Congratulations! May this thread guide the many thousands who read it to a successful braking system since we seemed to have touched upon pretty much everything that could possibly go wrong . . . :cyclopsani:
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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drober23
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Re: Another Hot Rear Brake

Post by drober23 » Wed Dec 12, 2012 5:59 pm

Amskeptic wrote:
drober23 wrote:Getting a little chilly for busses in Ohio nowadays. He may make you wait till spring!
It is not too chilly for you get out into your treasure trove and start restoring your sixtymillion thousand Volkswagens languishing piteously.
Colin :sunny:

Well, I have an excuse this time... I'm in Beijing, China for work until the 21st. Haven't seen any air cooled VWs here at all. They say over 11 million people live here. I think they all were in the subway station with me last night. A veritable sea of people. But the people I have met have been great, and the sights in Beijing are worth seeing.

DJ
DJ

'75 Westfalia, '79 Deluxe
(plus more busses than sense)

In a time of chimpanzees I was a monkey

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vwlover77
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Re: Another Hot Rear Brake

Post by vwlover77 » Sat Dec 15, 2012 3:02 pm

Hmmmm.... Apparently I declared victory too soon. I drove the Bus for a longer time today and it still slews left under hard braking. After the drive, the driver's side brake drum was much warmer than the passenger side, but there is no drag on either side. The shoes are nearly new with less than 2000 miles on them. All of the rubber hoses were replaced 2 years ago and have traveled less than 10,000 miles. Both rear wheel cylinders are new within the past few weeks. The driver's side brake drum is new, too.

The only thing left that I can think of is to replace the solid steel lines from the tee to the right rear wheel. They look fine on the outside, but maybe they are restricted somehow on the inside?
Don

---------------------------
78 Westy
71 Super Beetle Convertible Autostick

"When we let our compassion go, we let go of whatever claim we have to the divine." - Bruce Springsteen

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Amskeptic
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Re: Another Hot Rear Brake

Post by Amskeptic » Sat Dec 15, 2012 8:16 pm

vwlover77 wrote:Hmmmm.... Apparently I declared victory too soon. I drove the Bus for a longer time today and it still slews left under hard braking. After the drive, the driver's side brake drum was much warmer than the passenger side, but there is no drag on either side. The shoes are nearly new with less than 2000 miles on them. All of the rubber hoses were replaced 2 years ago and have traveled less than 10,000 miles. Both rear wheel cylinders are new within the past few weeks. The driver's side brake drum is new, too.

The only thing left that I can think of is to replace the solid steel lines from the tee to the right rear wheel. They look fine on the outside, but maybe they are restricted somehow on the inside?
You know Don, you are just begging for a real Itinerant Air-Cooled appointment sort of day where i have to put my reputation on the line to guarantee you a successful result. Meanwhile, there is no way that a line can restrict initial application of brake without also restricting release. Might there be a plug o'crap at any one of the junctions that feed the right? This is amazing. It has piqued my interest.
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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vwlover77
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Re: Another Hot Rear Brake

Post by vwlover77 » Mon Dec 17, 2012 3:12 pm

It is amazing to me too.... How can a system so basically simple not work? I feel my own reputation is on the line here too!
Don

---------------------------
78 Westy
71 Super Beetle Convertible Autostick

"When we let our compassion go, we let go of whatever claim we have to the divine." - Bruce Springsteen

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