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Rear Drum Brakes Locking On (1972 Camper)
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Ben Middleton
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PostPosted: Wed Jun 27, 2018 3:17 pm    Post subject: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

I have tried almost everything to stop my rear drum brakes locking on. I have replaced with new: the brake servo, the master cylinder, all 4 of the rubber brake hoses and all of the hardware in the brake drums (springs, wheel cylinders, brake shoes, etc). The brake shoe adjusters are as low as possible and the handbrake cable is basically inoperative. The wheel cylinders never manage to pull the brake shoes all the way back to the stop. Both of them only get about halfway.

When I start driving, the brakes appear to be OK. However, within a minute or two the bus gets very sluggish. The engine gets very hot and the drums get extremely hot.

Can anyone point me to the source of the problem? I am thinking it might be the metal brake lines or the brake pressure regulator. Although, the pedal moves freely now so I don't think it's the metal brake lines. I just don't know enough about the pressure regulator to know if this could be a symptom of its failure.


Last edited by Ben Middleton on Wed Jun 27, 2018 3:23 pm; edited 1 time in total
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PostPosted: Wed Jun 27, 2018 3:22 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

how did you bleed the lines?
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PostPosted: Wed Jun 27, 2018 3:25 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Someone pumped the pedal while I bled each wheel. I did it in the order front right, front left, rear right, rear left (as per Bentley).

A previous owner appears to have replaced the front right caliper with one from a later year. It has two bleed nipples, which a '72 shouldn't. I didn't see this as a problem.
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PostPosted: Wed Jun 27, 2018 3:43 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

there are some things that will help you (and others) work thru this.

Underneath the bus there is a portioning valve that reduces brake fluid going to the rear wheels when the bus brakes hard and the nose dives. If you jack up the back of the bus to work on the brakes and it is significantly higher than the front, you are emulating a hard braking nose dive. That will reduce fluid to the rear brakes. While this isn't the cause of the problem, it can cause things to change between when the bus is jacked up in the back and level. So when you test a wheel, try to get the jack just under the hub carrier so the wheel can be jacked up an inch off the ground when you spin it. That will tell you if the wheel is free or not when you spin it by hand. When you spin it feel for out of round. Also push on the tire a little to see if the edges of the shoes are rubbing on the drum when it moves a little on the axle.

When you bleed the brakes, the front and rear are on different circuits. This means that if there is say air left in the rear, and the cylinder gets hot, as that air expands in the rear cylinders it will cause just the rear piston to move outwards. If you used say some kind of brake cleaner in the lines that left puddles of itself, that will boil at a low temperature and expand the shoes until they rub. Water in the brake fluid will too but it has to get hotter.

When the master cylinder is released, there is a port that fluid in the lines is released back into the brake fluid reservoir. If the master cylinder is not adjusted right with the booster then that port can get slightly covered and never open, holding a little residual pressure in the lines. The proper way to adjust the booster to master free play is in the Bentley. It has to be there or the pressure in the lines can't release.

There is probably more but I have to run to pick someone up.
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Bus Engine Cooling Issues? https://kentcomputer.com/77VW/BusEngineCooling.pdf
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Wildthings
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PostPosted: Wed Jun 27, 2018 4:15 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

When did the problem start? Has it ever been right during your ownership?
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PostPosted: Wed Jun 27, 2018 5:34 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Crack the bleeder valve on the pressure regulator and see if the wheel cyl returns to its stop.

Please open and read
Brake Pressure Regulator t2 211 612 501

Good luck
Tcash

Ps some have been able clean the press reg with brake clean to free up the ball.
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PostPosted: Thu Jun 28, 2018 7:14 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

I cracked the bleeder valve, closed it back up and inspected the brake shoes. They had returned to the stop. After a few presses of the pedal, they were not returning again.

Does this indicate a bad regulator?

I also had a read of that thread. If you think the regulator is the problem, Iíll remove it and attempt to clean it. Does it require any lubrication or just cleaning?
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PostPosted: Thu Jun 28, 2018 7:28 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Ben Middleton wrote:
The brake shoe adjusters are as low as possible

Please elaborate on that statement, do you have them backed off?, or tightened to where they won't turn anymore and then back a few clicks so the wheel turns with a slight drag?

Super loose brakes will be very grabby and lock up occasionally.
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PostPosted: Thu Jun 28, 2018 7:56 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Ben Middleton wrote:
Does this indicate a bad regulator?


Seems rather unlikely. There's really nothing in the regulator that would prevent release of fluid pressure from the rear lines, unless there was
massive corrosion in there. But if that was the case, the rear brakes wouldn't be operating normally initially, as you're telling it.

The new brake booster would be my primary suspect. It can cause problems similar to yours at both the front connection to the pedal linkage, and at the
rear interface with the master cylinder, where the internal pushrod contacts the front piston of the m/c. There needs to be a little free play at each of
those points.
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PostPosted: Thu Jun 28, 2018 8:00 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

I had one bus where I adjusted the slack from the E-brake and then when tightening the lug nuts couldn't turn the wheel by hand..
crack the lugs and turns easily by hand.


I had another that had improper aftermarket rims. (was a GW chrome steel offering) that would randomly drag one rear brake, and not always the same side.. the lug nuts weren't the correct type and pulled the rim face to the drum and tweaked the drum slightly.
we changed and loosened everything till I saw the clamping surface of the rims in relation of the drum.
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Ben Middleton
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PostPosted: Thu Jun 28, 2018 8:03 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Busdaddy - at the moment theyíre completely backed off because when I tried to set them initially, they were still grabbing even at the lowest setting due to the shoes not returning to the stop.

I installed a Brazilian brake servo with a Varga master cylinder. I have tried disconnecting the connecting rod entirely and it doesnít release the pressure at the drums. I was under the impression that the internal push rod in the servo is not adjustable. Therefore, how would I solve this problem if it is blocking the compensating port in the master cylinder? And how would I even check it?

The e-brake is operating at about 12 clicks. I havenít set it yet because I would prefer to have the reassurance that it isnít the cause of the issue. My wheels are standard wheels.

Thanks for all your advice and suggestions so far.
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PostPosted: Thu Jun 28, 2018 8:12 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Ben post your general location in your avatar.

My instinct is that the return relief port in the master is blocked. You can test that theory by jacking a rear wheel up an inch and trying to turn the wheel. According to your description it should be tight. Using a flare nut wrench loosen the steel line to/from the rear brakes AT THE MASTER until it leaks fluid out. Let it sit a minute to equalize then check that rear wheel again. If it is still tight then the problem is between the master and the wheel. If the problem is gone then the problem is forward of that point - and since the master is the only thing forward of that point there is your culprit.
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* VW Buses and VW cars share many of the same systems but if you haven't owned a bus and maintained it for awhile, you really don't know how different it is.

Bus Engine Cooling Issues? https://kentcomputer.com/77VW/BusEngineCooling.pdf
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PostPosted: Thu Jun 28, 2018 10:01 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Master cylinder has been replaced. That should rule out the compensation ports and the residual pressure valve.

If the ball is hung up in the pressure regulator then it would restrict the fluid flow back to the master cylinder I would think. But the pressure should not hold, it should bleed off slowly. Easy enough to crack the bleeder or the return line and see if that relieves the pressure.
Brake Pressure Regulator t2 211 612 501

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.


The other thing you mentioned was the hard lines. If they where clogged, you would not get much fluid coming out of the bleeder. When you bleed the brakes.

Good luck
Tcash
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PostPosted: Thu Jun 28, 2018 10:09 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Tcash wrote:
Master cylinder has been replaced. That should rule out the compensation ports and the residual pressure valve.

If the ball is hung up in the pressure regulator then it would restrict the fluid flow back to the master cylinder I would think. But the pressure should not hold, it should bleed off slowly. Easy enough to crack the bleeder or the return line and see if that relieves the pressure.

The other thing you mentioned was the hard lines. If they where clogged, you would not get much fluid coming out of the bleeder. When you bleed the brakes.

Good luck
Tcash


ever bought a defective part Tim? Or replaced the wrong part a PO put in with one identical to it? I am thinking that the MC has to be eliminated first to be sure it isn't the cause. Lines rarely plug other than the rubber ones, which he replaced.
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*You can do it right the first time, or do it over, the choice is yours. It is a free country. As to brakes, steering, tires, axles etc. - you may only get one chance at doing it right.

* VW Buses and VW cars share many of the same systems but if you haven't owned a bus and maintained it for awhile, you really don't know how different it is.

Bus Engine Cooling Issues? https://kentcomputer.com/77VW/BusEngineCooling.pdf
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PostPosted: Thu Jun 28, 2018 2:09 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Ben Middleton wrote:
... when I tried to set them initially, they were still grabbing even at the lowest setting due to the shoes not returning to the stop.
I was under the impression that the internal push rod in the servo is not adjustable. Therefore, how would I solve this problem if it is blocking the compensating port in the master cylinder? And how would I even check it?


What is this "stop" you keep referring to? There is no "stop" in standard bus rear brakes. Do you have VW's experiment with self-adjusting rear brakes?
Some booster pushrods are adjustable, and some not. I don't know about the VW Brazil booster.
You can test by removing the master cyl. 0-ring seal and dropping the m/c into place on the booster as you would when installing. You can pretty
much feel if the pushrod bottoms on the m/c piston before the m/c contacts the booster surface.
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PostPosted: Thu Jun 28, 2018 4:40 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

The stop Iím referring to is the slot in the bar that connects the two brake shoes. I thought the springs were supposed to return the pin completely into that slot.

Anyway, I decided to dismantle the pressure regulator. It was completely caked in grit and dirt. The ball couldnít move, as you can imagine. I cleaned it all out and it seemed functional so I refitted it.

The left rear brake now functions correctly. The right rear brake is still locking on. I tried to bleed the right rear brake without first bleeding the pressure regulator, as suggested by Bentley, but that didnít work at all. Nothing came out, not even air. I bled the pressure regulator and the rear brakes would then bleed.

The pressure regulator bled very slowly and not much liquid came out. The rear right brake also bled very slowly. The rear left brake bled quickly.

I suppose this suggests the brake lines are blocked? Whatís the best way to proceed?
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PostPosted: Thu Jun 28, 2018 6:46 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Quote:
I thought the springs were supposed to return the pin completely into that slot.


?? usually the cross bar sits in slots in the shoes. Image from the Samba Gallery of Seventy3Bus

Image may have been reduced in size. Click image to view fullscreen.

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*You can do it right the first time, or do it over, the choice is yours. It is a free country. As to brakes, steering, tires, axles etc. - you may only get one chance at doing it right.

* VW Buses and VW cars share many of the same systems but if you haven't owned a bus and maintained it for awhile, you really don't know how different it is.

Bus Engine Cooling Issues? https://kentcomputer.com/77VW/BusEngineCooling.pdf
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PostPosted: Thu Jun 28, 2018 9:19 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

For a Type 1 there are all different kinds of slave cylinders out there. Some are just plain incorrect in how they work. I don't think I have ever experienced the same on a Type 2 but I wouldn't be surprised to find it that there were incorrectly designed slave cylinders for a Type 2 as well.
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PostPosted: Thu Jun 28, 2018 11:14 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

You can try cleaning the brake lines with brake fluid and compressed air. You may end up needing to replace the lines in the end.
Good luck
Tcash
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Ben Middleton
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PostPosted: Fri Jun 29, 2018 5:18 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

The Ď72 has a one year only drum brake set up. The crossbar is parallel to the hub, rather than perpendicular. You can see how the shoes werenít returning to the stop, in the first photo below.

Iím going to have to try and clean through the brake line I guess. Should be fun lol.

Hereís a few pics. Two pics of a Ď72 drum brake and one pic of a component from the rear brake pressure regulator, just to show the level of residue that was in there.

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.
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