Rear Drum Brakes Locking On (1972 Camper)

[Ben Middleton]

I do have a hard copy of the Bentley which I’ve been using for this.

If I adjust the brakes up tight then the pedal does rise higher. The parking brake is currently slack because I was waiting until I could confirm everything else was set correctly.

I don’t have enough jars or hoses right now to do the gravity bleed like that. Could I gravity bleed each point individually? How long do you have to leave it for?

[Wildthings]

[Ben Middleton]

Well, I’ve had no success with the gravity bleeding. I decided to try and bleed the master cylinder again.

I took off the inlet line into the rear brake pressure regulator and tried to bleed it from there, because that is a direct line from the master cylinder. The brake fluid just poured out without me pressing the brake pedal at all and would have continued until both reservoirs were empty. Is that correct? My assumption was that, after some fluid from the line had come out, no more fluid would get past the master cylinder until I pressed the pedal. In which case, the master cylinder must be defective or maybe I have rebuilt it incorrectly.

[kreemoweet]

[Ben Middleton]

I’m so confused. I replaced both of the bungs, if you go back in the thread you will see the photos I showed of the new bungs. I guess they must be the wrong type?

I know it’s a long thread, so not everybody will keep up with the order of things. I bought a new master cylinder and fitted it. I later removed it, took apart, cleaned it out and rebuilt it using brake fluid and the ATE rebuild paste. I didn’t use a rebuild kit. I did this purely to ensure there was no crap inside it.

[ToolBox]

Have you verified the push rod adjustment????

[Ben Middleton]

I was satisfied that it was correct but I think I will disconnect the master cylinder from the servo and see if the flow stops. If it does, I guess we can assume that the push rod is holding open the master cylinder. If it doesn’t, then I guess I’ve got to dismantle the master cylinder again.

[Ben Middleton]

I tried to do the procedure I described in the previous post but it didn’t seem to have much of an effect, which suggests that the push rod was not causing the issue.

I dismantled the master cylinder and checked to see if I’d rebuilt it correctly. Everything looked to be in the correct order so I assumed I’d rebuilt it correctly. I’ve now packaged up the master cylinder and sent it back for a replacement. Let’s hope the next one is not faulty. Is there a way of bench testing a master cylinder?

Here’s some photos of the internals of the master cylinder, laid out as they were inside the master cylinder before I removed them. If anyone can see the cause of the problem, it might be useful to know for future reference.

Varga servo master cylinder internals:

[kreemoweet]

There's nothing obviously amiss with your m/c. The parts are a little different from the internals of the Varga m/c
I have (over 20 yrs old). An internal m/c leak is the most likely cause of a persistently mushy or too-low pedal
after shoes have been adjusted and reasonable effort put into bleeding.

I've never understood the difficulties people sometimes have bleeding the brake system. Just last week, I had the m/c out and brake lines
open to the air for a couple days. The reinstalled m/c "self-bled", i.e. just about all the air bubbled all by itself up into the reservoir and then
up the tube and out the refill reservoir. (I think the bus has to be fairly level for that to happen). A few pedal pumps discharged from each
wheel cylinder, and it was good to go. The Bentley manual says the bleeder (if there is one) on the pressure regulator should under no
circumstances be used to bleed the brake lines. Don't ask me why!

As far as checking the booster pushrod-to-m/c clearance, I don't think you need to measure anything: if there is interference, the m/c (without seal
ring installed) will not sit flush on the booster without pushing on it. If it does, you can conclude the clearance is zero or greater. Excessive clearance
doesn't seem to be a real possibility with the boosters available nowadays.
_________________
'67 bug: seized by the authorities
'68 bug: seized by the authorities
'71 kombi: not yet seized by the authorities

Stop dead photo links! Post your photos to The Samba Gallery!

[Ben Middleton]

OK so, I have fitted the replacement master cylinder and the problem persists.

PLEASE HELP!

When the brakes are slammed on, the camper just slowly comes to a stop. The pedal is soft and the brakes begin to work after about 2 inches of pedal travel, when the pedal hardens up a bit. The pedal travel is almost all the way to the floor - about two inches from the floor.

If the rear brake shoes weren't adjusted high enough, would that provide this poor braking performance? I was under the impression that these buses would stop somewhat effectively even with just the front disc brakes.

I think there is a possibility that the clearance between the push rod and master cylinder is now too large, and the brakes aren't engaging quickly enough. However, surely the brakes would still be fully functional when doing an emergency stop - but they're not.

Any ideas?

[kreemoweet]

[Wildthings]

[Westfalia73]

[SGKent]

did you look inside the master to be sure that there are no pits (usually dark spots) where the fluid can bleed around the seals?

Did you try pressure bleeding the system? They are inexpensive and do an outstanding one person job.

Is the bus pretty level? if it is not level the rear system will not bleed properly and air will stay in that part of the system. The reason is the bus may think you are in a nose dive and divert fluid in the proportioning valve. Did you bleed the proportioning valve? The early valve has a separate bleeder on it. The brakes should be rock hard until you start the engine if they are properly bled and the booster is exhausted of vacuum.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Ben Middleton]

Thanks for the suggestions guys. I replaced the master cylinder and this one is behaving exactly the same, so I will assume that neither of them were faulty.

Whenever I bleed the bus, I do it on level ground. I noticed that the right rear brake bleeds extremely slowly until I bleed the pressure regulator. After that, the right rear will bleed normally. I'm not sure why this is.

I now realise that I may have purchased the wrong master cylinder grommets. Some retailers, apparently including Volkswagen themselves, list 211-611-817/A as the correct part for all Transporters 1967-1979 (7mm ID, 18mm OD). However, some retailers only list that part for the non-servo buses. They list 357-611-817 for servo buses 1971-1979 (12mm ID, 22mm OD). This is obviously a much more recent part number, so I'm not sure what the situation is here.

If I have fitted the smaller bungs and the seal isn't perfectly tight, could this cause the brakes to be soft? Technically, the grommets are on the gravity-feed side of the braking system, so I've been told it wouldn't make a difference. Providing you're not leaking brake fluid, it isn't a problem if the seals don't fit tightly. However, my concern would be that air is entering the system.

Does anybody know more about this situation?

Here is an example of a British retailer who lists both grommets:

Grommet for non-servo buses (211-611-817/A)
https://www.justkampers.com/211-611-817-a-master-c...-1979.html

Grommet for servo buses (357-611-817)
https://www.justkampers.com/357-611-817-brake-rese...-1992.html

[kreemoweet]

I think JK is confused. It also is not clear exactly what is being measured. The OD of the reservoir nipples is 8.4 mm, and the ID of the
m/c bores where the reservoir nipples is inserted is approx 18 mm with an entrance lip of 15 mm. Therefore a bung with (uninstalled) ID
of 7 mm and OD of 18 mm is exactly right. That is what my genuine ATE bungs measure, and they fit perfectly. They are ATE #3.3304-1000-1.

If fluid is not leaking out, then air in not likely to be leaking in. There would have to be some sort of suction to draw air in, and there is just
the opposite, i.e. gravity pressure of the fluid.

I think your trust in m/c's not being faulty just because new, is misplaced.
_________________
'67 bug: seized by the authorities
'68 bug: seized by the authorities
'71 kombi: not yet seized by the authorities

Stop dead photo links! Post your photos to The Samba Gallery!

[Ben Middleton]

[Zed999]

Whereabouts in Englandshire are you Ben?

[Ben Middleton]

[Zed999]