Hello! Log in or Register   |  Help  |  Donate  |  Buy Shirts  See all banner ads | Advertise on TheSamba.com  
TheSamba.com
 
Rear Drum Brakes Locking On (1972 Camper)
Page: Previous  1, 2, 3, 4  Next
Forum Index -> Bay Window Bus Share: Facebook Twitter
Reply to topic
Print View
Quick sort: Show newest posts on top | Show oldest posts on top View previous topic :: View next topic  
Author Message
Tcash
Samba Member


Joined: July 20, 2011
Posts: 12844
Location: San Jose, California, USA
Tcash is offline 

PostPosted: Fri Jun 29, 2018 8:45 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Sure looks like the pistons are not collapsed all the way.
Yours
Image may have been reduced in size. Click image to view fullscreen.

One from the Gallery.
Image may have been reduced in size. Click image to view fullscreen.


Another thing to look at is the Rubbing blocks on the backing plate. This is where the brake shoe rubs against the backing plate. They can get grooved and not allow the shoes to fully collapse.


They are the four rectangular blocks in this picture. File them flat and apply anti seize to them.
Image may have been reduced in size. Click image to view fullscreen.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Wildthings
Samba Member


Joined: March 13, 2005
Posts: 38473

Wildthings is offline 

PostPosted: Fri Jun 29, 2018 12:48 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Ben Middleton wrote:

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


Do the shoes pull in when you open the bleeder on the slave cylinder?
Back to top
View user's profile Send private message Gallery Classifieds Feedback
SGKent Premium Member
Samba Member


Joined: October 30, 2007
Posts: 28831
Location: Nor Cal
SGKent is offline 

PostPosted: Fri Jun 29, 2018 1:44 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

that cylinder is expanded. I concur that there is pressure in it holding it out.
_________________
*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 those 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
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
Abscate Premium Member
Samba Member


Joined: October 05, 2014
Posts: 8653
Location: NYC/Upstate/ROW
Abscate is offline 

PostPosted: Fri Jun 29, 2018 6:42 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

That parking brake bar is hung up and holding the shoes out. Iím guessing it isnít in right

Remove it, temporarily, and see if your hang ups improve.

Your Bus hang ups, I mean.

The spring should be resting in full compressed position.
_________________
.ssS!
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Ben Middleton
Samba Member


Joined: April 11, 2016
Posts: 78
Location: England, UK
Ben Middleton is offline 

PostPosted: Mon Jul 02, 2018 4:30 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Well chaps, looks like the handbrake cable was causing the problem in the right rear drum. I disconnected it and the cylinder closed up fully.

Iím glad I didnít spot that earlier because I have replaced a somewhat blocked rubber brake hose and refurbished the rear brake pressure regulator in the process of trying to isolate the cause of the problem, problems which I may not have noticed otherwise.

I am a bit confused by the handbrake cable. The Bentley manual tells me to unbolt the cable from the backing plate - I canít find a bolt anywhere. Is the Ď72 different?

Also, the left rear brake drum has had its handbrake cable replaced at some point. It appears to be functional, but the spring doesnít fully close up when disconnected. It looks different from the original style spring on the other drum.

The handbrake cable in the right drum doesnít move freely. Should I just remove it and grease it, or does it need to be replaced?


PS - Today I intend to use an air compressor to blow through the brake lines, just to be sure theyíre not blocked at all.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Wildthings
Samba Member


Joined: March 13, 2005
Posts: 38473

Wildthings is offline 

PostPosted: Mon Jul 02, 2018 8:00 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Ben Middleton wrote:
Well chaps, looks like the handbrake cable was causing the problem in the right rear drum. I disconnected it and the cylinder closed up fully.

Iím glad I didnít spot that earlier because I have replaced a somewhat blocked rubber brake hose and refurbished the rear brake pressure regulator in the process of trying to isolate the cause of the problem, problems which I may not have noticed otherwise.

I am a bit confused by the handbrake cable. The Bentley manual tells me to unbolt the cable from the backing plate - I canít find a bolt anywhere. Is the Ď72 different?

Also, the left rear brake drum has had its handbrake cable replaced at some point. It appears to be functional, but the spring doesnít fully close up when disconnected. It looks different from the original style spring on the other drum.

The handbrake cable in the right drum doesnít move freely. Should I just remove it and grease it, or does it need to be replaced?


PS - Today I intend to use an air compressor to blow through the brake lines, just to be sure theyíre not blocked at all.


For later Transporters the cables are not particularly expensive, can't say for your one year set up.

Your picture doesn't make it look like the cable is at fault though???
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Abscate Premium Member
Samba Member


Joined: October 05, 2014
Posts: 8653
Location: NYC/Upstate/ROW
Abscate is offline 

PostPosted: Mon Jul 02, 2018 9:20 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Quote:
functional, but the spring doesnít fully close up when disconnected.


Pretty much nails it
_________________
.ssS!
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Ben Middleton
Samba Member


Joined: April 11, 2016
Posts: 78
Location: England, UK
Ben Middleton is offline 

PostPosted: Mon Jul 02, 2018 2:46 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Well, hereís another depressing update.

I removed the handbrake cables. Only the right one was broken and the pic I sent was of the left one, thatís why it looks OK.

Firstly, I blew compressed air through the rear brake circuit and confirmed there are no blockages.

After removing the handbrake cables and bleeding the brakes again, the problem persisted. I bled the pressure regulator first, then the right rear and left rear brakes.

Initially, after bleeding, the brake cylinders closed up and the drums were free (indicating to me that the shoes arenít catching on the backing plate). I pressed the brake pedal and it went low and soft. The brake drums didnít lock up after releasing. However, after more presses of the pedal, the pedal got harder and higher. Eventually it felt like a good brake pedal but the rear brakes were now locked on. I re-bled the pressure regulator and the brakes freed up again. Once again, after multiple pedal presses, the shoes locked on.

Itís like the pressure is building up and forcing the cylinders out after repeatedly pressing the brake pedal.

I have also double checked the servo pushrod clearance. I can rattle the connecting rod back and forth about 1-2mm without any considerable pressure while the brakes are locked on, which makes me assume that the pushrod clearance is correct and no pressure is being applied to the servo when the brake pedal is released.

The Bentley manual mentions that locked brakes could be caused by a blocked compensating port. Could it be blocked with anything other than the servo pushrod?

I am starting to think that I havenít managed to refurbish the pressure regulator correctly. I didnít apply any grease inside because I assumed that only brake fluid was required. Does anyone know if thatís correct? I know they apparently fail but the seals were good and the ball moved freely, so I canít see what the issue is, if it is indeed not functioning correctly.

There is a possibility that some brake fluid is leaking from either the tube connecting the upper reservoir to the lower reservoir, or from the master cylinder bungs (or both). Would this cause this problem with the brakes locking on?

Otherwise, Iím stumped!
Back to top
View user's profile Send private message Gallery Classifieds Feedback
raygreenwood
Samba Member


Joined: November 24, 2008
Posts: 15013
Location: Des moines Iowa
raygreenwood is offline 

PostPosted: Mon Jul 02, 2018 3:43 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Ben Middleton wrote:
Well, hereís another depressing update.

I removed the handbrake cables. Only the right one was broken and the pic I sent was of the left one, thatís why it looks OK.

Firstly, I blew compressed air through the rear brake circuit and confirmed there are no blockages.

After removing the handbrake cables and bleeding the brakes again, the problem persisted. I bled the pressure regulator first, then the right rear and left rear brakes.

Initially, after bleeding, the brake cylinders closed up and the drums were free (indicating to me that the shoes arenít catching on the backing plate). I pressed the brake pedal and it went low and soft. The brake drums didnít lock up after releasing. However, after more presses of the pedal, the pedal got harder and higher. Eventually it felt like a good brake pedal but the rear brakes were now locked on. I re-bled the pressure regulator and the brakes freed up again. Once again, after multiple pedal presses, the shoes locked on.

Itís like the pressure is building up and forcing the cylinders out after repeatedly pressing the brake pedal.

I have also double checked the servo pushrod clearance. I can rattle the connecting rod back and forth about 1-2mm without any considerable pressure while the brakes are locked on, which makes me assume that the pushrod clearance is correct and no pressure is being applied to the servo when the brake pedal is released.

The Bentley manual mentions that locked brakes could be caused by a blocked compensating port. Could it be blocked with anything other than the servo pushrod?

I am starting to think that I havenít managed to refurbish the pressure regulator correctly. I didnít apply any grease inside because I assumed that only brake fluid was required. Does anyone know if thatís correct? I know they apparently fail but the seals were good and the ball moved freely, so I canít see what the issue is, if it is indeed not functioning correctly.

There is a possibility that some brake fluid is leaking from either the tube connecting the upper reservoir to the lower reservoir, or from the master cylinder bungs (or both). Would this cause this problem with the brakes locking on?

Otherwise, Iím stumped!



Yes....this sounds like a compensation port. Some things that can cause this:

1. You noted its a NEW master cylinder. Is it NEW...or NOS (new old stock)?

On new old stock cylinders it is VERY common that the brass flap valves which are the compensation port flap valves....are stuck to teh pistons and not opening due to moisture and age corroding them to the piston faces.

Even on some new MC's I have found stubborn dried assembly lube gluing the flap valves down or clogging the ports in the piston.

2. As you already know....the pedal push rod must have free play between it and the piston so that the piston does not move down the bore and cover fluid inlet ports from the reservoir. Since you have a power brake booster....make sure that the free play between brake pedal and booster...also is allowing actual gap between the booster pushrod and the MC piston like in the picture below.

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


3. Another way this can happen...and is also really common with brakes that pump up and then will not release is that the plastic elbow in the brake fluid feed line from the reservoir...on some master cylinders...where it sticks through the rubber grommet in the top of the master cylinder...can be pushed slightly too far in. This can cause the flood of the recess to close off teh flow of replenishment fluid during a brake movement...as well as the back flow of fluid into the reservoir when you let off the pedal.

This can also happen if the grommets in the top of teh MC are installed upside down.

This is not actually a blocked compensation port...but acts just like one. You can see this effect in this link if you scroll down to the very bottom of the post.

https://www.thesamba.com/vw/forum/viewtopic.php?t=...highlight=

Ray
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Ben Middleton
Samba Member


Joined: April 11, 2016
Posts: 78
Location: England, UK
Ben Middleton is offline 

PostPosted: Mon Jul 02, 2018 4:39 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Thank you for that in-depth reply Ray, I really appreciate your advice.

The master cylinder I bought is a Varga/TRW one, presumedly Brazilian-made. Do you think I should dismantle it and rebuild it as you describe in your other post? The servo is also Brazilian-made.

I think I should get some new seals for the lower reservoir because I reused the old ones as they seemed a tight fit, but they are possibly leaking. I will probably also install a new reservoir-to-reservoir hose.

Do you know of a good method for measuring the clearance between the servo push rod and the master cylinder?

Finally, when I rebuilt the pressure regulator, I initially used an alcohol spray but then used brake cleaner to remove the debris, as I thought it would be more appropriate. Was that the wrong decision?

Again, thanks for your help. It looks like itíll be many more hours before I can stop my camper.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Wildthings
Samba Member


Joined: March 13, 2005
Posts: 38473

Wildthings is offline 

PostPosted: Mon Jul 02, 2018 5:27 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

When removing an old master cylinder and installing a replacement, it is possible from crap to break loose in the outlet and end up blocking the outlet on the new cylinder. This blockage may act like a check valve.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
raygreenwood
Samba Member


Joined: November 24, 2008
Posts: 15013
Location: Des moines Iowa
raygreenwood is offline 

PostPosted: Mon Jul 02, 2018 6:31 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Ben Middleton wrote:
Thank you for that in-depth reply Ray, I really appreciate your advice.

The master cylinder I bought is a Varga/TRW one, presumedly Brazilian-made. Do you think I should dismantle it and rebuild it as you describe in your other post? The servo is also Brazilian-made.

I think I should get some new seals for the lower reservoir because I reused the old ones as they seemed a tight fit, but they are possibly leaking. I will probably also install a new reservoir-to-reservoir hose.

Do you know of a good method for measuring the clearance between the servo push rod and the master cylinder?

Finally, when I rebuilt the pressure regulator, I initially used an alcohol spray but then used brake cleaner to remove the debris, as I thought it would be more appropriate. Was that the wrong decision?

Again, thanks for your help. It looks like itíll be many more hours before I can stop my camper.


Personally.....I started many years ago ....cleaning out all brand new brake cylinders. Simply disassemble and clean with high quality denatured alcohol. What I mean by that.....is check the SDS for whatever brand you buy. Make sure its not a blend of the wrong stuff like I noted in that MC rebuild thread.


As for brake cleaner.....I never use it.....but....it is for external components ONLY. All internal seals of brake parts are made of EPDM. This rubber type breaks down with contact of any VOC.

Seals like the caliper external dust boots are actually viton to work with exposure to high heat, oils, foad salts etc. Brake cleaner is fine for those.

As long as you do not get brake cleaner inside of components you should be fine. Ray
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Tcash
Samba Member


Joined: July 20, 2011
Posts: 12844
Location: San Jose, California, USA
Tcash is offline 

PostPosted: Mon Jul 02, 2018 8:58 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

The Bentley manual mentions that locked brakes could be caused by a blocked compensating port. Could it be blocked with anything other than the servo pushrod?
Yes, by debris in the Master cylinder.
You should be able to see fluid return to the Brake fluid fill reservoir upon releasing the brake pedal.

I assumed that only brake fluid was required. Does anyone know if thatís correct? I know they apparently fail but the seals were good and the ball moved freely, so I canít see what the issue is, if it is indeed not functioning correctly.
Only brake fluid is required.
You need to start cracking brake line fitting starting at the master cylinder. Crack the fitting, brakes don't release move toward the wheel until it does release. Then therefore your problem lies in the section between that fitting and the master cylinder.
Make sense
Tcash
Back to top
View user's profile Send private message Gallery Classifieds Feedback
OB Bus
Samba Member


Joined: February 09, 2003
Posts: 1922
Location: Ocean Beach in Beautiful BLUE California
OB Bus is offline 

PostPosted: Tue Jul 03, 2018 6:15 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

I'm not nearly as adept as most of you here, but an idea. Early on I remember the OP saying that he backed the adjusters way off. Did he ever properly readjust them? Could the slave cylinders be over extending and then not return?
_________________
Larry in OB
Stop dead photo links! Post your photos to The Samba Gallery!
Go ahead, play golf. That is how to show respect.
69 Westfalia and 67 Single Cab.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
CarlosZ
Samba Member


Joined: April 23, 2016
Posts: 255
Location: Los Angeles
CarlosZ is offline 

PostPosted: Tue Jul 03, 2018 6:38 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

OB Bus wrote:
I'm not nearly as adept as most of you here, but an idea. Early on I remember the OP saying that he backed the adjusters way off. Did he ever properly readjust them? Could the slave cylinders be over extending and then not return?


Interesting theory. I just did my rear brakes on my Ď72. I hit the brake to see if the brake cylinder worked and the pistons (not sure the correct term) in the brake cylinder popped out all the way. I had to disassemble and push back in.

OP - Maybe too much slack due to the stars being loosened up all the way? I think by tightening the stars youíll reduce the travel of the pistons. Does the locking still occur with both brake cables completely disconnected?
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Ben Middleton
Samba Member


Joined: April 11, 2016
Posts: 78
Location: England, UK
Ben Middleton is offline 

PostPosted: Tue Jul 10, 2018 5:31 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Thanks for the suggestions guys. The star adjusters are still completely loosened off. I donít believe this is causing the issue because when I opened the bleeder valve on the pressure regulator, the wheel cylinders closed up nicely.

I have decided to remove, dismantle and clean the master cylinder. Ray, I noticed in your article that you say there are different rubbers of similar appearance used inside your example master cylinder, and these may be installed incorrectly. Could this be the case for a T2 servo master cylinder?

Also, you recommend denatured alcohol for cleaning of the master cylinders, should I just use brake fluid to rebuild it or some sort of assembly paste?

I am also replacing the bungs for the top of the master cylinder. I have noticed that the rubber insert at the bottom of the reservoir-to-reservoir pipe is perished. This rubber has broken up so maybe particles of it have blocked the master cylinder. Are these inserts available to purchase?

Thanks,
Ben
Back to top
View user's profile Send private message Gallery Classifieds Feedback
busdaddy
Samba Member


Joined: February 12, 2004
Posts: 40290
Location: Surrey B.C. Canada, Land of the giant flying moose!
busdaddy is offline 

PostPosted: Tue Jul 10, 2018 5:52 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Yes the master cylinder reservoir grommets are available from most vendors.
Silicone grease or brake assembly paste is best for lubing everything when putting it back together, alcohol or brake kleen for washing it out if you are drying everything right away.

They will always be grabby if you don't tighten up the adjusters, loose shoes are hard to regulate.
_________________
Rust NEVER sleeps and stock never goes out of style.

Wanted, OG paint 1971 Niagara blue decklid.

Stop dead photo links! Post your photos to The Samba Gallery!
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Tcash
Samba Member


Joined: July 20, 2011
Posts: 12844
Location: San Jose, California, USA
Tcash is offline 

PostPosted: Tue Jul 10, 2018 8:03 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

After the pressure reg, loosen the brake line at the master cylinder.
Wheel cylinder does not close up. Line between the pressure reg and master is plugged.

If the hose between the fill reservoir and the master reservoir where plugged, both front and rear brakes would be locking up.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Wildthings
Samba Member


Joined: March 13, 2005
Posts: 38473

Wildthings is offline 

PostPosted: Tue Jul 10, 2018 8:25 pm    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Ben Middleton wrote:
Thanks for the suggestions guys. The star adjusters are still completely loosened off. I donít believe this is causing the issue because when I opened the bleeder valve on the pressure regulator, the wheel cylinders closed up nicely.


Try cracking the line for the rear brake circuit at the master cylinder and see what happens.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Ben Middleton
Samba Member


Joined: April 11, 2016
Posts: 78
Location: England, UK
Ben Middleton is offline 

PostPosted: Wed Jul 11, 2018 2:08 am    Post subject: Re: Rear Drum Brakes Locking On (1972 Camper) Reply with quote

Iíve already removed the master cylinder and pressure regulator again. I forgot to crack the line at the master cylinder and check if the brakes free up, but I know I want to clean out the master cylinder and replace the rubbers anyway now. Iíd already refurbished the pressure regulator, and blown compressed air through the line between the regulator and the MC so I knew that wasnít blocked.

Iíll take a photo of the perished rubber that I need to replace, just to show bad it looks. Part number 211-611-833/C.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Display posts from previous:   
Reply to topic    Forum Index -> Bay Window Bus All times are Mountain Standard Time/Pacific Daylight Savings Time
Page: Previous  1, 2, 3, 4  Next
Page 2 of 4

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum

About | Help! | Advertise | Donate | Premium Membership | Privacy/Terms of Use | Contact Us | Site Map
Copyright © 1996-2018, Everett Barnes. All Rights Reserved.
Not affiliated with or sponsored by Volkswagen of America | Forum powered by phpBB