Sprinter van rear brake MOT fail

[KrissyB]

Hi guys
Our van failed, AGAIN, on the right rear brake. We've replaced the brake balance valve, pads and calipers, yet STILL the right rear brake isn't efficient to pass. We are about to replace the master cylinder. If this fails to help, does anyone have any advice / suggestions?
Thanks
KrissyB

 

[turbopete]

try the rear flexible hoses first. they can fail internally and cause a 'blockage' limiting the fluid pressure available to the calliper. assuming, of course the brake is only failing on the footbrake and not the parking brake also

 

[KrissyB]

Thank you. It has just failed again on the brake (post new master cylinder), so we are off to get hoses. I'll keep you posted.

 

[KrissyB]

Ok...yet AGAIN, failure! Replaced EVERYthing connected with the brakes, including a new master cylinder and brake sensor for the troublesome right side. Can't find a brake system diagram on wonderfully useless Google! Does anyone know if there would be a T piece connection for the brakes, under the fuel tank?
Thanks guys, and sorry!

 

[LostKiwi]

Without knowing exactly what your Sprinter is its hard to know but this si teh diagram for one with a VIN number starting 901312 so should be close I think:


You can see there are 2 lines to the rear and they go into a what looks to be a load proportioning valve. That would be a good place to look.

This is for a non-ABS version but the ABS version is similar but with the ABS pump at the front of the vehicle.

 

[KrissyB]

Without knowing exactly what your Sprinter is its hard to know but this si teh diagram for one with a VIN number starting 901312 so should be close I think:
View attachment 36918

You can see there are 2 lines to the rear and they go into a what looks to be a load proportioning valve. That would be a good place to look.

This is for a non-ABS version but the ABS version is similar but with the ABS pump at the front of the vehicle.

Thank you! Extremely helpful. Ours is non-ABC (1998) so we will be looking at your suggestion.
Krissy

 

[KrissyB]

Update: just swapped the left hand with the right hand brake pipe at the balance valve and there was no difference to the right wheel, so pipes are fine. We can only think it has to be something on the right rear wheel. I am falling out of love with our van rather rapidly!

 

[om613]

Looks like a seized caliper piston then - were they new or used?

 

[ernieh]

Did the replacement caliper bleed OK? Does the wheel lock up with the car on a jack and you apply the brakes? what like are the disks? Is the inner face or both for that matter, worn or scored. Other than those and the other suggestions, I'm stumped but would like to know the eventual outcome.

Ernie

 

[LostKiwi]

Presumably the brake on the right rear bleeds ok?
If so the issue must be in the brake itself.

 

[KrissyB]

Hi folks, thanks for the replies. Did some more work on it yesterday. The brakes can be locked on stands but not good enough for MOT. All bled ok.
I have tried swapping the output pipes from the compensator valve (left for right) and it was just the same. So it must be caliper related (they are new! :-( ). More to follow - will let you all know if/when I find the answer.

 

[ernieh]

Hi folks, thanks for the replies. Did some more work on it yesterday. The brakes can be locked on stands but not good enough for MOT. All bled ok.
I have tried swapping the output pipes from the compensator valve (left for right) and it was just the same. So it must be caliper related (they are new! :-( ). More to follow - will let you all know if/when I find the answer.

Were the replacement calipers new and were they from MB? You did replace both rear calipers didn't you? (the text suggests that you did!). Do you have any figures for the brake efficiency on each of the rear brakes? Does your handbrake work on separate drums? Do you have ABS? If you have, there might be a problem in the ABS unit that is limiting pressure to the problem wheel. Finally, have you tried another MOT station?

Sorry for the questions, but I once had a similar problem with a car I bought second-hand except that one of the rear brakes was locking up. The problem was that someone had a fitted a rear wheel slave cylinder that physically fitted, but had a larger bore, thus exerting a greater braking force on that drum.

Ernie

 

[KrissyB]

Were the replacement calipers new and were they from MB? You did replace both rear calipers didn't you? (the text suggests that you did!). Do you have any figures for the brake efficiency on each of the rear brakes? Does your handbrake work on separate drums? Do you have ABS? If you have, there might be a problem in the ABS unit that is limiting pressure to the problem wheel. Finally, have you tried another MOT station?

Sorry for the questions, but I once had a similar problem with a car I bought second-hand except that one of the rear brakes was locking up. The problem was that someone had a fitted a rear wheel slave cylinder that physically fitted, but had a larger bore, thus exerting a greater braking force on that drum.

Ernie

Ernie -Thanks for the reply - There is no ABS and the hand brake is a drum setup and working ok. It's the service brake that is 30% lower on the o/s/r compaired to n/s/r. Both calipers were replaced (pattern - not MB though, couldn't afford them). I replaced all the components after the van failed it's MOT on the brakes, so I'm thinking it would be unlikely the new calipers had the same fault as the old ones. Can't rule it out though, as there's nothing else left to replace!

 

[henrysmerc]

Assuming its failing on the footbrake,and the handbrake is ok,it could be debris in the brake fluid, causing a partial blockage,so may be a complete drain,flush,and refill will cure it.

 

[ernieh]

Assuming its failing on the footbrake,and the handbrake is ok,it could be debris in the brake fluid, causing a partial blockage,so may be a complete drain,flush,and refill will cure it.

Ernie -Thanks for the reply - There is no ABS and the hand brake is a drum setup and working ok. It's the service brake that is 30% lower on the o/s/r compaired to n/s/r. Both calipers were replaced (pattern - not MB though, couldn't afford them). I replaced all the components after the van failed it's MOT on the brakes, so I'm thinking it would be unlikely the new calipers had the same fault as the old ones. Can't rule it out though, as there's nothing else left to replace!

Krissy, I'm starting to clutch at straws now, but I don't see any reference to the discs having been changed. If they were scored or badly lipped and one was worse than the other it could give you your problem, particularly if you have fitted new pads that haven't yet bedded in. The only other thing I can think of is a flap of *rap somewhere causing a blockage when the brakes are applied. Oh, and are your calipers single piston, meaning that the sliding mechanism needs to be free for the system to work efficiently. Finally, finally... one final check that there are no cracks in the hub carriers where the calipers mount that might be allowing excessive play. I would also check that there no excessive end float on the drive shaft on that side.
I know that a lot of the above is unlikely, but everything obvious seems to have been tried!

Hope you get it sorted soon,


ERnie

ps Sorry, Honeymerc, I've copied your suggestion, apologies.

 

[KrissyB]

Krissy, I'm starting to clutch at straws now, but I don't see any reference to the discs having been changed. If they were scored or badly lipped and one was worse than the other it could give you your problem, particularly if you have fitted new pads that haven't yet bedded in. The only other thing I can think of is a flap of *rap somewhere causing a blockage when the brakes are applied. Oh, and are your calipers single piston, meaning that the sliding mechanism needs to be free for the system to work efficiently. Finally, finally... one final check that there are no cracks in the hub carriers where the calipers mount that might be allowing excessive play. I would also check that there no excessive end float on the drive shaft on that side.
I know that a lot of the above is unlikely, but everything obvious seems to have been tried!

Hope you get it sorted soon,


ERnie

ps Sorry, Honeymerc, I've copied your suggestion, apologies.

Thank you! The last two will be investigated, once the rain clears off!