Cup Rear brakes MOT

[Jamess182]

Took my Cup in for it's dreaded MOT today, and surprise surprise, it failed- on quite a few things.
I know this one has been mentioned a few times across this forum

*Brakes imbalanced across rear axle*

It's also failed on worn rear discs, so I'm obviously going to get these changed along with bearings & pads. Hopefully that'll cure the problem, but if not I've heard it's pretty common on the Cup models that the rear brakes play up on the MOT due to how they came from the factory, or something like that?

Does anyone have a PDF of the VOSA sheet saying that the Cup rear brakes are essentially useless? Searched this forum and can't find a copy of it anywhere, just loads of people saying 'show them the vosa certificate' -- I don't even know what it looks like.

Also, can anyone suggest any other things to try along with new discs, bearings and pads. Maybe a complete brake fluid change?
Cheers guys

 

[JamesBryan]

Page 8

http://webarchive.nationalarchives....k/vosa/repository/MoT Issue 31 - Apr 2006.pdf

 

[Jamess182]

Page 8

http://webarchive.nationalarchives.gov.uk/20121207053848/http://www.dft.gov.uk/vosa/repository/MoT Issue 31 - Apr 2006.pdf

Legend, thanks so much

 

[charltjr]

Not sure that covers imbalance across the rear axle? It would cover front to rear imbalance i.e. rear brakes putting in little braking effort but if one side of the axle is putting in significantly less effort than the other that's not great and I wouldn't have thought it would be caused by the preset on the load sensing valve - feel free to correct me if I'm wrong.

The fail sheet says you've got one side binding and one side recording little effort, along with the comment about imbalance across the axle, so I doubt it's the load balancing valve that's at fault.

• Offside Rear rear brake binding (3.7.B.1)
• Nearside rear brake recording little or no effort (3.7.B.5a)

 

[Jamess182]

Not sure that covers imbalance across the rear axle? It would cover front to rear imbalance i.e. rear brakes putting in little braking effort but if one side of the axle is putting in significantly less effort than the other that's not great and I wouldn't have thought it would be caused by the preset on the load sensing valve - feel free to correct me if I'm wrong.

The fail sheet says you've got one side binding and one side recording little effort, along with the comment about imbalance across the axle, so I doubt it's the load balancing valve that's at fault.

• Offside Rear rear brake binding (3.7.B.1)
• Nearside rear brake recording little or no effort (3.7.B.5a)

Fair point.
Hoping that when I come to changing pads tomorrow, I'll push the pistons back into the calliper and will hopefully free them up a bit? Meaning the offside shouldn't bind and therefore balance out both sides? Am I on the right tracks here?

 

[Jamess182]

Not sure that covers imbalance across the rear axle? It would cover front to rear imbalance i.e. rear brakes putting in little braking effort but if one side of the axle is putting in significantly less effort than the other that's not great and I wouldn't have thought it would be caused by the preset on the load sensing valve - feel free to correct me if I'm wrong.

The fail sheet says you've got one side binding and one side recording little effort, along with the comment about imbalance across the axle, so I doubt it's the load balancing valve that's at fault.

• Offside Rear rear brake binding (3.7.B.1)
• Nearside rear brake recording little or no effort (3.7.B.5a)

Nice homework btw, checking the MOT history.
In my defence, I asked them to stick the plate on before the test (as I didn't have any tape) - for some reason they decided to completely ignore that and just add it to the failure list - just from that you can tell the MOT tester had it in for me and/or the car.

 

[JamesBryan]

Rebuild the rear brakes, it's a fairly easy job really.

The seals inside do swell over time and cause them to seize on.

 

[Coops Mk1]

yeah check the pistons (they wind in) and the sliders too as they can seize up

 

[Jamess182]

yeah check the pistons (they wind in) and the sliders too as they can seize up

Rebuild the rear brakes, it's a fairly easy job really.

The seals inside do swell over time and cause them to seize on.

Will do guys!

 

[charltjr]

It’s still a useful thing to have, the tester may turn round and try to incorrectly fail it for low rear braking effort even once the binding is sorted out.

Hope I didn’t creep you out by checking the fail sheet, it just seemed quicker than asking a bunch of questions and your reg is in your profile pic. Didn’t occur to me until afterwards that some people don’t like that kind of thing.

 

[Jamess182]

It’s still a useful thing to have, the tester may turn round and try to incorrectly fail it for low rear braking effort even once the binding is sorted out.

Hope I didn’t creep you out by checking the fail sheet, it just seemed quicker than asking a bunch of questions and your reg is in your profile pic. Didn’t occur to me until afterwards that some people don’t like that kind of thing.

Lol, no it wasn't creepy, doesn't bother me at all haha - I was just surprised how quickly the fail sheet was uploaded to the gov website

 

[jamesycc]

Had this on my old Cup. Left to right imbalance.

Turned out the rear compensator was corroded up and no fluid was getting to the right rear caliper and the left was just a token effort.

The calipers were fine, new discs and pads as a matter of course but if the compensator is knacked none of those things do anything.

The mechanic only found this out when he undid the bleed nipple and no fluid came out, not a drop...

 

[Jamess182]

Had this on my old Cup. Left to right imbalance.

Turned out the rear compensator was corroded up and no fluid was getting to the right rear caliper and the left was just a token effort.

The calipers were fine, new discs and pads as a matter of course but if the compensator is knacked none of those things do anything.

The mechanic only found this out when he undid the bleed nipple and no fluid came out, not a drop...

Was it a case of a new compensator? Or would a bit of wd40 and elbow grease sort it? Haven't had a chance to look at mine yet

 

[jamesycc]

Was it a case of a new compensator? Or would a bit of wd40 and elbow grease sort it? Haven't had a chance to look at mine yet

No, it was properly corroded. It doesn't help where it's located right in front t of the rear axle. It collects all the crap off the roads very well.

It was beyond saving. I got one from euro car parts for about £80 last year when it was replaced. GSF dont stock them from memory.

The rear brakes are prone to seizing up as it's only about 30% of the braking balance that goes to them iirc.

 

[mintno1]

Had the bias valve/compensator replaced on mine along with all the rear brake lines etc. mine was also properly corroded and doing nothing, car was off the road at the time so made sense to do all the work together. Doesn't help as the rear brakes aren't doing a lot anyway even with a fully functioning valve :smile:

 

[Austin-182]

Rebuild the rear brakes, it's a fairly easy job really.

The seals inside do swell over time and cause them to seize on.

Any info on this mate? Or know if theres a guide on here somewhere?

 

[JamesBryan]

Any info on this mate? Or know if theres a guide on here somewhere?

Not sure if there's a guide, but all you need is brake fitting knowledge. If you can wind a piston back and fit a few rubber seals, then it's not too hard.

The rear brake pistons are on a screw thread. Once you've got the caliper off you can turn the piston anti clockwise until it's off the thread and then pull it out from the inner seal.

Remove the inner seal and replace with a new one, using the red rubber grease to lubricate it. Clean the piston up or if it's badly pitted then replace it. Lube the piston up too and push it back in until it reaches the thread, then wind in clockwise. Fit the new dust boot seal over before the piston is all the way back in.

Bigg Red or Brake Parts International are the places to get the kits from.

 

[Austin-182]

Not sure if there's a guide, but all you need is brake fitting knowledge. If you can wind a piston back and fit a few rubber seals, then it's not too hard.

The rear brake pistons are on a screw thread. Once you've got the caliper off you can turn the piston anti clockwise until it's off the thread and then pull it out from the inner seal.

Remove the inner seal and replace with a new one, using the red rubber grease to lubricate it. Clean the piston up or if it's badly pitted then replace it. Lube the piston up too and push it back in until it reaches the thread, then wind in clockwise. Fit the new dust boot seal over before the piston is all the way back in.

Bigg Red or Brake Parts International are the places to get the kits from.

Thanks for the detailed reponse.

I have zero brake fitting knowledge so think i will have to book it into a garage. My rear brakes are not working (i dont think) Rear passenger disc is all rusty (rather than just the lip around it) not sure what the problem is but imagine they will need taking apart to find out. Discs and pads have done less than 1k

 

[JamesBryan]

Thanks for the detailed reponse.

I have zero brake fitting knowledge so think i will have to book it into a garage. My rear brakes are not working (i dont think) Rear passenger disc is all rusty (rather than just the lip around it) not sure what the problem is but imagine they will need taking apart to find out. Discs and pads have done less than 1k

Tbh the garage will just want to replace the calipers. Getting them to rebuild them would put the labour cost at more than new calipers.