Technical Rear right brake not braking correctly

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Technical Rear right brake not braking correctly

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Nov 28, 2019
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The car failed inspection as the rear right brake wasn't braking enough. The pads and discs were changed and a garage bled the whole system and changed brake fluid. At the re-test, the same problem again.

My next thought is to replace the piston and seals.

Any other advice most welcome. Thanks
 
It could be that the right hand brake compensator is jammed or not functioning correctly so not allowing full force to the brake ?????
 
You don't write the year and if you have ABS.
Early cars, none ABS had brake compensators with a lever attached that relied on a return spring. These have known to go missing and caused a problem at the mot. Get safely underneath and have a look if there's a spring on the good side. Springs are available.
I also agree with the comment above regarding compensators not working.
 
I have 1996 with ABS and have these simple pressure regulators without levers or springs.
Still suffer because of weak rear brakes https://www.fiatforum.com/barchetta/459777-misery-rear-brakes.html
But in my case, both rear brakes are equally weak. Basically when I ask my wife to press the brake pedal as hard as she can, I can still turn rear wheels by hand. I have already renewed everything that brakes (except master cylinder) and honestly don't know what to do.

In your case, as you only have weak brake on one side, I would check the piston and seal as you suggested. Pressure regulators are simple devices and it is unlikely that it would lock up and not let the pressure thru. But if caliper is ok then pressure regulator is the next one to blame.
 
Thanks, I have a piston repair kit, for both sides. Not sure if I should do both or just the problem one. Hoses have been ordered and on their way. Hopefully this will fix the problem!
 
Still no luck. Pads, discs, hose and brake power regulator change. Still have weak braking on back right. Anyone have any thoughts?
 
Could it be the ABS unit under the bonnet? I don't know exactly how it works but doesn't it have one pipe going to each wheel?
 
I have a similar problem, but I have about 35% power between them according to the MoT tester

Could it be the ABS unit under the bonnet? I don't know exactly how it works but doesn't it have one pipe going to each wheel?

Mine definitely has 4 pipes coming out the top of it, presumably one to each corner
 
I believe that if the ABS detects a wheel locking up it reduces pressure to that wheel to prevent skidding. It may be that the ABS unit is faulty or thinks the wheel is locking up. Could it be a faulty ABS sensor?
 
I believe that if the ABS detects a wheel locking up it reduces pressure to that wheel to prevent skidding. It may be that the ABS unit is faulty or thinks the wheel is locking up. Could it be a faulty ABS sensor?

Don't think so. After all ABS only engages after vehicle has reached speed 6km/h, and disengages after slowdown below 2.75km/h (otherwise it wouldn't be possible to bring the vehicle to complete stop).
But at least in my case, the rear brakes are very weak even when stationery, with engine working on idle.
And of course, faulty ABS would result in red dashboard light.
 
You really do seem to have eliminated all the obvious stuff so I'm rather grasping at straws here but, I'm wondering if there might be an internal fault with the caliper (I can't think what though!) Is there any way you can lay your hands on another one and try it in it's place? If you get the same result then you can pretty much be sure your existing caliper is not the problem. - Maybe a forum member could lend you one temporarily?

When bleeding does it bleed well or is the flow poor? (compared with the other side). I'm scratching my head here because you seem to have tried all the things I would have but I'm wondering, if you can totally eliminate the caliper as a problem, and bearing in mind you've replaced the flex hose - which I have seen cause this sort of problem when they internally start to collapse - Whether you do have an ABS unit problem. I can't see it being the sensor because it sends a signal to the ABS ECU which the ECU then compares with the other 3 outputs to compare rotational speeds between the wheels. As you say, if there was a problem you'd expect it to light a warning light and it shouldn't have any influence at low speeds anyway. HOWEVER. I think there could still be an internal problem with the ABS unit? Do you push the caliper pistons back without opening a bleed nipple? This might, especially on an older vehicle where there is a high likelihood of contaminants in the fluid, cause internal ABS unit problems with valve units etc? I have to say that in newer vehicles I have no problem with pushing the pistons back in the time honoured fashion, but once over about 5 years I like to always open a bleed nipple and allow the fluid to bleed out rather than being forced back up the pipe.

As I said above, I'm grasping at straws here, but I think if you can definitely eliminate that caliper by substitution then that will take one of the big question marks out of the equation?

Sorry I can't be more helpful. Good luck.
 
The Coupe suffers similar problems as the set up is practically the same. Two things come to mind here, is the brake compensator set up properly, although pads have been changed the guides still may need cleaning. Just a couple of ideas but worth looking at.
 
The new piston goes back in ok. Bleeding is no problem and the flow is good. Next step is either the caliper of the brake master cylinder but it looks like it's hard to get to under the ABS unit. Not sure how much stuff I need to dismantle to get to it.
 
The new piston goes back in ok. Bleeding is no problem and the flow is good. Next step is either the caliper of the brake master cylinder but it looks like it's hard to get to under the ABS unit. Not sure how much stuff I need to dismantle to get to it.

Keep us informed P, cheers. :)
 
I've decided to get a new caliper. Getting one from Autodoc. The only make I recognise that has stock is Ferodo. Brembo not available, don't know the other makes. Once I've fitted it will let you know if it passes inspectionn!
 
I've decided to get a new caliper. Getting one from Autodoc. The only make I recognise that has stock is Ferodo. Brembo not available, don't know the other makes. Once I've fitted it will let you know if it passes inspectionn!

I replaced both calipers on mine and that got the balance sorted out on the back brakes
 
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