Technical 100HP rear brake grabbing

[DaveMcT]

Ive had a couple of occasions where the driver's side back brake has grabbed enough to squeal the tyre. Pretty scary TBH especially as there was no ABS action.. I've rechecked by braking hard (in a straight line) to trigger the ABS. The ABS does work as it should. There are no warning lights.

There is no binding on the brake so can anyone suggest the cause? I don't want to do a strip-down only to find its the same afterwards and it really needs an exchange caliper.

Has anyone else had this issue? Grabby rear brake that does not bind.

 

[09 johno]

Could it be a sticky handbrake cable/mechanism on that side?

 

[A3jeroen]

Surfacerust on one of the discs?

gr J

 

[rmjbn1]

I assume the wheel only locks when you're on the brakes?

EBD isn't known to misbehave is it? And send too much bias to one brake?

Or a rusty seized piston on the other caliper (left rear) causing the right to do all the work?

But then ABS would still intervene and stop it locking up would it not?

 

[portland_bill]

I would expect the ABS system to react with a wheel lockup. Does it pulse the pedal and show the warning light?

I'd be inclined to check the pads first. If the friction material is coming unstuck, it could cause a lockup, and releasing the pressure might not affect that until stopped. Whilst there, check caliper fixings are secure, and that the caliper moves nicely on its slide pins, not tilting and binding.

 

[DaveMcT]

It was very odd. I approached a RH bend too quickly and had to brake hard. Bad driving I know. However the back end locked on the right causing the car to slew to the right. I came off the brakes, reapplied and it recovered, but there was no ABS action. It's fortunate that I grew up before cars had ABS and still had the necessary reactions.

I later tested the brakes to trigger the ABS. I all worked normally with front tyres pulsing. It's impossible to know what the rear ABS was doing and I am not daft enough to purposely do that in a bend. In a straight line, there was no sideways pull (left or right) at the back end. This begs a question about ABS operation when only one back wheel loses grip. The brakes are 13 years old so I have bought a Big Red caliper repair kit containing two sets of seals and two pistons.

https://www.ebay.co.uk/itm/FIAT-PANDA-2004-2019-REAR-L-R-Brake-Caliper-Seal-Repair-Kit-Pistons-BRKP425/312746719854?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

 

[portland_bill]

I wonder if the bend just has an area of lower grip, a bit of oil spillage, or gravel, perhaps. Odd that the ABS didn't operate.

The ABS has four separate channels, so should pulse that one wheel. My guess is still mechanical. You could try disconecting the sensor on that wheel. ABS light should illuminate, so testing the system for you.

ABS light does come on for 3-4 seconds when ign turned on?

 

[DaveMcT]

Hi Bill,

I have not noticed any brake pulling in normal use but wonder if your theory about the LHS rear brake not gripping properly has legs. I plan to strip both sides and renew the seals and pistons.

The locked wheel actually smoked the tyre(!) so I doubt it was crap on the road but who knows.

 

[DaveMcT]

The LHS rear caliper was a nightmare to get off the brake disc. There is no sign of rusting or uneven wear. The pad and disc wear rates looks the same. However the left was clearly not as it should be.

I'll start a new thread with pictures.