Right Front Brake locks up too much

-Joe · 2nd September 2019, 20:48

When I drive the car with mild to medium braking no problems, but when I brake hard, or on loose gravel the ABS triggers for the drivers front wheel.

The car seems to do this with extra passengers or in it's usual driver only loading.

Testing on a gravel track with hard braking reveals the car wants to spin but the ABS seems to correct this.

The car tips towards the front right under hard braking. I think the ABS system is working fine. I have replaced all the ABS stuff too many times!

So this makes me think the Front Right Wheel wants to lock up under hard braking.

And this is the new parts I've tried to fix the problem with

Brand New Discs and Pads all round.
Pair of new Control Arms and Bushes
New RH Front Hub inc Bearing and ABS Sensor, Old ones now good spares

4 Springs Front and Back
3 Shocks Not the problem corner yet! though the brake problem pre-existed before the week of Shock Horror! and besides that no leaks there

2 x Droplinks
2 x Tie Rod Ends

Efforts to fix the problem.

Cleaned Brake Callipers

Cleaned greased Caliper Pins
Renewed Front / Rear Hub Backplates
4 Wheel Tracking done
Cleaned ABS bearing magnets / Sensors
ABS wiring 100% scar free
On changing the discs all brake parts inspected all seem ok
Bleed the Front Brakes once and then again recently, no bubbles, no change

So what could it be Callipers? LH or RH, Air in the ABS box? Help!

SCP440 · 2nd September 2019, 21:25

If one wheel is locking and the other is not it would suggest the non locking one is at fault, it could be a partially seized piston or slides or even both.

If you push the piston back can you easily slide the caliper on it slides?

If you push the piston back on both sides does one come out before the other? They should both come out at the same rate.

-Joe · 2nd September 2019, 21:58

Yes I'm thinking Calipers off for testing off-disc. Is a good idea.

I will try to be careful about level of fluid in the master cylinder and avoid risk of crushing fingers.

-Joe · 6th October 2019, 20:27

After close inspection of the calipers working off the vehicle I noticed. The RH caliper did not suck back in too well on brake release.

I purchased a good 2nd hand RH caliper unit from a scrap yard. Retreiving the new part and fitting it went suprisingly well. Off the car the RH caliper seemed to suck back in nicely.

Result.

Well it doesn't ABS under heavy then light braking like it used to. So a definate worthwhile improvement.. but it still seems to overly ABS the drivers front in my opinion. It's hard to get it to ABS other wheels without reckless braking on loose ground.

I have now changed almost everything on the drivers front right corner and I still it's not perfect and stopping distance is marginally increased by this problem.

Any ideas?

COLVERT · 6th October 2019, 20:36

It's the ABS unit itself.

-Joe · 6th October 2019, 22:33

The ABS has had a pipe off in the past. At an MOT the steel brake line burst and was replaced with a copper one and a new hose fitted. I didn't do this job, I paid a fortune for the garage to fix it as the car was undrivable from the MOT garage I had no alternative. Maybe at this time they did not have a t4 to bleed brakes correctly.

Secondly I once had the LHF ABS cable get ripped by road debris and short out the thick wire to the car body. This killed the ABS cpu. I replaced the ABS cpu without disconnecting the hydraulic pipes. Old ABS cpu contains lots of solid Gold wires! (very thin) (one melted broken wire too) and naked silicone chips floating in gel.

Reminds me of fuse question. Was Rover 75 fitted with to high an ampage value ABS fuse in glovebox fusebox?

2nd September 2019, 20:48	#1
-Joe Avid contributor Rover 75 Classic SE 1.8T Join Date: Dec 2008 Location: wink Posts: 135 Thanks: 0 Thanked 20 Times in 15 Posts	Right Front Brake locks up too much When I drive the car with mild to medium braking no problems, but when I brake hard, or on loose gravel the ABS triggers for the drivers front wheel. The car seems to do this with extra passengers or in it's usual driver only loading. Testing on a gravel track with hard braking reveals the car wants to spin but the ABS seems to correct this. The car tips towards the front right under hard braking. I think the ABS system is working fine. I have replaced all the ABS stuff too many times! So this makes me think the Front Right Wheel wants to lock up under hard braking. And this is the new parts I've tried to fix the problem with Brand New Discs and Pads all round. Pair of new Control Arms and Bushes New RH Front Hub inc Bearing and ABS Sensor, Old ones now good spares 4 Springs Front and Back 3 Shocks Not the problem corner yet! though the brake problem pre-existed before the week of Shock Horror! and besides that no leaks there 2 x Droplinks 2 x Tie Rod Ends Efforts to fix the problem. Cleaned Brake Callipers Cleaned greased Caliper Pins Renewed Front / Rear Hub Backplates 4 Wheel Tracking done Cleaned ABS bearing magnets / Sensors ABS wiring 100% scar free On changing the discs all brake parts inspected all seem ok Bleed the Front Brakes once and then again recently, no bubbles, no change So what could it be Callipers? LH or RH, Air in the ABS box? Help!

2nd September 2019, 21:58	#3
-Joe Avid contributor Rover 75 Classic SE 1.8T Join Date: Dec 2008 Location: wink Posts: 135 Thanks: 0 Thanked 20 Times in 15 Posts	Thanks Yes I'm thinking Calipers off for testing off-disc. Is a good idea. I will try to be careful about level of fluid in the master cylinder and avoid risk of crushing fingers.

6th October 2019, 20:27	#4
-Joe Avid contributor Rover 75 Classic SE 1.8T Join Date: Dec 2008 Location: wink Posts: 135 Thanks: 0 Thanked 20 Times in 15 Posts	Update After close inspection of the calipers working off the vehicle I noticed. The RH caliper did not suck back in too well on brake release. I purchased a good 2nd hand RH caliper unit from a scrap yard. Retreiving the new part and fitting it went suprisingly well. Off the car the RH caliper seemed to suck back in nicely. Result. Well it doesn't ABS under heavy then light braking like it used to. So a definate worthwhile improvement.. but it still seems to overly ABS the drivers front in my opinion. It's hard to get it to ABS other wheels without reckless braking on loose ground. I have now changed almost everything on the drivers front right corner and I still it's not perfect and stopping distance is marginally increased by this problem. Any ideas?

6th October 2019, 22:33	#6
-Joe Avid contributor Rover 75 Classic SE 1.8T Join Date: Dec 2008 Location: wink Posts: 135 Thanks: 0 Thanked 20 Times in 15 Posts	Abs The ABS has had a pipe off in the past. At an MOT the steel brake line burst and was replaced with a copper one and a new hose fitted. I didn't do this job, I paid a fortune for the garage to fix it as the car was undrivable from the MOT garage I had no alternative. Maybe at this time they did not have a t4 to bleed brakes correctly. Secondly I once had the LHF ABS cable get ripped by road debris and short out the thick wire to the car body. This killed the ABS cpu. I replaced the ABS cpu without disconnecting the hydraulic pipes. Old ABS cpu contains lots of solid Gold wires! (very thin) (one melted broken wire too) and naked silicone chips floating in gel. Reminds me of fuse question. Was Rover 75 fitted with to high an ampage value ABS fuse in glovebox fusebox?

2nd September 2019, 21:25	#2
SCP440 I really should get out more....... MG ZT-T 260 Join Date: Feb 2016 Location: Witney Posts: 2,504 Thanks: 6 Thanked 910 Times in 571 Posts	If one wheel is locking and the other is not it would suggest the non locking one is at fault, it could be a partially seized piston or slides or even both. If you push the piston back can you easily slide the caliper on it slides? If you push the piston back on both sides does one come out before the other? They should both come out at the same rate.

6th October 2019, 20:36	#5
COLVERT This is my second home R75 Saloon. Join Date: Feb 2009 Location: France/or Devon. Posts: 14,003 Thanks: 3,851 Thanked 2,167 Times in 1,816 Posts	It's the ABS unit itself.