Favorit - front offside wheel locking under heavy braking after work on brakes

[anewman]

Just replaced the nearside front brake pipe for MOT due to corrosion and bled the entire system using the order described in the Haynes manual. Did this with one of those one man one way valve things (the eezibleed just kept leaking).

Now when I brake hard (I mean emergency stop style braking) the front offside wheel locks. I suppose one interesting thing is it never seemed like I could get any wheels to lock up with the brakes before. I was wondering if this was indicative of some problem.

My guess would be air could still be in the front nearside pipe causing uneven braking? If so can I simply bleed that one?

I'm starting to think leaving the brakes to a garage to do would have been a good idea now.

Thanks in advance.

[Lummox]

I would think like you said you probably have a slight imbalance. Get it back on the brake tester and see what its coming up with.

[anewman]

Have bled the one with the pipe replaced again, yet to test drive. From what I understand the 2 hydraulic circuits are separated for front right and rear left, and front right and rear left for stable braking should one circuit fail, so I guess it is possible one circuit has lower efficiency hopefully just needs bleeding and not a new master cylinder.

The braking still seems relatively even (not pulling to one side) with no excessive pedal effort required.

Brakes actually seem better than before, just the increased tendancy for the front right wheel to lock when slamming the pedal down is a little worrying.

Will ask the MOT tester if they can do the roller test on re-test.

[rigsby]

It could be something as simple as a different coeficient of friction between the two front tyres and the road , especialy if the tyres are of different makes

[KenONeill]

I'd suspect tyres, or maybe even corner weights.

[bobob]

I suspect the problem is with the side you haven't done (offside) and the nearside is overcompensating.

[anewman]

Originally Posted by bobob

I suspect the problem is with the side you haven't done (offside) and the nearside is overcompensating.

Have bled the entire system in order described by Haynes. Have since re-bled the secondary circuit (nearside front, offside rear) and swapped the two front tyres over. Yet to test again as don't fancy hard braking on wet roads. I have sent over a litre of brake fluid through the system. Not sure how much brake fluid bleeding usually takes.

[richardsfavorit]

When I have bled brakes, I have always bled enough so that there is no air in the system - you can tell by seeing whether there are little bubbles in the fluid that is draining out. When the fluid appears to be completely clear then it is usually ok.

[anewman]

Still happening after swapping wheels over at front and bleeding secondary circuit again. Will have to leave it to the MOT now. I suspect possibly it was the same before but that now I have bled the system with new brake fluid it's more apparent. It did seem to move a little on the roller test on that side.

Only other thing I can think might be that my weight in the drivers seat may be causing the effect. However, I would have thought the weight would mean more traction with the ground on that tyre and hence less likely to lock. Will see what the MOT says anyway, might have to consider leaving brakes to a garage in future if I have messed it up.

[PD75]

Long shot, but maybe the pistons are sticking in one of the callipers?

[shytot]

If the brake pedal feels like it did before and not soft or 'spongey' then you've almost certainly bled the system correctly. Whichever part of the 'split system' is working doesn't really matter as each front caliper is connected by a single pipe. The split system thing happens at the master cylinder before fluid gets to the new pipe you fitted.
I strongly suspect that the problem was there before and that (if it isn't due to different tyre treads) there is an imbalance in the brakes which is within the tolerances for MOT purposes. A sticking piston might be the cause but that would usually cause some drag which the MOT test would have picked up. I'd be more inclined to suspect siezed sliders on the O/S caliper. I'd bet that the pads on the O/S have worn unevenly and that the one on the piston side has worn the most because the (partially) siezed sliders have stopped the other pad making sufficient contact with the disc. (Hope you know what I mean here...).
Put it in for the re-test and hope for the best!

Good luck!
Simon H

[anewman]

It's passed anyway. It was failed on the brake pipe rubbing the servo. They just clipped it to another pipe.

If it is seized sliders I suspect they simply need to be removed and greased up? Probably best left until the pads need changing and get it done all in one go.

[richardsfavorit]

Pleased to hear it passed ok mate Not bad for a 14 year old car

[shytot]

Originally Posted by anewman

It's passed anyway. It was failed on the brake pipe rubbing the servo. They just clipped it to another pipe.

If it is seized sliders I suspect they simply need to be removed and greased up? Probably best left until the pads need changing and get it done all in one go.

Yes, it's just a case of dismantling and greasing. Unevenly worn pads are a sign of sticky sliders, not the cause.

Glad it passed, anyway. Nothing to worry about for another year!

Simon H