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Brake imbalance

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Paul Fraser

New member
Failed MOT with front brake imbalance (35-40%) after fitting new discs and pads to cure offside vibration.
Tester suggested it might be the hoses so I replaced the underperforming nearside last night with a Goodridge and the rhs still locks up before the lhs and there is slight pull to the right before that.
What is next: I'm pretty sure I checked the lhs caliper funtion and WD40d the piston while doing the disc but I'll check again. Do I need a new caliper, or will a rebuild kit do? Could it be anything else?
 
I'm sure I had a similiar MOT problem and I was just on the edge of 'legality' and I was passed.

There was a thread on this before, maybe last year, but I can't remember what the solution was.

I'm sure you will get a response on here, hold back from any further expense/time until you do.
 
I'm pretty sure I checked the lhs caliper funtion and WD40d the piston while doing the disc
Click to expand...

WD40 the other side and it will probably balance..........but you might not stop[;)]

Mike[:'(]
 
When I had this it turned out to be the dreaded plate lift on one side being worse than the other and so restricting brake pad movement. You don't say which model you have, but something is causing one side to grip more than the other so a strip down is going to be necessary
 
I doubt it is plate lift as I can't recall seeing any -- they are the bog standard (ATS?) floating calipers with one piston.
 
I had this issue earlier in the year and tried replacing hoses and freeing up the pistons, but in the end had to go for a recon caliper which finally sorted things out and got me an MOT pass. If I remember rightly it was around £75 from eurocarparts.
 
ORIGINAL: Paul Fraser

I doubt it is plate lift as I can't recall seeing any -- they are the bog standard (ATS?) floating calipers with one piston.
Click to expand...

They don't have the plates that the later Brembo brakes do so in a way you are lucky as they cost a fair bit to sort out properly. As Nathan said you can get reconditioned sliding callipers fairly cheaply
 
Yes, I'd spotted the recon calipers on ECP, it's just the further £75 if your exchange caliper isn't up to scratch and the hassle of returning it etc. that put me off that option. That, and I'd feel I would have to change both the fronts...
Have just received some caliper seal kits from Berlyn Services; might try taking the caliper to bits and see what the condition of the piston and bore is like.
 
Ok, now I am really flummoxed. Just rebuilt the caliper with new seals and I am getting exactly the same symptoms, i.e. pulling to the right.
The piston had very little corrosion on it and neither did the socket. Cleaned both up, very very little pitting at all left on the piston, put in the new seal, popped the piston back in and put on the dust cover. Greased the groove on the floating part and reassembled. It looks like a perfectly serviceable caliper. Bled it twice with brake application inbetween.
Anyone have any ideas what might be wrong?
 
Remember the callipers are driven by different circuits from the master cylinder. May be something in there....

 
Yes, I was wondering about the master cylinder. Does anyone know what is in there? I thought it was just a hollow manifold but is there more to it?
 
Paul,

Have a look HERE

If there are problems / blockages etc then the force transfer to the second circuit may not be inline with the first.
 
hang on dogon minute. [8|]The master cylinder tube has two pistons with seals. Each piston operates one half of the braking syatem t.One piston operates the front and one the rear not right and left side . The idea is if you have a leak on the front system the rear brakes will still work normally and vice a versa.
If there is a difference in pressure between right front and left front it can't be anything to do with the master cylinder but the pipes, hoses and calipers /pads ect.
Its an intriging problem.
You really need to substitute another complete caliper assembly really in order to verify that one of the caliper/pad assemblies are faulty

I'm wondering if the problem lies with the RHS over braking rather than the nearside underbreaking !?
Might be worth stripping and checking the offside as well . Check the pistons are returning cleanly and that the pads are not grabbing due to residue on the face of the pads
 
Well having consulted my tech manuals..... you're right [&:][:mad:]

The 944 doesn't have a diagonally split dual circuit ~ it splits front to back.

I therefore (munch) eat my (munch) previous words.

(And christ, you wouldn't want to suffer a failure of the front circuit! [:eek:] )
 
So spooky this happened to me last year, I ended up changing the master cylinder, you can get a good second hand one tested from Douglas valley breakers for about £35 this sorted the problem out for me. you can get a repair kit but it's more reliable to fit a replacement. One note be careful not to break off the redundant pipe on the fluid reservoir.
cheers
Les Day
 
it wouldn't help with this problem though Les for the reasons just explained. The master cylinder could't split the brakes left and right side of the car could it !? otherwise if the right side failed imagine what would happen when you braked !
This problem is not related to the master cylinder. The pressure from the master cylinder to either circuit (front or rear)is equal as it comes from the same piston and splits after it leaves the master cylinder.
 
ORIGINAL: Paul Fraser

Failed MOT with front brake imbalance (35-40%) after fitting new discs and pads to cure offside vibration.
Tester suggested it might be the hoses so I replaced the underperforming nearside last night with a Goodridge and the rhs still locks up before the lhs and there is slight pull to the right before that.
What is next: I'm pretty sure I checked the lhs caliper funtion and WD40d the piston while doing the disc but I'll check again. Do I need a new caliper, or will a rebuild kit do? Could it be anything else?
Click to expand...

Hi Paul,

I have noticed this before in my car but with the LHS and after I had replaced the pads/discs. Also had it again a couple of weeks ago when I replaced and adjusted the wheel bearings. After several 60-0 heavy braking tests and a few hundred miles of use it appears to be cured again.

I believe that in my instance it was probably contamination of the pads/discs that cleared up after burning off etc.

When were the brake hoses last replaced ? Could be time for some new ones....

Just noticed you mentioned replacing the disc/pads to cure offside vibration. Did you replace both sides or just the offside ? Changing one side would definetly cause a brake imbalance.

Regards

Dave K.
 
You lot have been busy posting!
OK, in order:

Mik, thanks for that link: really useful as I now have a much better understanding of the master cylinder whether or not it is part of the problem.

Peanut, yes I kind of figured out the primary-front, secondary-back system myself from the website and the physical construction of the cylinder (going from back to front of the car the left and right pipes are for the front and the last one for both the back brakes). Nice to have my theory confirmed though. I have just rebuilt another older caliper this afternoon and will substitute it as soon as the rain stops (during daylight hours ;) ). I don't think the rhs is grabbing as the car goes straight when driving normally, and there is a new disc and pads on that side. I'm fairly sure I exercised the caliper when I replaced them too. Also, under hard braking/skidding the car stops skidding on release of brakes. Before any skid there is a pull of the steering wheel to the right (ten o'clock/four o'clock approx.)

Les, don't think it is the MC... yet, due to the theory above, but if this asymmetric braking happened to you and a new MC cured it then it is something I won't discount as a possibility. Did you source and price a repair kit. I've found it on the PET so assume an OPC will have one.

Dave, I cleaned off the discs with electrical contact cleaner before driving. Both sides had new discs and pads (I don't think I could have only changed one side!). The hose on the lhs was the first thing I changed when a got back on Tuesday evening but it had no effect (Goodridge hose fitted).

I'll change the caliper over tomorrow and see what I get. After that it is the brake pipe I suppose (although the caliper bled normally enough). After that it will be the master cylinder, probably a rebuild kit. Don't ask me why but my gut feeling is this is the problem...
 
ORIGINAL: Paul Fraser

You lot have been busy posting!
OK, in order:

Dave, I cleaned off the discs with electrical contact cleaner before driving. Both sides had new discs and pads (I don't think I could have only changed one side!). The hose on the lhs was the first thing I changed when a got back on Tuesday evening but it had no effect (Goodridge hose fitted).

I'll change the caliper over tomorrow and see what I get. After that it is the brake pipe I suppose (although the caliper bled normally enough). After that it will be the master cylinder, probably a rebuild kit. Don't ask me why but my gut feeling is this is the problem...
Click to expand...

No worries I thought you would have changed both sides [:D] but you'd be surprised what some peoples idea of safe maintenance is [:-].

How many miles have you done with the new discs/pads ? and have you been gentle with them since they have been fitted ? Could it be that they are still wearing in and aren't completely matched together (pad to disc wear). How safe does it feel when you pull up quickly, any pulling sharply to the right hand side ? or does it stop in a straight line ?

Dave K.
 
They were fitted and then more or less straight back to the MOT station about 6-7 miles away with me using the brakes regularly, so not totally bedded in yet. Still, wouldn't expect a 40% split on new discs/pads. Pulls to the right on braking, but not sharply... until the rh wheel locks up.
 
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