sticking front brake?

rockdemon

rockdemon

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When I brake to a standstill and then pull off again I am getting a little creaking and squealing. Disappears quite quickly but wondering on the probable cause. Likely to be the flexible pipes?

Thanks

Rich
 
In all likelihood yes. It's possible it could just be a load of crud/congealed dust around the caliper preventing it from budging slightly on the pins when pedal is released. Extract the pins and pull out the pads for a clean/inspection, but I would be tempted to replace the flexi pipes as a matter of course if you don't know how old they are. I went for the braided steel goodridge type - a bit pricey at £50, but they're guaranteed for life and do make the pedal firmer if you properly mash the brakes on!
 
If the brakes aren't hanging on I can't see it being the flexible hoses, if they are it could be, more likely it's just pad noise which you might get rid of by chamfering the pads, and coating the backs and edges of the front pads, and the anti-squal shims with Coppaslip, and making sure that they're free in the caliper. There should be anti-rattle springs on the pad retaining pins as well. Most of the time it tends to be the fronts rather than the rears that cause the problems. You could prove the point by coming to rest using the handbrake rather than the footbrake, and see if the same thing happens.
 
And, as Harvey has reminded us previously, it could just be a bit of play in the wheel bearing, causes the pad to bind until it has wobbled about sufficiently to push them all the way back.

Chris
 
Thanks guys. I'll investigate... They do stay squealing for 10-20 yards then it goes off but doesn't seem to actually impede progress at all...
 
OK... Done a little investigation this morning... Both sides are sticking on. I can prise them apart quite easily b :D ut that means. Must be hydraulic problem? The servo makes a hissing noise when applied with engine running and the engine speed increases markedly when the pipe to the inlet manifold is removed. The pipe from the front of the servo to the slave cylinder isn't great but doesn't appear to be problematic and I think there has been about an inch of brake fluid lost in the last 1000 miles...

So... Where should I be going next with this?

Thanks

Rich
 
Re: sticking front brake

If you are losing fluid I would make this my primary concern. Is there any tell-tell sign of corrosion on the system that would indicate a leak? Not sure how a leak would cause slight sieizing of the front brakes though? One possibility may be leaking at the caliper piston seals and this has corroded the pistons restricting their return? I haven't had any experience on P6 brakes (yet!) but this is what I have usually checked first on other cars with sticking front brakes. I would remove the front calipers and have good look here, clean them up and, as already suggested, chamfer the pads and smear some copper grease on the back of them. I usually clean up the pins that retain the pads and smear coppaslip on them as well. This is maybe an easy/quick first thing to try?
 
I haven't had a calliper off yet, but have copper greased up the pins and once released I can then jiggle the pad. Will get a caliper off later with a little luck.

Rich.
 
Hello Rich,

After pulling to a stop, when you then start to move forward again, can you feel the brakes dragging? If you snap the pedal quickly, do the brakes come off? If the answer is yes to both, then I would go straight to the air control piston in the booster slave cylinder.

Ron.

P.S : the run out in the disc pushes the pads back a tiny fraction of an inch once the pedal is released and the car is moving forward again. Upon inspection they still appear to be in contact with the disc, but the pressure behind the pistons is removed after the pedal is released.
 
Hi ron... That's exactly right.... Thanks for that :) guessing you've had this before?


Rich
 
Hi Rich,

Yes indeed.. :wink:

Most mechanics and brake places will tell you its the master cylinder or the front calipers etc, but usually the booster is the key. How long has it been since your booster was overhauled?

Ron.
 
The braked are untouched since I bought the car so I don't know to be honest. Looks in reasonable Nick from the outside but that means very little. I'll look up parts with a view to sorting it soon :)

Thanks

Rich
 
Hi Ron,

Just to be sure, Is the part the piston under the Brake servo air Valve/ air control valve? (Just to make sure i'm looking at the right part in my haynes book of lies!)

Thanks,

Rich.
 
That's the one Rich. If it starts to stick then it prevents the correct operation of the air control valve, as the probe on the diaphragm pushes against the piston in question.

Ron.
 
Cool. I've read around and seems sometimes these pistons are fitted with double seals which can cause sticking, and often can be sorted with a clean. I'll have a tentative look around that area tomorrow :)

Thanks again for your help :)
 
Hi Rich

The other thing to check is to pull the adaptor that the vacuum hose beds onto off the vacuum tank of the servo. A judicious finger inside will tell you if there is any fluid in there. If so, that is where your brake fluid has been going! I'm fairly hazy about the precise methodology of servo faults, but I do agree that it is a likely suspect. Where I get confused is the relative functions of the air valve and the hydraulic bits! I'll leave that to Ron to explain.

Chris
 
I did work it all out once, prior to rebuilding the brakes on Sparky.

IIRC, when you apply the brakes gently the system works on just your foot pressure allowing greater control. When you hit them harder, the fluid pressure is enough to move the air valve piston up and opens the system to vacuum pressure which gives you your extra braking. If the air valve piston stick open then you will get servo assistance when the brakes are not being applied.

Richard
 
Cool will check this all today. Hopefully can get it sorted before rugeley although the brakes aren't overheating so its not a huge problem...

Rich
 
Hey all,

I've had a go at this this affternoon. The spring in the top of the air return valve is slightly corroded and not working particularly well, and a previous owner has put a big spring under the rubber diaphragm in the air return valve - I guess to compensate. The piston flew out on first application of the brake so no problem getting out. A little crud in there now cleaned out. Now though after touching it the brakes are now hanging on much more than previously.

So: I need to confirm the i) the big spring is an addition that shouldnt be there, ii) getting an overhaul kit for the air return valve is the way to go?

Chris: The inside of the servo appears dry, though I have spotted a seep from the nut which attaches the pipe from the servo cylinder to the Multiway joint below the servo.

Any advice? Anything I need to do or check or is it just a case of getting the return valve kit?

Thanks,

Rich
 
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