Brake issue

[Kinger]

Hi Guy's,

Have a bit of an issue with my bakes just now, Now that I've got my MOT I thought I'd put on my new CL5's ( Didn't put them on pre MOT in case they pulled a bit during bedding in etc. )

Stuck new pads on all round, and no problem driving to work next morning, went for a wee run on way home and the brakes got progressively tighter to the point where I had to change down gear just to get the car off the road. The rear pads were roasting hot. Twenty minutes later they had cooled of and the car was rolling OK with just a push.

Today I took the hand brake cable off completely as it was looking a bit scabby and I thought it may be binding on.

At the same time I thought I'd check everything again, took all the pads out, front pistons were free to move without much effort. When I got to the back piston they were turning freely but weren't winding back in. I put on a bleed tube and cracked the bleed nipple and the piston then screwed back in allowing me to get the new pads back in, Did same at other side.

Went for a run, 3 miles in brakes started to blind again. By the time I got a place to pull in they felt like they were almost locking up.front and rear pads were all roasting hot !!! Then Sat for half an hour letting them cool down with the intention of getting it home in stages.

Brakes were fine all the way home, so went for a 20 mile drive getting it up to speed and they didn't heat up even with some high speed stuff and some heavy braking. Fronts seem to be a bit fierce but not sure if that's just ne hard barking in the wet.

Would appreciate your thoughts, I'll get it out tomorrow again to see how it is, but a bit concerned as I couldn't see what was causing it.

Cheers

[mckeann]

If it is the handbrake, just removing the cable probably isn't enough. Take a small hammer and chap the handbrake mechanism (where the cable connects) and chap it back to make sure it's entirely disengaged.

[Kinger]

If it is the handbrake, just removing the cable probably isn't enough. Take a small hammer and chap the handbrake mechanism (where the cable connects) and chap it back to make sure it's entirely disengaged.

The spring loaded handbrake lever on the calliper is free but not sure how it operates inside the calliper, I'll need to see if I can see an exploded view of the calliper.

Cheers

[robin]

It's a ratchet mechanism - when you apply the handbrake you ratchet the piston a little to take up wear in the pad.

When fitting new pads you must screw the piston back in, not push it back in (actually you have to push and screw - most people use a pair of long nose pliers in the holes in the piston face, push and screw it back in.

Cheers
Robin

[Kinger]

It's a ratchet mechanism - when you apply the handbrake you ratchet the piston a little to take up wear in the pad.

When fitting new pads you must screw the piston back in, not push it back in (actually you have to push and screw - most people use a pair of long nose pliers in the holes in the piston face, push and screw it back in.

Cheers
Robin

Hi Robin,

It wouldn't screw in today with the little tool than locates in the face of the piston, screwed in OK the other night when I was fitting the new pads. Today it was just rotating but the piston wasn't winding in until I cracked the bleed nipple to let some fluid out. only very small amount of fluid came out of each calliper, not enough to half fill the bleed hose I attached.
Cheers

[111Robin]

I've replaced the rear caliper pistons on my golf before, they should all be similar mechanically. It is just as simple as the piston having a coarse female thread in the centre that screws onto a male thread in the cylinder bore. When the handbrake is operated the centre screw is pushed out a fixed amount by a cam mechanism therefore pushing the piston out and returns under the spring action. If you are able to rotate the piston I don't see how it's possible for it to not retract unless it's been pushed out so far it's disengaged from the male thread. Perhaps by venting the bleeder you've made it a bit easier to push the piston back far enough to catch the thread then enabling it to be wound back in. Perhaps collapsed hoses are causing hydraulic lock causing the brakes to bind and overheat. If the pistons can be wound back easily and the hoses are fine perhaps the glide pins are seized or even just tight this would also cause binding.

[Kinger]

My Dilemma deepens.

After a clean 20 mile rune yesterday afternoon, I took the Elise u=out this afternoon to see is it was OK. Well only got about 3 miles and the brake brought it to a halt again. And I mean the brakes were very tight, no chance of moving in third. I let them cool down for 30 mins and headed home. By the time I got to the house they were at there worst again, I jacked the car up to see if I could see things, It was then I noticed all four wheels were solid couldn't even turn the fronts using the wheels. Let everything cool down and everything turns by hand.

I'll thinking of putting all the old pads back in to see how it is, my next thought was to bleed and flush the brake fluid.

To recap, Piston all free to move front and rear, rear caliper sliders free to slide, spring loaded hand brake lever on caliper move by hand and hand brake cable currently removed.

Any more suggestions welcome.

[111Robin]

I would think that if all four callipers are ok mechanically and hydraulically then it has to be the master cylinder at fault, possibly not returning therefore causing hydraulic lock. I would remove it and fit a seal kit and replace the fluid.

[rawsco]

Probably not much help but what you describe is very similar to brake pump that closed brake systems on mountain bikes of yesteryear suffered from before they started fitting expansion resevoirs. Maybe the the port/valve that allows fluid into the expansion chamber is blocked somehow effectively making the braking system closed?

[111Robin]

During the three mile trip when they locked on, how often and how hard did you apply the brakes ?. If you're just braking normally for that distance there's no way it's anything to do with fluid expansion due to heat transfer. The piston must be sticking in the master cylinder bore. It probably comes back gradually after its been sitting a while.

[robin]

I agree it's probably the master cylinder (or pedal) sticking; as soon as it starts to bind it will get worse very rapidly as the pads and fluid heats, it applies more pressure, gets hotter, etc. ...

[111Robin]

A new cylinder is only around £70, that would be the best idea, there's no telling what sort of mess the bore will be in.

[Kinger]

Thanks guy's,

I'll get a new one ordered tonight, now you mention it the peddle did seem different very high and absolutely no movement at all.

Cheers

[Dominic]

I would also refresh the brake fluid due to the temperatures that it has been subjected to. It will be well past its best IMHO.

[robin]

That's a polite way of saying that it will be utterly shagged. (though it's quite hard to replace the master cylinder and not replace the fluid, no doubt somebody will tell me there is a way).