Brakes have a mind of their own !

[rookie]

Hi Guys

just bought a Synergie HDi 2000. I was warned by previous owner that the brakes "Lock On" whenever they feel like it.
Towing it home last night and after about 30 minutes, sure enough, the tow car slowly ground to a halt.

Checked the Synergie and all 4 wheel were locked solid and smoking hot.

Had to wait until they had cooled and then remove all 4 bleed screws and leave them out until I got home. There was pressure in the braking system. !!!!!

Given that the Synergie was being towed without the engine running, has anyone any idea what causing the problem ?

[Stickyfinger]

[Peter.N.]

In the olden days before ABS I would have suspected the master cylinder rubbers.

Peter

[citronut]

spoz its not possible all four flexi hose's have collapsed internally?????

[Stewart(oily)]

I had this with my dispatch van once, I think somebody had bodged the master cylinder to hide the problem which was apparently caused by the load sensing valve, I replaced all of the brake flexis too.

[rookie]

Thanks for the reply's
I am still confused as the car was being towed at the time with the engine "OFF" and the battery disconnected. I screwed the 4 bleed screw out of the calipers (just let the fluid go) and no more problems whilst i towed it home. That would indicate that whilst the bleed screws were in, something was causing the system to pressurise even without the engine running or the foot brake being pressed, but what ?

The car had been driven off the sellers drive when I got there before I hitched it up to the tow vehicle, could the vacuum created during that engine run have somehow caused the brake to lock on whilst being towed ?

I have noticed today that the car has a brand new Master Cylinder fitted at some point in the recent past, don't know if that was an attempt to remedy the fault or if that was what has caused it ????????????

[Stewart(oily)]

Those are the symptoms my van had, mystery pressure in the braking system, I left the job before it was fixed but the load sensing valve was apparently to blame, it would just apply its brakes on its own, it got through a lot of pads, the bodge was to increase the free play between the brake pedal pushrod and the master cylinder piston which made it happen less often, still a pain though in what seems to be a very conventional braking system.

[rookie]

Hi Stewart
That sounds very similar then.
I was thinking that maybe as the car was travelling the brake pedal was perhaps bouncing up and down ever so slightly and applying the brakes. But then you have to wonder why the pressure was not coming back off again once the pedal bounced back up.

I also have just found that I have a lot of exhaust smoke when the engine is running. Starts first time every time at the very first turn of the key, revs freely with no misfire but clouds of light blue smoke out the exhaust. Injectors perhaps ?

Cars done 223,000 and if it wasn't in such good condition I would probably break it.

This list is growing Lol.

[citronut]

sounds to me either the brakes were already binding/stuck on before the seller moved it off there drive,
or the moving it off the drive caused them to stick on,

so what type of tow was used, and was there someone in the cab whilst being towed,

engine running or not whilst towed should make no difference,

does this wagon have a remote servo and master cylinder, if so it could be the linkages sticking on,

[rookie]

Hi Citronut

I drove the car off the drive and the last owner told me that he was selling it because the brakes lock on whenever they feel like it.
It was towed back with an "A" frame (It's a manual box) with the ingnition on, battery disconnected .
There was no evidence of the brakes binding at all when moving off the drive.
It's a Citroen Synergie 2.0 ltr HDi 2001
Has had a brand new Master Cylinder fitted.

About 20 minutes after setting off, the tow vehicle was finding it harder and harder to pull. To such an extent that on a perfectly flat road the tow car came to a stop.
When I looked at the Synergie all 4 wheels were smoking hot.

Released the bleed screws (all were pressurised) and just let the brake fluid run out. No further problems for the rest of the 140 mile journey home.

The last owner told me that when the brakes locked up on him, he left it for an hour or so and then found that the brakes would have freed off.

I'm a bit (no, I mean I am totally) confused as to what could cause the brake system to pressurise on their own.

[rookie]

Sorry, forgot to mention, the servo is on the opposite side of the car to the brake pedal, so if that's what you mean by "Remote servo" then I would say "yes, it has" and there was no one in the cab whilst towing.
Cheers

[RichardW]

Does it have ABS?

[Mandrake]

Does it have ABS?

Good point.

Plain ABS doesn't have the ability to apply brakes (only release them) but ABS/ESP systems CAN apply the brakes on their own. (Eg to prevent a spin when cornering)

Although I would have thought with the battery off only a mechanical problem with the ABS/ESP system could cause the brakes to come on on their own. I wonder if the car has ABS/ESP, and if so whether the control block has been replaced ? Reading the fault codes from the ABS/ESP system might be enlightening too...

[Stewart(oily)]

The vehicle that did this to me was a relatively simple 04 Dispatch van, no ABS or other complications. try fitting a heavier return spring on the brake pedal.

[Ianhw77k]

Just a thought, but could it be possible that the load compensator is somehow pressurising the braking system? Every time it hits a bump that valve arm will be moving up and down. I'm not entirely sure how it all works inside but if one of the non return valves or something similar is knackered, it could be a possibility, or I could be barking up the wrong tree.