CLASSIC RENAULT FUEGO

renman · Posted: Thu Apr 16, 2009 7:32 pm Post subject: "Phil" has sticking on brakes

My younger daughter's Fuego GTX which we've just registered has a problem with the brakes.

Work I've done to lead up to this problem Embarassed

:
One year ago, I sent the rear wheel cylinders and the brake master cylinder off to get re-sleeved and rebuilt/new seals.
So bear in mind that the brakes were bled and we've had a good pedal for a year or so - and with absolutely new fluid everywhere -

BUT....the car hasn't been driven to use the brakes until last week.

The symptoms are:
Drive it normally for a trip involving a half dozen or so of brake applications (needs only to be 2km or so) and the brakes slowly begin to apply by themselves.
The brake pedal gets harder until it is right up (no movement) and the front brakes apply themselves more and more.
The brakes obviously get hotter and hotter, and the problem worsens.

My thoughts have been:
Firstly that the rebuilt master cylinder (with presumably slightly different seals than the original) isn't allowing the fluid displaced during application to fully vent back to the reservoir upon release.
I did have some difficulty bleeding the front brakes last year Rolling Eyes

Next, I wondered about brake hoses. They've been known to fall apart internally and constrict the free return of pressure after a brake application.

What I've checked:
1: While the brakes have been locked on, I've loosened a caliper bleed nipple and seen that fluid was pressurised resulting in quite a spurt of brake fluid from the bleed nipple. Immediately of course the car rolled freely.

2: I've repeated this experiment from both sides of brakes (only loosening one nipple) and the results have been the same - the car can roll freely again. So this seems to mean that the hoses aren't the problem because presumably the other caliper would still be locked.

3: I've sent the master cylinder off today to get it checked by the company which reconditioned it. They very kindly performed many hydraulic checks on it and pronounce it OK.

4: I've checked the mechanical freeplay at the pedal and found it to be suspect i.e. not sufficient. This is a subjective measurement because to check freeplay, you're pressing against firstly the pedal's own spring - and then of course the big springs in the booster and finally the springs within the master cylinder itself Confused

This morning - there seemed to be insufficient freeplay at the pedal (you check it by hand).
This afternoon I checked the distance that the adjustable pushrod from the booster into the master cylinder projects from the front face of the booster and it was spot on. The measurement is 9mm.

Although the Haines Manual shows that the pushrod at the pedal is adjustable, this car has a solid and non-adjustable rod.

SO - tomorrow I'll fit the master cylinder again and bleed it up and see what happens.

My current thinking is that everything I can think of has been checked and found to be okay.

Hmmmm.....we'll see what happens

_________________
If it wasn't mine I think I'd have to steal it.

renman · Posted: Fri Apr 24, 2009 8:51 am Post subject:

Fixed the problem Very Happy

There was insufficient free play at the pedal.
Actually the pushrod in the booster was pushing in the master cylinder's piston a bit too much when I bolted the cylinder on.
The result was that as things warmed up and the fluid expanded a little, there was insufficient travel for fluid to vent back to the reservoir.

The only reason I can imagine for the difference might be a slight difference on the seals themselves.

Anyway, since nothing was adjustable (although the manual shows that both the pushrod at the pedal, and the one at the booster are adjustable - not the case Evil or Very Mad

) I had to resort to shortening the booster pushrod and grinding the end round again.

With the proper amount protruding, no problem.
_________________
If it wasn't mine I think I'd have to steal it.

Westair · Joined: 12 Apr 2007 Posts: 167 Location: Australia

Good explanation & result- will help others in future if they have this problem

------------------------------