Hi,

I'm looking for a few suggestions about my current brake issues. On numerous occasions I thought I had the problem fixed but it keeps coming back. Note my brakes system is PRE ABS even though its a 1988 model. When I bought the car in 2001 the ABS had gremlins so a pre ABS system was retro-fitted and it has worked perfect for all these years.

Several months ago my master cylinder was leaking (rear seal) and I replaced with a reconditioned unit. At some stage since that replacement (perhaps it started straight after, I can't be sure) I've run into a problem where on short trips (5-10min) the brakes work fine but on longer trips the brakes begin to drag.

Just in the last few weeks I've replaced the rear calipers and rear brake hose. The front calipers and front hoses and < 5years old. On the weekend I changed the brake booster as an experiment but no change. Rear pads are new, front pads have plenty of life left.

When the car is first used, there is normal brake pedal travel. But through maybe use or extra heat on a longer trip, the pedal travel decreases and you can notice a constant braking drag on the car when there is reduced brake pedal travel.

The brakes don't pull there is no pedal softness. They've been bled several times in recent weeks due to all the attempted fixes going on. I suspect the problem is both front and rear. At speed the problem can cause strong vibration through the steering wheel, suggesting front brakes. But when I rebuilt my rear end, the rear pads were badly worn suggesting they had also been dragging.

Is is possible that a reconditioned master cylinder is faulty and is somehow holding pressure in the system?

 

With the brake pedal released is there a tiny bit of slack at the pedal-to-booster rod/linkage? There should be

That's what I'd look for first

Cheers
DD

 

Hi Doug,

I should have mentioned, I've also tried tinkering with the rod. I have previously removed the booster to master cylinder rod and screwed it in a little to reduce its length. That bought me more pedal travel when hot or cold but I still suffer problem of reduced pedal travel and dragging on longer trips. I don't think I could shorten it any more as I would have too much pedal travel when cold. Cheers

 

The master cylinder is faulty, I would say. A new one would almost certainly fix the problem.

 

I agree with Greg.

The early ABS cars had a weird set up, and that retro is getting common, BUT, I remember, and it was 15 years ago, that when we did one, the pressure differential valve had to be swapped out. Thats the one on the RH inner guard hidden by the air cleaner. I simply cannot remember what the " fault" was, but as soon as that was swapped for the Pre ABS unit, all was sweet.

If I remeber, I will repost, but dont hold your breath please, as the owner has passed on, and the car is, I DUNNO.

 

Thanks all. I'm going to fit a spare master cylinder tomorrow, hopefully it will be problem solved.

Grant, I think I know the valve you mean, certainly on my car there is some sort of in-line valve close to the firewall but it's on the rear brake line. Even though initially I thought I only a rear brake problem, at times I get a strong vibration through the steering wheel so I'm now thinking it's both front and rear.

If the master cylinder switch doesn't work however, that might be the next place I have to look

 

Guys
I have a RHD factory OEM non ABS car. The system does not have a pressure limiting valve. There is a T junction fitting just below the M/C which serves to divide the fluid from one half of the M/C between the front brakes and just a straight coupler fitting to connect the other half of the M/C to the rear brakes, neither has any valving. As Grant said, if your car did have a valve when it was ABS and it is still there, then I would remove it to start with.
It is worth checking that the correct part of the M/C has been connected to the front and to the rear brakes: the FRONT section of the M/C supplies the FRONT brakes. As can be seen in this photo, the green brakeline going to the front brake through the wing terminates where the M/C will be fitted, as the FRONTMOST of the two. The new copper rear brake supply line is seen (not yet connected or cut to length) rising up past the rear brake coupler in the photo, and this one ends up at the REARMOST port of where the M/C will be.

 

Damn that bloody trip to France is really going to cost me now.

YES>

That valve was swapped out for a standard Brake T joiner, provided by Power Brakes here in Adelaide, and that made it possible for the Non ABS system to do its thing on the 1988 Convertible.

Hind sight, HAHAHA, we could have nicked the T Joiner from the brake system on the spare rear suspension he had sitting there at the time, but we were never that clever, and probably way too many beers by then,