HOT FRONT DISC BRAKES

[griffonmark]

After being stood for 15 years I have finally managed to get my supposedly magnum based kit car on the road after 2 years of frustrated ownership. However, the front disc brakes are giving me real problems as they lock on solid after 3.5 miles which just happens to coincide with my journey to work. When I set off the brakes don't appear to be binding as I can push the car easily, but in the last 100yds of my journey they are firmly locked on with a rock solid brake pedal and are good for frying eggs. It is just the front brakes locked on. I did overhaul the calipers fitting new pistons and seals before getting the car on the road, but haven't been able to get discs yet. They do look worn out. The pads were fitted by the previous owner and as the car had never been used I put them back. As soon as the brakes cool down they appear free again. Any suggestions?

[Geeza]

Hi.
Sounds like a master cylinder problem to me.I had a similar thing with a Dolomite a few years ago.Cured it with a recon. master cylinder.
Unless anyone else has any ideas I think thats where I would start.
Hope that helps Sean.

[shamm]

I had a problem with my servo'ed front brakes which was similar.

The servo was dragging the brakes on very slightly with the engine running. This caused the disks to heat and expand and then they grabbed even more. Result, very hot disks and poor performance.

Easy to test, just disconnect the vacume hose from the servo and go for a drive.

Steve.

[griffonmark]

Hi Steve, I disconnected the servo hose as you suggested and the brakes have been perfect ever since. Everyone was telling me it was siezed calipers or that I had put them together wrong, but I couldn't understand why the brakes locked on so hard and why the pedal went rock solid. The brakes work great without a servo, better than my wife's Scirocco! What do I do now? Do I leave the servo disconnected, or do I get another servo from somewhere? What do they cost? Is it an easy job to do? Not something I've done before. Many thanks, Griffonmark

[lambaj]

If your happy with the performance of the brakes without the servo - remove it...... if you can and just have the master cylinder. Thats simple with a remote servo, but not so simple with a "all in one" unit.
If a car has a servo fitted, it has to work (MOT!) Maybe you could transplant a non-servo master cylinder from somewhere. Suggestions from other HB/HC owners as I only know the HA brakes

Cheer
Tony (HA21)

[shamm]

I have yet to investigate mine as I also think they work fine without the servo.

Looking at the manual there is a 'off state' adjustment to the push rod out the front of the servo. As the servo works fine otherwise I think that this could be the problem, for yours as well as mine.

You have to remove the servo to check and change it, but thats less work that moving all the brake pipes etc.


Steve.

[griffonmark]

Steve, thanks for that explanation following which I've looked at my manual and that does look like a probable cause. But it looks like you have to dismantle the bloody thing completely. For the time being the brakes are fine without a servo as I'm not brave enough to drive at much over 50mph, but I might have a go in the summer holidays. If you try before let me know how you get on. I am thinking this may be a potential waste of time though. The labour involved in taking it off and stripping may not be cost effective if exchange units are available at a reasonable price. Regards, Mark

[shamm]

My car slows down from 80 ok, and I imagine my HC is alot heavier than your car.
The servo's are around but I would not call them common, the 2300 one is a bit larger than the 1256 type but they both do the same job and you can't tell the difference when driving.

I will be doing this job soon as the MOT is looming, will have to make a tool to open the servo up but once inside it should be simple-ish providing nothing falls apart.

P.S.
Did you blank of the vacuum feed from the engine, otherwise the hose acts as a vacuum leak.


Steve.

[griffonmark]

My car is fitted with the bigger Magnum servo as the guy that tried to build the kit couldn't be bothered fitting the smaller 1256 item which is recommended by Griffon. I'm glad to see your car brakes OK. Your right, my car is a lot lighter. You don't need a jack, you just drive over a small child, tell them to breath in for up, out for back down.

I didn't bother plugging the vacuum hole, if you saw the *Bleep* SU carb it currently has you'd realise it needs every bit of air it can get!

Regards

Mark