34 replies to this topic

[JXC Mini GT]

My 1980 Mini GT has had lots of work carried out by Mill Road Garage recently   but only had brake flexible hoses changed as part of the works.

When I picked up the car from Ben everything seemed fine with the brakes, after a short drive the pedal travel increased but pumping the pedal made no difference. I took the car back to Ben and he re bled the brakes which restored the pedal to the original position.

After driving it for about 300 miles I now have different problem, the front brakes seem to stick on (slightly) after a short drive, I have checked caliper pistons/pads and everything seems fine.

 

Could these problems be caused by a faulty master cylinder? I would welcome views on what else I should be looking for.

Many thanks

John

Edited by JXC Mini GT, 20 August 2020 - 05:28 PM.

[Quinlan minor]

I’d check the callipers first.
Jack it up, see whether one, or both, are binding. Push each pad back to check that they’re moving freely. If that’s all good, make sure the pedal is moving freely, too.

Edited by Quinlan minor, 20 August 2020 - 06:02 PM.

[sonscar]

Is there enough free play at the pedal to let the master cylinder piston to fully return?Steve..

[JXC Mini GT]

Thanks for the suggestions, I will check the calipers/pads and for pedal free play tomorrow.

[JXC Mini GT]

Pads removed calipers pushed back and forward a few times, everything seemed fine, checked pedal for free travel and lubricated pivot although all seemed fine.

Took it for a drive and everything seemed ok, until approaching a roundabout when the pedal travel increased to about half distance, the car pulled up square, I continued driving and the pedal returned to full pedal the next time I braked. Throughout the drive the front brakes did not appear to be sticking.

Any thoughts?

Edited by JXC Mini GT, 21 August 2020 - 01:56 PM.

[Quinlan minor]

I've experienced similar in my Alfa when one of master cylinder seals was a little tired. If you slowly pressed the pedal you got long travel (as, I think, fluid moved past the seal, at low pressure), if you jumped on the pedal, it was fine (I think, as the pressure built up quickly the seal did what it was supposed to do).

Try applying only gentle pressure, on the pedal, and see if it goes long.

If it does, then it's, probably, at least an overhaul kit or replace the master cylinder.

Edited by Quinlan minor, 21 August 2020 - 03:24 PM.

[Spider]

Check that with the pedal up, that it's 'hanging off' the master cylinder pushrod and that it's not contacting the bodywork at all, ideally, you'd like to see about 2 - 3 mm clearance under the part of the pedal where it enters the bulkhead to connect to the Master Pushrod. If it doesn't come all the way back, the system can't 'breath' and with road vibration, the brakes will gradually come on.

 

The other thing, as Quinlan suggested above is that the seals in the master cylinder may have swelled and that will have a similar effect with road vibration bring the brakes on.

[JXC Mini GT]

Thanks for the suggestions, I am going to change the master cylinder as it’s the only part of the braking system that hasn’t been changed since I have owned the car.

[JXC Mini GT]

Update:

I changed the master cylinder, bled the system and then took it for a run, both front brakes were still sticking, the only component I hadn't changed was the http://www.minispare...600/FAM7821.jpg
Brake limiter valve, so another minispares order (thanks Ivan for dispatching it so quickly) and its now fitted and all is well.

Edited by JXC Mini GT, 28 August 2020 - 09:01 AM.

[richmondclassicsnorthwales]

If the master is 40 years old, and is the original, you have done very well regards longevity, may be time to retire it and get a newer model.

 

Brakes is something that is certainly top of my list. The brake limiter valves are bloody awful things, Russian roulette them things, cant really know if they are doing their job properly or not, I have my own views on them, but won't open that can of worms

[Spider]

,,,,,,,The brake limiter valves are bloody awful things, Russian roulette them things, cant really know if they are doing their job properly or not, I have my own views on them,,,,,,

 

 

Fair enough if you don't wish to 'go there' but I think I share your views. The late 4 and 5 port 'FAM' type valves are dreadful things, I can't bin them fast enough.
 

[richmondclassicsnorthwales]

2 words   Bloody things !

 

Non serviceable,  who ever designed them needs shooting !! 

[JXC Mini GT]

My braking issue has returned in a different way.

The brakes were working well since changing both the master cylinder and the brake limiter valve back in August 2020, however about a week ago when I took the mini for a short run, when I went to slow down the pedal travelled about half way down and I seemed only to have rear brakes, I drove back home slowly and started investigating today, I loosened off the pipe from the master cylinder serving the front brakes and to my suprise no fluid came out, I then asked my wife to push the pedal slowly and hold it down, this released some fluid and some air, I then bled the front brakes which had some air in the fluid.

I thought this had solved the problem, however when I drove a short distance the front brakes were locked on, I cracked the master cylinder pipe serving the front brakes and this released the brakes, I then drove a few miles and all seemed fine but when I got home the front brakes were locked on again.

I believe the problem must be the master cylinder but would welcome expert views in case I have missed something.

[sonscar]

Free play in the pushrod not enough?pedal not fully returning? would be my first thoughts,Steve..

[JXC Mini GT]

Free play in the pushrod not enough?pedal not fully returning? would be my first thoughts,Steve..

I did check the free play in the push rod when the problem 1st started back in August 2020 and all seemed fine, I will check again tomorrow.