Morris Minor Owners Club

Hi

We have recently finished restoring my Grandmother's 1968 4 door saloon and have been enjoying taking it out and about at weekends. However, this weekend when I have been driving it after about 5 miles the brakes start to tighten gradually to the point where they are fully locked on and the brake lights are on constantly. Also the brake pedal is then in the up position and is under pressure so cannot be depressed. It only seems to be the front brakes that are locking on.

The only things we have found that work is to leave the brakes to cool down (approx 30mins) or undoing the bleed valve to release the pressure (only when brakes are cool enough to touch!! ).

We have also tried slackening the brake shoe adjusters and this hasn't worked.

Has anyone else experienced a similar problem or could suggest a solution?

Thanks in advance!

Kat

I believe a servo can cause this, do you have a servo fitted?

I had this problem and after hours spent fiddling with the break adjustment it turned out to be the return spring snapped on the master cylinder/foot pedal in the chassis leg.
As the piston was not being pulled back enough the little holes that allow the expanding fluid past (caused by breaking generating heat) where covered by the piston rubber.
In my case all breaks started to bind, but for some reason the front were the tightest.
Hope this helps
Reg

Was a new master cylinder fitted?

There should be some free play in the pedal before the brakes start to work to allow for expansion. So when you push the pedal there should be maybe as much as 1/4" to 1/2" before it starts to move the brakes. There is an adjustable rod that goes into the back of the master cylinder and this probably needs to be screwed back a few turns to stop the pressure building up when warm.

This happened me about 10 years ago just after I rebuilt my blue saloon and of cousre it was on a motorway on the way to work.......

Welcome to the forum - since no one else has done so! I suspect (assuming no servo) it could well be the snapped/missing return spring. Best lift the small section of floor over the master cylinder and check it.

My new brake shoes were to big so had the metal part had to be filed down

I would guess that the brake master cylinder has been replaced during the resto.

Most common cause has already been mentioned by Dave - if the push-rod isn't correctly adjusted, the master cylinder can't return to rest position and therefore prevents the pressure bleeding off. The bleed function at rest (master cylinder piston is fully home) is essential to prevent the symptoms you have and also to compensate for fluid volume changes with temperature and any leakage.

It's not unheard of for new parts to be faulty, so if you DO have enough clearance to the rod from the pedal, but the brakes are still under pressure then it is likely to be the master cylinder itself.
I've never heard of this happening on an old master cylinder (blocked bleed channel) but if there is debris and sludge in there, this may have blocked the bleed aperture - or has physically blocked the piston travel (e.g. debris built up against the main circlip)

bmcecosse wrote:Welcome to the forum - since no one else has done so! I suspect (assuming no servo) it could well be the snapped/missing return spring. Best lift the small section of floor over the master cylinder and check it.

Roy
If you look up the replies you will find I did mention the spring
Caused me a great deal of wasted time, before I figured it out: Reg

Yes Reg - I was agreeing with your suggestion! My 'welcome' remark was 'because no-one else had done so'. I'm sure you have pinpointed the fault.

bmcecosse wrote:Yes Reg - I was agreeing with your suggestion! My 'welcome' remark was 'because no-one else had done so'. I'm sure you have pinpointed the fault.

OOps
Yes on re reading I can see thats what you ment.
Apologies
Reg