26 replies to this topic

[MinesRed]

Hello all.
My first post here,so hello.
Just bought a 1989 Mini City that has a 1275A+ motor in.
There is a slight issue with the front brakes whereby after a mile or so they stick on.
The car has had a new driver's side caliper and the master cylinders don't look very old.
If I leave the car a while the brakes are completely free.The rear brakes and handbrake all seem fine.The car has only done around 300 miles in 4 years,but has always been MOT'd and there is no mention of brakes on the MOT history.The brake pedal also goes very hard as the brakes stick on but is normal when you first drive off.
Has anyone got any thoughts on this?
Thanks in advance.

[Spider]

Welcome to the forum

 

First thing I'd suggest here is to be sure the brake pedal doesn't contact the car body when your foot is off the pedal, essentially, the pedal must 'hang' off the master cylinder.

 

Not the easiest place to look, but you'll need to check for this by looking at the top of the pedal, where it is connected to the master cylinder push rod

 

I'll find a photo.

 

<edit: Photo

 

 

The arrow is pointing to where you need to check.

 

If you find this is making contact here, there are (or were) shims available for this, however, often when master cylinders are replaced, the gasket on which they sit is removed and that's all it will take. >

[Magneto]

If it has a new master, it could need a shim under it to space it up a bit, if it's too tight it doesn't release. Same as holding your foot on the pedal slightly. sometimes the thickness of an extra gasket is all it takes to remedy this.

[MinesRed]

Guys..
Thanks for this,I'll investigate further so I can confidently take her out without the brakes sticking on.
Thanks again.

[Thelowrider]

I assume this doesn’t have a servo?

[MinesRed]

I assume this doesn’t have a servo?

The lowrider.
Yeah,car has a servo,looks like it could be original as well.

[GraemeC]

Moke's advice is a quick and easy check.

 

It could be the servo acting as a one-way valve, although generally this doesn't give you a solid pedal. I'd also expect this to lock up all 4 wheels.

It could also be the flexi-hoes breaking down internally and blocking themselves off when they get warm.

Or if its not been driven much it could just be the caliper piston seals being a bit dry - with heat the rubber softens a little and doesn't have the 'strength' to pull the pistons back.

[Thelowrider]

Easiest test is to disconnect the servo one way valve and see if the issue disappears (do this test when you’ve driven it and he brakes are locked on, or the issue you are describing happens) I’ve had it before on modern vehicles similar issue turned out to be the one way valve also had issue on an LDV van which was water ingress between servo and master cylinder which built up rust between the two, not allowing the piston to return fully meaning the front brakes locked on all food for thought.

[MinesRed]

Thanks again folks,plenty to go at here...

[MinesRed]

Should there be free play in the linkage from the brake pedal into the servo as it all seems very tight.
Is there a set measurement for the bracket where it connects to the threaded pushrod into the servo?
Thanks again.

[Bat]

Hi,

I'd back the pushrod off a bit to give a little free play, it sounds like that could be your problem.

Cheers 

[Ethel]

Plenty of sleuthing suggestions already.

If it's the servo then it should effect all 4 brakes, but could be less noticeable on the back. Also consider seized caliper pistons, though it's less likely both sides would be stuck on equally.

The discs and pads would need to heat and expand through friction so would need a bit of driving to bind, whereas a hydraulic fault would happen as soon as you used the brakes and the servo would kick in as soon as the engine starts.

[MinesRed]

Hi,
I'd back the pushrod off a bit to give a little free play, it sounds like that could be your problem.
Cheers 

You mean the servo pushrod?
I presume I adjust it on the end that connects to the linkage for the brake pedal?

[genpop]

• Do not touch all the linkages, have the ruber brake lines changed .They are swelled ,brake fluid goes to the calibers because of the pressure but it flows back only very slow because of the maceration. You should do that for the rear axle as well .

[Bat]

Hi,
I think there's a clevis pin on the under bonnet side with an R clip in it?
If there is you could pull that out once the brakes bind up and see if it releases them.
As you can see from all the replies there's more than one thing that can cause this, coupled with the uncertainty of what's gone on before could make this a tricky one to solve...
Cheers :)