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Sticking brake master cylinder - any ideas why?
Steve Lovelock - 19/9/10 at 05:23 PM

I was sprinting the Luego today and during the third run I developed a problem with the bakes binding. I didn't actually realise something was wrong until I was on the starting grid for the fourth run so just continued. By the time I'd finished it the brakes were on with some force. I got back to the pits and started playing with the brake pedal and when I tugged it back the brakes instantly freed. I then drove the car home with incident.

Any ideas why the master cylinder might stick?

It is a pedal box / balance bar set-up and has only done 3,000 miles so not exactly old. I know that the brakes take a hammering during a sprint but I have done several events without trouble.

rusty nuts - 19/9/10 at 05:37 PM

Sticking pedal pivot point, over adjusted push rods or needing a return spring on the pedal would be the first things to check

cairnnut - 19/9/10 at 05:45 PM

Hi steve You need to adjust to give a slight clearance between the actuating rod and the master cylinder to allow for expansion.
john

Hellfire - 19/9/10 at 05:47 PM

Is it a Sierra master cylinder? If so, it is very easy for dirt and grit to get into the bore and prevent the piston from returning fully and causing the brakes to bind.

Phil

jacko - 19/9/10 at 05:49 PM

It could be the seals in the m/cylinder that are letting oil pass them stopping the peddle returning

britishtrident - 19/9/10 at 05:56 PM

Quite often it is the mushroom on the end of the pushrod is too big and fouls the stop washer at the end of the cylinders.

britishtrident - 19/9/10 at 05:57 PM

quote:
Originally posted by Hellfire
Is it a Sierra master cylinder? If so, it is very easy for dirt and grit to get into the bore and prevent the piston from returning fully and causing the brakes to bind.

Phil


Not unknown --- easy enough to check.

britishtrident - 19/9/10 at 06:00 PM

quote:
Originally posted by jacko
It could be the seals in the m/cylinder that are letting oil pass them stopping the peddle returning


Not really but one thing that it could be is too much fluid in the reservoir. An air space is required to allow for fluid expansion when hot.

austin man - 19/9/10 at 06:38 PM

over adjustment
crap under pedal
angle of rod into cylinder
then what everyone else said

Steve Lovelock - 19/9/10 at 08:26 PM

Thanks for the advice. I'm going to look at the bias bar set-up first as I know that's not what it should be.

Steve Lovelock - 26/9/10 at 03:50 PM

I had a look at the set-up today and discovered that the plunger shaft for the front master cylinder was bent. I also realise that the set up wasn't true which probably contributed to the distortion. Think I have it sorted now.