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Brakes locking up again!
Alan_Thomas - 16/6/04 at 09:11 PM

Got a problem with the front brakes (std. cortina discs) locking on after fast hard braking blat.
rear shoes let go and wheels are completely free but pedal is rock hard with no travel and front wheels are locked to the extent the engine cannot move the car.
No servo, std, new, escort tandem master cylinder with the front circuit feeding front brakes and the rear cylinder circuit feeding the rears. pedal returns fully and allows rear brake shoes to push fluid back.
Front calipers rebuilt with new seals and the polished pistons move freely. Can only think it is the master cylinder but what? Could the rear circuit be pushing the double piston in the master cylinder fwd to the point that the feed hole is still blocked.
Will take it off again this weekend but could not find anything wrong last time (new MC)
Only change I can think is to feed rear circuit to front brakes and front circuit to rear.

Anyone any ideas?

britishtrident - 16/6/04 at 09:19 PM

Simple test
When brakes are binding slacken mastercylinder mounting bolts a few turns and pull it fowards 3 or 4mm --- do the brakes instantly free off ?

Mark Allanson - 16/6/04 at 09:21 PM

Rear adjusters are not holding. As the shoes over retract, fluid is pushed back into the system and the only place it has to go is into the front calipers, locking the front brakes

rusty nuts - 16/6/04 at 09:23 PM

Try releasing a bleed nipple on one of the calipers, cover it first with a rag to stop fluid getting onto paintwork. If this then releases front brakes it sounds like the master cylinder push rod maybe holding the piston in master cylinder partially applied, it may be possible to adjust your push rod to shorten it?? Rusty

Baldrick - 17/6/04 at 10:26 AM

Similar thread here,

http://www.locostbuilders.co.uk/viewthread.php?tid=12599

As I noted then "This happened on mine. Problem was cured by fitting positive return spring on pedal. Just the friction of the pedal/pushrod etc. was enough to keep the brakes hard on once applied."

I have had no re-occurrence since I fitted the spring.

Alan_Thomas - 17/6/04 at 12:54 PM

quote:
Originally posted by Baldrick
Similar thread here,

http://www.locostbuilders.co.uk/viewthread.php?tid=12599

As I noted then "This happened on mine. Problem was cured by fitting positive return spring on pedal. Just the friction of the pedal/pushrod etc. was enough to keep the brakes hard on once applied."

I have had no re-occurrence since I fitted the spring.


Thanks I will try this and let you know the outcome. - Alan

Alan_Thomas - 17/6/04 at 10:37 PM

OK, cracked it!!
Everybody was on the right track with the master cylinder preventing the fluid returning. The cause was the shorter push rod bought to replace the standard one.

It had a larger 'mushroom' head, which preventing the cylinder piston from fully returning by about 2mm. Filed down the head to fit and now fluid easily returns.

Thanks to all for suggestions,

-Alan