Odd Sprint brake problem

[Mark W]

I've owned my drop head Sprint for 25 years, I rebuilt it 20 years ago but cannot work out what is wrong with the brakes.
Basically all 4 don't release reliably, SOMETIMES they lock on and the harder you've braked the harder they stick. If you wait a few seconds they release, faster if you turn the engine off.
I replaced the callipers, lack of use maybe and a failed experiment with silicon fluid....no change. I replaced the master cylinder.... no change. Checked the non return valves.... again no change, changed the servo as by now I'd worked out it didn't happen with the servo vacuum line disconnected.... no change.
Can it be delamination of the flexible hoses? If it is it's all 4 of them . The system bleads easily.

HELP Regards Mark

[alexblack13]

Your Servo is holding the brakes on. V common prob' There are lots of posts etc regarding but basically there is a little mod to fix. No experience of this so can't help much further. But more than likely the servo.

Stand by for the cure from some of the others

Don't worry.. Not a big issue to fix I am told.

Alex B.....

[alexblack13]

sorry Mark,did not notice you had changed the servo. Sure the replacement was good?

AB...

[elansprint71]

Old flexible pipes will balloon inside and become effective one-way valves. For the cost of elimination of this possible cause, it is worth fitting a set of braided hoses.

[types26/36]

Check you have some "free play" in the master cylinder push rod, is the brake pedal sticking down slightly and building up pressure in the system? failing this you could make up a pipe to bridge the inlet and outlet pipes on the Servo, you would then know if the Servo is the problem.

[Robbie693]

Your Servo is holding the brakes on. V common prob' There are lots of posts etc regarding but basically there is a little mod to fix. No experience of this so can't help much further. But more than likely the servo.

Stand by for the cure from some of the others

Don't worry.. Not a big issue to fix I am told.

Alex B.....

The fix Alex is referring to applies to the Lockheed servo. Basically they stopped installing the return spring on the air valve on manufacture. This can cause the brake hang-on you're experiencing.

If this is the case, you need to source a spring.. Or contact Dephi, they sometimes recommend lubricating the piston and sent me some red grease to do it but I found the spring sorted it so left the piston as it was.

If you have a Girling servo, ignore me!

Robbie

[Mark W]

Thank you gentlemen, I will get on it today and report back. I have never really liked braided hoses on the Elan though, I think they make the pedal a bit hard and mine does like to lock up if her driver is "surprised".

Thanks Mark S4 Sprint DH

[Mark W]

The orriginal servo was a girling this new one is a Lockheed. I checked the brake pedal and there is plenty of "float". I remounted the servo in line with Lockheeds recomendations which meant rotating it about 30 degrees. I drove the car with the acuum line blocked, if there was any drag I didn't feel it, and the brakes were great, unblock the line and occasional sticking returns but perhaps not so often. I think I will change the hoses and if that doesn't fix it run without a servo.

regards Mark

[alexblack13]

I very much doubt it will be your hoses....You above say that blocking off the servo cures it! How can it be the hoses?

But hey!!

Alex B....