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

[Elanintheforest]

Well, Mark, it sounds like the flexi hoses are the only bits that haven't been changed...so change them!

Do you have the original Girling servo, or a Lockheed replacement by any chance? The Lockheeds were well known for locking the brakes on, and a mod is available to put a different spring in the vacuum release valve. It may also be worth changing over the vacuum rubber hoses as well.

Were the callipers professionally reconditioned? I.e. re-plated, bores measured and pressure tested? They are now getting old enough that a home job of replacing the seals, which I've always done, sometimes doesn't work because of the bores being damaged or out of true.

But I suspect the servo!

Mark

[Mark W]

Thanks for the reply Mark. The callipers are from Classic Car Automotive and have covered less than 5 miles. The servo was a Girling but is now a Lockheed. I am sure it's the servo, today I drove it with the servo air line blocked off and it was fine, the brakes were surprisingly good. I checked the "float" on the pedal and it is sufficient, I remounted the servo in line with Lockheed recomendations, I had installed as per the old one which meant I had to rotate it about 30 degrees, it still locks up occasionally although the frequency may have reduced. WTF?
I guess I will do the hoses although I have an old Shadow which has 20 fexi hoses so I am well used to what a delaminated one feels like and the Elan doesn't.
Where do you get the spring mod from?

regards Mark w

[david.g.chapman]

I had a similar problem on my +2. It turned out to be that the external return spring on the brake pedal was mounted the wrong way around - that is pushing the pedal down! The pedal would not come up fully (only a few mm short) but enough to keep some pressure in the system. There is a valve in the master cylinder that needs to reset.

You can check this quickly by hooking your foot under the pedal and lifting it up. If there is movement and the brakes free up you have your answer.

Dave Chapman.

[Elanintheforest]

Mark...have a chat with Classicar Automotive. Just say 'Lockheed.....locking brakes....Elan' and they'll know what you mean! They have the spring, and are a very helpful bunch.
Mark