Brakes locking on

[jimj]

Quite a while ago, and some thousands of miles have passed uneventfully since, sadly, I had to tow the Elan into a garage. The last stretch was largely downhill and my wife is not the greatest tower. I had to brake almost constantly and when we got there the brakes were locked solid.
Dave, the mechanic, cranked off a brake nipple releasing excess pressure and all was well. He suggested everything had become too hot. It never recurred.
Last week at Throckmorton there was LOTS of violent acceleration and viscious braking over short distances with little time for cooling and half way through the day I could feel the brake pedal becoming firmer and firmer until, again, the brakes were locking on. Again, a quick crank loose then tight of a brake nipple and all was well. Someone suggested I may have a slight leak past the seal in the master cylinder but is this likely or is it just the unusually excessive heat generated?
Jim

[ardee_selby]

Jim,

Couple of questions...

What brake fluid are you using?

Are you servoed? (though I can't think why a servo would suffer from what you describe)

Good Luck

Cheers - Richard

[Galwaylotus]

Jim,

Couple of questions...

What brake fluid are you using?

Are you servoed? (though I can't think why a servo would suffer from what you describe)

Good Luck

Cheers - Richard

Servo was the cause of my brakes locking. Situation was slightly different and for a while I could release them by a sharp stab on the pedal but eventually took the servo off, converted to a tandem master cylinder, steel braided lines and Green Stuff front pads. I wouldn't go back to the original setup.

[alexblack13]

Never had the problem myself, but I do understand that the servo is the cause of the majority of brake sticking isues. Apparently a sticky valve ass'y within the unit. The fix is a strip and clean / rebuild. New fluid and hey presto..

Someone who has had the problem and fixed it will no doubt be along soon..


Alex B....

[UAB807F]

Hi Jim,
Like the others here I've also had the sticking servo syndrome, but usually it's been after the car has been hanging around unused for ages, not when it's being driven regularly. I seem to have vague memories of master cylinder problems not returning fully as well although it's too long ago to be accurate. I think I'd check the m/cylinder first then the servo, assuming it's a problem on all 4 brakes at once. If one wheel is affected more than the others then it could be just a caliper sticking, again not fully returning & binding on. Do you get a nice uniform coating of brake dust on all 4 wheels ?

But I'm struggling to think of a situation where heat alone could cause the problem, I'd have thought excessive heat would have caused fade, not super-duper braking !

Brian

[elansprint71]

Bin the servo- add more lightness. I did. Fit +2 discs and calipers (which puts a bit of weight back on but means that the fronts will lock before the rears, which is nice).

Sticking brakes can be caused by the flexi-hoses swelling inside and not releasing the pressure when you take your foot off. This phenom can come and go, seemingly at random but possibly as a result of temperature change.

How old are your flexi-hoses, Jim?

[Foxie]

Hi Jim,
I seem to have vague memories of master cylinder problems not returning fully as well although it's too long ago to be accurate. I think I'd check the m/cylinder first then the servo, assuming it's a problem on all 4 brakes at once. Brian

I had this problem a long time ago, brakes sticking on, only released by letting the pressure of by cracking the m/c outlet. Traced to master cylinder not retacting sufficiently to open lock valve. Cured by putting spacer washers on the m/c mounting.

[jimj]

No servo, DOT 4. All the brakes were on with the pedal rock hard at the top of it`s travel, no problem today with different brakes getting hot....
Jim

[ardee_selby]

No servo, DOT 4. All the brakes were on with the pedal rock hard at the top of it`s travel, no problem today with different brakes getting hot....
Jim

So...no servo. That narrows it down a bit...

Looking at the two incidences i.e. being towed & the Throckmorton outing: Doubtful the heat build up would be the same degree for each...unless being towed at high speed and a solid pedal would indicate the seals are OK.

Sounds like it was the frequency of braking (not the heat as such) with M/C acting as a pump, not allowing fluid back into the reservois quick enough...think Sean has nailed it wrt mounting of cylinder/pushrod free play (But if that checks out OK..weak piston return spring? sticky seals?...or as Pete has said all flexi-hoses collapsed inside and acting as one-way valves)

Cheers - Richard

[elansprint71]

Sounds like the master cylinder then. Classicar Automotive, at Chelford, looks like your next port of call Jimbo.