Brakes locked on

[steve_d]

Took a journey Yesterday in my 87RRC based Dakar.

About 2 miles into the journey the brakes began to bind and very soon were being applied quite hard and the pedal was rock solid. I stopped and smoke was coming from at least the front offside but I assume the others were the same as the braking was even and the pedal hard indicating (to me) that it is a master cylinder/servo issue and not something happening to a specific wheel. On later analysis I realise that the issue may only apply to one of the dual systems.

I pumped the pedal hard a few times and the pedal eased so I started off again but they again progressively applied (without having touched the pedal). Before I got to the point of having to stop again the problem cleared and was OK for the remainder of my 40 minute trip.

The same thing almost to the letter happened on the return trip and again cleared.

Any ideas?

To me it seems as if the servo is holding the vacuum and not releasing it. I had hoped that there may be a servo vacuum release valve I could inspect or replace but my Haynes makes no mention of one.

Many thanks

Steve

[western]

where the vacuum hose connects to the servo, that connection should have a non-return valve in it, it maybe faulty or the master cylinder is sticking partly in the brakes applied posiion & causing the brakes not to fully release.

[rtbarton]

I had this problem on an RRC

I could release the brakes by pulling the pedal back with my toe hooked underneath it.

It was the servo, in particualr the valve that surrounds the actuating rod the pedal connects to. A service kit sorted it out.

If the non return valve between the servo and inlet manifold fails open you loose vacuum and the servo won't assist the brakes properly. If it fails closed you can't generate vacuum with the same symptoms.