Remote servo causes brakes to bind on

[MegatronUK]

So here's something interesting that I've just noticed since we've now got the engine running - when we apply vacuum to the two remote MGB servo's we're using, the brakes bind on, without the pedal being touched.

The system is connected up as follows:

Twin fluid pots to bias pedal box with twin Wilwood cylinders.
Twin cylinders to the twin remote servos
Each servo has a single fluid inlet and a single outlet.
One servo serves the front circuit, the other the rear.

The vacuum line from the Cossie intake plenum runs to a t-piece and then a line to each of the servos - normally it would just be a single line to the Sierra master cylinder. There's a non-return valve in each of the lines that allows for vacuum only - I believe this is correct as otherwise on-boost there will be no servo assistance.

Problem is that as soon as we run the engine the brakes lock on! Disconnect the vacuum line and of course everything works fine, just with no assistance.

Has anyone come across this problem with a remote servo before?

[Graham]

yes last week on an s type jag! under the white vented cap on the side of the servo, is a spacer spring and piston if theres something wrong with one of them the servo will pull the brakes hard on.

[MegatronUK]

Ah, nice one Graham. I'll check that the cap is one properly and that the spring is in place. I do remember that the cap got knocked off at one point, but it was put back on. Wonder if the spring wasn't replaced centrally or something like that.

At least gives me something to check, cheers!

[Graham]

i also seem to recall a short rubber tube in there, at least you have two so you can compare them!