Brake master cylinder - part no.

[tyasman]

I have problems on my 1968 Elan S4. I have suddenly got long pedal movement on the brake. (The brakes still bring the car to a halt - but my foot is nearly on the floor). There is no loss of fluid, and pumping doesn't help. I'm advised it may be that the seal on the master cylinder has gone, allowing fluid to bypass it. Does this seem to be the correct diagnosis before I start dismantling it? Also does anyone have the part number for the brake master cylinder if I need to replace the whole unit?`
Thanks

[fasterbyelan]

I have this number for the brake master cylinder - 64068324. This would be a Girling part no.

[oldokie]

The simplest test I've found for internal by passing is hold the brakes on with the car on a slope, if the pedal goes down after a minute or so it's bypassing.
From what you have described, I'd suggest checking the 'runout' on your discs, a warped rotor can cause exactly that condition.
Do you have a single or dual system? Do you have a booster?

[SADLOTUS]

If the seal on the master cylinder has 'gone' wouldn't there be fluid behind the rubber domed seal around the actuating rod? A prod with a screwdriver would spew it onto the pedals....or can the internal seal allow the fluid back into the reservoir?
Do you have a servo?

[tyasman]

Thanks to all