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MG MGB Technical - Brake servo follow-up.

Right, all done now and I just thought that I'd run through this for the record.
It seems that my diagnosis of the fault was spot on. The master cylinder had filled the Servo with brake fluid, causing the non-return valve to give up. Thus, no servo and no other symptoms. Given that I got this right, it's a bit of a pain that I didn't bother to aquire a new non-return valve to start with. I haven't stopped kicking myself yet, although I am slightly mollified by my thoughtful aquisition of a new M/C.
Anyway, contrary to information gleaned elsewhere, rebuilding the Servo is a fairly easy task. The worst bit was cleaning all the brake fluid out of it(!) Getting it apart was, as expected, somewhat tricky. The technique that seems to work is to clamp the two studs (with nuts on) at the "round" end in a good, heavy vice and then lever the backplate round. Two people, some tea while the penetrating oil soaks in and some serious welly is required here. From there on it's just a case of noting what goes where and swapping the old bits for new ones and, yes, it is a big spring and you won't be able to note what went where if you're not careful when opening the thing. On reassembly, it's helpful to "tap" the cover at each securing "lobe" to seat it before attempting to rotate it back into the locked position. Dire warnings from Lockheed accompany the kit about setting the pushrod protrusion correctly. The correct amount is helpfully described as "application specific" and, since this information doesn't seem to be available anywhere, I went for the "leave it alone" approach, which has worked well.
Other things to watch for are that the lower, offside nut securing the Servo to the pedal box is a right SOB to get at and that replacing the clevis pin attaching the Servo lever to the brake pedal is a two person job. Preferably the two people concerned should have double-jointed 10 inch fingers...
Another thing to note is that the late-type non-return valve is NLA and substituted by the early type from the remote Servo. As the early valve does not have a 90 degree bend in it, this means rerouting the vacuum hose to suit. In my case there was enough hose in situ to accommodate this.
All in all, I'd say that rebuilding the late-type Servo is a perfectly viable option. Basically, if you've got the skills to get the damned thing out and back in again, you've got the skills to rebuild it :-)
T J C Cuthill

This thread was discussed on 10/03/2003

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.