SIII Brake Woes

[Apis Mellifera]

Although the brakes still work in my SIII 88, I seem to have more pedal travel than before and the pedal does not return all the way when I let off. Both pedal return springs are present and springy. The truck doesn't pull or shudder under braking. It squeals as usual. I've check the fluid level in the MC and it's fine, hasn't dropped, is a little blackened, but fine otherwise. No leaks on the four corners. The plastic reservoir on the MC is deteriorating. The pedal is firm, not spongy.

I've got an idea of the pedal-no-return problem, any guesses from you guys?

Anyone have a rebuildable, dual line, servo brake master cylinder available for purchase? Must have a solid reservoir. (Hopefully solitation of items for sale won't warrant deletion of this post)

Many Thanks

[LaneRover]

Broken return springs at the top of the pedal assembly?

[Apis Mellifera]

Both pedal return springs are present and springy.

Checked that already.

[Sputnicker]

I think you are on the right track replacing the master cylinder. There is plenty of evidence to suggest that the seals in the master could be the culprit. When I made a living as a British car mechanic in the 70s I saw a lot of degraded seals in brake and clutch cylinders and we attributed most of them to natural rubber seals (unique to Girling and Lockheed) and the wrong (i.e. incompatible) brake fluid. My impression is that things have improved since those days (better seals/better fluid) - otherwise this forum would have much more discussion of this phenomenon.

More often than not, they just started leaking. On some occasions, however, they failed in other strange ways:

1) Intermittent bypassing of the main seal(s) - especially under light pressure. Fluid would leak into the servo and not be visible on some cars
2) Seals sticking in the bore - preventing return of the piston
3) Seals that distorted and/or expanded to twice their size when removed
4) Flex hoses breaking down internally and acting like a check valve (i.e. they wouldn't release pressure
Note: One of the characteristic symptoms that accompanied these failures was a fine black sediment in the fluid (including the reservoir)

My guess is that these failures can still occur now and then, notwithstanding the improvements - and some of them could explain your symptoms.

Finally. I'm a big proponent of prevention - especially when it comes to brakes. So, since you will already have the braking system opened up, I'd probably replace any and all of the seals and hoses that haven't been replaced in the last few years.

Good luck and let us know what you find in there.