Amazon: 1970 Amazon brakes

[142 Guy]

So, the servo may be OK and all you need is a new MC. I did not find any mention in the factory service manual of that seal which would be rather critical to the correct operation of the servo.

[packers1712]

Good evening Guy,

So I decided to do a re-seal of my existing master cylinder despite the recommendations to replace it and first impressions are good, the brake pedal feel is good statically I’ve yet to try it down the road, providing the rain stops for at least an hour tomorrow I’ll give it a run and report back!
I’m not entirely sure the servo doesn’t need replacing as when I exhaust it with the engine off and then start it the brake pedal barely moves, can’t say I’ve ever done that test before so don’t really have a base line to compare against , the proof will be in the pudding/drive tomorrow!🤞

Thanks for everyone’s advice,
Doug.

[142 Guy]

I hope the MC rebuild works out for you. If you honed the bore of the MC to remove the wear ridge in the cylinder this may work out. My experience with a rebuild was on my 1987 745 turbo. It worked for about three weeks and then the piston seals failed again because I obviously had not honed the cylinder adequately to remove the wear ridge. After that experience I replaced the MC rather than attempt a second rebuild.

Unfortunately the Volvo green book provides no advice on checking the servo. The only test I am aware of is 'pull a vacuum on the line to the servo check valve and see if it holds a vacuum'. If the servo has a significant air leak then it has failed (notwithstanding the potential leak at the base of the MC which the green book says nothing about). If the servo holds a vacuum then it is not obviously broken. It may not necessarily be OK; but, not obviously broken.

[packers1712]

All,

Post road test report, after the M/C rebuild the brakes are better but not quite right, they don’t appear to have the bite they had before so I’m hoping that there is some residual air in the system, if I stamp on the brake pedal I would expect to be able to lock at least one wheel but I can’t and it is a bit damp out so that should be achievable - after another bleed I’ll update!

Doug.

[142 Guy]

Given the lead-in from your first post, I am assuming that you have not fiddled with the pads / shoes? A change in or new friction material can result in a change in the friction coefficient on initial pad contact (initial bite!).

When you bled the calipers after the MC repair is there any chance that you got some brake fluid on the disks which may have contaminated the pads? In that particular case I would expect there to be some pull on the steering during heavy braking. If you do have pad contamination you can try cleaning with brake system cleaner; but, I would just chuck the pads and replace with new.

If the range of pedal motion appears to be greater than it was before then air remaining in the hydraulics may be the answer. I am not familiar with the hydraulics on the 1970 Amazon; but, the dual diagonal system on my 142 (same as on the later all disk 1800) is a take forever to bleed system unless you use a pressure bleeder.

If the range of pedal motion seems normal then air in the hydraulic system may not be the problem. When I restored the my 142 the brakes were pretty much as you described. I had to exert a huge amount of pedal pressure to generate significant braking. Diagnosis was a failed servo which allows me to bring 'been there - done that' advice!. If you can, I suggest vacuum testing on the servo's vacuum line to the intake manifold to find out whether the servo still has a vacuum leak. You might still have an air leak at the interface between the MC and the servo body.