Sticky brakes. immediatly loose when engine is switched off, Solved!

PepijnWK

Active Member
#21
Thank you Barten! Yesteray i saw on a picture in the repair manual that the springloaded thingy indeed is supposed to be there. I have not opened the old cilinder yet but I suppose it is in there as well.
I hope replace the master cilinder this afternoon. followed by the bleeding which I know is a pain . I once fitted a one way bleedscrew in the rearbrakes so that helps I hope.
 

PepijnWK

Active Member
#22
So succes!!!!!

I used the old connectors from the old master cilinder. They fit like Barten pointed out.





I ended up using the backplate of the actionvalve because the new one had very little room between the cilinder and de hose. The old one was poining the right direction and has moor room for a hoseclamp.

I mounted the new master cilinder and we have brakes!! Bleeding went wel. Blocked the 5 way junction with a torx bit. Then first bleed direct at the brakeservo . Then the frontwheels and then the rear. Luckily there was no air in the rear!

Thanks all for your help!! The mastercilinder was the culprit!
 

Tor

Active Member
#25
As I've said, mine is irregular, and can be pumped to give resistance further out. Which indicates that the rears aren't ratcheted up as close as they should. Sometimes, the pedal action is softer, progressive and smooth exactly like a modern. But usually not. Glad you've sorted yours!
 

Barten

Active Member
#26
Glad to hear your brakes are sorted. Are you happy with them, if you compare to a newer car? My brakes could have been much better, but i am searching for the reason why they are not as good as I had hoped. It seems like they have no servo assistance.
 

PepijnWK

Active Member
#27
Glad to hear your brakes are sorted. Are you happy with them, if you compare to a newer car? My brakes could have been much better, but i am searching for the reason why they are not as good as I had hoped. It seems like they have no servo assistance.
I am happy compared to what it was. My 1980 Volvo 245 or 2006 Volvo V70 brakes much better. All is relative. I think this is as good as it gets for now.
But I agree it could be better indeed
 
#29
Chaps - I've begged stole and borrowed for time today to look at my sticky brakes - I've added my post here because it is related.

I suspect a leaky air valve assembly / servo ( with the small piston getting stuck in situ) and have a replacement diaphragm/spring/ housing to fit.

I am unsure if the small piston (once cleaned up) is fitted dry, lubricated with brake fluid and /or brake grease. I seem to have missed any references to this within manuals or here on the forum.

Guidance on this would be much appreciated. Many thanks and regards, Simon
 

sdibbers

Well-Known Member
#30
Chaps - I've begged stole and borrowed for time today to look at my sticky brakes - I've added my post here because it is related.

I suspect a leaky air valve assembly / servo ( with the small piston getting stuck in situ) and have a replacement diaphragm/spring/ housing to fit.

I am unsure if the small piston (once cleaned up) is fitted dry, lubricated with brake fluid and /or brake grease. I seem to have missed any references to this within manuals or here on the forum.

Guidance on this would be much appreciated. Many thanks and regards, Simon
The little reaction piston should be fitted with lube (brake fluid is fine). It is actuated by brake fluid when in use. You can easily test its operation. Before dismantling: remove the valve plastic cover and rubber diagram, but leave the steel plate on. With a suitable Allen key push the piston down through the center hole of the steel plate. Now press down on the brake pedal. Does the piston come up again? If so it’s working as intended. If you see brake fluid it needs a new seal. If you can’t push it down or see it move up it’s most likely seized. I have gotten away with drilling and tapping the piston in situ then using a screw to pull it out in the past. Followed by reaming with a 3/8” reamer and then polishing the bore with 600 grit wet and dry wrapped around a dowel in an electric drill. If you’re very lucky and the bore is good you may get away without reseleeving. This was for a 2000TC servo so double check sizes for yours.
 
#31
Thanks sdibbers - I had a look at it today. To me there feels to be a fair bit of resistance moving the piston up and down manually (after removing the steel plate) - presumably the the O Ring at the base of the piston is doing its job. I cleaned up the piston and wiped around the centre hole.

I noticed that the spring in the replacement air servo housing is much stiffer than the current spring (because it is new), but I still felt that this would not overcome the resistance felt by moving the piston manually.

That said, when all reassembled, my first thoughts are that the brakes are not active as has been the case after initially depressing the brake pedal.

The test I have been doing until now it to see if the car pulls away when in drive without using the accelerator pedal (auto box) - and it does so more freely now (for the time being) without the 'graunching / mild squeaking' noise I have got used to...

Maybe the mpg will return to more 'expected' levels. The front brake lines are still to be checked yet.

Thanks again for guidance - Simon
 

sdibbers

Well-Known Member
#32
Sounds very positive Simon. The piston has a small cup washer as a seal, now it’s moving more freely just keep an eye on it for weeping. Having it move now could have worn the seal slightly if there was a little corrosion in the bore. I would drive the car for a while and then ship off the plastic air valve cover and just check for wetness. If it’s still dry all is good. If you find some brake fluid it might be salvable with a small rebuild kit and just replacing the seal for the reaction piston.

Quick edit: the brakes probably have a little more travel now that the service isn’t holding them on all the time, that could explain the difference in pedal feel.
 
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