Discussion
Just come in from replacing the brake master cylinder on the ol' Mini. We have no air in the fluid, no leaks from any part of the system and no brake pressure at all!?!?!?!?!?!?!? 
My next thought is the compensator valve? well its this or a full system rebuild !
Any help or suggestions gratfully received
Benny M
My next thought is the compensator valve? well its this or a full system rebuild !
Any help or suggestions gratfully received
Benny M
I expect you'll find you have got an air lock somewhere. If you've drained the system you will need to look at all the places that an air bubble could sit and chase them out. This might mean turning calipers around to chase air up to the bleed nipples, probably need to bleed the m/c separately, likewise the bias valve. Just pushing fluid through won't do any good for this.
For clarity its an 81' Mini City with drums all round, front / rear split on a non servo, yellow tag tandem master cylinder.
We've passed about a litre of brake fluid through as I said with no leaks, no air bubbles and absolutely no brake pressure at all
Maybe I should try one of those Gunnsons Eezibleeds that use tyre pressure to push the fluid through?????
We've passed about a litre of brake fluid through as I said with no leaks, no air bubbles and absolutely no brake pressure at all
Maybe I should try one of those Gunnsons Eezibleeds that use tyre pressure to push the fluid through?????
It is a vertical tandem master cylinder.
If so, these are notorious for failure. If it is a new one there should be no problems, but if it's second-hand with just new seals fitted that could easily be the problem. I once worked on a '79 car with that configuration and in the end I had to fit a brand new master cylinder, even though the original problem was a leaking front wheel cylinder! It appeared to be al bled out, but there was a slight 'step' in the master cylinder which just allowed rthe fluid to cycle back and forth inside the master cylinderIt turned into an expensive exercise for the customer!
If so, these are notorious for failure. If it is a new one there should be no problems, but if it's second-hand with just new seals fitted that could easily be the problem. I once worked on a '79 car with that configuration and in the end I had to fit a brand new master cylinder, even though the original problem was a leaking front wheel cylinder! It appeared to be al bled out, but there was a slight 'step' in the master cylinder which just allowed rthe fluid to cycle back and forth inside the master cylinderIt turned into an expensive exercise for the customer!
1. Do you get a 'pedal' when you pump it? If you do, then it's air still in the system. If not, then it's almost certainly a 'duff' master cylinder. A 'duff' wheel cylinder would leak and with a litre having gone through you would probably notice to pool on the flor!
2. As the rear brakes are pressure regulated, you need to open the rear bleed screws BEFORE pushing the pedal down. If you push down, then open the bleed screws you can already have cut off the pressure to the rear at the regulating valve. Unusual, but it has been known (by me on a Cooper 998 many years ago!).
3. With discs it is possible to fit a caliper 'upside down', but with drums all round this can't happen. Sometimes a bubble of air can be quite persistant.
4. If you have a proper flexible-brake-pipe clamp, you could clamp off each flexible in turn and see if you then get a 'pedal'. That way you can isolate where the air is.
That's a few thoughts for you and I hope it helps.
Peter
2. As the rear brakes are pressure regulated, you need to open the rear bleed screws BEFORE pushing the pedal down. If you push down, then open the bleed screws you can already have cut off the pressure to the rear at the regulating valve. Unusual, but it has been known (by me on a Cooper 998 many years ago!).
3. With discs it is possible to fit a caliper 'upside down', but with drums all round this can't happen. Sometimes a bubble of air can be quite persistant.
4. If you have a proper flexible-brake-pipe clamp, you could clamp off each flexible in turn and see if you then get a 'pedal'. That way you can isolate where the air is.
That's a few thoughts for you and I hope it helps.
Peter
I think I've got somewhere tonight!
Got the Eezibleed thingy hooked up pushing fluid etc, went round the car once - still nothing!
Calmed down a bit then we for another go, this time the bleed nipple on the RH rear litterally fell out in my hand and simply would not screw back in - well not tight or with any sort of sealing effect?
So now gonna look at pulling off the drums and see what the wheel cylinders are up to.
Something else came to mind, will the master cylinder only push fluid through with the cap on? for some reason I don't ever recall having to mess about putting the cap on, bleeding then pull cap off to top up??? but the master cylinder will only push fluid out of the top union with the cap on?
Maybe I'm just going very slighly mad?
Got the Eezibleed thingy hooked up pushing fluid etc, went round the car once - still nothing!
Calmed down a bit then we for another go, this time the bleed nipple on the RH rear litterally fell out in my hand and simply would not screw back in - well not tight or with any sort of sealing effect?
So now gonna look at pulling off the drums and see what the wheel cylinders are up to.
Something else came to mind, will the master cylinder only push fluid through with the cap on? for some reason I don't ever recall having to mess about putting the cap on, bleeding then pull cap off to top up??? but the master cylinder will only push fluid out of the top union with the cap on?
Maybe I'm just going very slighly mad?
It should all bleed out with the filler cap off of the master cylinder. It certainly sounds like a master cylinder problem, assuming the rear bleed screw was in properly earlier on. If it was not in you would have about one litre of brake fluid under one rear wheel hub!
It's unlikely to be a wheel cylinder, as yuou would have a fluid leak. If there are no leaks, it really has to be a master cylinder issue.
Do you get any sort of 'pedal' when you pump it with the bleed screws all done up? If you do, then it's some air. If not then it's the master cylinder.
It's unlikely to be a wheel cylinder, as yuou would have a fluid leak. If there are no leaks, it really has to be a master cylinder issue.
Do you get any sort of 'pedal' when you pump it with the bleed screws all done up? If you do, then it's some air. If not then it's the master cylinder.
AHA I think I've nailed it!
Had another go the other night with the Eezibleed thing (very good, helped no end by keeping continual pressure on the system) - anyway got to the RHR nipple only for it to fall out in my hand!!!
It wouldn't go back in for love nor money! and looked very rusty up to the last two threads? looking down the wheel cylinder hole the threads look clean and strait???
So yesterday went down the local factors and got a new bleed nipple got her up on four axle stands tonight took a look round the first three "clean" corners - all good. Got to the RHR corner - new nipple didn't exactly glide into place, even more Winnie Pooh style thinking ended in a bit of a "wiggle" to help it home (the bleed nipple, not me )
Well, the new nipple wouldn't seal either AND I noticed that with a spanner on it the nipple doesn't rotate in a nice circle but a nasty oval
Wheel cylinder on order, should get me going I hope?
Had another go the other night with the Eezibleed thing (very good, helped no end by keeping continual pressure on the system) - anyway got to the RHR nipple only for it to fall out in my hand!!!
It wouldn't go back in for love nor money! and looked very rusty up to the last two threads? looking down the wheel cylinder hole the threads look clean and strait???
So yesterday went down the local factors and got a new bleed nipple got her up on four axle stands tonight took a look round the first three "clean" corners - all good. Got to the RHR corner - new nipple didn't exactly glide into place, even more Winnie Pooh style thinking ended in a bit of a "wiggle" to help it home (the bleed nipple, not me )
Well, the new nipple wouldn't seal either AND I noticed that with a spanner on it the nipple doesn't rotate in a nice circle but a nasty oval
Wheel cylinder on order, should get me going I hope?
The compensators are very reliable. So long as it's not leaking, it'll not be the cause of your problem. However, if you have changed the hydraulic lines into or out of the compensator, be aware that the threads on the compensator are METRIC whereas the other ends are still Imperial (UNF).
Spoke to MC supplier again today, absolutely confident that the rest of the system is fully functioning but we agreed that I would have one last go trying the long press method - failing that he said I could pull the piston out and look for obvious signs of failure.
Still nothing, stripped it down and the only thing I found is that:
A: the circlip that holds the lower piston and push rod was not in place and that it is possibly an external circlip? with the "lobes" on the outer edge?
B: I can now get the bloody thing off, stripped, rebuilt and back on in little over half hour very useful. lol
Now I really want to try a new cylinder.
Still nothing, stripped it down and the only thing I found is that:
A: the circlip that holds the lower piston and push rod was not in place and that it is possibly an external circlip? with the "lobes" on the outer edge?
B: I can now get the bloody thing off, stripped, rebuilt and back on in little over half hour
very useful. lolNow I really want to try a new cylinder.
It's official - I'm beaten - beaten by one of the worlds most simple braking systems 
At this stage I have replaced:
The master cylinder (MC only using the origonal resevior)
The pressure reducing valve
The flexi hoses
All six wheel cylinders
Along with three copper pipes sacrificed in the name of diagnosis (I cut and crimped the two from the MC to finally rule this part out)
Now I can bleed the system with no apparent air or bubbles only to achieve a working brake pedal when pumped (three full pumps then she starts braking!?)
What have I missed??? could this be the result of contaminated / poor brake fluid? I have always used Comma Dot 4 conformaing to SAE J1703 or whatever it says in the Haynes manual, from the same local factors???
So hopefully my local garage will take a look next week to point out how stupid I really am?
At this stage I have replaced:
The master cylinder (MC only using the origonal resevior)
The pressure reducing valve
The flexi hoses
All six wheel cylinders
Along with three copper pipes sacrificed in the name of diagnosis (I cut and crimped the two from the MC to finally rule this part out)
Now I can bleed the system with no apparent air or bubbles only to achieve a working brake pedal when pumped (three full pumps then she starts braking!?)
What have I missed??? could this be the result of contaminated / poor brake fluid? I have always used Comma Dot 4 conformaing to SAE J1703 or whatever it says in the Haynes manual, from the same local factors???
So hopefully my local garage will take a look next week to point out how stupid I really am?
I know this is a stupid question but have you adjusted the shoes properly and are the adjusters in good nick (not seized or rounded off) because it will take a few pumps of the pedal for the shoes to move onto the drums if they are not adjusted correctly. Also did you prime the mc with fluid before fitting,this would have extracated all the air in the cyl.
Fault Found!!! AT LAST
Front brake adjusters!?!
Although I had been adjusting the front brakes correctly, the adjuster weren't tight enough against the back plate and basically pushed back round by the brake shoe return spring - hence no pedal and no bubbles!
This is probably common knowledge but the main Mini specialists will try and sell you new back plates with the adjusters riveted in (£85 + vat per each!)
It just so happens that series one landies also run these type of adjusters but are fixed by a nut on the back - £8.55 + VAT and postage much better.
So she'll be fully on the road by Friday afternoon
can't wait!
Anyway
Many thanks for all the help and advise received - a fresh pair of eyes solved my problem and all is well that ends well
TTFN
Ben M
Front brake adjusters!?!
Although I had been adjusting the front brakes correctly, the adjuster weren't tight enough against the back plate and basically pushed back round by the brake shoe return spring - hence no pedal and no bubbles!
This is probably common knowledge but the main Mini specialists will try and sell you new back plates with the adjusters riveted in (£85 + vat per each!)
It just so happens that series one landies also run these type of adjusters but are fixed by a nut on the back - £8.55 + VAT and postage
much better.So she'll be fully on the road by Friday afternoon
can't wait!Anyway
Many thanks for all the help and advise received - a fresh pair of eyes solved my problem and all is well that ends well
TTFN
Ben M
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