6 replies to this topic

[ClassicAsh]

Hi all. any advice on bleeding the mini brakes (1995 mini cooper spi). I have replace most of the components in the braking system, full new copper pipes, new discs, refurb calipers, new brake pistons, new master cylinder  etc etc etc, following the instructions in the Haynes manual, front brakes  bleed fine and work a treat, however I cant get fluid to the rear brakes at all, if I crack open the T piece at the rear sub frame there is no sign of fluid.. I looked and cleaned the brake pressure reducing valve that's is bolted to the bulkhead, fluid is present at the two in ports, and at the out port for the front brakes, but not at the out port for the rear brakes. However if I remove said valve and use an air line the ports are open and air passes through fine.... I am assuming that this valve must be faulty, even if it does seem to work with air line pressure... so before I bite the bullet and buy a new valve does any one have any ideas?

 

Thanks in advance.

[brivinci]

I believe the valve is not serviceable. I'm not aware of a way to really test these. I was having issues on my brothers 95 SPi with his back brakes locking up before the fronts. Ended up just replacing that as a matter of course. To me, it sounds like that is your issue if you are not seeing any fluid coming out.

[MacGyver]

What method are you using for bleeding the brakes? Easy-bleed?
If so you might be locking the limiter with it.
If you open the bleeding valve on the rear brakes BEFORE plugging in the Easy-bleed, it should work or just gently pressing the brakes to slowly building the pressure so the limiter won't lock.

[brivinci]

That is an interesting point. I built my own "power bleeder" to match something like this:

 

I have not used it on the Mini but now I wonder if it would even work. This system attaches to the brake master and pushes the fluid through, under about 5-15lbs of pressure.

[ClassicAsh]

Thanks for the reply's, I am doing it the old fashioned two person manual way as described in the Haynes manual. but I think I now have it sorted, the brake pressure reducing valve that's bolted to the bulkhead was indeed the problem, and although the Haynes book says these are not serviceable, I have taken it apart and spotted the problem. Its to do with a little spacer shaft that's keeps a ball off its seat, think of it as a check valve that if closed fully will not let fluid through, if the ball is off its seat it will let fluid through. on mine the spacer shaft was showing signs of wear, so I made a new one and fitted that, just 1mm longer, this now keeps the check valve just open and allows fluid to pass to the rear brakes... so hopefully problem solved. .. thanks for all the suggestions.

[brivinci]

I applaud your efforts...but be very careful making your own brake components. It is very hard to tell if you indeed fixed it. Heres fun story:

 

My brothers 95 always seemed a bit tail happy. I ran an event with the car and it was certainly fun but always sideways. I think that over time, it got worse but I wasn't really driving it. Well, one night he was out and (at least I think) hit a bridge too fast that had a sharp turn after it. He hit the brakes, rears locked up instantly, car went sideways, sliding into a ditch and then rolled the car. Now, after we beat the shell back into a basic Mini shape, I took it out and tested the brakes. In a straight line, the rears would lock up soooo easy. Turns out it was the valves failure. I replaced and the car now brakes as it should. Had we know the issue before, the car might not have ended up on its ear in a ditch.

 

Point of the story: Be VERY careful when it comes to brakes.

[ClassicAsh]

Scary stuff indeed and you are right to warn to be wary of things, Luckily I have only replaced a component that mirrors the original apart from being that little bit longer. The car is in its final stages of rebuild after a restoration so once its done it will be off to the MOT station to be tested so I would hope that any problems with the brakes will be spotted by them. Being an engineer myself who has repaired various hydraulic pressure valves etc, I am reasonably confident that's it should be fine.... famous last words eh !  and if it causes any brake problems I will be sure to replace it .... then scratch my head again why it wont bleed lol... watch this space !