9 replies to this topic

[rasputin22]

Hi there

I have a 1988 mini city and has been standing for a while. It has a front to rear split system with a yellow band master cylinder and a balance valve thing on the bulkhead (not an aftermarket brake bias valve) just below the master cylinder. In the past have put a 7.5in brake setup on and everything was working fine. Even went through an MOT like this a couple, ahem, of years ago.

The problem is i can't get the rear drums to bleed properly. This evening i have taken my rear brake cylinders off the backplates and dismantled them for inspection. On one the bleed nipple hole was full of crud and dirty nappies (well not quite dirty nappies) from the inside. So replaced the really dirty one with new and the other didn't seem half bad so that went back together and back on.

Then i took the brake balance, whatever its called, valve thing off the bulkhead and managed to take that apart and even more crud in there and made sure everything is free to move when put back together, nothing was siezed. Then blew the rear brake line with an air hose making sure i was getting air out of both the near and offside pipe from the front. I did this until nothing more could come out. Seem like there is alot of dirt in my braking system i was not aware of. I even blew the shorter lines from master cylinder to the valve whatever you call it and they were good.

I managed to bleed the front brakes with success, but can't get anything out of the rear. I've tried releasing the bleed nipple and getting my mate to pump fast on the brake pedal just to get something out but nothing. Tried open, down, close, up a fair few times and nothing.

I wonder if the master cylinder has gone awry or is it the valve thingy gone wibble??

Can i just bypass the valve thingy or is it needed???

Is it easier to have a single circuit???? or do i bite the bullet and get a new master cylinder????

I don't want to buy one thing and it be another. I could get some brake lines made up to bypass the balance valve thingy just to see if it is the master or the balance valve thingy. Would this be an idea or not??

Thanks Ryan

[Ethel]

The valve you took to bits isn't supposed to be serviceable. How have you connected the master cylinder, the top should go to the front.

[Cooperman]

Rear brakes can be a bit difficult to bleed out at times.
First of all, if the brake balance valve is not working properly, which would be unusual, it could be shutting off the fluid path to the rears when you pump. It could also, as you surmise, be the master cylinder.
Try undoing the rear brake pipe union where it goes into the balance valve. Don't fully disconnect it, just 'crack' it off a bit and give it a lightish pump. Fluid should come out (catch it with a piece of rag - don't get it on the paintwork).
If it pumps fluid without any air bubbles, do that union up and undo the rear brake outlet pipe union at the balance valve and try that.
Work through the system until you find the problem.
Remember, you can't pump fluid out of the rears unless you undo the bleed screws before starting to push the pedal down as the balance valve will shut off.
You definately MUST have the balance bvalve in the system and it must be working properly. if not, the rear brakes will just lock up under relatively light braking and you'll spin down the road.

[rasputin22]

Ethel - are you a member of autsportlabs, megajolt???? And i know its not supposed to be servicable, but i didn't understand how its works so as usual i took apart. Anyway it all went back together ok.

Cooperman - i did try undoing the feed to the rear brakes just above the valve and pumped the brakes. Some fluid did come out but only did this a little bit and didn't notice the air bubbles to be honest. Will give it another go.
oger bleed valve open first, then pump. I'm sure i was doing this but will try again.

The saga continues........

[rasputin22]

Had another session again with it tonight and still no luck

I know its difficult describing this over the internet but please bear with me.

The top outlet of the master cylinder does go to the front brakes via the left hand side of the limiting valve.

I have cracked open the pipework for the rears between the master cylinder and the limiting valve and had brake fluid come out with some pressure felt on the pedal. But i can't get any come out directly after the limiter valve.

I can still bleed the front brakes and get decent pressure, just nothing at the rear. Although i do know you have to bleed rears first and then fronts with this type of front-rear split system. I have even tried sucking the fluid through whilst pumping the pressure and still no luck, out of the pipe to the cylinder and not just the bleed nipple.

I have completely stripped the master cylinder of all parts and all the seals look very healthy. Gave them a good once over and can't find any splits. The cylinder bore is in very good condition. And got rid of any debris which may of blocked the tiny oil inlet to the cylinder from the reservoir. Debris consisted of a gold plate off some plates between cylinder and reservoir.

I know i shouldn't of but when i stripped the limiter valve it all looked good inside with decent seals and all parts moving. Plus it all went back together correctly.

Does anyone know how the limter vlave thing works?? I may just bypass this limiter valve until i get to the bottom of this. I wont e driving it on the road like this for sure. Just while i problem solve.

[bmcecosse]

Sounds like the hopeless taper nose pressure valve is jammed. As far as I know they are not serviceable. One option (which I did) is to get rid of it - and use the old style pressure limiting valve in the rear line only. If you mount it up front - added advantage that by adjusting the internal spring - you adjust the pressure to the rear drums. No more rear lock-ups!

[rasputin22]

Thanks for your help bmcecosse i think that is the route i shall choose. I won't have it in the cockpit, i shall just replace the pdwa with an adjustable bias valve in the same location so that its easyish to get to.

[1968mk2inleic]

are you sure the rear brake hoses haven't collapased internally?With someone pumping the pedal, try cracking each joint off in the steel brake pipes and starting at the front and see if fluid comes through then work you way towards the rear

[rasputin22]

I've blown them through with an air line from just after the PDWA to each side of the rear brakes so they are fine. I proved air coming out of each side with the help of a friend

[rasputin22]

Right the i have ordered one of these to fit in place of the PDWA valve. It was decent price, just hoping its ok quality.

http://cgi.ebay.co.u...id=p3286.c0.m14

I'll have to make a new brake pipe from master cylinder direct to where the pipe went into pdwa for the front circuit. Hopefully this valve should fit nicely in place where the pdwa was but may need some new brake pipe fittings to fit.