10 replies to this topic

[zebigfatman]

Hi everyone, I have pretty much completely re built/ replaced everything on my mini. everything works properly except for the brakes...

 

I have a KAD disk conversions all the way round, they are properly bled and on short test drives up and down the street would appear to work.

However after a couple of miles they start to bind as they heat up (all of them) until the pedal is absolutely solid.

 

I have been looking for a definitive answer as to the plumbing of the yellow tag master cylinder into the proportioning valve and have found pictures of the brake lines both ways round.

 

This is the illustration I followed when plumbing it in.

 

 https://images.googl...&source=sh/x/im

 

I have also read up on the brakes binding issue and people have solved it by adding spacers under the master cylinder? 

no idea why I would need to do this because the brakes worked fine before I took the car apart and the master cylinder is the same one as is the pedal box.

 

Once again I would very much appreciate your input mini wizards!

[Spider]

I'd say the plumbing is fine however, if it's been sitting around a while the seals can swell and even in a rest position, still cover the ports inside, so the brakes never completely release or it could also be that your brake pedal is resting on the body (or something) where it should be 'hanging' off the the Master Cylinder Push Rod.

 

If the seals wave swollen or the pedal rests on the body or is hung up, the seals won't come down past the ports, as you drive, normal road and engine vibrations work on the pushrod and with the way the seals are, they act like a one way valve, continually pumping up the pressure until the brakes lock.

 

The cure for the later is spacers under the Master Cylinder. There were factory spacers for this in fact. The cure for the former is to overhaul the Master Cylinder.

 

Have a look where the sun never reaches up under the dash to see if the pedal is indeed hanging off the master cylinder or not and that may guide you as to where the issue may lay.

[Deathrow]

Moke Spider has already beaten me to it confirming that your plumbing is correct. I was making up this diagram which traces the original pipework of my Mini. I'll include it for reference purposes anyway.

 

Red lines are brake pipes and the green line is for the clutch.

[zebigfatman]

Cheers guys, will put some washers under the master cylinder tonight (as a temporary measure) and cut a spacer out of plastic if it works.

 

Will let you know!

[Ethel]

Cracking a bleed screw open while they're bound would indicate if  non returning fluid is to blame. If it's stood a while a general easing off wouldn't hurt, and would help diagnosis - take the pads out one at a time and and push the pistons out with the pedal, then use a wind back tool or a big spanner to lever them back, repeat if necessary until all is moving freely. An old pad or bit of wood will stop you pumping the piston out, or just take it steady and look.

 

I've had new pads that were just too thick and bound even with the pistons fully pushed back.

[Sask_Mini]

Sure sounds like you need to space the master cylinder up a bit.  I  had the same problem last year and the wonderful guys on this forum helped me figure it out.  

 

Here is a link to my post  http://www.theminifo...r/#entry3484585

[zebigfatman]

So had an absolute nightmare trip in the car...

long story short the brakes are not fixed.
I suspect it is going to be a new master cylinder jobby.

If you want the whole saga (under 10 miles) read on!!

Spaced under the master cylinder, went for a drive, 1 mile later same issue.

Cracked a bleed nipple, issue apparently sorted.

Went to my Dads 3 miles away (where I get bits delivered) fitted new carb needles as I had a flat spot.

Car felt awesome so I decided to take it for a bit of a drive (down back lanes thank god).

The brake issue came back after 4 miles so we cracked the nipples again and tried to come back...

Then massive misfire started, then brakes bound again, then I lost 1st and second going up the steep hill to my house. Had to reverse it up the hill.

Then ended up having to tow it the last 100m because it wouldn't run.

I know its an ignition issue, not carb, and the roll pin in the linkage is sheered so its not the box.

The whole car has mechanically basically been replaced or taken apart so I was prepared for teething issues.

Anyhow I am 99℅ certain the brake problem is master cylinder related so I think I'll order one tomorrow.

[Sask_Mini]

That does sound like it was a nightmare of a drive

 

How much did you end up spacing the master cylinder?  As someone who has had a really similar problem I still feel like it could be the master cylinder not returning all the way.  But if you verified that the brake pedal is returning without touching the bulkhead then I don't know what else it could be aside from the master cylinder.  

[zebigfatman]

Spaced the cylinder up by 2 or 3mm. Did try removing the master cylinder from the bulkhead and pulling up on it to release the brakes (I made braided lines for it so its flexible).

Didn't work, car just sat there making angry hot disk noises at me.

Will go over at lunch and have another look at the clearances around the pedal.

[Spider]

Given your description and that you've moved the M/C, it sounds to me like the seals in the M/C have swollen.

[zebigfatman]

Hi everyone, just thought I should say, the problem was the master cylinder! Changed it and took the car for its first real drive, apart from some steering issues (combination of problems) everything works as it should. Thanks for all your advice!!