14 replies to this topic

[AlasdairM]

Hi folks- 1990 cooper

On Saturday I replaced the driver’s side rear brake piston inside the drum, as it wasn’t working very well.

Before I took the drum off, the handbrake was working well and the handbrake adjustor was adjusted so that the wheel would almost spin one revolution. If I loosened it off at all, then it would spin freely easily.

Anyway so I removed the drum (which was easy), replaced the piston, then reassembled the shoes. When I went to put the drum back on, it was fouling on the edges of the shoes- I.e. they were far too tight.

I then took the shoes off again, checked, squeezed the piston in (don’t know if that did anything), unwound the handbrake adjustor screw, and reassembled. This time, the drum went on but it is still very stiff.

The handbrake adjustor screw is very loose, and isn’t doing much (so I don’t think that’s the problem).

I put the car off the jack, and drove it for 50m, and it seemed to drive ok. On a slight incline, it would roll down a hill too. This made me optimistic, however when I reversed back into the garage and parked, I struggled to push the car back when it was in neutral- something which was easy before.

When I jacked the car up again, the wheel was still very stiff.

I should say I bled the piston too. I also tried squeezing it together with the bleed nipple open.

Do I just need to run it in? Does anyone know why it would have been so stiff after I fitted the new piston? Is there anything I can do?

[gazza82]

Not an expert on Mini rear cylinders but there are several types so my first thought would be is it the correct one?

[AlasdairM]

Good point, but yes- I ordered off mini spares and I held them up next to each other before fitting.

[Algordo1100]

The thing you're calling a hand brake adjuster, do you mean the brake adjuster itself? Sits at the top opposite the wheel cylinder? That adjusts the brakes as a whole, not just the hand brake operation. It's there to take up the slack as the brake shoes wear and should be checked periodically as the shoes wear.

When I do any rear brake work I loosen the handbrake right off via the cable inside the car so it isn't in the equation as I adjust the shoes. Once I've got it right on the brake adjuster in the drum I then set the hand brake adjustment inside the car. Might not be service book method but works for me.

[GraemeC]

The pistons all look the same visually, but could have different size pistons, however this shouldn't cause your issue.

If they are the same shoes then it sounds like something hasn't seated properly when you've rebuilt the brakes.

[AlasdairM]

Yeah I mean the brake adjustor sorry.

It is wound out so that it’s just hand tight, so it isn’t doing anything.

Where do you pinch the hydraulic cable to prevent brake fluid leaking out when changing the piston?

[andyapanel]

Can the quadrants swivel ok?

Have you tried opening the brake master cylinder cap?

Are the return springs on the right way?

Is there a ridge of rust on the inside of the brake drum that might be coming up against the shoes?

 

It sounds like something simple. Follow Haynes. Good luck.

[AlasdairM]

Quadrants swivel fine without drum fitted.
I will try opening the cap. I was just cracking the bleed nipple, but I suppose trying to get the oil to flow back to the master cylinder is a better idea.
Return springs are ok. They don’t foul on the hub etc.
No ridges of rust rust.
I’ll maybe just try driving the car and testing after a long drive. I suppose as long as the brakes don’t overheat- that’s the main thing.

[bpirie1000]

Have you tried to hit the drum either side to make the shoes centre a little better?

Also check to make sure the brake pipes and hoses have not been pinched in anyways she jack g up or down. Could have caused a fluid blockage.

[Spider]

It sounds a little to me you may have mixed the shoes up when re-fitting and didn't re-fit them exactly as they came off. While it's probably impossible now to pick which was the leading and which was the trailing shoe, that shouldn't matter too much, although they'll go back on either way, they do need to be fitted the right way around, it is easy to mix them up.

 

 

[AlasdairM]

Yes I tried centring the shoes by hitting the drum.

I should note that I didn’t pinch the brake lines (on purpose at least!) when changing the piston, I just pulled the line out and plugged it with my hand whilst a friend switched over the piston.

Thanks Moke- I also made sure the shoes were in the orientation as shown. What I didn’t do is take a picture of the way the shoes were fitted before I took them off. Could it be possible that they were fitted incorrectly before- and now don’t fit the ‘correct’ way?

[bpirie1000]

Did the drum have any kind of wear lip on it when you removed it?
Possible that the lip (if any) could have displaced the shoe.

[andyapanel]

Can you get someone to operate the brakes while you watch?

It is good practice to chamfer the ends of the shoes, but not doing it is unlikely to cause your symptoms.

[AlasdairM]

Hi all

Eventually the problem is solved- it was my fault as usual.

What had happened was that the lower arm of the handbrake mechanism wasn’t located properly. With fresh eyes today, this was patently obvious. So all I needed to do was to unhook, push the locator through properly (highlighted in the pic), and reassemble.

I then had to tighten the adjustor all the way back in again, and now the brakes work.

Thanks a lot for all of your suggestions and help.

Attached Files

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Edited by AlasdairM, 16 June 2020 - 01:56 PM.

[bpirie1000]

Well done.. massive sense of accomplishment...

Fair to say you will not do that again..