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MG MGA - Rear Brake Wear

Whilst I have the rear axle apart for my differential rebuild I had a look at the wear on the rear brake shoes. Rear right was even and fine. Left rear showed that only a third of the shoes was making contact as shown by the dark brown shiny strip adjacent to the back plate. The rest of it is unused and still shows a manufacturer's stamp. Interestingly it hadn't shown up in MOT testing - both rear brakes worked evenly and within limits.

I then spotted what might be a significant error on my part - hands up. I had installed the lighter strength spring adjacent to the brake cylinder and the heavier one adjacent to the abutment.

Whilst an error on my part I do not know if it was the culprit. Why should the shoes effectively tilt outwards to get this type of wear? The drums were brand new (dished version) when I did the WW conversion on a standard 1500 disc wheel axle about 15 years ago.

One possible answer is that I rivetted those linings in myself so it is possible there was uneven thickness across them? However, the other side is fine. I will do some measuring tomorrow.

Steve


Steve Gyles

Looks like the brown part tapers off to the sides pointing to the shoe not lining up(bent?)
Dirk Van Ussel

I don't think it's a shoe leaning problem as the wear would show up in more of a tapered arc rather than a straight line
The drum itself might be machined with a taper but that would be a bit oddball
I'm thinking it's a brake material issue
It'd be interesting to measure the thickness/height of the lining above the shoe and compare inside to outside
BUT
I've seen plenty or new shoes/linings that don't run true to the drum until they get settled in after a few kilometers
It would be interesting to also measure the ID of the drum itself just to compare inside/outside diameters
William Revit

All reassembled so I'm not in a position right now to measure the drums. They did both look in good nick though. However I did put calipers on the shoes and measured all 4 at various places. Including the thickness of the metal they were all within a few metric thou of each other, including the shiny bit in the photo: 7.71mm plus or minus 0.05mm.

Steve
Steve Gyles

The linings sound good then Steve, Could be a slightly tapered maching job in the drum ,but that'd be a bit unusual----but
I'd be tempted to put it out of your mind and drive on--it'll bed in
willy
William Revit

Bill. Entirely my view. I have swapped them over to the other side and put the springs in the correct place. Just going to do a thorough bleed to cover all eventualities then drive it for a bit before I have another look. I am intrigued with the reasoning for the different strength springs and also the bit in the manual that says the lighter one goes on the abutment. I just wonder if that had a bearing on the issue, perhaps holding that pivot point too rigid?

Steve
Steve Gyles

Road test excellent.

I bled the system. Not a drop of air came out of the fronts pads and rear right drum. I thought the same with the rear left and was about to tighten the nipple when more air than I have ever seen before in a routine check came out. I was quite astonished as I had not noticed any untoward soft pedal, So that probably accounts for most if not all of my observations.

Will have a look at the shoes again in a few weeks.

Steve
Steve Gyles

This thread was discussed between 06/06/2021 and 09/06/2021

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