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MG Midget and Sprite Technical - Rear hub fouls brake cylinder

This is the latest adventure in the story of converting drum brakes to discs which I'm sure some of you have done before.

I have a Frogeye rear axle, backplates from a later midget (believed to be BTA566/BTA567) and dual acting brake cylinder GWC1102Z.

I fitted all the brake components to the backplates before bolting to the axle. I replaced oil seal and bearings in the rear hubs and everything went swimmingly.

Fitted the rear hubs to the axle and did up the locating nut until it bottomed out the bearing on the axle then..... rotated the hub and it fouled on the brake cylinder.

I took off the hub assuming the bearing wasn't fully home in the hub carrier but it was. Reassembled and still the same.

The wheel studs inside the hub very lightly touched the metal of the cylinder but started to gouge a line in the rubber dust seal.

I took the hub off again and relieved the hub (angle grinder type relief) to give more clearance and now it just touches the rubber dust seal.

The brake cylinder moves about a bit on the backplate even though the C clip is on correctly, but even if I apply force to keep it hard up against the backplate the hub still catches the rubber dust seal.

I have thought of a few reasons why it might do this but wondered if anyone could think of something I haven't.
Rob aka MG Moneypit

Thanks Prop, you inadvertantly solved my problem.

Prop suggested we look at this impromptu tool for putting C clips on.

http://www.spridgetguru.com/TA0105.html.

I read the article and seeing the last image I suddenly realised what I had done wrong.

To see what was wrong see the attached image.

Rob


Rob aka MG Moneypit

I can't give you an answer as to why, but I had the same problem with the wheel studs catching the rubber dust seals. I carefully cut the half of the rubber off the inside protrusion of the dust seals. They fit fine like that. I've done this every time I've had the rear brakes apart - and that's quite a few times in the nearly 20 years I've owned the car. I wondered if its something to do with the studs themselves - like maybe they're not original ones?
Peter Blockley

Hi Peter, if you look at the image in the post above you can see one of the reasons. I put the C clip on with the back plates off the car then attached them to the axle. The position of the C clip meant part of it was between the backplate and the axle causing the wheel cylinder to sit closer to the hub carrier. The C clip is perhaps 0.5mm thick but it is a "wavy" shape so I reckon the gap is more like 1 to 2 mm. So the cylinder is maybe 2mm closer to the hub carrier than it should be. Also, the cylinder is the cheaper aftermarket type which may be a bit fatter than usual or the dimension of the bit that clips to the backplate might be a bit too big.

A previous owner painted the axle all over and the backplates have been powder coated. All these little bits add up to conspire towards reducing that gap.

After a frustrating day in the garage I think I have the measure of the problem and will tackle it tomorrow.

Rob
Rob aka MG Moneypit

Rob
What are you going to do about the wheel studs you grinded down? Do you think they will be ok?
I have a friend that used to over torque his a little bit and the wheel studs stretched and snapped off.
Do you think you removed enough material to be unsafe?

Just asking. Dont want to see you get hurt is all.
Steven Devine

No worries, I took about 2mm of the sharp corner near the studs, not really enough to weaken them.

In the image attached you can just see the different colour of the stud material (arrowed).

Rob


Rob aka MG Moneypit

I see, I pictured grinding the whole head down...looks like you took of as little as possible.

Thanks for the picture: Nice solve! :-)
Steven Devine

This thread was discussed between 02/02/2014 and 03/02/2014

MG Midget and Sprite Technical index

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