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MG MGA - Replacement rear brake cylinders

A couple of weeks ago I stripped down the rear brakes and decided to replace the brake cylinders, as the old ones were showing internal signs of rust and corrosion. Foolishly I threw the old ones away before the new ones arrived.

When fitting the new ones today, I've come to the conclusion that they're a different size (but of course I can't compare new with old!) I say this for 3 reasons:

1. The old cylinders were very difficult to remove from the back plate, whereas the new one slotted through with hardly any effort and no wiggling. In fact, when it was in position it felt like it could easily fall out of its own accord.

2. The 2 springs linking the brake shoes are under very little tension.

3. With the brake drum refitted, and the adjuster at its maximum setting, the wheel continues to turn.

So my conclusion is that the body of the new cylinder is shorter than the old one, possibly by as much as 5-8mm. It measures 62mm from top to bottom, including the dust cover (see picture)and my guess is that it should be nearer to 70mm. Can anybody confirm please?

Thanks




Robert Sinclair

Can I ask where you bought them? I replaced mine a few months agi from MGOC without problems, and I have both new and old ones?

I can measure old ones tomorrow if no one beats me to it.

Paul
Paul Dean

Robert where did you buy them from and what was the part number? From memory the MGA rear cylinders are of a type common to many British cars.
A Bowie

I bought them from MGOC, part number GWC1111. I spoke to them yesterday, to make sure that there wasn't a problem with the wrong part in the right box, but all seems OK at their end. I also spoke to the Tech Department, who agree with the logic of my conclusion but can't help any further as they don't have the original measurements of the units, just the internal bore size.

If you can measure yours I'd be very grateful. Thanks
Robert Sinclair

Seem to remember a similar thread years ago when I posted the attached picture (scale in cms).

Might be worth a look in the archives.................Mike


Mike Moore

Thanks Mike. I'll have a trawl through the archives and see if I can find it.

In the meantime, I reassembled one of the rear wheels this afternoon, putting a 5mm plastic shim between the brake cylinder dust cover and the adjuster housing ... and lo and behold the shoe springs are tight and the adjuster only turns half distance before the shoes bite, which sort of confirms my original theory about the new cylinder being too short. So if anybody out there has got an old unit tucked away in their spares box, which they can measure for me, I'd be very grateful.

Thanks

PS Don't worry about the plastic shim. I won't be driving it like that!
Robert Sinclair

An old cylinder of mine measures 58mm between the faces that the brake shoe flange sits upon, so approx. 65mm overall would seem about right Allow for parallax error in photo.

regards
Colin


Colin Manley

Robert. Sorry I can't measure as I appear to have thrown old ones away. Interesting what you say about adjustment as I was surprised how much I had to adjust new linings.

Paul
Paul Dean

Here again. Having sent last email I remembered I had somewhere the complete back plates off my first Coupe that I broke in 1972. I have now found them in garage loft. Unfortunately piston is missing but I have made same measurement as you minus missing piston/cover plate and it is 60.5mm as best I can do with ruler. Clearly this will be an original Lockheed cylinder considering it was on car in 1972.

I would also say new one went in easier for me but of course for that it is all about dimensions of slider part.

Paul
Paul Dean

Thanks for all the comments and measurements. It certainly looks like I've got the correct parts, but I'll have to make a small modification before the rear brakes work properly.

I've been trawling back through old threads and found one from 2009 about None Genuine Brake Cylinders. In it, Vin Rafter said that he made a couple of spacers of 5mm which he fitted to the bottom of the adjuster masks, thus raising the adjuster and gaining him an extra 10 clicks of adjustment. So I'll be doing the same!

Here's a copy of Vin's picture.


Robert Sinclair

Did you also replace the shoes at the same time? Some of the newer shoes have been noted as being a little on the small side, which can cause the adjusters to run out of adjustment. If you didn't replace the shoes, how was the brake adjustment prior to replacing the cylinders?

Fit of modern replacement cylinders to the backing plates does not seem to be terribly consistent. Mine were pretty tight... I had to scrape powdercoat from the mating surfaces on the backing plate, plus file the cylinders slightly to get mine to move freely.

If the return springs don't seem to have enough tension, check against pictures in the manual and also on Barney's site, since if I am remembering correctly, it is possible to install them wrong. New springs are available from the usual suppliers. Also, Barney has lots of info on adjuster modifications that can help make up the difference.

-Del
D Rawlins

Hi Del and thanks for your comments. No, the brake shoes haven't been replaced, although they haven't done more than 1000 miles since new. With the old cylinder the adjusters worked fine - maybe 6-8 clicks.

I've got the opposite problem to you with the cylinder fitting. The old ones needed a couple of taps with a hammer to get them out through the back plate, but the new ones fit easily (too easily for my liking)

I've found Barney's article on adjuster modifications, and it's the same one that I referred to in an earlier comment on this thread - ie Vin's 5mm spacer - so that's what I'll be doing.

Robert
Robert Sinclair

This thread was discussed between 31/05/2017 and 02/06/2017

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