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MG MGB Technical - Wheel cylinder rebuild

The rear wheel cylinder kit (Moss #180-475) seals are a different design than the ones I had on the car (79 MGB). The seals shape circumference is wider at one end than the other like the originals but the old seals had the wide part of the seal facing the middle of the cylinder. When I put the new seals on that way, they don't want to go into the bore and try to bend back on themselves when I attempt to push the pistons in. I did hone and clean the cylinders with brake fluid so that's not the issue and the size is correct for the bore. My question is if anyone else experienced this. If I put them in the opposite way as the old ones (wider circumference part of the seal faces out) then they go in fine. I bled the brakes and took off them drum afterwards and did not see any brake fluild leaking out. Just want to make sure this is okay since it appears that I'm putting the seals in backwards from the way they were. Please advise.
Joseph Maggiore

Joseph,

If I am understanding you correctly, you have put them together wrong. If you have put them in the wrong way around, there is absolutely no hope that they will work.

The larger diameter side of the seal must always face the direction of higher pressure. If you couldn't get them in that way, either they are wrong or you didn't try hard enough.

It is typical that you have to work them in by squeezing them smaller with your fingers so that you get them in without flipping them inside out. The new ones are probably just harder to get in because they are new. Don't use anything like screwdrivers or other metal tools or you may wreck the new seal. You should be able to do it with your fingers.

Also, brand new cylinders are pretty cheap so you might consider that as an option.

Charley
C R Huff

An obvious question but have you got the right size seals? There are different sizes of rear wheel cylinders. If you car has been modified (say changed from wire wheels to bolt ons) you can't necessarily be sure what size are actually on the car.
Simon Jansen

Use some brake cylinder lubricant or even just brake fluid to lubricate the bores and the seals, then work them in the right way. Cheers - Dave
David DuBois

I got the seals in the right way. Apparently I had to gently work them a little at a time in with a smoothed edge blade and lots of brake fluid. I've rebuilt hydraulic parts before, it's just this is the first time the seals gave me grief. Go figure!
Joseph Maggiore

This thread was discussed on 18/09/2009

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