Seized 190 piston
 

Just spent several hours working on a MG190 with a seized brake piston. The usual trick of pushing it out, greasing it, forcing it back in didn’t work - almost solid. Sorry I said to the owner, the piston’s like bad teeth, just has to come out and even that wasn’t easy, eventually had to knock it out.

The piston had a bit of rust but I’ve seen worse, the seal wasn’t too bad either but crusty with rust that you could scrape with your nail. Time to refit, dust cover gave some grief but the piston just wouldn’t go back in even though well lubricated.

Then, at day’s end, a lightbulb moment, I read someone who posted about the seal being chamfered on one side, and that was it, reversed the seal and in it went with just thumb pressure. I’ve never met this before, is it a 190 thing?

Whoever you are who posted - thank you.

cant say that the seals on my R40 75 were chamfered one side.so the 190 should i suppose be the same. more likely that the angle of entry into the bore by the piston was slightly out. it does not need much and then cannot be corrected by pushing in further or trying to. happen with mine and on the third attempt slipped in smooth as silk. ...

Thanks for the reply. But I’m pretty sure I read about someone who experienced the same thing, or bought some seals that should be fitted only one way. I agree with you that it’s uncommon and I’ve recently done all four pistons on my daughter’s ZS180 without any problem. But this 190 was different, tried for God knows how long to get the piston in, pressing, trying to screw it in but once the seal was reversed thumb pressure on both sides saw it just slide in.

All very strange

i would have thought that the piston seal kit would have had fitting warnings if they were directional fitting. the seals cannot be turned inside out due to their radius differences and cannot be confused either with the bore seals. did you buy them online ? if so you might see the seals if you can blow up the photos to see ... it does seem unusual ....

Thanks but no, this was the original 190 seal removed by the owner, cleaned and put back again, with a 50 / 50 chance of original orientation. Just funny that after countless attempt to refit the piston, and I've done a few, it slid back so easily with just thumb pressure once the seal was reversed.

I've tried to find the post which wasn't so long ago about someone who reckoned they had chamfered or directional seals but of course can't. But if anyone is struggling in a similar situation try reversing the seal.

Or I'm going mad:}