Morning folks

i was fitting rear pads to the rear brakes on BobC's old locost yesterday. Its nice wee Wilwood callipers on the back and i was using a g clamp to push back the piston on the nearside, with the reservoir cap off. There was a fair bit of resistance, followed by an audible pop on the other side of the car near the front, upon which the caliper piston retracted quite happily. I've now discovered that the brake pedal now has no resistance and will happily flap about with one finger. I'm guessing that i've blew a seal in the master cylinder due to the back pressure somehow. Does this sound about right?

I've added a couple of photos of the master cylinder arrangement fitted on the car to my photo gallery. Can any of you knowledgeable souls suggest where it might have come from/ what type it is so i can see about a replacement. Alas Bob C hasnt been on here for ages or id ask him myself!

Cheers

Graham

Not seen a vertically mounter MC before on a locost!



Description
Description

[Edited on 20-6-20 by 40inches]

Thanks for adding the photos 😊

Yeah not sure why Bob did it like this 😟🤔

Original Mini had vertical master cylinder

Sounds like you let air into the system by tillting a caliper piston just bleed it and should will be fine.
You should never need a excessive force to push the caliper pistons back that makes me think your brake pedal isn't allowing the the master cyilder piston to come full back. However any force you exert with a G clamp is nowhere near the the presure in the system during an emmergency stop.

if its a dual circuit master, I would expect the pedal to still work on the single remaining circuit, ie at least some pedal pressure to work the front brakes.
can you take some photos of the pedal assembly

Bled everything again but pedal still flapping. Have cleaned side of MC up and got number 3212 474C which appears to be, as suggested above, an original BL mini master cylinder, so I'll hopefully be in luck if it is fooked 👍

Forcing the pistons back may well have caused the master cylinder to fail , it’s a common problem on Vauxhall’s , better to release the bleed nipple with a hose attached before pushing the pistons in. If the master cylinder has failed I would remove it and look for any identifying marks or take it to your local friendly motor factors and have a word with an older member of staff that doesn’t rely on a computer or registration number. It’s been a while since I saw a cylinder like that one but have a vague memory of Metro’s using a similar item ? It is also possible to dismantle the cylinder and get part numbers off the seals , again your local motor factors might help ? Past Parts in Bury st Edmunds have reconditioned obsolete master cylinders for me in the past, in one case saving me £500 plus VAT

I've checked online and visually similar ones around 60 quid, plus I did spot a repair kit for £12 on eBay which may do. Hey ho you live and learn....