Master cylinder questions

Anonymous · Post by **Anonymous** » Sun Apr 10, 05 7:17 pm

ok decided to try and rebuild m/c.

first off, the secondary piston stop bolt is missing

What does it do and do I need one?
Cylinder was full of crud as I expected when I bled the brakes after having replaced them a couple weeks back. The fluid was black, suggesting corrosion.
The cylinder has a few corrosion pits (spots) along its` length. Don`t know if it`s done for?
The repair kit I got from Rodley appears to have one wrong rubber seal (see pic, seal on left) which should go on the secondary piston. The old seals are both the same diameter. This was after double checking that it was the right kit

Kit was a United no.696, dunno if anyone knows anything about that? M/C casting no.3461187 for front manual discs.

Also, should the new seals be a tight fit in the bore, cos they ain`t as tight as the old ones.
How do I get the pushrod off the old primary piston (by force)?

I think maybe I should just get a complete new m/c after all (grumble, moan, etc).

Pete · Post by **Pete** » Sun Apr 10, 05 7:19 pm

Replacement master cylinders are about ?50 from Rodleys, I know what I would do.........

Anonymous · Post by **Anonymous** » Sun Apr 10, 05 7:22 pm

yep, gonna be on the phone to them tomorrow I guess. Can`t be too careful when it comes to brakes, better be safe than sorry.

Dave-R · Post by **Dave-R** » Mon Apr 11, 05 10:40 am

Told you you'd end up doing that anyway.

Rodleys are great but they do tend to send you the wrong bits from time to time.

You should have left the pushrod attached to the brake pedal and then pulled the MC off the rod. I showed you the rubber ring that goes on the end to hold it in? You have to pull hard to get it to come out and it is a lot easier when the rod is still attached to the car.

Anonymous · Post by **Anonymous** » Mon Apr 11, 05 11:21 am

Dave said;

Told you you'd end up doing that anyway

Spoke with Rodley this morning and it looks like they did send the correct kit, and I have got a power brakes m/c, which is a larger bore. So having jumped to conclusions, I now eat my words

New cylinder on its way

Cheers for the bench bleed parts Dave. I believe the new cylinder comes with a plastic bleed kit as well, so I`ll be keeping that for future use if it`s any good.

Dave-R · Post by **Dave-R** » Mon Apr 11, 05 12:03 pm

No hurry for them back mate. I will not be re-fitting my brakes for at least another 10 weeks. Maybe a lot longer.

Anonymous · Post by **Anonymous** » Sat Apr 16, 05 7:03 pm

sorted.........

Ivor · Post by **Ivor** » Mon Apr 18, 05 1:17 pm

Blimey, that's all very "profeshnial" just like the manual.

Just as a matter of interest, I used two of those old Europat brake fluid dispensers, one in each compartment of the master cylinder and just bled the brakes normally...no problem and that was with a completely dry system.

Looks pukka Neil!

Kev · Post by **Kev** » Mon Apr 18, 05 2:03 pm

I suck mine out of the nipples with a big syringe.

Dave-R · Post by **Dave-R** » Mon Apr 18, 05 3:08 pm

You can't beat bench bleeding for getting every last micro bubble out of the M.C. first. It is worth doing.

Kev · Post by **Kev** » Mon Apr 18, 05 3:30 pm

I bench bleed first, Dave 8)

Anonymous · Post by **Anonymous** » Mon Apr 18, 05 3:47 pm

Ivor said;

Blimey, that's all very "profeshnial" just like the manual.

go by the book and you can`t go wrong. Had a spin thru to Daves to return his pipes on Sunday - no more squishy pedal.

Stops on a sixpence now and eased my nerves a little

Ivor · Post by **Ivor** » Mon Apr 18, 05 4:55 pm

mmmh.

You've got me thinking now, my pedal doesn't pump up, but it's by no means rock solid.

I noticed that the rear section of the master cylider was getting a bit frothy when I bled the system, but apart from a bit of initial squish seems fine.

Is your pedal rock solid Neil?...Dave? If so I'll do it all again.

I've got a big syringe Kev, sounds sensible to me.

Dave-R · Post by **Dave-R** » Mon Apr 18, 05 5:14 pm

I am not sure what it is. Maybe the foot pedal does not push the piston all the way down the cylinder? But bench bleeding a previously dry or air pumped MC is an absolute must if you believe the factory manual.

Put the M.C. in a vice and make sure it is completly level both ways. Make sure you get full travel when bleeding it.

Anonymous · Post by **Anonymous** » Tue Apr 19, 05 8:54 am

Ivor, my pedal reaches approx halfway between rest and the floor when braking. It now has a solid feel to it when pushing hard.
When I bench bled the cylinder, I used a mixture of long gentle and hard fast strokes to push out the air. I did this for about 5 minutes until I could see no more bubbles come out. I did check that the cylinder was level in the vice using a spirit level, just in case any air could remain locked in there. I must admit I was surprised by how much air did come out when I started bleeding the cylinder - especially the amount of micro bubbles that were evident after pushing the piston for some time. I guess these are the little blighters that will cause a problem later if they are allowed to reside in your system - possibly forming themselves into larger bubbles.

I`m now happy with my braking system, having now replaced all brake linings, master cylinder and a thorough fluid flushing. The only thing I have left to do is replace some/all of the footbrake cables as I`m on maximum adjustment at the moment - just enough to lock the rear when the pedal reaches the floor!!