Master Cylinder rebuild R90/6

[Red1974]

Well I got my rebuild kit from Bob's{great service},tore everything down and it looks like, well, not like new in there. Pits and stuff, did the old 1000 grit thing without much sucess. The MC was not leaking that badly to begin with so I'm gonna just rebuild it and see what happens. No way I'm spending all that $ for a new one. Should I be looking for a good used one? Thanks, Nils Red1974

[crazydrummerdude]

I'm a "see what happens" kinda guy.

Others will warn of the damage brake fluid might cause..

[lostboy]

If it leaks you have an excuse to convert to a handlebar master cylinder.

[krehmkej]

1000 grit? That wouldn't touch it. Honed mine with 240, IIRC. Never leaked a drop thereafter.

As always, YMMV.

[ccolwell]

I'll be happy to warn about brake fluid damage. Best paint remover there is. Works very quickly on frame and other paint.

I'd rebuild, protect the frame, etc., with plastic bags or what ever seems to work, and apply the brake for 20 minutes or so and look for a leak. I hold the brake lever in, wrap a soft tie around it and then use a rubber band to hold that in place to keep a brake applied while I check for leaks.

[Barron_Williams]

For consideration before you buy a new master cyclinder - I rebuilt the master cylinder on my 1974 R90/6 probably ten years ago, but have still had a (small) bit of fluid leakage from the back of the plunger.

My solution has been to put about half a piece of paper towel, folded to fit, inside on the bottom of the rubber boot. I bleed the brakes every spring and while I'm doing that, I replace the slightly damp piece of towel with a fresh dry one. Seems to work ok. By that, I mean that any leaking fluid is caught by the towel and contained inside the boot, never getting to the frame or other places where it can do damage.

There are probably better more absorbant materials than paper towel. Again, seems to be a workable solution for a situation like mine where there is some leakage, but not to the extent that over a season the fluid level drops to where it needs refilling.

Barron

[mymindsok]

It might be worthwhile, if the bore is frakked, to simply go onto Ebay and replace the MC with a decent one. I recently sold a stock R-90 master cyl that had already been rebuilt and it only brought $55 and IIRC, I paid almost that much for the rebuild kit!

And curing a leaking MC by stuffing Paper towels into the rubber boot? :bolt

Thats a level of cheapscatedness that I will never ever drop to. If my brakes arnt working 100%, I'll park the bike untill I get em fixed.