Intrigue! Mystery! Front master cylinder issue!

[JimWilling]

After finding that the previous owner of my bike had not only ridden the bike with virtually no front brakes (ok, entirely none), I went on to discover he had put brake fluid above the dust cap in the front master cylinder. Upon removing the brake assembly, the filthy, probably rusty master cylinder has proven nearly impossible to remove from its bore. Even with a safety wire/slide hammer jury rig, the piston refused to comply. Soaking in PB blaster, WD40, bile, hatred, etc., seemed to only have strengthened the piston's resolve. Perhaps I'm missing something.

The circlip was removed. No problem. Then the dust boots and a rubber ring. Now the rest of the piston should slip out, right? It doesn't seem to think so. Ideas? I'm going with the rust hypothesis.

And a new master cylinder would solve all of these issues. But I got this bike for half what it'll cost me to register it. So dirt cheap is my budget.

[sharpy]

Budget and dirt cheap. mmmmm wonder why it wont work. Even if you do get it apart it be corroded or have a severe lip on the bore. Bite the bullet and get a 2nd hand one or a el cheapo imatation one.

[Agemax]

maybe worth a try if you have already given it a good soaking, fill the reservoir with brake fluid, refit the cap tightly and pump away with the lever. it may build up enough pressure to dislodge the piston.

[hjfisk]

And a new master cylinder would solve all of these issues. But I got this bike for half what it'll cost me to register it. So dirt cheap is my budget.

And you are planning on riding it with a ? master cylinder. Don't value your life much, a good used master wouldn't cost you that much $20-$30 or a new after market $139. pretty cheap insurance to be able to stop

[Steve]

maybe worth a try if you have already given it a good soaking, fill the reservoir with brake fluid, refit the cap tightly and pump away with the lever. it may build up enough pressure to dislodge the piston.

It's not the piston at the wheel caliper that's stuck, it's the one in the master cylinder.

Upon removing the brake assembly, the filthy, probably rusty master cylinder has proven nearly impossible to remove from its bore.

.

[TooManyToys]

Soaking it with petroleum based products is not going to improve your odds as the seals will expand making the removal harder.

Other then a replacement M/C, you could try drilling into the piston so a lagbolt could be inserted, then try prying out the piston.

[Agemax]

It's not the piston at the wheel caliper that's stuck, it's the one in the master cylinder.



.

yeah i know, but brake fluid may act as a lubricant on the seals in the master cylinder and pumping it may free it up enough to pull it out

[JimWilling]

The consensus seems to be a new assembly is in order. I'm not averse to shelling out for this bike. The fluid and gunk in the resovoir is reddish brown, and the corrosion in the cylinder makes me think rust. I've tried blowing the piston out with compressed air, but it doesn't seem to care at all. I've heard of threading a grease gun into the banjo fitting, and building enough pressure to get it out, but my feeling at this point is if it doesn't submit willingly, having a recalcitrant master cylinder isn't worth the money saved. To eBay! methinks.

The question is, can I use master cylinders off of other model years and engine sizes? Is a 450 or a 550 master to small? Would a 1100 or anything bigger than an identical 650 component be acceptable?

[Agemax]

any M/C should be OK as long as the donor cylinder comes from a twin disc model. (assuming you have twin discs)

[Octain]

Put the MC in a vice, grab the piston with a pair of pliers and yank.
It'll come out.

[JimWilling]

Octain-

I've had the bugger in a vise, with a slide hammer attached to it and really only managed to make my rather heavy workbench jump. Pliers proved fruitless way before I cracked out the slide hammer.

[Octain]

Yup, see that now..
Funny, there's really not anything holding it in there.

[JimWilling]

I imagine it's just rusted in there neatly. But it's REALLY in there, so who knows? I'm butting right up against the comfortable limits of persuasion with this part.

[tkent02]

Another option is to attach it to another master cylinder (attach it to the banjo bolt for the rear brake caliper) and use that one to pressurize it, the piston will have a ton of force pushing it and should pop out. Fluid and parts may travel a fair distance, wrap it in a towel or something to catch the parts.

Whatever you do, the front brake is probably the most important part of a bike which must be reliable, a brake that won't come on sucks but it is nowhere near as deadly as a brake that locks up with no warning, without even touching the lever. Either of these failures are common with neglected brakes. Get it right.

[bwringer]

Even if you do get the piston out, the bore will be entirely buggered beyond saving.

It should be quite easy to find a used MC that will work, or is at least easily rebuildable. Just about anything from a Japanese or European bike would work fine. Perhaps you can score a decent late-model MC at your local boneyard.