Nasty front master cylinder

I finally got the cover off my KZ750 front master cylinder, and now I kinda wish I hadn't. Is this thing salvageable? Besides the sludge, I cannot get the bottom right screw out, even with an extractor. I have not even tried the top right one yet (Both broke off when I used a screwdriver on 'em). Funny thing is, the front brakes work!! :ohmy:

Mine was kinda nasty, I used brake fluid and a brush to clean it up. You have nothing to lose, and if it gets destroyed there are plenty on ebay to replace it. You can buy some new ones, I saw some for $80 that would handle a single disc.

Yea, my metal state is about there - go for it. But I am kinda stumped on how to get these screws out. The extractors are just tearing them up, and they are NOT coming out of the threads.

OKC_Kent wrote:

Mine was kinda nasty, I used brake fluid and a brush to clean it up. You have nothing to lose, and if it gets destroyed there are plenty on ebay to replace it. You can buy some new ones, I saw some for $80 that would handle a single disc.

Exactly what Kent said...giver a go...but just remember...a rebuild kit($)...the struggles of getting the broken screws out...the time involved in a rebuild,etc.
It would be great if it all worked in Your favour,BUT...again...like Kent said...You might want to concider another one from ebay.:whistle:

What are You using for an "Extractor?",btw.
I ask this,because I don't see any holes drilled in the screw...
(or am I just blind?,lol)

Work on getting those screws out,and give it a good cleaning(plus a complete system flush)...pick away at it,and let Us know how it goes...

I don't think rebuild kits are available for that model, at least I have never been able to find one. That is a 78-79 KZ750B master cylinder, and is also used on a couple of years of 1000's (77-78 I think).

If you can get the two screws out of the bottom of the resevoir and get it off, I have a spare you can have.

Post edited by: steell, at: 2006/09/16 16:21

get yourself a stubby phillips driver of the correct size. hold it and the master in your hand and give the screws a few good whacks straight on. im talking good whacks here and no harpooning your hand. now try to loosen the screws. this worked for me and mine looked as bad if not worse then yours. i wouldnt use a vice unless you got something soft to hold it right with....good luck...steve

For that I would use my Craftsman " Screw Out" set. Its always worked so far. Does look like a toughy though.

Sandy - The bottom right was an extraction attempt - a 6MM Craftsman - the type with the bit on one end, and the extractor on the other. I may need to drill down a bit more. My first attempt got the head broken off, but not the shaft of the screw.

Steell - Thanks! I have the top, but two screws stuck (I am thinking two might be enough to hold it down anyhow?).

I have the thing off the bike now on my workbench. Now, I am not what one would call a mechanic of any sorts ('cept computer), but I don't think brake fluid is supposed to be the color and consistency of melted Hershey bar, right? This poor baby has had no love in a looong time. The shaft is rought, but the piston edges and cylinder itself look remarkably good, considering.

The two screws at the bottom of the cylinder are indeed stuck tight. I am soaking it in brake fluid now, we shall see in the morning.

I see a master cylinder on ebay now, for a couple weeks. $50. That may have to be mine tonight. Alternatively, can anyone point me to an aftermarket (new) one that will work on a 79 KZ750? I am getting to the point of ready to pay some bucks. I need to get it through VA inspection!

Thanks again to all - you guys will get me rolling on this baby yet!

Jim,as far as getting a non-stock master on Your bike?...they all pretty much use a standard 10mm fitting(at the banjos).
As a matter of fact,the one on My KZ is off of a 1996 Honda,CB650,and it bolted right on(had to mod for the mirror on that side).It came complete with the adjustable style lever,so You can set it up to fit Your finger reach,etc.
So as long as You can get one that will still allow You to use Your mirror(if that's even an issue) then I would say that You could get one off of almost any bike,and make it work on Yours.
I can post a pic if need be,just to give You an idea...

If you don't wanna do the clean up, check out eBay seller: usa-motorcycles-inc

I recently bought a new front master from them for a single disc set up including reservoir,cap, gasket, lever, brake switch, mirror hole, banjo bolt and crush washers...in other words the complete assembly. They sell em for 29.99 + 15.00 shipping from Miami. The assembly is "decent" quality, but turns out it's made in China...go figure. For the price, I was pleased, it's new and it works well. Just hope it lasts 25 years like my original!

ps: I am not affiliated with this seller, only a one time customer so far. And...there are also a ton-o-used ones on the auction block that look pretty good. Maybe you can find a better deal than new.

Post edited by: neilage66, at: 2006/09/17 00:05

I've had two that were that filthy and I just used a toothbrush under a running faucet to scrub them out.

I would advise against taking it apart as I was never able to find an exact fit for the O-ring under the white reservior and the MC body and it's not available seperately. I got one that was close and it seeped for a while.

As for those screws, heat is out of the question. PB Blaster might help, but they're probably frozen due to electrolosis between the dissimilar metals--effectively welded.

- Nate >>

yeah that is the same 1/2" mastercylinder they used on 78 kz1000s.i was wondering if it would be possible to have one bored from 1/2" to 5/8" and using 5/8" rebuild kit in it.if you are really ambitious and want to get those screws out if you can drill a pilot hole down through the screw you might be able to use the square pointed end of a real small chainsaw file as an easy out,dont laugh ive used this trick before!