Rear Master Cylinder - Overhaul Required?

Rode to work on Friday and all seemed as per normal with bike including brakes. Hopped on at the end of the day heading slowly to the exit of the sub building carpark where I keep the bike during the day and went to apply the rear brakes as I approached the boom gates and...kept sailing forward. Yikes. Rear brake pedal had no resistance at all.
Long story short, bled the brakes and a huge amount of air was in the line (strange as I only bled and replenished the brake fluid a few weeks ago). Dismantled the rear brake master cylinder, cleaned all the parts and reasembled. Bled the brakes and was OK for a short time but after a while again no brakes. I think I can see some wetness on the outside at the bottom of the master cylinder piston. I guess this means that an overhaul kit is required - any members confirm this?
Also, apart from Yamaha, has anyone acquired a rear master cylinder overhaul kit for the XJ900?
Thanks

Karl

 

Great hopin' horny toads! Karl, you are very lucky nothing bad happend to you. Glad you came out of that experience unscathed. DO order up a rebuild kit and get the brakes up to snuff pronto. Not much to rebuilding one of those cylinders but the kits tend to be pricey.

 

Great horny toads indeed (or Cane Toads in Oz!). Just as well I was only going along at walking pace when it happened. Much worse if it was as I was coming into a corner. I think we can all relate to a scenario where we're riding as per usual and something doesn't work as it should.

Have acquired a rear brake rebuild kit at the outrageous price of AUD$87 - that's US$70 (from Yamaha - where else at that price!) - when the spart parts guy told me that (and that's with a discount!) I felt like I needed the crash cart and paddles applied to my chest. We don't have the extensive aftermarket suppliers here in Australia as you do in the US so competition in these things is non-existent. In any case I was hard pressed to find on the web REAR master cylinder rebuild kits - plenty of front kits though but no rear ones for an XJ900.

Point of interest in this is...rear brakes working fine till I did the brake flush/bleed recently. Looks like I might have flushed out old sludgy thick brake fluid and then replaced it with clean stuff: it might have just done the trick having new clean thinner brake fluid to leak past the old and worn piston/rubber rings. Was going to happen anyway soon, just as well it happened at less than 10 km/hr with a car park boom gate rising in front of me! Could have been much worse.

Will rebuild the master cylinder on the weekend so all should be well; I'll report back for the benefit of others that this is actually the fix for the problem.

Cheers,

Karl

 

I EAT TOADS! :twisted:


Glad to see you made it off the bike in one peace BTW. Breaks are #1, be sure to get that worked out my man before you ride again.

 

You don't want to get a mouthful of those cane toads, you won't live long. No kidding.

 

Just a follow up on this topic.

Got my rear master cylinder rebuild kit - all nice and shiny stainless steel bits by the look of it. Interesting to note that the actual piston with the spiral grooves in it was much wider on the raised spiral landings than the original. The rubber caps were a bugger to put on (they came separately with the kit and had to be installed, right way up; i.e. with the open end facing up on both as per the original). Once that was done the rest was a breeze to put back together.

And boy what a difference. I think the old one was going for a while. Usually had to pump it once or twice to get some real brake feel but now it feels firm and positive. Problem with old one was the rubber seals had worn to the extent that they were leaking out the bottom of the cylinder and not providing any pressure for moving the brake fluid through the line.

Next step next year is to replace the front master cylinder piston and seals and then bright blue stainless lines all around.

KarlH

 

Great to hear about your success, stay safe and sane eh? And try (not too hard) to avoid those toads. I watched a little animated short called "Cane Toad" produced by a couple of your fellow Aussies. Funny as all heck, keep 'em comming!