Egads! What’s this crud in my master cylinder?

Hi All!

I recently picked up a low mileage XJ650J. Even though it already seems to run great, I decided to do some basic maintenance on my bike before embarking on any long distance trips. I noticed the brake fluid looked pretty nasty thru the sight glass so I picked up a big bottle of DOT 3 and started bleeding. When I opened the master cylinder, however, I found some grime had accumulated on the bottom and sides of the reservoir. The diaphragm was also badly stretched. I’m guessing other than an occasional top off, this master cylinder was never serviced. I ended up dumping the entire reservoir so I could clean this stuff out (looked like coffee grinds) and refilling and bleeding the brake with new fluid.

Is it common to find this crud in old fluid / cylinders? What causes this grime to form?

Cheers!

 

If your horn works, the brakes are redundant.

In all seriousness, I just changed mine and it was not cruddy at all. It may be time to switch to stainless brake lines or rebuild the calipre.

 

Master cylinders accumulate crud with time. Brake fluid attracts moisture and this leaves a gummy like syrup behind. The "coffee grinds" may be actual rubber bits as suggested from the brake lines or cylinder parts. I would bleed the brakes to replenish the system with a good Dot 3 or 4 fluid and after making sure no air is in the lines and the brakes work fine then ride.
The calipers are too low fro me to think the bits are from it. Gravity would keep that in the caliper. Main signs for rebuiling the calipers are 1. fluid leaking at the caliper piston. 2. Dragging brakes that suggest the piston is not fully retracting.

 

Thanks for the feedback!

The bottom of the reservoir was not flat – it had a depression at one end like it was anticipating buildup of some sort. This area is in fact where I found most of my sludge. That’s why I was curious if this crud buildup was somewhat normal given the probable age of the fluid.

 

Blue is right Bird, the rubber dies over time (and yours is the right age), necessitating replacement. First chance for new lines and rebuild kits, spring for them and get yourself safe again.

 

Can't argue with that advice, Robert!

Can anyone recomend a good online outfit to order these parts from? I'm trying to save a few bucks over the dealer's cost.

Thanks again!

 

I can recommend 2. www.partsnmore.com & www.oldbikebarn.com/

 

Bird:

My recently acquired '82 Seca 400 also had sludge in the master cylinder. It looked like gooey mud.

I took the master cylinder off, disassembled it, scrubbed it and sprayed it with brake cleaner, and blew it out with canned air.

After reassembly, it took FOREVER for it to "prime" and start pumping. I had just about decided to give up and chalk up an expensive mistake when it started working. Yes!

It seems to be working fine now, and the fluid through the site glass is beautiful.

Good luck-
Herb