No brakes

[rgm]

The brakes on my '05 900 (with a coast valve installed) started feeling soft this spring, then it got to the point where the first push on the pedal went to floor. 2nd or 3rd pump would slow it down. I didn't mind it, but the Mrs. didn't care for it at all, so it got moved up on the 'to-do' list.

Bled the lines, there was a little air in the right front, but it didn't really change anything. Rear brake adjustment was OK. Next on the troubleshooting list was the master cylinder. Installed the rebuild kit I bought from Messick's, no change.

Next thought was the brake pads themselves. I thought maybe having the coast valve installed and all of the winter plowing had worn down the brakes because they weren't designed to be used all that much with the amount of engine braking it originally had.

When draining the front hubs I found out that the right front hub was pressurized, the UDT spraying all over me was the first clue.......

The problem ended up being that the O-rings in the front brake cylinder weren't containing the brake fluid. Applying the brakes was pressurizing the entire hub. This had contaminated the hub UDT with brake fluid so I still had to change the friction plates.

I was actually surprised at the old friction plates, they showed absolutely no signs of wear. Except for being wet, they looked exactly the same as the brand new ones.

The brakes work great now, and I don't have to worry about others driving it.

All is well, but I still have to wonder why it happened because the O-rings didn't show any wear or damage. The only two other things I can think of is either one of the few people that drive it stood on the brakes going down a hill instead of downshifting. Or perhaps last fall when I found the hubs low on fluid, it had actually caused damage.

Rich

 

[DennisDarrow]

So the O-rings in one of or both the front wheel cylinders was shot?......What was the bore of those cylinders like? Pitted and scored????.. ......The RTV uses DOT 3 brake fluid, which is hydroscopic. It attracts and holds water. So when exposed to water vapor (air) the H2O is captured and then it accumulates in the Oof the wheel or master cyclinder. It then corrodes the wall of the cylinder and when one then moves the piston in the cylinder it scores or tears up the O-ring and then one gets leakage.
This is pretty much the only reason to have to bleed and replace the fluid on an annual basis......
The fix of course is to change the fluid on an annual basis as recommended. Few do this, so.........Hone the cylinder by various methods and install new rings or even if bad enough to bore and reline the wheel or master cylinder...........God bless..........Dennis

 

[rgm]

Dennis,

There wasn't any pitting, scoring, or visible damage to the piston O-rings. The very fine air bubbles and the pressurized hub are the only things that make me think that the O-rings failed in the right hub. Everything looked factory fresh, and well designed. Heck, each piston has 4 O-rings!!!

There wasn't anything I found during the rebuild that gave me the feeling I had found or even fixed the problem. It wasn't until after it was all reassembled, filled with UDT and DOT3, and bled that I realized it was OK. It was actually pretty frustrating because the whole time I'm doing all this work I was thinking to myself 'what else could it be', because I hadn't found a problem.

When I was servicing the RTV last fall I did flush new DOT-3 thru the brake system. That was only because it was time, not because there were any issues.

I talked to the mechanic at a local Kubota dealer, he hadn't ever opened the wheel hub and seen the brakes of an RTV. Their parts department, along with Messick's had never ordered the friction plates before so thankfully it seems this isn't a very common issue.

Rich