Rear Caliper stuck

[Jean Luc]

I wanted to share an interesting story. Last Monday it was 60+ degrees here in Detroit, so I decided to take the XJ out and blow the cobwebs out of her.

I put a new paint job on her over the winter, so the fuel system was BONE dry. I found it interesting that I put some gas it the tank, pushed the petcocks to Prime, and hit the starter button. Within 5-6 good cranks the beast thundered to life.

I am about 5 miles from home, and I notice that I am holding a steady speed, but I am cracking the throttle more and more. Not Good. By this point, I am approaching a gas station, so I pull the clutch to pull in. I hadn't applied the brakes yet, but the bike slowed so abruply I swore I had a handful of binders. Not Good.

As soon as I stop, I look at the front wheel, looks OK. I then look at the back and notice the rear rotor is glowing bright orange (like a toaster). I cannot even push the bike - the back wheel is locked. I pulled out the toolkit, and tried pushing the pads back - No Go. I then crack the bleeder, and boiling brake fluid spews forth. I have NEVER seen brake fluid boil. With the bleeder open, I can now force the pads back. I sit and wait a while to let things cool, and I drive carefully home only using the front brake with downshifting.

Hey, she seems a LOT faster on the way home .

Today I am taking the rear caliper apart for a good cleaning.

[xssiveone]

Cleaning the caliper can't hurt, but I don't think you will find it to be the problem. Check here for a "how-to" on cleaning the fluid return hole in the master cylinder.

Master Cylinder "Spooge Holes"

If you haven't already done so, check the out all the Tech Tips on this site.

[Jean Luc]

I thought about the spooge holes, but I do not think this is the root cause.

Here is my thinking - The XJ has a linked braking system. As we know, stepping on the brake petal activates the rear and one of the front calipers.

If it is a plugged spooge hole on the rear master, wouldn't I have had two glowing rotors, not just one?

[nashville_bill]

It is hard to reason why letting brake fluid out of the system would help if the problem was a stuck piston in the caliper. I think I would try the master cylinder.

[xssiveone]

Originally posted by Jean Luc
I thought about the spooge holes, but I do not think this is the root cause.

Here is my thinking - The XJ has a linked braking system. As we know, stepping on the brake petal activates the rear and one of the front calipers.

If it is a plugged spooge hole on the rear master, wouldn't I have had two glowing rotors, not just one?

Well, I guess that's what I get for not paying attention!!

Didn't realize you had an XJ. Still, something in the master cylinder me thinks. Not too familiar with the XJ, but I seem to remeber something about a metering valve in the system to limit the braking to the rear and increase the braking to the front.

[buffalo]

I have worked as a mechanic for almost 30 years and have seen this problem caused by internal breakdown of the brake hose on numerous occasions... to check if the problem is there apply rear brake and release, wheel is locked or dragging,
loosen line at master cylinder, does the brake release?
If yes, then problem is at master, if not, loosen bleeder, if brake releases problem is in the line. A stuck caliper piston will rarely release when bleeder is opened.

[Jerry]

The XJ linked system has a proportioning valve built into it. At low pedal pressure there is more pressure on the back caliper than the front. That is, the rear caliper is applied first; the calipers are not applied at the same time. Therefore, it it possible that you gently applied the brakes at one point and the spooge hole plugged, locking the rear caliper but not the front.

I had the same thing happen to my XJ, but I caught it before the rotor got that hot. The condition seems to happen more frequently with a bike that has been out of service for a period of time rather than one that gets ridden frequently. I went to SS lines after cleaning the Master Cylinder...some of the crud is from the inside of the brake lines that have deteriorated over the years.

Others have reported the same problem. While there is a *small* possibility the problem is elsewhere, I would bet the problem is a plugged spooge hole in the rear master cylinder.