2004 Jaguar XJ8. 163,000 trouble free miles. (needed a rear ball joint assembly at 100k, but even at $500 that's nothing).

Replaced the rear pads today and the result is that the brakes catch late and the pedal is mushy. It is not driveable. Even a "panic stop" at 5mph doesn't stop the car immediately.

I used the correct rotating piston retraction tool. I did unhook the battery, let it sit while I did the brakes, pumped up the brakes rock hard, put the battery back on and reset the parking brake.

On one caliper, when retracting the piston, one of the dust seals got just a little brake fluid...a touch, on the rim. I figured, retracting the piston it is bound to lose a tiny bit. Once reassembled, STANDING on the brake pedal nothing leaks out of that caliper. There is no leak.

So why do I have such poor pedal pressure?

Should I just buck up and bleed it tommorrow?

-John

 

John, what you are describing is a classic syndrome of new pads fitted to an old and worn disc. The pad needs to bed into the disc wear pattern, and this can take quite a few miles. If your discs are really scored and have lips you can get this very badly, in fact, most garages will recommend a disc change.

So the question is - what are the discs like ? Have you checked for scoring and minimum disc thickness ?

Other thing is you don't mention letting any brake fluid out, so really there should be no need to bleed the system.

 

Yeah I didn't let any fluid out on purpose, but the tiniest bit creeped out around one of the pistons as I was retracting them. I just thought that perhaps that air was let in at the same time?

The rotors look to be in great shape with no metal ridge (a slight rust crust ridge) but I will measure them instead of eyeballing them tonight... if I can't just buy new ones on the cheap. Looks like Rock Auto has them for about $25 each.

 

A couple of questions:

1. Did you release the parking brake before disconnecting the battery? The parking brake utilizes the rear calipers as its braking device and it must be released before caliper reomval and rewind of the pistons.

2. Did you do the front brakes too?

3. Did you push the old fluid back through the system, or did you release the bleed screw when you rewound the pistons?

Without any answers to the questions, I would first bleed the entire system, then check to see where you are. If no improvement, then I would go back over the park brake reset procedure.

 

Hi Steve-

I did release the parking brake before disconnecting the battery. (Unless it comes on automatically by itself??? I mean, I didn't set it on, so it was off.)

Just the rear brakes this time.

I did push the fluid back, and did not open the bleed screw.

The pedal does feel exactly like unbled brakes, but I never opened the system. I will definitely bleed it anyway assuming there are no special procedures beyond what you would do on any other car.

-John

 

Does your parking brake work perfectly after the pad change?

 

Thank you all for your help. A bleed did it... which makes no sense, because the system was never opened! That trickle of fluid past the piston must have been what did it. Rather than hope it was a one time event, I will be replacing the calipers.

-John

 

Glad you're back up. The rear brakes on the X350 are a little tricky...more than they should be.

Best,

BTW - NH is a nice place. Lived in Merrimack for 3 yrs.