Brake master or power booster leaking fluid

I have a 1984 3.6 manual. Have been losing brake fluid. I shoved a piece of newspaper up under the master cyl. The stain indicates the leak is at or near the juncture of the brake master cyl and power booster. Should I replace both? Or is there an easy way to determine the likely culprit? Any GM crossovers on the power booster? Thanks in advance. Harry

Have you checked the hoses going into the M/c? I was loosing BF on my S11 and it was just loose hose clamps.

BF has no place in the booster…

Carl

Checked the hose and fitting. No leak there. Thanks

Carl is correct: There is no brake fluid in the booster. It’s the master cylinder that is leaking, and there is a deliberate leak path at the joint between master cylinder and booster.

You definitely need to R&R the master cylinder. Whether or not the fluid has damaged the booster, I dunno. It’s not a terribly expensive part if you choose to go ahead and replace it. You might want to take it out simply to address the brake fluid that’s been leaking underneath it, as brake fluid damages paint.

So the consensus is brake master. I know the list of usual suspects that sell Jag parts. Any particular sources recommended? Thanks again to all that replied!

If you have fluid coming between the booster and the master cyl, then chances are the rear chamber on the master cyl is leaking. It’s time to get that fixed.

I would replace both. brake fluid is corrosive, and will make short work of the brake booster over time. Both are readily available at RockAuto.com. Wagner or Centric would be my first two choices. Wagner brake (parts) have been around for nearly a half a century - not that I know that first hand. I did work in an auto parts store in high school and Wagner was the least returned product line. Centric wasn’t around then. I do use Centric brake parts in all of my XJ’s and have been very pleased.

If left unattended, the end result could end in a very exciting drive to a catastrophic ending. Been down that road in my XJ-S.
It was a very exciting drive ending in a 4 wheel drift into a car park; and me checking my pants after it was all said and done.

Even if there’s no problem at all, just pull off the road and call a tow truck, it’s still exciting. There’s just something about pushing on the stop pedal and feeling it fall away under your foot.

So one last question (and yes, I’ll replace both - I believe the booster is 1984 factory unit). Is there a General Motors cross over for either or both units? We all know if it sez Chevrolet, it probably will cost quite a bit less than when it sez Jaguar.

Thanks, Harry

Kirbert
Author of the Book, former owner of an '83 XJ-S H.E.

    March 1

alt MLee:
the end result could end in a very exciting drive to a catastrophic ending.

Even if there’s no problem at all, just pull off the road and call a tow truck, it’s still exciting. There’s just something about pushing on the stop pedal and feeling it fall away under your foot.

For the booster, yes, it’s a standard Chevy part, but I dunno the part number. For the master cylinder, I don’t think so, it’s unique to Jaguar.

Do you have a plastic remote reservoir with a brown cover over the level switch? That thing’s a POS, I recommend replacing it with a reservoir from a Mitsubishi which has a floating magnet switch that is much more reliable and a diaphragm in the cap that’ll keep moisture out of the fluid. You would have to fab a mount for it, though, and you’d have to buy a pair of hose adapters as the hose connections on the Mitsubishi reservoir are a size larger than those on the Jaguar master cylinder.

Mine let go as I was coming off the motorway at about 70mph. Pedal went to the floor and I couldn’t get it pumped back up enough to slow to a manageable speed. E-braked it to get the back end around so I was heading in the right direction in this case for the car park. There was no way I could get it gathered up and slowed down enough to stop at the red light 1/2 block away; a parking lot was my best bet. Fortunately for me it was on a Sunday evening and the lot was empty. That could’ve ended up in a very bad way.

Check out Rock Auto. The parts aren’t that expensive - not much more than what you’ll pay for a GM equivalent. Heck, I can outfit two XJ-S’s with brakes for less than what it cost me to fit the brakes for my 3/4 Ton 2002 Chev suburban.

With some effort, I was able to locate a brake master cylinder. Power booster is either out of stock, or no longer available! If anybody knows of a GM equivalent/interchange. Please let me know.

The power booster is currently functional, but is 36 years old. While I’m twisting wrenches in that area, sure would like to replace it now rather than later.

Thanks, Harry