My 1994 XJS (28,000 mi) (convertible) has locked rear brakes. I have gone throught the hand brake system and the mechanicals all seem ok. The calipers, also, seem to fuction fine. But when all is hooked up, something is triggering the parking brake to engage and stay on.

Is there an electronic element to this system that make be malfunctioning? Maybe an antilock issue?

 

tlr6779,

The handbrake is completely mechanical from a cable to the rear outboard brakes. No abs or electronics.


See if you can check if theres a handbrake cable connection jammed on the back of the backing plate on the hub and that the cable is freeing off properly.

If all ok there, try backing off the brake shoes through the access hole that is visible when the wheel is off. Try and turn the access hole to the 12 o'clock position then use a flashlight to see where is the toothed adjuster. Then use a screwdriver to try and back off the shoes, then remove the disc and see if there's anything unusual in the shoe setup.

Good luck,

Paul

 

Thanks Paul,

Have checked the brake cable and lever, micro switch and tension adjustment. I will try the manual back off as you suggest and re-post my results.

Thanks again

Tom

 

Hi Paul and all watching. The issue was my '94 XJS 2+2 6cyl. rear brakes were locked tight. Wasn't the parking brake, wasn't the ABS, wasn't the calipers. It wass a little klnown part called a "pressure delay valve" in the brake line running under the power stearing reservoir, front right of the car. An 11 mm & 13mm wrench and a spaner got it done in 1 hour. Very little brake fluid escaped, which I caught in a gauze sponge. So happy! Thanks Jagbits and all that listen to me.

Tom
1994 XJS 2+2 six
2006 XJ8L Super V8

 

Good find, and thanks for posting. I've seen that in the parts diagrams, but hadn't heard it could cause issues. Might be a simple proportioning valve to retard pressure to the rear brakes to prevent lockup. Not sure why it would be needed with ABS, unless it is to prevent unnecessary ABS activation under normal braking.

 

tlr6779,

Glad you got the problem sorted. It sounds as if somehow, the valve had got jammed. Hopefully you don't need to now bleed the rear circuits. But if you do, check back in here as the rear brakes on the Teves system need to bled in a speciifc manner, not like a conventional brake system.

The "pressure delay valve" is a actually a "pressure reducing valve". Not sure why the Jaguar parts system call it a "delay" valve. The reason it is fitted is because the rear brakes are not driven by pedal pressure. They take direct dynamic pump-driven pressure that is actuated by a shuttle valve that is opened when the pedal is depressed. Without the valve,the rear brakes could receive excess pressure in the circuits compared to the front which is "statically" (non-pump) activated under normal conditions. The valve works to hold a difference of 87psi between the front and rear brakes.

Hope that helps

Paul

 

Possibly a related question, On my 94 I find the rear brakes are doing more work than the fronts, I've never been happy with the way the brakes work on the car. Could this valve be faulty?

 

Jagboi64,

I think your valve may be in the early stages of failing. Paul (above) make the refrence to the pressure difference, front to back brakes.I'm not sure how to test that but it's worth exploring.

tlr6779

 

I had the same issue with my 94 XJS. It now has all new rotors, calipers, e-brake pads, and hoses. I cooked the rear brake system completely. I wish you luck finding the delay valve. They are pricey when and if you do. I am pretty sure they are NLA. I was lucky to have a few parts cars with the same valve. One from an 89 thru 94 will work. After that they went to a different one. I believe the later one will work but you have to do a little plumbing. I have one and will let it go for a discount. I paid over $186.00

 

FYI. I just looked up the pressure delay valve part # CDU-4233-u. Welsh has it listed at $ 275.00 but I don't think it is currently available.

 

The Pressure reducing valve is CBC4233. Jaguar haven't had it available for some years. As I've not seen a pattern part previously advertised by anyone, I don't think any of the major aftermarket suppliers will have a replacement part available, but happy to be proved wrong.

Paul

 

After much looking, I found a USED valve.....$275....oof. Took a chance that it was good...and it was.

Tom

 

As I mentioned in a previous post, the delay valve from 89 through 94 are the same on the XJS. The valve on the XJ40 for those years should also be the same. This makes the valve available used.

 

Adjustable aftermarket items exist:
https://www.wilwood.com/MasterCylind...CylinderValves

 

That's what I'd do, since the only available original ones are used, and they may be no better than the old one. I've used an aftermarket valve on another brand of car before.

Jon

 

Pressure delay valve for XJS
I bought mine from Jagbits. They list it today 5/26.

Tom

 

I just checked it out. They have a used one listed for $ 275.00. I have four if anyone needs one that is more reasonable.

 

I think if mine fails, I'll consider going down the adjustable route as suggested by Greg.

Paul

 

Hallo Paul,
mein Name ist Michael, ich bin neu im Forum und suche ein gebrauchtes CBC4233 Reduzierventil.
Können Sie mir hier helfen?
Vielen Dank und beste Grüße aus München,
Michael

 

Hello Paul,
sorry, not in german:
My name is Michael, I'm new to the forum and I'm looking for a used CBC4233 reducing valve.
Can you help me here?
Many thanks and best regards from Munich,
Michael