1990 XJ-S V12 Front Brake Locking

[emery]

Hi everyone!
I just joined in your discussion forum. I have a major problem with the front brakes locking up on one wheel on either side. That is the reason why the previous owner got rid of her. The car is in mint condition having covered only 43,000km to date. It has been parked for the last four years or so. The brake system is TEVES with ABS. According to the last owner, the problems started when he fried the brakes coming down a very steep and long hill. When he got to the bottom, smoke was coming out from everywhere with a nasty smell of burnt brake linings. Since that time, the car always behave the same way. It brakes normally when the car is cold. After a 10km trip to the store and being parked there for 10 minutes, one wheel will lock up (either one) and pull the steering wheel off your hand, spinning you 180 degree on the road. Scary experience!
Front Brake Calipers, Brake Pads, Hoses, Tires have all been replaced. The system has been flushed, the fluid replaced with CASTROL LMA; The system was bled accordingly.
No change! No improvement!
After consulting with experts??, he was told that the Hydraulic Control Module, consisting of Brake Booster/Master Cylinder/Valve Body Assembly, had to be replaced. Does it sound right?

 

[jessebogan]

I would find a copy of the genuine factory repair manual for the car first. They are on Ebay f5rom time to time. The best are the 4 volume hard bound sets that came from the dealers... Then you need to TEST the hydraulic unit. It could be an electrical fault that is energizing one or both front wheel solenoids. The solenoids have 3 positions. Open(normal brakeing), pressure hold( sounds like what is happening to you), and release pressure(directs fluid back to the reservoir). All of this was done to modulate the brakes as the antilock functioned. There were repair kits for the valve block at one time, but I have no idea if they are still available. Given the price of a new unit, good used might be the way to go, or the entire master cylinder, pedal box and brake lines can be converted back to the pre ABS system, but even that might take a parts car to be cost effective.

Good luck,

 

[DrEntropy]

Given the price of a new unit, good used might be the way to go, or the entire master cylinder, pedal box and brake lines can be converted back to the pre ABS system, but even that might take a parts car to be cost effective.

That'd be my ~first~ choice. Yestertech brakes ain't tryin' to outguess driver input. Anitlock is great for Hundai 'n Honda drivers. Not so much for Jag pilots.

My 2p. :wink:

 

[emery]

My library consist of JAGUAR XJ-S Repair Operation Manual and JAGUAR Parts Catalogue. Valve Body Repair Kit is not listed. The Brake Pedal Housing, P/N CAC3897 is the only one listed for 5.3 Litre XJ-S W/ Automatic Transmission. I am going to look for a used Brake Servo P/N CAC1227; used Brake Fluid Reservoir P/N CAC4578; and a used Vacuum Tank P/N C36471. I will by a new Master Cylinder P/N CAC1583. My intention is to remove the TEVES Booster , Master Cylinder and Valve Body only and leave everything else in place, i.e Pump, Brake lines and Accumulator. I can easily fabricate the tubing necessary to connect to the existing ones, as per the Pre-ABS configuration. I am in no hurry. I have other cars to work on and drive.
Thanks for the advice.

Pat
1990 Jaguar XJ-S conv.
1987 Jaguar XJ12 VDP
1969 Marcos 3L V6 Wooden chassis
1961 Daimler SP250

 

[DrEntropy]

Oh dear.... another SP owner!?!? :laugh:

Great, Pat!!! And I forgot to say: WELCOME to the Forum! :thumbsup:

 

[emery]

Thank you Doc. I'll be glad to help anyone on technical issues related to the cars I own.
Pat