Hi all,
I picked up a very nice 1995 XJS in excellent shape. The brake system on this car is the one with hydraulic booster system.
I must say the brakes feel awkward to me. Seems to stop OK but feels strange (hard to explain). I had 1995 XJ6 and that had the normal vacuum booster setup. I also saw an 1995 XJS with the vacuum booster.
My question is , does anyone have more information about this. Were these cars offered with two different brake systems? Can the hydraulic system be converted to the vacuum system.
Thanks a whole bunch

 

Omid,

If your XJS has a VIN lower than 198335 then you have the early Teves ABS system. It's not known as a "hydraulic booster" system, so I would refrain from calling it that as it will just confuse people.

The system is very different from a traditional braking system with a vacuum servo, as you may realise. It doesn't have a typical Master Cylinder. It uses a very complex and non-traditional Actuation Unit which is linked to a Pump and Accumulator and then has an ABS valve block attached to it. There is a lot of information available relating to its maintenance and the known potential problems which have become apparent in recent years.

The XJS never had an "option" as to which system was fitted. The early Teves system ran from c 1988 to 1995. At VIN 198335, it was updated with the later system which reverted to a traditional master cylinder and vacuum servo, but with an ABS pump and valve block.

I'd not personally suggest replacing the early Teves system with the later system There would be an awful lot of work to literally rip everything out and replace all the components and electronics and ABS ecu and wiring etc. I don't know anyone who has attempted it. ;It would be really significant and I'm not sure if it would contravene any local vehicle legislation. (I'm not sure what country you are in?)

If you've got problems with the system, post back and I'm sure there are people who will be able to help.

Cheers

Paul

 

@ptjs1 thank you so much for all that information. Its great to know. My VIN is 196757 and I am in Phoenix Arizona USA. I am not experiencing any malfunction per se. The brake pedal just feels unusual to me I guess I am just not used to the feel of the Teves system. At one point i felt like the car jerked to the right when I was coming to a very normal stop. It could have been an uneven surface I thought. It just didn't feel very nice.
I looked it up briefly and Teves system is definitely much a complex system than a conventional vacuum assist which a master cylinder. The part I did not quiet understand is the rear brakes operation. I think I understood the high pressure side where the pressurized brake fluid is used for brake assist and the actuator is similar to a master-cylinder but only supplies pressure to the front brakes.
I read some stories about the brakes on these cars behaving very badly and throwing the car into a spin etc due to the ABS malfunction. Some people actually suggest in those situations to disable the ABS by pulling the fuse.
Do you guys have access to the brake system diagram for these cars.
I really appreciate all the help.

 

As Paul said, it sounds like your car has the Teves 3 ABS system. If the brake fluid reservoir is pretty large and rectangular, you have the Teves 3 system. The fluid reservoir is triangular on the Teves 4 system, uses a conventional style brake booster and master cylinder, and the ABS pump and computer is a unit on the opposite side of the car. The two systems are completely different. The Teves 3 system requires specific procedures to bleed, and there are a lot of posts here on the maintenance of that system.

The Teves 4 was added at the VIN Paul stated, and was part of the 1995.25 update, where other changes were also made. Jaguar made a surprising number of changes in the last couple of years of the XJS. The V12 (and 4.0 XJS) had 1994, 1994.75, 1995, and 1995.25 update documents. Other changes Jaguar made in the 1995.25 update include adding larger rear calipers and vented rear discs, an updated engine PCV system, and numerous electrical changes.

Some people have backdated the Teves 3 system to the early non-ABS braking system.This entails eliminating the Teves 3 system in its entirety, and replacing it with the early model pedal cluster, vacuum brake booster and master cylinder, and redoing some hard brake lines. I agree with Paul that retrofitting the Teves 4 system would be difficult, and very expensive; used (and new) components to do the retrofit are far more rare.

Jon

 

For a system description of the Teves 3 system, go to the website below, and download the main 1989 model year update. It provides a complete description of the Teves 3 system.
JagRepair.com - Jaguar Repair Information Resource

 

I agree, the system you have is awful, rubbery feel with non linear feedback. I have driven on both types, no comparison, the late (1995.25) system with the later vaccuum brakes is far better.

 

Hi Omid

I've got both types on my Cars:

Teves 3 Master Cylinder Actuator with the Big Square Reservoir like yours and also a Car with the Teves 4 with Brake Booster and Triangular Reservoir

As for me I much prefer the Teves 3 like yours because if it goes wrong then I know how to fix it

So if your Car is Pulling to the Right, when you Stomp on the Brakes then its probably one of Two things

(1) Most likely a Broken Ribbon Wire in the Valve Block (easy to repair and cheap to Fix)

(2) Stuck Valve in the Valve Block (which may or may not be an easy Fix depending if you can free it off)

So Best go with Number (1) at least to begin with

(1) Unplug the Big Electrical Plug on the Side of The Master Cylinder Actuator and then Test it with a Battery as I have done in the Video
Easier to do if its off the Car but you don't want to remove it unless you have to

The Test should confirm that either you have a Broken Ribbon Wire in the Valve Block which is Attached to the Side of the Master Cylinder Actuator or a Stuck Valve (as you won't hear it Clicking when you Dab it with 12 Volts

In either Case the Master Cylinder Actuator needs to come out! (Not to Panic this is a dead easy job) ish!

Take the whole thing out all in one piece: Including the Reservoir and the Pedal (it's only 4 Bolts) so how hard can it be

Just don't Break the Brake Light Switch! as they Cost 'Megabucks!'

Then do the Valve Click Test again just to see or should that be hear that one of them isn't Clicking!

Then with the Master Cylinder Actuator laying on its side with Valve Block Uppermost

Very/Very/ Carefully unbolt the Lid on the Valve Block and Very/Very Carefully Lift it off BUT DON'T LIFT THE VALVE BLOCK OFF! or even disturb it, or all the 'O' rings could and probably will fall on the Floor including the Valves!! that can break the internal Ribbon Wire under their own Weight

Just Trust me when I tell You that you don't want that to happen! Not on any day of the Week!

Now with the Lid Off the Valve Block take some Photos of where all the Ribbon Wires all go and Connect up as well as a Quick and Dirty Sketch

Assuming that you can now see a Broken Ribbon Wire, resist the Temptation to Fix it but instead now Carefully put the Lid back on and just do the Bolts up Finger Tight, then take it to the Radio Shack (or Similar) and get them to rewire all the Valves using High Temp Silicone Wire

This will replace the Fragile Ribbon Wire, making it good to go for many Years

Then Bolt The Master Cylinder Actuator back in the Car reconnect the Brake Pipes and put the Big Electric Plug back in and that should be Done and Dusted

Repairing the Teves Mk3 Master Cylinder Actuator if your Car Suddenly Pulls to the Right without any warning when you Jab the Brakes

Loads of Photos to Help you Fix this Problem dead easy really as 'The Radio Shack' do the Critical Bit' which is the perfect Soldering required to do this job

 

Thanks everyone for chiming in. @jal1234 thanks for pointing me in the direction of the documents.
@orangeblossom very informative. Thanks very much.
After reading the posts and the documents I think I understand the Teves 3 system. Under normal operation the actuator acts as a normal master cylinder suppling pressure to the front brakes and the rear brakes are operated by the boost pressure via a pressure reducing valve. Under ABS operations both front and rear brakes calipers use the boost pressure and the pressure is modulated by the solenoid valves via the ECU.
So one would expect that the system would behave deterministically under normal braking. Correct? One would not expect dynamic strange behavior unless the ABS system is activated. Am I correct?
QUESTION: Do people intentionally turn off the ABS system to avoid the uneven braking experience. What is the best way to do that ( I guess pull the fuse)? Could the brakes behave unexpectedly (sudden jerking etc) even if the ABS is turned off?
Thanks guys for all the info.

 

Omid,

That's almost correct. There are a couple of key elements though. The pressure being applied to the rear brakes is not driven by the pressure being applied to the pedal. The pedal merely actuates a valve which allows the boost pressure to be sent through the actuation Unit and hence to the rear wheels. However the fluid pressure to the front wheels is always determined by the pressure applied to the brake pedal. When boost pressure is applied to the front, it is still being applied to the back of the piston which is being pushed forward by pedal pressure.

The other key element which may be affecting your what is happening in your car, is that ALL of the fluid being sent to the wheel circuits is going via the Valve Block. So, even when ABS is not being operated via electronic actuation of the valves, you're still at the vagaries of those valves being correctly open / closed in their steady state. One of the known failure problems is when minute amounts of sediment get lodged under one of the "normally closed" valves. This then causes a bypass of fluid to that caliper and the car can dive to the opposite side.

That's why you should

- always change all the fluid every 2 years to ensure you do not have contaminated fluid in the system.
-never allow fluid to get pushed back to the valve block where it can disturb any sediment. for example, if you ever push the pads and pistons back, always attach a tube to the caliper bleed nipple and open it first.

If you keep the system well maintained, then there should be no reason to turn off the ABS. And if you've got a problem, turning off the ABS may not help it anyway, if you've got a valve jammed open when it should be closed.

Cheers

Paul .

 

Makes perfect sense. I really enjoy driving this car and want to drive it for as long as I can.
Appreciate the help.