A few weeks back I began to notice the steering pulling to the left when pressing the brakes. It became more frequent until it always pulled and then began to pull very hard and suddenly when braking. Calipers were old, so I replaced both fronts, including pads on all four. I bled the system, which is a little different than in other cars I've done. I thought I had solved the problem. The brakes felt great for a day. The next day, the car pulled very hard and suddenly left (again) when braking. I put the car up on jacks and spun the front wheels one at a time while my wife pressed the brake pedal. The RF wheel never stopped. I tested the rear and they worked just fine. This made sense as to why it pulled left. I had no brakes only on the RF wheel. So, I've read a LOT about the ABS valve block going bad and many posts about the tech bulletin Jaguar put out for the replacement kit, very expensive and hard to find. I've determined that no fluid is coming out of the valve block to the RF side by tracing the lack of flow all the way back to the valve block. Initially, when I did the job I was able to bleed all wheels just fine (thus the brakes working great for a day).

Am I missing anything, or do people agree that the only solution is to replace the ABS valve block? I can not find anything on opening them up and rebuilding them. I see a lot on rebuild kits for the ABS controller though. Looks like I can either buy a new one for $$$ or a used one for $$. I'd rather not just put another used one in not knowing how long it will last.

Thanks all in advance!

 

Please add your model year and engine in a signature block.

It'll save us all some time in the future.

 

Thanks for the reminder. I've read the new member info and have updated accordingly. Apologies for the newbe maneuver!

 

Update: I've found two options. This blog link describes how to simply test the valve block and how to use a less expensive XJ6 ABS valve block as a replacement, http://www.rennsportkc.com/jaguar-xjs-ate-abs-repair/. However, the measurements in ohms on the blog leads to an incorrect assumption. He states that bad valves will read 6 ohms while good ones read 3 ohms. In fact, inlet valves will read 5-7 ohms, while outlet valves will read 3-5 ohms when functioning properly. You should read 3 of each to total the 6 valves on this unit.

I was also just lucky enough to find an 89 ABS valve block on ebay for $56. I'm going to test my current one per the link instructions. I'll test the one I just bought before installation. I'll update you all on the results in the next two weeks.

 

Hi Djinaustin

Guess what!

I have got exactly the same problem as you, with the Brakes on my 1990 XJS V12 Convertible.

You can drive along braking as normal and everything is OK then suddenly and without warning, you go to put the brakes on and the Car pulls 'Violently' to the left.

If conditions were wet this would spin it no problem at all!

I too have replaced all the Calipers and put in new brake shoes but it still doesn't make any difference.

I would like to buy a complete new Master Cylinder with Actuator etc but they cost an absolute fortune! (if you can find one!) I was quoted £1,000!

If you manage to fix your brakes, please would you post how you did it.

Just wondering if the unit from a more modern Jag might fit, that would bolt straight on and connect up in place of the Teves one.

If its in current production, it would possibly be a lot cheaper?

Hard to believe the Teves is the only one you can use and I am seriously considering an older non ABS unit.

 

Hi Orangeblossom,


Over the weekend, I verified that it is in fact the abs valve block that is attached to the master cylinder. I measured each valve resistance, including the main valve near the front of the mc. Inlet valves (4-6 ohms), outlet valves (3-5 ohms), main valve (2-5 ohms). So, the valve electronics do not show any dead ones. Rule out electronics, look for a mechanical issue.


I re-measured them from the ECU connector in the trunk to verify the wiring harness was not at fault. What I was able to do was take the car out, run it about 5-10 mph on my neighborhood road and intentionally jam on the brakes locking them up to engage the abs. Since I had replaced the calipers and flushed the fluid twice, the brakes worked great if I used them gently. After about a mile the pull started to happen mildly. So, I was able to really see the effect. After locking them up, the one valve to the RH side (front) stuck, blocking fluid to that caliper. I put up the front and spun the wheels, tested the brakes to verify the RF was not engaging at all. To finally rule out the abs ECU (computer in the trunk), I rolled down a hill in my neighborhood with the car off. Be careful, that isn't easy to control. I engaged the brakes to find the valve still sticking with the ignition off, computer off. Result was determined the valve is in fact sticking.


There seems to be no rebuild option. I was lucky enough to find a used one on ebay for $60, while all the other used and new ones were $400+. I don't know at this point if the used one will work or how long it will last. I will receive that unit this week. I'm posting a pic here.
The actual valve block is the unit bottom left with the fluid lines coming out and it attaches to the master cylinder, coupled by 4 small O-rings. You can either replace the entire mc assembly, or just the valve block.


I did find this as a lower cost option:


"So at this point you have options. One way is to change the solenoids. Another is to buy the whole assy from a breaker. I found that even used the prices were very high so I chose option 3. I bought a more affordable ATE ABS/master cylinder unit from a 1988-94 XJ6. The block must be removed from the XJ6 master and I changed the faceplates. It looked like the spacers on the newer unit would have been ok but since all was out, why not go back to what was in the car. You must also remove the locator tabs from the newer 7-pin connector. Even though the pinout is the same for some reason the locators are different."


Cheers

 

Hi David

Many Thanks

Did this finally manage to solve the problem and is your braking system working ok now?

It hard to believe how difficult it is to find a replacement and they certainly know how to charge for it if you do!

You would think this part was common on lots of other Jags and so would be available off the shelf but that does not appear to be the case.

If I brake very slowly, then everything works ok but if you have to brake suddenly then it's 50/50 whether it pulls to the left or not, which is a gamble I don't want to take.

A friend of mine had got the self same problem but he gave up and sold his Jag for spares, which is something I don't want to do.

Please update me if this has finally fixed it, although it looks like it has?

The problem started when I changed the front brake pads and didn't think to clamp the front brake hoses.

Which I have never had to do on any other Car I've had before and afterwards the brakes went on the blink, so pushing brake fluid back up the lines may have messed up one of the valves.

Thanks for your help and glad I found your post.

 

The replacement valve block will be here tomorrow, so I'll work to install it in the next week or so. I'm procuring new o-rings as well to mate it to the master cylinder. I'll let you know how it turns out. I'm confident this will resolve the issue. I'm also going to create a work document to summarize what I went through, how I troubleshot this, and what to do to fix it when I'm done. If I had a doc like that to start with, it would have saved me a lot of time.
I'll put it together with pictures and procedures.

Do NOT give up on your brakes. You have a stuck valve solenoid. The XJ-S is too profound to give up on it. I find this part of the 'fun' of having and restoring a fine automobile such as this. Learning the details of each system is a privilege to me. Hang in there. There are options, such as using an XJ6 assembly or just scale back and ditch the ABS altogether. The off-the-shelf rebuild kits are out there, but are expensive.
I'm also going to take my old one apart to see if it is possible to rebuild.
It is very dangerous to drive with one front brake out, so please be careful, if not garaging it until you fix it.

 

This is all interesting. Is there any chance you have replaced the rubber brake lines? I know it sounds crazy, but with bleeding, there is no resistance, and fluid passes easily. With resistance, i.e. normal operation, a old line can become so soft on the inside, that the rubber actually "wads" up(?) not allowing the fluid to properly apply pressure on and/or off. I have had brake problems on two different Jags that both wound up being the rubber brake lines. The XJS I recently purchased, I replaced all the calipers, all the hoses (ALL even the one under the hood from ABS pump to rear brake line), and flushed liberally. I take great interest in these types of threads, as I know these cars are going to become harder to maintain due to availability of parts (it would seem)

 

First, consider the brake hose.

The lining may have deteriorated to the point where it can act as a one way valve or is completely blocked. Also look for kinks introduced in prior work.

 

Hi David

You are a real 'Trouper' of the highest order!

It would be amazing if you could put that 'document' together including pics, because I know that it would help a lot of people including myself and maybe even save a life or two!

It would also be a great help, if you would explain the process in ABC style non Tech speak, as I've often found that 'so called experts' assume that people know a lot more than they actually do!

Don't worry I'm not giving up on my XJS though sometimes the problems of ownership drive you to distraction, where if it can go wrong it often does.

In stark contrast to my Merc, that just keeps on trucking, with very few problems encountered in the 8 years that I've owned her, apart from the ignition switch which was an absolute nightmare to replace!

I absolutely love my XJS V12 to bits, as there seem to be very few sporting cars on the road in the UK except for the MX5 which isn't what I would call a real head turner.

To me the XJS is a piece of iconic sculpture on wheels and when its running and on the road, nothing around can touch it for looks or road presence, and not to mention this is a Car that can 'snap knicker elastic'

Cheers

Ajay

 

Thanks for the ideas gentlemen. The brake hoses were replaced when I replaced the calipers. The issue was exactly the same before and after the replacements. After the car sits for a day, the valve spring pulls it back into place and the brakes will function normally for a mile or so if I use the brakes gently. I can deliberately lock the valve up now by engaging the abs system. I was able to bleed the brakes with no issues. Clean fluid comes out of all four bleed valves at the calipers. Only when the valve is locked closed will no fluid come out, until the valve opens again.


Looks like I'll have the replacement valve block tomorrow and I am hoping to get it installed in the next week. Of course, I'll measure the valve resistance before installing it. I'll definitely let you know how it turns out.
Thanks again for the ideas!

 

Snap knicker elastic. I may have to borrow that one

 

Hi Flint

(Next to the 'e' Type It's The 'Greatest Crumpet Catcher Known To Man'!

So what else were you expecting me to say!

It has the same effect on girls as a girl in a mini skirt does on guys!

In any event it makes you better looking! so you are Welcome to borrow my quote.

 

Checking back in.
I've received the new/used valve block, removed and disassembled my old one, and am going to open the new one to verify the valve screens are clean before installing it. I've measured the valve resistance on the new one and it checks out. In valves measure 6 ohms, out valves measure 3.5 ohms. All 'click' when 12V is applied to the pins.
To my surprise, I found a missing or dissolved square edge o-ring that goes between the valve block and master cylinder. There should be 4, there were only 3!
Here are a few pics of what I have.

 

Hi David

That is interesting! please keep coming with more pics and info, as you certainly seem to know what you are doing.

To me it's 'Rocket Science' at the moment!

 

This weekend I'll begin assembling the system. I cleaned the fluid reservoir this week with hot water, soap and a bunch of small steel nuts I threw in to shake around. It worked very well. I dried it in the hot dry windy air we had over the week. It is squeaky clean now. No moisture. I've received new o rings made of EPDM material. That is the best for systems with brake fluid. I also have the new abs gasket/o-ring rebuild kit I bought online for about $30. I got a few liters of DOT 4 brake fluid and looks like I'm ready.
The only thing left to check are the little screens in the new valve block solenoids before I assemble it to the MC. Can't have gunk in there and go through the entire job to find that out.


So:
New brake hoses, new calipers on the front, new/used valve block, all new fluid, new ceramic pads all around.


Wish me luck.

 

Some additional information to pass along: After opening up my old valve block, I found some cracks in the flex circuit to the valves that control the RF caliper. I'm going to post several pictures including the solenoid that was not working. I removed it and the flex circuit was so brittle, it snapped off. Assuming the 'new/used' block has the same 25 year old flex circuit, I removed the entire flex circuit, created a schematic of the wiring of the flex circuit and then hand soldered new wires in place of the old flex. I then measured resistance at the 7-pin header to verify the soldering job and schematic. I also connected 12V to pins 1-6 with gnd on pin 7 and verified each solenoid activated.
Currently cleaning out the engine compartment under the MC, going to touch up paint and then reinstall everything.

 

So I guess the obvious question is was that broken flex-circuit the root cause of the failure?

Marty......................

 

That broken flex was on the solenoid that controls the RF caliper, so I'm pretty certain the intermittent voltage on that puppy burned it out. It was sticking open prohibiting brake fluid and pressure from being applied to the RF caliper. Under normal conditions, that is what it is supposed to do very quickly for the front and rear wheels. I know it was stuck open. Why? I can only assume from what you can see in the images.
I am sure the old cracked flex didn't help the situation.
I can't believe they only designed the parts to last 25 years. That beauty is just entering her prime...