Yesterday, I went to my grandfathers house to pick up the 1994 XJS 4.0 he has. About 2 years ago, the breaks suddenly didn’t work all that well, and since then it’s sat until yesterday, when I was going to pick it up and bring it to my shop to fix it.

2 years ago, when the brakes stopped working right, it would go all the way to the floor and have a little bit of stopping power at the bottom of the pedal travel. But yesterday, it had no brakes. I couldn’t even stop it when it was rolling down a 2 degree gradient, and the handbrake cable is broken so I couldn’t stop at all. The only way I can get it to stop is if I stomp on the pedal rapidly, and then the pedal briefly gets hard and it stops, but you have to slam it into park when you do that to come to a complete stop.

After that ordeal, I parked it back in the garage and that was that. I didn’t want to fly off the trailer or not being able to stop when it’s coming off the trailer.

As far as the problem goes, it doesn’t have a leak anywhere. The master cylinder is full of dark and nasty brake fluid, and there are no lights on the dash. I’m inclined to think that the master cylinder is at fault here, because I don’t think the master cylinder is pushing fluid to the calipers. I also wanted to ask people who have experienced this issue before as well, because I’ve seen some posts about this issue, but some of the fixes are the ABS Unit, some are the master cylinder, and some are the brake booster.

I really want to fix the brakes because I don’t think it’s even safe to get towed on a flatbed if it was dragged on and off. Let me know what y’all think!

 

pineapple_tree,

Sorry to hear of your problem.

First of all, if you have an XJS built or registered in 1994, you will have the early Teves system. This system is complicated and does not operate like a typical brake system. So, first of all, just confirm that your VIN is prior to 198335.

So, to clear up a few points. This Teves system does not have a separate Master Cylinder or a Brake Booster / Servo Unit. So it's best to avoid using those terms.

The system has an Actuation Unit, on the side of which is bolted an ABS Valve Block. The brake fluid reservoir is mounted on top of the Actuation Unit.
On the other side of the car is the brake pump, which feeds fluid to an Accumulator (the large black ball-type object. The pump's operation is limited by a Pressure Relief Valve.

Those are the major mechanical components of the Teves System. In general, the Actuation Unit doesn't fail. That's not a guarantee, but I've never seen a failed Actuation Unit. The problem nearly always lies somewhere else.

You mentioned that "the master cylinder is full of dark and nasty fluid". I assume from that you actually mean the plastic reservoir is full of dark and nasty fluid? If so, that's a concern as it sounds as if the fluid hasn't been changed every 2 years. The system really needs clean fluid all the time. The ABS valve block in particular must have no sediment in it.

If it I were my car, I would do 3 things first, in this order:

- Perform the Blink test to verify if there are any fault codes recorded in the system. If you don't know how to do this, report back and we'll explain how.
- Perform the 32 Continuity tests. Again if you don't have the workshop manual, post back and we'll explain.
- Then fully flush the brake fluid. If the fluid in the reservoir is as bad as you intimate, then I would syphon out as much of the fluid as possible, then carefully remove the reservoir and clean it. Once replaced and filled with clean fluid, flush the system. This is complex. You need to bleed the low-pressure side, then flush through to the wheel circuits. You must do this in a very specific manner. Again, if you don't have the manual, I can direct you here.

Once you've done all of the above, you can reassess the situation.

Cheers

Paul

 

Wow. I had no idea that the braking system in this Jag was as complex as it is. I thought it had a typical braking system, consisting of a master cylinder and a brake booster.

Anyway, yes, the fluid in that plastic container above the Actuation unit is tar-like. All this car has done for the past 10 years is sit, only driven once a year to get a state inspection, so it doesn’t surprise me that the brake fluid is as bad as it is.

Regarding the “blink test”, I’m guessing it would involve flipping the key in a specific pattern and watching the ABS blink and then compare the blinks to a chart for ABS codes. I’m not sure how efficient that would be, because I just replaced the battery since it was completely dead. Maybe it stored something when it was running, no idea. I would like to know how to do that test though.

As far as the 32 continuity test goes, I have no idea how to do that. I would love for you to enlighten me.

And regarding flushing the system, I’m guessing it’s not like a typical brake fluid flush, where you suck the fluid out of the container, fill it with new fluid, crack the brake bleeders open, (rear right, rear left, front left, front right), and keep topping the fluid off. If that’s not the way you bleed this system, please tell me how to properly do it.

Also, thank you for that incredibly detailed response. I’ll do some homework on how the brake system works in this Jag, that way I have a better chance at fixing it, rather than just throwing parts at it

 

pineapple_tree,

Drop me a PM with your email address. I'll send you:

- Details on the Blink Test - It doesn't use the key, you bridge terminals on the ABS control unit
- Details on the 32 continuity tests
- The bleeding routines
- A doc that explains how the Teves system works

Cheers

Paul

 

I just wanted to give an update here, as I have finally fixed the brakes!

My grandpa ended up having it towed to my shop, so I had all of my tools and all of the expertise of everyone at the shop.

First off, it’s not a 1994. While it was built in 12/94, the VIN is registered as a 1995, and it does not have the TEVES system. It has a master cylinder attached to the booster, and the ABS module on the passenger side.

Regardless, a very long story cut short, there was a piece of debris stuck in the metal hard line to the front left caliper. I cleaned that line out, and flushed the system with a pressurized brake bleeder, and now the fluid is crystal clear and the brakes are back to factory!