Hello all,

It's that time of year again. After the pinging magically sorting itself out (the arcing not being the issue) and the temp gauge miraculously started working properly, I was all ready to start enjoying my '91 XJ-S a bit before I sell it. However, the other day, thankfully at very low speed, the brakes suddenly failed on me. All was normal until then, though it was a long day of hours of bumper to bumper traffic. Finally, when I went to put my foot on the brake, all was good for half a second; the pedal was its usual firmness for a moment. Then, halfway through the pedal's travel, it just gave way, with only the slightest pressure at just above floor height. I managed to get off the highway, gradually losing any braking in the process and modulating the park brake and switching from drive to neutral repeatedly. When I stopped, I tried pumping the brakes to see if pressure could be built. After many pumps, pressure could be built, but pressing the pedal would cause it to slowly lose pressure and return to the floor. Not pressing the pedal again after pumping would cause it to also slowly lose pressure, until nothing happened again. The strange things are that:

1. The reservoir is well above max, concerningly so. I don't think it was anywhere this high before the incident.
2. There is no visible fluid loss. I checked under the car right when I stopped and when pumping the brakes. Not a drop at the master, booster, or anywhere under the car.
3. The pedal seems to hold pressure better when the pump is off. Turning the ignition on and running the pump causes air to audibly be pumped into the system, like the sound of a power steering system low on fluid when one tries to turn the wheel. This causes the pressure from pumping the pedal to disappear and prevent pumping to build pressure
4. The fluid in the top of the reservoir appears to be a different color, almost like water, from the rest of the fluid inside. Further, pumping the pedal with the cap off causes the fluid in at the top to become similar to "forbidden milkshake blown head gasket special" oil-water mixture, though not as frothy or thick

To make clear, yes, this car has Teves ABS. As always, advice on the matter would be appreciated. I may try bleeding the brakes on Monday, but it will be hard with no helper.

 

JChandler,

I'd suggest that there are only a few things that can cause the pedal to sink to the floor on a Teves II system:

- A leak somewhere in the brake lines / calipers. From what you've said, that sounds like it isn't the case. And eventually, you'd see a significant reduction in the reservoir fluid level.
- A failing of the seals in the Actuation Unit. (You don't really have a separate "Master Cylinder"). That is possible but, in my limited experience, very unlikely. I've never seen one fail, and have only heard of one person who has rebuilt an Actuation Unit.
- Air in the system somewhere. Possible, but difficult to see how that would suddenly happen in the middle of the press of a pedal.
- Water absorption / contamination in the brake fluid. This is possible and, potentially coupled with the next item. could be the cause of the problem.
- A failing of the operation of the valves in the ABS valve block. That could happen allowing one circuit of the brakes to allow pressure of the pedal to recycle fluid back and not send it to the wheel. If that happened, it would technically mean that the wheel on that failed circuit was not getting brake fluid pressure so you'd possibly notice the car diving to the opposite side, but not necessarily (if it was on the back wheel circuits).

At first thought, the last one feels the most likely, especially as we know of two reasons why those valve blocks can fail. Those are:

- sediment in the valve block getting under the seat of the valves and holding them opened when they should be closed
- deterioration of the ribbon cable that actuates the valves open and closed.

The description of fluid backing into the reservoir and also potentially having water contamination might also reinforce that the problem lies in the valve block

What would I do next? I'd start by running the blink test to ascertain if you have any fault codes which may indicate where lies the problem.

You might also want to do a full and careful flush of all the brake fluid. But you must do it the correct way and know exactly how to bleed the rear brakes in the correct Teves, not Jaguar, procedure.

Cheers

Paul

 

My guess would be you have a seized caliper piston. Pad is jammed against the rotor causing heat buildup which leads to the fluid boiling. Forces fluid back through the system causing your increase in fluid level and no brakes. Same thing happened to me a few years back. Pulled calipers off, cleaned the pistons and bores, put in new seals and flushed the system with fresh fluid

 

Good thought, Stuart.

Definitely a possibility. If so, when everything fully cools down and the car turned off and static, the pedal should return to its normal firmness.

Does that happen?

Paul

 

I suggest that you search through this forum. I recently had the same total brake failure and had to take similar actions to get home safely (1990 XJS convertible). In fact I printed out pages and pages of different comments, including blink testing, pump timing, and extensive descriptions of taking the valve body apart and cleaning the solenoids. There were also discussions about the accumulator and other vehicles that use the Teves III system (Buick Reatta for one) with a GM part number that works on the XJS. Frankly I believe that the Teves III system is too smart by half. The very fact that one can experience total brake failure due to a bad accumulator or a failed pump or gunk in the solenoids should have been sufficient to not have this system. The split systems that most cars use that protects against total brake failure (unless the master cylinder completely fails), provides much lower risk.

Enough of the rant about Teves III. Do the search and it may go back 10 years or more but we are not alone in having this problem.