Hi, I'm hoping i could get some assistance with this persistent brake problem I have.
My 1994 XJS 6.0 lt has a issue where I can pull up at the lights with my foot just holding on the brake and after a short time the ABS light comes on them the red warning light beside it and 5 sec after that the ABS will come on and the peddle vibrates. it doesn't do this every time however.
It will also do the same thing sometimes if i have my foot on the brake when i first start the car.

Any help would be much appreciated.

John

 

Hi Johnosjag

Check to see if the Front Calipers are Sticking

If not you may need to Bleed the Brakes by using the Method perfected by Paul (ptjs)

Could you also Clarify if your Car is a 6.0 Litre or a 4.0 in line 6 cylinder and does your Teves Brake System have a Square Brake Reservoir or a Triangular Reservoir

 

Hi John,

That's a very confusing symptom!

Further to OB's reply, you'll have the Teves ABS system with the square reservoir. However, your description of the symptom is very strange!

IN THEORY, the ABS can't operate with the vehicle at rest. The signal to the ecu and thence to the valve block is triggered by a sensing of one of the ABS rotors having locked whilst the others are rotating. That obviously isn't happening, which implies a faulty signal?

At the risk of questioning your diagnosis, is it possible that the vibration you are hearing / feeling is not really the ABS pulsing but the pump running?

If I were you, I would try the following:

- Turn off ignition
- Press brake repeatedly (30+ times until pedal has gone very hard)
.- Turn on igniiton
- Time how long the pump runs before it cuts out and brake lights go out (expected 25 - 60 secs)

That's a very basic way of doing a test on the pump, accumulator and pressure switch. Not infallible, but a reasonable start.

If that's successful:

- Run the Blink code test on the stored DTCs (Failure codes) and see what manifests.
- Run the 32 diagnostic tests

Let us know if you need any more info.

Good luck

Paul

 

Hi guys and thanks for the information,
Some time ago I was away working interstate and I sent the car to a shop and they replaced the pump and accumulator trying to fix this issue. No different.
I will do a full bleed of the brakes on the weekend just to make sure its right.
I did a code check and got code 21 and that was after having a disconnected battery.
What vale is that they refer to.? They list a few possibility's in the checking procedures, is there some this common?

 

John,

A couple of thoughts:

I'm not sure why a shop would change a pump and accumulator without verifying if they were at fault? That's a very expensive way of attempting a fix, particularly as there are simple tests which would have verified if there was anything wrong with them? Are they Jaguar specialists that really understand the Teves ABS system?

- A DTC 21 is symptomatic of Main valve failure (a component part of the actuator that is linked to the piston assemblies. During ABS operation the Main valve allows boosted pressure to the front brakes but also pushes back against the positioning sleeve which then causes push-back on the pedal. However, a Main Valve error also causes the ABS to disengage and the ABS MIL to illuminate.

I'd suggest an initial bleed of the system would be a good idea, especially as the pump and accumulator have been disturbed. You MUST bleed the low-pressure side first. (The shop really should have done this after changing the pump and accumulator.) Otherwise you have a risk of never getting air out of the system. After that, bleed the rear wheel circuits (the proper Teves way), then the front circuits. Then I'd run the blink test, note any codes and clear down the DTC 21 (or any other code still in the system). Once all DTCs are clear, I'd run the diag tests, if you can do that.

Cheers

Paul

 

Good afternoon,
Bleed the brakes today as per the instructions posted previously on the forum, I found an unusual condition that I'm unsure is normal or not., when bleeding the back it pumped a lot of fluid through both on the left and right rear.
When I did the front I got no pump pressure despite the pump running, more like a normal brake bleed.
Is this normal or should I have seen the same as the rear.

 

John,

If you've bled them exactly as per the Teves routine that I've posted previously, that's not unexpected. Under normal ignition-controlled condition, the rears are activated by the pedal, but not pressured by the pedal; they are pumped directly via the accumulator pressure. The front fluid displacement is determined by pedal stroke.

At the risk of sounding like a stuck record, did you bleed the low-pressure side of the system before you did the wheel circuits? You must do this if there has been a break in the reservoir - pump- accumulator circuits. As you've had a new pump and accumulator, this needs to be done first.

Cheers

Paul

 

Hi Paul,
Thanks for your time on this , It sounds like what I'm getting is normal then.
I didn't do the low side. Sounds like I need to start again. where do I bleed the low side? I will do this tomorrow.
John

 

John,

The low side is an easy one-man job to do, you just have to be a bit careful to use a container to catch the fluid as it flows. It basically involves ensuring the reservoir is topped up, then removing a pipe that runs from the reservoir across the engine bay and attaches to the pump via an elbow pipe. You then let fluid flow until there's no bubbles then reconnect the pipe whilst the fluid is flowing. It's not difficult, just be careful not to break the clip and be careful where the fluid flows.

It's necessary, because if you can't remove the air in this pipe, it will leave an air-pocket in the system prior to being pumped to the wheel circuits and you'll never get the system air-free.

Alex (orangeblossom) wrote a helpful post with pics on doing the job and I'll dig it out and post back.

Cheers

Paul

 

John,

Alex's thread here:

Cherry Blossom - Restoration 1990 XJS V12 - Page 19 - Jaguar Forums - Jaguar Enthusiasts Forum

Scroll down the page and you'll see the post and pics!

Cheers

Paul

PS I know it's a pain, but then go back and do the wheel circuits again.

 

Hi Paul,
Finally got back to looking at the brake issue on the XJS, carried out the bleed doing the low side first as you suggested. The fluid trickled out and i didn't notice any air bubbles and the problem is still present.
In one of the first replies OB mentioned are the calipers sticking. i checked this while it was on the hoist and both the front are very tight, the issue doesn't release when the bleeder nipple is cracked so i thinking the calipers need overhauling.
Can this cause the problem I'm having?

John

 

Hi Johnosjag

That certainly sounds like the problem right there

As Sticking Brake Pads can and do cause all sorts of problems, as the Brake Pads need to slide easy in or out of the Calipers just using a finger and thumb

So whenever I fit New Brake Pads, I always Skim a little bit off each side of the Backing Plate just as a matter of course, either using a grinding wheel or preferably a Flap Disc in a Grinder, until I get what I consider to be the perfect fit, not too loose and definitely not too tight

Here is how I do it including lots of Photos

Skimming the Brake Backing Pads for The Perfect Fit 'A nice easy job'

As you also mentioned you Calipers may need rebuilding, which is also easy once you get 'The Knack' and very Satisfying to know that you've just saved a 'Shed Load' of Money over what a Shop would Charge and here is how I did mine, including lots of Photos as a Step by Step Guide

How to rebuild the Calipers on an XJS V12

There is no point in Bleeding anything until you have the Brake Pads and Calipers sorted out, or you will be for ever just going round in Circles and getting nowhere

Hope this helps

Alex (OB)

 

John,

Further to OB's thoughts and suggestions on the pads binding and caliper overhaul , DO NOT push back the pads and caliper pistons without slackening the caliper bleed nipple and attaching a pipe to allow the fluid to escape. You MUST NOT allow fluid to get pushed back up the lines to the ABS valve block on an ageing Teves system. This is really important. I would suggest also carefully clamping the flexipipe to also try and control this.

Good luck

Paul

 

I don't want to hijack this thread, but what is the method for clearing the codes Paul? Is it driving the car over 30mph? Thanks

 

Hi Paul,
Finally got the parts and time to get back to sorting out this issue. overhauled front and rear calipers, new pistons seals and pads. the front calipers were in bad shape.
Most of the pistons were seized in and it took a bit to get them out. All done and bled now. Undid the small elbow and bled the low pressure side. first.
Issue is the problem is still there.
The issue again is i apply the brake peddle and after 10 sec or so the red warning light comes on then 10 sec after that the ABS light comes on. Around 20 sec after that the ABS fires and the peddle goes hard and vibrates. Is like ABS operation, reduced braking efficiency when it happens.
I was checking the accumulator and pumped the peddle till it was hard and when i started the car with my foot on the brake the same scenario with the vibrating peddle and ABS was present straight away.
John

 

It sounds to me like your acutator is kaput. I have a feeling you are in the UK which is too bad. I happen to have a good (LHD) ABS actuator from a running/driving 94 XJS V12 here, but they are not the same as RHD....

Question- have you replaced your accumulator- is it fresh/new???


XJSC-Guy

 

Hi, Yes accumulator has been done several times, interestingly i drove the car a little yesterday and the problem didn't occur at all on that run, usually it would have.
Im going to take it for a long drive and see how it goes.