Lost Brakes! Where to start?

[Jared]

Hi JEC,
I decided to take the old gasser out for a drive today, '88 V12.
The first thing I noticed was there was not much resistance when I depressed the brake pedal so we didn't go for a drive. I can press the pedal all the way to floor (this is with the engine switched on.)
The brakes were rebuilt last year, new rear calipers, discs etc and worked fine.
I've looked under the car and cannot see any fluid leaks and the reservoir level is between max and min.
I can't see any leaks under the bonnet either.
I last drove the car in January and felt that there was more travel in the brake pedal than before.
My car has the ABS accumulator fitted.
Do I bleed the brakes (I've found the "how to" on this forum) or has some other component expired?
Any help or suggestions please

[Brakebuster]

i would start by looking at the pump in the engine bay

it has its own fuse

you should be able to press the brake pedal about ten times and it should go hard

then turn on the ignition, if you don't hear the ABS pump running,then that would be a good place to start

BB

[davidr]

You mentioned that your pedal goes right to the floor which suggests a few possibilities. Firstly, you could have air in the system. Were they bled properly after the recent work?
Secondly, you may have a leak in the system somewhere so that when you push the pedal down the fluid takes the path of least resistance out of the leak.
Another possibility is that the seals in your master cylinder are shot so fluid gets past them instead of pressurising the brake lines.
If you're at all unsure I would suggest that you get them looked at by a professional. I would further suggest a Jaguar specialist because your brakes (having the Teves ABS system) are not the same as most other cars and have a special bleeding procedure. The uninitiated can easily burn out your pump and they are expensive to replace!
Hope that helps
David

[Jared]

Hi,
Thanks for the replies.
I can hear the pump when I turn the ignition on.
I'm presuming the system was bleed properly because the brakes worked fine last year and the mechanics knew what they were doing.
There is no fluid on my garage floor so no obvious leaks but I guess that's not conclusive.
So, bleed the brakes and if that doesn't work a recon kit for the master cylinder may be the way forward.

[ptjs1]

Jared,

If you know there are no leaks, and the pump runs then cuts out when reaching pressure, I would suggest that you start by bleeding the brakes.

I know it's been said before but these brakes are NOT typical of other cars. Are you really sure that your mechanics know how to bleed a Teves XJS braking system? It's really not the same procedure as other cars. Also, there's a difference between bleeding the Low Pressure side and bleeding the High pressure side. You HAVE to do the LP side first is there's any likelihood of air on that side. Unless they are Jaguar specialists, I would be extremely surprised if your mechanics bled the LP side of the system.

Spend some time reading through the brake section of the workshop manual. It's very complicated but you'll understand the system so much better. Then ignore the Jaguar procedure of bleeding the rear brakes and do it the Teves-described way. Then once you've bled from the wheels, do it again! After all of that, see where you are and report back.

Good luck

Paul

[Jared]

So I finally got my XJS trailered to a specialist. It appears I need a new ABS brake master cylinder actuator, part no. JLM1475. There does not seem to be any easy way of dismantling this or a repair kit available from the usual sources.
Does anyone have a decent one for sale?
Thanks

[ptjs1]

Jared,

Without wishing to criticise your specialist (is it a Jaguar specialist?), have they explained exactly what is the problem? Which part of the actuation unit do they feel is at at fault and how have they diagnosed that? Of all the problems that we're starting to see with the Teves ABS system, failure of the actuation unit seems to be unusual (although it's possible). The difficulty is that there are a number of reasons why you can get a soft pedal that are not the result of a failed actuation unit. The most common after undertaking a brake rebuild is still having air in the system, particularly on the Low Pressure side. This is often misunderstood by even quite knowledgeable people. The second (and increasingly common) cause is failure of a valve within the ABS valve block. Although this is bolted to the actuation unit, it's a separate component.

As the actuation unit is NLA and by far the most expensive component (£1000 when new!), I would still start by checking correct operation of pump and accumulator. Then go back to bleeding the LP side. Then properly bleed the wheel circuits (using the Teves rather than Jaguar procedure for the rear circuits).

Good luck

Paul

[PaulGover]

Having had a problem with my V12's Teves brakes, I can confirm that there's likely to be air in the rear brake system. I got through about 3 litres of fluid bleeding mine, following both the Jaguar workshop manual and the "special" Teves instructions; as far as I can tell, they are about equally (in)effective.

FWIW, I got a guaranteed replacement valve block (and associated pedal) from one of the modern breakers yards for about £300.

FWLIW, I did manage to find a part number for a valve block overhaul kit, possibly in the depths of the Jaguar Classic web site. (No, I don't recall it.) No idea what it included, and whether it's possible for an amateur to use it, though AFAIR other bits of Tevery I've had came with very good instructions. I took my old one apart to see what was involved; there were some very delicate-looking valves made out of some transparent plastic, if I remember correctly. I suspect overhauling it really would need a clean room - one of the manuals refers to one of the bits inside needing something (clearance?) of about 1/10 of a thou.

I asked my long-established local Jaguar agents if anyone there could offer any advice; they said they were sure no-one there had ever taken a Teves system apart or done anything beyond the routine maintenance.

[poprivet]

First off, with keys out, operate the brake pedal 20 times. The pedal should go hard, if it is still soft this confirms a problem. The brake pedal can feel strange on the Teeves cars when pressurised.

If the pedal is soft, as the problem has only been since the overhaul of the rear brakes that is likely where the problem lies. As others have noted, possibly air in the system, the Teeves fluid reservoir has twin compartments and its easy to look at the level on one and not realise the other is very low when bleeding the brakes. I would also be measuring the run out of those rear discs.

The manual has a detailed section on Teeves brakes and the associated problems, well worth getting.

[PaulE]

Are all XJS's fitted with the Teves system or only certain years? Can anyone tell me the details please.

[davidr]

PaulE - the Teves system came in with the introduction of ABS around 1987/8 and continued through the facelift until about 1994/5 when the more conventional vacuum servo system from the X300 saloon was adopted. For example my 1989 V12 has the Teves system but my 1996 Celebration has the newer system.
I can't remember the exact dates but I'll look them up later.

[ptjs1]

Paul,

In order to avoid derailing Jared's thread, I'll drop you a PM with the VIN of start & finish of Teves Mk 2/3 before it moved to the Teves Mk 4 on the last XJSs.

Paul