A car I am looking at has a red brake dash warning light that flickers on occasionally.
The ABS system for the vehicle has been disconnected historically, but brakes work fine without it. The car is very well sorted and I am not concerned about lack of ABS provided it meets safety certification requirements (seems that cars weighing <2,000lbs don't need ABS here in Ontario).
An experienced XJS mechanic diagnosed a new accumulator sphere required to fix the warning lamp issue for safety certification here in Ontario, as any brake warning light coming on is an immediate 'fail'.
I have read that the accumulator is ABS related, also that it is part of the servo-assist for the power brakes.
Can anyone please clarify what the accumulator actually does, as if it is primarily ABS related, then I am wondering if the ABS is disconnected then why is the red dash light coming on?

Thanks in advance!

 

Mozambique,

I'm not sure what has been to "disconnect the ABS" but if the accumulator sphere has failed, the car would be virtually undriveable as the brake pedal would be so hard as to really worry you.

The accumulator effectively provides the storage of brake pressure to drive the boost for the brakes. As the rear brakes are fully activated by the accumulated pressure, not the brake pedal, then the pedal would be almost rock hard when there is no boost pressure available to the system.

We can talk you through the Teves ABS system, which is very complicated, but it would be really helpful to know exactly what state it is in? Do you know what has been done? Have the ABS ecu plug been disconnected, fuses removed etc etc?

Paul

 

Paul,
Thanks for getting back to me.
Not sure what was done to disconnect the ABS.
So your explanation matches the mechanic's opinion when he told me that if the accumulator totally fails then you will lose all power assist.
So replacing it will hopefully cure the occasional red brake dash warning light which is what the mechanic said.
If it can be certified in Ontario without ABS being operable even if fitted, I can't say it would bother me much.

 

I wouldn't change the sphere unless I really knew it had failed.
Without the rear brakes being driven by the accumulator pressure, I can't see how anyone would "certify" it. Here in the UK, if you had no pressure in a Teves ABS XJS, an MoT tester wouldn't pass it, as the car is effectively undriveable.

I would start by getting the the ABS "connected" and then there are a series of tests which will help to pinpoint the problem.

Paul

 

Hi Mozambique

Agree with everything Paul (ptjs) has said but if you haven't bought her yet, then I would consider walking away from this one!

A Shop could charge you a Fortune to Fix it and that could cost more than the Car!

And if you had an Accident and the ABS wasn't working, then you could get done for driving a Car that's not fit for the road and there is also every chance that your Insurance Company might decide to disown you in the event of a Claim

Though if you can give us more details as Paul (ptjs) has suggested, then we may be able to help you fix it

P.S. Don't go unscrewing the Black Accumulator Ball, unless you really know what you are doing, as the pressure inside it is about 2 BAR which is more than enough to take your head off your shoulders and punch a hole through the Bonnet/Hood

 

Gents:
Apologies, as my lack of info ain't helping you much.
The mechanic is very experienced with old jags and is confident changing out the accumulator sphere will fix the warning light issue.
Costs associated with doing this this are the owners responsibility.
In Ontario vehicles made before 2000 weighing less than 4,500kg do not need a functioning ABS, even if fitted. Straight from the safety certification handbook.
The mechanic is responsible for certifying the car, so will listen on what he has to say after the replacement accumulator has been fitted.

Help appreciated!!

 

Mozambique,

Let us know what unit he fits, whether he can source the original part or if he has to purchase an equivalent.

Ask him (politely!) if he knows that he should bleed the low-pressure side of the system before the wheel circuits, and whether he knows the exact Teves (not Jaguar) procedure for bleeding the rear circuits

Good luck

Paul

 

Paul,
thanks!
Current plan is the owner has obtained two used spheres from a contact who has several scrapped jags. So the mechanic will be fitting one of those.
I have no direct contact with the mechanic, but he does seem very knowledgeable which inspires confidence. The brakes with ABS disconnected work fine. The goal is to eradicate the intermittant warning light.

 

Sounds encouraging. But if the accumulator has failed completely, the brakes will NOT function fine! I can guarantee that!

So I don't really know what they mean by the "ABS us disconnected" but that sphere is working to some degree or the brake pedal would be rock hard. Trustt me!

Paul

 

Paul,
when the mechanic saw the intermittant brake warning light his immediate response was the accumulator needs replacing as he has seen this before. Brakes fine at present with full servo assist.
Fingers crossed.......

 

Hi Mozambique

The Front and Rear Brakes are on Separate Circuits

The Front Brakes are Conventional and are Bled in the Conventional way

But the Rear Brakes need to be Bled by a different method with the Ignition on

So just wondering if you only have the Front Brakes working at the moment which was done by Jaguar to give you some Braking in the event of Brake Failure

Paul (ptjs) can elaborate on this as he is the expert here

 

Hi,
Thanks for getting back to me.
I drove the car a few weeks back and the brakes felt fine. As part of the safety test, they would also be checked by the mechanic, so at the moment, my assumption is that front and back are working.
Should learn more next week.

 

So what would happen if the actual ABS box is electrically disconnected? What I mean is disable the solenoids that open and close when needed to prevent blocking of the wheels, if the pressure sphere is working properly the brakes will work just with out ABS, correct?

 

Well that seems to be the case. I admit that the ins and outs of ABS systems and their integration into the regular braking system is not something I have ever looked into per se, let alone on vintage ABS systems.
I will try and determine exactly what was disconnected. Bottom line is that the brakes work fine with the ABS disabled.

 

Hi alpecsa

I had to do exactly that to get me home when I had ABS Failure as when I went to hit the Brakes, there was a sudden pull to the right that very nearly spun me off the road

I was quoted Mega Bucks to fix it and we are talking of around £500! (UK)

Though since I won't let any Shop anywhere near my Car, as I work on the principal that if they can fix it so can I (only better and cheaper!)

I Rewired the Master Cylinder Actuator for about £25 (although I got a Radio Shop) to do the Actual Soldering as that needs to be perfect, so I let the Experts do that bit, as you can't take chances with the Brakes

And when I fitted my Car with a Brand New Accumulator Ball, I didn't use a Jaguar one but instead I got one made by WABCO that I got from Island 4X4 for only £150 Brand New!

 

Hi Guys

Sorry I forgot to mention a couple of maybe useful things to know

If the ABS Light Comes on for no apparent reason, one of the first things to check is the Fuse that powers it, which on a UK Car is inside the Fuse Box that is behind the drop down panel of the Passenger Knee bolster panel, where you will see a couple of Fuses that are grouped together on their own (from what I can remember I think they are green) One of these is for the Brake Pump and the other for the ABS

As far as the Dash Lights are concerned if the Yellow ABS Light comes on, then the ABS may not be working as it should

But if the RED BRAKE LIGHT Comes on, or even starts to Flicker, then that indicates a far more Serious Problem and I for one would not be wanting to be driving the Car until the cause of this has been found and fixed

Also big Shout out to 'Brake Buster' for saving me a Fortune on the Cost of a Replacement Accumulator Ball by finding a Generic one from Island 4X4 that was about half the price of OEM but I can't remember the Number of the Ball you need, Robbo might know as I think he also fitted one as well

The dimensions of this were exactly the Same as the OEM (except of course for the bargain price tag!)

Although in a moment of some might say Madness, I opted to go for the next size up to hopefully give me greater braking Capacity (ie more pumps on the pedal) which was a little bit Overkill and not really needed

But pleased to say it worked out well, even though it only just fitted underneath the Sway Bar with virtually Zero in the way of Clearance! and was only a few dollars more

So you pays your money and takes your chance on that one

 

During my 30 min test drive there was an occasional red flickering light on dash. Was not sure which one, and did not pursue further as I was planning on pre-purchase inspection in any case. Yelliw ABS has not come on. My experience with contemporary brake warning lights is that they indicate pads are getting thin. Seems more reasons for coming on with an XJS. good tip about the aftermarket accumulator sphere. Approx how much did it cost?

 

Mozambique,

It's not the pads as XJSs don't use sensor pads.

As mentioned, it needs the blink codes read, which is a fairly simple task if the mechanic kniws how to do it and should be the first thing he does.. Im a great believer in properly diagnosing the problem befire changing any exoensive parts!

Cheers

Paul

 

Hi Mozambique

The Generic Accumulator Ball was about £150 though might be a bit more now

If your buying this Car from a Garage, I would want everything working, including the ABS or if not I would walk away, as if you can't or do not want to work on her yourself, She could cost you a fortune in the long run and if you ever wanted to sell her, then any potential purchaser would also want everything working, especially the Brakes!

There's always another XJS and it always sometimes never pays to buy the first one you see

 

thanks Paul,
Will wait to see the outcome next week and will casually mention some of the points you have kindly raised if brake light still an issue.