ABS Brakes Daimler DD6 MY 1991 (XJ12 Serie III)

My car is a Daimler DD6 MY1991 (same as XJ12 Serie III) with ABS brakes. Since I got this car I always feel brakes are harder than in my XJS He MY1987 or in my XJ6 MY1978. As I have plenty of free time now I would like to check all this ABS brakes system. Unfortunatlly the DVD JHM1122 (XJ12 Series III parts and Service Manuals 1979-1992) bought some years ago to JDHT doesn’t give informations about ABS brakes!
I spent several hours to search within all the Services Bulletins, on the web without finding one document or wiring diagram showing this particular brakes system.
This Serie III brake system is different from XJS and XJ40 as I got brake vacuum booster and electric pump with valves.
Who can give/send me some information??
regards, Daniel

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‘…feel brakes are harder than…’, Daniel; do you mean much higher pedal pressure is required for the same brake effect - or more ‘grabby’, or what…?

The ABS set-up is too complicated for thorough description in Jaguar workshop manual, DIY not encouraged. Though it should give a general description of function - and rough function testing should be the same for all ABS systems…?

Frank
xj6 85 Sov Europe (UK/NZ)
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Hi Frank
When I drive my DD6 I “think or feel” that I need to put higher pressure on brake pedal than on my XJS (1987) or my old XJ6 (1978). Both of them have no ABS.
When I read the XJS workshop manual the ABS brake section is not so complicated but on my DD6 it’s not the same arrangment.
I’m still checking all the Technical Service Bulletins I got maybe somewhere I will find something :slight_smile:
Daniel

Welcome Daniel,

the force required on the brake pedal is determined by the brake booster. Frankly, so far I’ve only heard of total failures of brake boosters resulting in “heavy braking”, but that sort of “heavy” that most of us would be lucky not to wet their pants when encountering this frightening experience for the first time. From the way you describe the problem it seems your booster is working correctly.

So, all I can see is a change of respectively a wrong booster fitted at some point during the last 30 years. From the distance I would guess that an ABS car would be fitted with a stronger power assist than a non-ABS car. So maybe your XJ has the wrong booster? Can you provoke the ABS pulsating on any surface and at higher speeds (+50 mph)? If you’re located in the US - you might wish to add indications on the specifications of your car and your location either to your signature line or your profile - it should be JLM10735 while non-ABS 12 cylinder SIII cars use CAC1227.

Another thing that springs to mind: your rear brakes might not do any braking work any more, due to oil from the diff on the rotors or due to seized calipers - many babied powerful sedans tend to the latter defect.

Finally, your brake pads might be too hard or glazed and not have sufficient friction any more requiring higher pressure.

Start with the cheap and simple things like checking the correct boosters, oil at the rear rotors and front brake pads, then move to the expensive things.

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)

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Look up ABS, Daniel; Wikipedia has a general description off history and variants - which may indicate what variation you have…?

Testing is as per Jochen, and might prove something - but there should be a warning lamp showing if the system is not working.

The pump is required for rapidly restoring pressure when the system is activated near lock-up - the booster may be a fall-back if the ABS/pump fails. Or may be used when hefty braking is not required - and may therefor be ‘weaker’ than the ordinary set-up? Making the characteristic of the braking different - which is likely anyway between ABS and non-ABS systems?

Different, and harder pads, may be used with ABS - altering braking characteristics. And as Jochen also says; pad contamination or other factors irrelevant to the ABS, may be involved - and his suggestion of testing the system with heavy braking is certainly relevant. Indeed; without braking assist, ABS or otherwise - superhuman efforts is required for any braking effect…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
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Hmmm. Sounds like a Teves IV system, which didn’t make it into the XJS until 1994 or 1995 I believe. If so, good system – as opposed to the Teves III which was dangerous junk that IMHO should have been recalled.

If you can, post a photo of the pump and/or valves. Perhaps someone here can identify it.

Would it be possible that the booster is smaller or the vacuum hose to it has collapsed?
One would think that the ABS wouldn’t restrict normal brake effort. As the electric pump only turns on when the system activates, the brake booster will surely be the only boost in any situation but traction loss?
I’d ask any shop that knows a little about modern cars and ket them have a look if it is a) the usual system and b) if they have any idea if something is wrong… or another lucky person with two xjs to compare follows up.
Maybe run the tests Jochen put together. Also - is it easier to push with higher rpm - how long do you have boost when the engine is shut off…

Thanks for your help!!
Good idea to have a road test with hard braking. I will do it as soon as my car will be on the wheel. Now I am adjusting geometry and it’s not an eay task.

There is no oil on disks or pads I have done a IRS and IFS complete rebuild 6 years ago every things is still ok.

The car is a french spec as I live in France and my car seems to be one of the last Serie 3 sold in France.

Cover,Pumpe and Valves

Pump and valves

Booster

Fascinating. That brake fluid reservoir doesn’t look familiar to me at all.

Kirby,
That brake fluid reservoir (Jaguar part number CAC1223A or CAC3217) is commonly used in all the Series III XJ6s and XJ12s. Attached are two pictures of the one in my Canadian market 1990 V12 Vanden Plas with that reservoir circled in red. My car is essentually a Daimler Double Six badged as a Jaguar and very similar to the car being discussed except that the 1990 MY cars did not have ABS.

Paul

It is apparent, then, that the saloons went from non-ABS to ABS without altering the master cylinder or reservoir? How did the XJ-S get stuck with that godawful Teves III system with its overpriced master cylinder and pump?

I’m guessing that reservoir won’t fit in an XJ-S, hence they went to the remote reservoir scheme. Does it still have a cork float for the level sensor? Does that reservoir fit on the same master cylinder that has the remote reservoir connected to it in the XJ-S?

My guess is the pump is a Bosch product. Looks exactly like the ABS pump used in early 90’s Volvos.

Sure is Bosch (it has Bosch all over, too), and mine (84) has a plastic float. Which is fine - but the switch itself is rusty and gets stuck at times.

David hi, I have the same unit on my XJ12, 1992…abs warning light is on all the time. it seems the sensors on the wheels are OK. You wrote about rusted switch…where is that switch on the pump? Do you have any advice where should I start to search what causes warning light on?

Thanks,

Cene

Hi, seems I was talking about the brake fluid level warning light/ switch. If that is on you can try shorting the two spade connectors under the brown rubber cap.
I can’t help you with the ABS unit itself I’m afraid. You seem to have a problem with that unit. Good luck!

David

Oh, I see, yes. I thought you meant that abs pump.

Thanks, anyway.

Cheers, Cene

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The usual suspects are the sensors at each wheel, Cene - constantly exposed to road water…

However, the fault may be deeper, and the best advise is to seek professional help - and fixing ABS is usually not cheap. The main DIY problem is lack of complete ‘map’ of components and functions - electric and mechanical…

Frank
xj6 85 Sov Europe (UK/NZ)
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Frank, thanks for that… I will check the sensors, yes. Once, years ago it was quite that issue.

Do you know, by any chance, where ABS unit itself is located? I guess in the trunk somewhere? Just in case…

Best, Cene

Had an intermittent problem with my ABS on my 1990 E190 Merc (and by the way the ABS pump is identical) and it was a broken cable in one of the front sensors.

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No chance, Cene - the various parts are sort of scattered around. Other listers, please…

Frank
xj6 85 Sov Europe (UK/NZ)
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