My car is 89 with ABS, swapped a rear cage/differential out of a 1994 XJS.

After install the brakes acted weird, ABS was activating all the time and then ABS light came on. On advice of Greg, I counted the teeth on the reluctor rings on 89 and 94, both had 48 teeth/ridges. BUT! The spacing is different. See pics below. I'm assuming that the distance is confusing ABS computer.

Soooo, any experts got ideas for (easy) solutions? My ideas so far:
-use 94 ABS wheel sensors and hope they send correct signal to ABS computer
-drive my car into a lake

 

Andy
This is only theoretical, but I think you should have the same rings front and back (ie with the same spacings). Is it doable to swap over the front ones so they are the same as the new rears?


Second point, is the actual ABS "brain" the same in the two systems, or was the new rear axle's OEM system different from the old one on your car? If different, then you have to keep the fronts as they were and get the original ring onto the rears somehow, and use the original sensors to get it working properly, I would think.
Greg

 

Andy
A further thought, and this might be the most foolproof eventual fix. If none of the above ideas work/or are doable, you can quite easily remove the diff from the new axle and install it in the old one, with which the ABS did work. I assume you only changed the axle to get a lower geared (numerically higher) diff ratio?
Greg

 

Thats what I was thinking too. I had some sort of driveline vibration that I was hoping to get rid of as well but I may chance it and swap the diff in.

Is it a straight swap? Any gotchas?

 

3 issues that need to be checked.

1. The early vs late XJS ABS sensors are indexed 90 degrees off. I suspect you reused your 89 ABS sensors and now they are 90 degrees off. You need to get a set of XJ40 or late XJS abs sensors. The sensors are directional. You can not see this on the XJS sensor as there is a metal cap covering what looks like a single tooth. The tone wheel teeth have to be run parrallel to the tooth under the cap. If it's off 90 degrees you will not get a good signal.

2. The depth of sensor needs to be checked and proper air gap has to be established. There is a slight difference in the early vs late stuff, I dont recall exactly. One used an o-ring and one didn't, this changes the sensor depth which alters the signal. It's been awhile but my recollection is you can see and measure the gap from the back side of the hub.

3. Make sure the tone wheel teeth are clean. Compressed air, mineral spirits and a brush will help. Use no harsh solvents that can damage the bearings.

I had the same problem when I upgrade my IRS. As retrofit ABS to 70's there was no on-board diagnostics to be had. I had to buy an oscilloscope and watch the signals. At that point it became clear the rear ABS sensors were wonky and not producing the same signal as the fronts. Upon investigating I had one or all the issues detailed above.

Oddly when I did my first ABS retrofit on a 70's jag I used C4 corvette ABS sensors in the rear with a hodge podge of spacers and connections. You could measure the gap...with a ruler. It's worked flawlessly, those sensors had no metal cap and perhaps offered a stronger and cleaner signal.

 

If the tooth count is the same, the computer should be happy. The sensors may be different electrically, so the computer isn't seeing the signal it wants to see. I'd start by trying to get the 94 sensors out before you tear down the IRS and swap diffs.

 

That was my first thought as well but it doesn't appear to be an option, near as I can tell.

According to JDHT all XJS with ABS used the same front ring, CBC4704. However, two rear rings were used; CBC4706 and CBC4705....with the latter listed for 4.0 and 6.0 cars.

So, IF we conclude that the rings are the problem then the only choice is swap disassemble the rear hubs and use the earlier rings, as you mention below



Later cars used a DAC10056 brain. Earlier cars used a DAC5863 brain. I have no idea what the difference is between the two

The '5863' is superseded by the '10056' which suggests, but does not positively confirm, that they are forward/reverse compatible.

Cheers
DD

 

Just a word of caution the lengths of the halfshafts between the early "round top" type hub carriers and the later square style hub carriers is not the same. The late XJS shafts are the same as XJ40/X300 and not backward compatible or you'll have camber problems. The hub carriers are the same, with different brackets for the callipers, and the callipers are also different between late XJS and XJ40/X300.

Be very careful mixing and matching between the early and later style IRS's.

 

Thank you for this insight! I think this might be my problem. I happen to have a set of ABS wheel speed sensors from a 4 door car from pull-a-part. they have are labeled x300 to swap out.
The first pic is the stock 89 wheel sensor and the second one is the x300 sensor, is that groove in the metal what you're talking about? They are 90 degrees off from each other.

 

Also, can I cut and splice the wiring on a ABS wheel sensor?

 

BINGO! Yes, see that dimple line...that's it. I woudnt splice. I would check your depth, and fashion an S bracket out of thin sheet metal to hold the sensor 90 degrees off and test. Then get the right sensors, might take some time but I think the XJ40 one are cheap and will work. I recall the late XJS sensors cost a fortune.

 

Test run about to start, turned them 45 degrees and zip tied to see if that does it. Also disconnected the battery, not sure how ABS computer stores codes or for how long, assuming that battery disconnect for a few minutes will lose them.

 

WE HAVE A WINNER!!!!!!!!!

Brakes work normally, no ABS light and ABS activated when I locked up brakes in my gravel alley. I've still got some assembly to do but that appears to be the trick.

I was about to cry thinking about buying $300 wheel sensors that might not solve problem to swapping differentials and other parts and one man's knowledge saved me. (Thanks icsamerica !!!)

For future searchers, that are swapping differentials or messing with ABS wheel sensors, pay attention to the direction of that groove!

 

FANTASTIC NEWS.
and HONOUR goes to ICSAMERICA. Brilliant stuff.


FWIW, Andy, your driveline vibraiton is probably the propshaft going home. Mine did last year, they are actually a two piece affair with a huge rubber bond in between the wide part and the thinner part. news ones are available from Jaguar and are not too badly priced. Fixed my vibration no problem.
Greg

 

I think you are right about the driveline vibe--its still there with new rear cage. I'll take a look at new one, but I've got my eyes on a manual conversion so may hold out.

 

Glad it worked out. I've been there, sometimes trying to improve or upgrade your ride doesn't work out as planned but one must be patient, seek knowledge and persevere, then find the opportunity and humor in it and keep going forward.

I purchased a PC based USB oscilloscope to help me with a similar issue and I've used it for about 3 other issues since. For 80$ but it was worth it in learning alone. My 9 year old took an interest in the oscilloscope too and now has an understanding of electrical waves few other do.

Zip ties... good idea.

 

Not sure if this new problem (in thread below) is connected to the problems in this thread but wanted to connect them for future searchers.


https://www.jaguarforums.com/forum/x...ht-not-175935/

 

Whew: Perfect function of the forum. So, far, knock on wood, my only car with ABS works just fine. My 94 Jeep Grand Cherokee.


As my other car is the 83 XJ wuzza six, sans ABS, each responds to brake pedal input differently.


Gotta drive the cars, not merely ride in them. I'll more than likely ever get to a driverless car!!! Suits me just fine.


But, here, are there not two systems in play? One on the hub to sense speed for braking purposes, and the other on the ring gear to sense speed for engine management, cruise, trip computer, speedometer, etc. Separate and apart or inter dependant? I don't know. Do I need to? No, for practical purposes. Yes, to satisfy my curious nature.


Carl