Instrument Cluster Compatibilities

I have an 88 XJS that had an instrument cluster in poor shape. I just purchased and installed one that is in excellent condition, from an 89 XJS.
Theres an anti lock light and the battery charge light is in a diff place (but it works), but I assume they are compatible.

One reason my previous was bad, odometer busted, and speedometer intermittent.

Now my speedometer doesn’t work at all. Now I’m thinking the transmitter was going out before, and now it’s totally out?
But before I go replacing that, I want to make sure a 89 speedo works with an 88 car?

My 88 was built in 87, Vin 141xxx. This 89 cluster has manufacturing stamps from 1988.
Vin 144,262 was last car to have transmission transmitter.

Oh crap, just read that in 89 the transducer was moved to the diff? And mine is on the trans? Am i screwed?

Yeah, you might be screwed. OTOH, perhaps you can add a sensor at the diff and upgrade to the newer speedo. Adding an internal pickup to the diff would be tough (unless you replace the entire diff!) but we recently discussed the possibility of just fabbing a bracket to hold the pickup on the outside and fabbing a toothed wheel to trigger it.

I think the newer scheme also involves a black box of some sort that takes the signal from the pickup and conditions it somehow for speedo, odo, trip computer, cruise control, etc.

Thing is, the clusters look the same, although I haven’t looked inside yet at the speedo.
I’d have to assume Jaguar only changed the way they feed a signal to the speedo, but not change the actual speedo, until they totally changed the cluster and got rid of vertical gauges.

Where are the transducer hookups for the trans? May be worth checking that wiring first, on both ends, as the speedo rarely worked before i switched clusters.

Silly little gearbox on side of tail housing on tranny. Sensor right on it, wire connections inches away.

BTW, another possibility is that the speedo gear itself is stripped. It’s plastic, GM part, cheap and easy to replace. The problem might be the drive gear, ya gotta remove the tail housing to get at that. but supposedly it can rust and the rusty part wipes out the plastic driven gear.

Thanks, I’ll take a look soon.

So do you think it could be the speedos are the same between 88 and 89, but two different transducers feeding identical signals? (I hope so)

If it were me designing the later transducer, I’d design it to produce the same signal the earlier sender did. Especially if a conditioning box is involved; that would seem to make it all the easier to make the signals match up.

It’s not me, though – and it may not even be Jaguar. The earlier setup already has that silly gearbox holding the transducer, evidently a scheme to make the GM tranny calibrate correctly for the Jaguar. Now, do you suppose that pickup in the diff is a Jaguar design? Because I’d presume that idea was used in zillions of cars that use the same diff, and perhaps Jaguar had to make the change because Dana would no longer provide diffs without that sender port. The carrier on the inside has to have the teeth that the pickup detects, and that’s not the kind of thing that Jaguar would order special just for their cars, it almost certainly was common with Camaros and Corvettes and a zillion other cars.

So, presuming that Jaguar was having to utilize a carrier and pickup designed for a Camaro, would it have the same signal that the original transmission sender did? I doubt it. It should have some signal, though. If it’s the same type of signal, I’d expect the speedo to work even if it were calibrated incorrectly. Which means the fact yours doesn’t work could mean either that 1) the diff sender sends a completely different type of signal that the old speedo can’t deal with, or 2) something’s not working in your car. Given that something wasn’t working in your car to begin with, I’d put my money on #2.

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It seems like that transducer is a high failure part, I am also assuming that it’s been going out on me over the last few weeks as the speedo has worked less often. I took a look, it’s right next to exhaust, and end if it looked a bit burnt.

Also, I see there is a ‘black box’ in trunk for 89 diff transducer, if I were a betting man, I’d bet that converts signal back to what speedo could read a year prior when it was trans transducer.

The diff mounted transducer feeds a little black box in the upper boot on the left side. Outputs are speedo, trip computer and I think something to do
with cruise ctrl… I could be mistaken there. Anyway, there are two part numbers for these boxes, one for “sports pack” and one not. Sports pack pn is dac4591.
So, if the trans mounted transducer feeds a similar black box on your 88 you should be gtg, signal wise.

FWIW this is the direction I will explore shortly to get away from speedo transducers altogether. In theory should work but I failed to check output of dac4591 with scope before moving to non-transducer diff so I am not sure if the speedo wants a square wave or what. Square wave would be most common and logical but this is a Jaguar…

But wouldn’t your speedo not work when going thru tunnels?

When I changed the 1979 coupe to a 5 speed manual box I had to ditch the mechanically drive OEM speedo. I bought a 2nd hand cluster from ( I think ) a mid 80s car. The new speedo needed a 200Hz pulse to register 100mph. The Supra turbo box gave a much higher pulse rate. So I made up a printed circuit with a divider function where I could select many different divider ratios. That way the speedo registers correct speed.
My guess is Jaguar just took whatever was a standard pulse output from gearbox or diff manufacturer.
The speedos in those days would use a 555 I.C. to convert pulses to a DC signal to drive the gauge.
Quite easy for Lucas or Smiths Instruments to change a resistor value in the speedo to give the correct calibration.

The pulse does not have to be a square wave, although you need a reasonably sharp edge to trigger a 555. With a bit of electronic experience you can pull the speedio apart and change the calibration to suit any reasonable pulse frequency.

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The jaguar parts catalog lists a different speedometer part number at the exact same VIN break that transducer/speed sensor change took place. Of course it doesn’t describe what is actually different about it…but it’s a fair conclusion that transducer systems used xx-speedometer and speed sensor systems used yy-speedometer and that they can’t be mixed-n-matched.

It also lists a different tachometer part number, Lucas ignition versus Marelli. Does the tach on your replacement cluster work OK ? An '89 XJS could be Lucas or Marelli. If not, the cluster probably came out of a Marelli car


The confirmation would come from checking the part number for the speedo itself. If it didn’t change, you are correct.

One theory promptly shot to #$%$#!

Tachometer works fine.

The difference is almost sure to be a change of calibration resistor in the speedo. Of course that generates a different part number. You will find any shop that deals with fixing car instruments will know how to change that resistor. They just need to know the pulse frequency in terms of Hz/mph.
If they have dealt with Smiths and Jaguar combinations before they may already know that Hz/mph for the transducer type. If so it is a 15 minute job. Say $25 ?
Down this part of the world there were Jaguar speedos with dual mph and km/h dials for a while.

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I would be pretty sure that you cannot add a sensor to the Dana differential- the Salisbury diff with the sensor has the trigger notches machined into the LSD unit. Dana wouldn’t have them. All the more reason to switch to the later Salisbury.

I’ve ordered a new speedo transducer for my transmission, as it’s a high failure part, and my earlier speedo was acting erratically, and working less and less as I drove.

I know it’s not proof, but reading a lot of posts about the transducers from mid-80s on transmissions, and late 80s/early 90s on differential, both claim to put out 8000 pulses/mile, so hopefully I’ll be OK. Otherwise, I’d either adapt speedo with resistor, or buy an older speedo and sell this newer one.

I’ll post next weekend with my results.

When you install it make sure the wires are routed away from the exhaust pipe. It’s a tight area, if the wires are not secured/routed properly they’ll flop against the exhaust.


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Are you talking about part # for individual speedometer or entire instrument cluster?

Individual speedometer