Speedo gear replacement

How does one replace the speedo gear? I have replaced the transducer and speedometer still drops to zero when car warms up (about 10-15 miles of driving). I have a new speedo gear but would like info on how to install it? I have a 1988 XJS.

There are two speedo gears, drive and driven.

The drive gear is on the output shaft of the transmission. You’d have to remove the transmission rear extension housing to replace it.

The driven gear resides in a small housing that fits into the side of the transmission case. It’s removed by removing the bolt and small clamps that affixes the housing to the case and then wriggling the housing outward. A bit of ATF might spill out.

With the housing removed the driven gear simply slides out and the new gear slides in.

The housing has two seals that you might consider replacing at the same time. A small gear-to-housing seal and a large housing-to-case seal.

All that being said…

Why do you think the gear is causing your problem? I’d be leaning towards a wiring problem and/or a grounding problem at the cluster, poor contacts at the cluster. Pretty common on these cars.


I also have a 1988, my mph is flakey and odometer doesn’t work at all. I’m sure it’s the little electronics board on the speedo. Only way to fix for me will be whole new speedo. You could have same issue.

I had corrosion on entire cluster affecting gauges, which I managed to fix. But that little board on speedo looks quite delicate, and I think mine is toast.

have checked the wiring and found and fixed an issue under car. Speedo worked for awhile then dropped to zero again. replaced the transducer, again works for about 10-20 miles then drops to zero. I figure when the speedo gear heats up it stops turning the transducer arm.

Jon Sundelof


My speedo used to work 100%. When I took out speedo to figure out why odometer wasn’t working, I saw electric board was corroded. I sprayed elec cleaner on it.

Now my speedo does exactly as yours. Sometimes works, intermittently goes straight to 0.

I would guess you also have elec problem with speedo? But hard to prove without swapping speedo.

The speedometer transducer provides the signal to the speedometer/odometer, but it also provides signals to the trip computer and the cruise control. If your trip computer distance and MPG are somewhat accurate and/or if your cruise control holds speed properly then the speedometer transducer is OK and the problem is with the speedometer gauge.


The trip computer and odometer also stop working.

So… if this is a speedo with the transducer on the diff, what is the gear in question??
Or are we taking about a cable driven speedo?

I don’t know what year the change was. My 89 is transducer on the diff. No cables or gears.

I believe that the speedometer transducer was located on the transmission through MY 1987 and after that it was moved to the differential. Jon said his car was a 1988 so that should mean the transducer is on the differential, but I could be wrong about that.

Jon, Is your speedometer transducer on the transmission or the differential?


Since the OP mentioned ‘speedometer gear’ I assumed he actually had a speedometer gear :slight_smile: …and thus a transmission mounted transducer

My model year 1988 XJS (VIN 139xxx 1987 build year) had the transmission mounted speedo transducer.

The change to the differential mounted speed sensor was at VIN 144xxx or 142xxx…something like that…which was sometime during 1987 calendar year but during 1988 model year in USA-speak


The typical failures of the speedo gears is stripping outright or ‘apple coring’…where the middle area of the teeth become concave. I’m skeptical the either failure would present itself only when hot…but I’ve been wrong before.

In any case a visual inspection of the gear will reveal something, hopefully.


Was the wiring for the transducer in contact with the exhaust pipe? It happens.


I had a melted speedometer transducer wire once that resulted in losing the speed signal to the speedometer, trip computer, and cruise control. After repairing the wire and reinstalling the transmission mounted transducer I used a couple of plastic spot ties to hold the speedometer transducer wires well clear of the exhaust pipe. I can’t remember which Jaguar this was on, but probably one of my XJ6s or maybe the V12 Vanden Plas (XJ12).


Replaced the speedo gear and still have problem, the problem now seems to be in connector from the transducer to car’s harness. Will hardwire the thing and hopefully solve the problem .

It is on the Transmission

Ok, hardwired the connection from the transducer to the car (replaced old connectors with shrink wrapped bullet connectors), Anyway, I still have the problem. After a few miles speedometer drops to 0.
Now for the which comes first scenario. I have assumed that the trip computer not working is due to the speedometer problem, but since the trip computer clock constantly has to be reset I am thinking perhaps the trip computer is causing the whole problem. I will unplug it and see if the speedometer continues to work.

OK folks here we go again. I pulled out and disconnected the trip computer and took the car for a ride. Lo and behold the speedometer seems to be fine. My trip computer has been acting weird lately, like not keeping the time when the car sits and giving me 0’s for fuel consumption and mpg etc. I assumed the computer was messing up because of the speedometer problem, but I guess the opposite was true. Will leave the computer out for awhile and see what happens.

i happily ripped out my computer and put in two temp gauges (one for each bank) and one oil pressure gauge. Love it!

That will be an interesting data point: That a failing computer can actually suck the signal to zero and kill the speedo. I presume the cruise control didn’t work either?

I thinks it’s a bit surprising that any of the TCs have soldiered on as long as they have. I have several dead ones.

What I missed was having a clock. My radio has a clock but it is too much of a nuisance to bring it up (aftermarket radio, tiny buttons, too many functions…you know the routine)

I bought a nice digital clock and incorporated it (sort of) into the TC housing. I bit of a bodge but it doesn’t look entirely out of place, IMO. A non-Jaguar person probably wouldn’t notice. Not a quick glance, at least.

Sorry about the thread hijack !