Thread: 3.9V8 RR speedo problems

Couple of things you may want to do first. (And i am assuming that the 1990 has the same speedo drive as my 1985/92 Vogue hybrid, but others will soon jump on me if I'm wrong)

Lubricate the speedo cable - you access it by uncliping the cover from the rear of the instrument binacle ( the pod sitting one the dash panel) there is no screws or anything. On the speedo cable you will find a knurled nut on a right angle drive. (tie a bit of string around the cable below the nut and tie the other end to something like the gearstick. That way you don't loose the end of the cable or the nut down in behind the dash. You should be then able to remove the inner cable.

It's very oily and yukky so be careful. Clean off the cable and check to see there are no kinks then lubricate it with something like sewing machine oil the whole length and re-insert the cable.

You could also use something like lithium grease on the right angle drive to lubricate it as well. Then reassemble.

Visually check the path to see that there are no tight kinks in the cable outer or even burn marks where it may have been resting on an extractor or exhaust pipe. If the path is correct and no damage see if the lubrication makes any difference. (It may have been 18 years since it was done).

3.9s do not have a speedo cable,except for a short one to the VSS which is on the LH chassis rail next to the auto.
I would thonk the VSS may have died. I have heard that they can split in two pieces and can be reglued.
Regards Philip A

remove the automatic, install a manual then recaliblrate the tacho to indicate speeds for various gears at various RPMS....

ok auto jab for the week done.

start at the speedo drive side make sure its all neat and proper and there is no fretting of the cabley bit or the drive gear inside its housing then follow everything back

if the electric sender moduley bit is cracked or oily it can give lots of fun problems

and finally check the earths for the instrumentation dash and the module.

Originally Posted by GuyG

Hey Folks,

I've got a 1990 3.9 rangie which the speedo sometimes reads way to low compared to the speed that I'm actually doing. It says I'm doing 40 but it feels more like 60. Problem is its doesn't do it all the time, then it sometimes catches up with itself ie rapidly increases to where it should be on the gauge. Currently the torque convertor locks up when the unit is reading 70km/h when it should be about 85km/h

Q - where do I start looking? Is it a case of pulling the instrument panel out and getting it checked or is there somewhere else I should start?

Cheers Guy

By any chance does your alternator / battery light have a slight glow??
Also .. the electrical module at the end of the cable (from gearbox) controls idle / speedo ... as blknight.aust says