twitchy speedo - what does it mean, and does it matter?

The speedometer on my 93 XJ 4.0 auto has started behaving oddly from time to time (and no, you're not allowed to say ".....like its owner...."!).

Sometimes when the Jeep first starts and rolls, the needle sits at zero and doesn't move. Now I don't much like getting out of bed first thing in the morning either, but even so....

Other times it seems to work OK, but then starts reading 70-80mph when I know I'm only doing 40. Yeah, sometimes I think I'm a swift mover too, but then someone tells me I'm kidding myself....

In either case, a quick hard tap on the instrument panel gets the needle to the right place on the dial, and all is well.

My only questions are - why is it misbehaving? And does this signify something more serious that needs fixing? None of the other gauges on the instrument cluster are affected - all read steadily and normally. Since a tap on the panel puts the needle right, does this just mean there is a bit of dirt or rust somewhere around the needle pivot, or at the back of the gauge? I assume that if it was a problem with the gear at the transfer case then the twitching would be evident all the time, or the needle just wouldn't budge.

Not a crisis in the grand scheme of things, and something I can live with if I have to. But I wonder if this small issue indicates there is a more serious underlying (electrical/electronic?) problem.

The most common reason for weird symptoms is that the spedo cable need lube on one with a cable, but your problem sounds more like the bearings on the meter movement are getting gummed up and need to be cleaned.

91 and later don't have a speedo cable, though that was my first thought too.

Either your VSS is getting gummy, or more likely, the wiring to the VSS is shorting out on something. It's a frequency based signal, so if the signal wire insulation is worn through and it's vibrating against a ground, you'll get really crazy speeds indicated due to the extra pulses making the speedo think you're going much faster.

I haven't yet tackled this problem (too busy with other stuff, and anyway I have a GPS in the XJ which shows speed). Meanwhile the speedo isn't just jumping or reading oddly: it now remains permanently at, or below the zero on the dial.

But I'd like to narrow down the investigation and aim at the right target areas. In particular, whether to focus on the wiring and connections down by the sensor and gear at the transfer case, or whether to rip out the entire gauge cluster and start looking at the back of the gauges.

Incidentally everything is OEM: I have never changed tyre size or messed with speedo gears and have owned the Jeep from new.

Do the symptoms point in the direction of one or the other area to work on?

• all the other gauges work absolutely fine, so I'm assuming there is no problem of power supply or fuses to the cluster;
• when I switch the ignition on, the speedo needle does move slightly, which also suggests the speedo circuit is getting power;
• the odometer and trip are still working normally. What does this signify? Are they driven entirely separately from the speedo needle?

These bits of evidence suggest to me that maybe I don't need to dismantle the dash and the cluster of gauges, and that maybe as kastein suggests the VSS is faulty or the wiring or connection down by the transfer case is shorting or bad.


However on the other hand, until recently, a good hard whack on the dash, or on the face of the speedo, activated the speedo needle and made it work normally. But that brute force option seems no longer to have any effect. So is the problem up at the cluster? A stuck needle, or a bad contact behind the dial?


Any guidance on where and what to look at first would help!

Both seem like very reasonable places to start. The dash is not hard to pull apart, and the wiring underneath is somewhat easy to inspect. I'd start with the dash, laying on the ground kinda sucks. Especially if you have crap falling in your face.

Yup, BigK, I tend to agree with you..!

I have just been taking a close look in daylight at the speedo dial, and I have spotted something which may be interesting and is also weird.

Normally (if I recall correctly) when ignition and everything is off, the speedo needle rests horizontally, in line with the zero mph mark, which in terms of clock-face orientation is at 9 o'clock on the dial.

There is in fact a little pin there, sticking out from the dial, on which the needle evidently rests.

Now..... I have just been out to look closely, and I observe that with the ignition off, the speedo needle is actually pointing downwards (roughly to 7 o'clock). When I switch ignition on, the needle rises.... but only until it is stopped by the pin at the 9 o'clock position. So, not surprisingly, when rolling along the road at any speed, the needle cannot move any higher up the dial. It is below the pin at the zero position, and thus physically prevented from rising up the scale in the normal way.

OK - so what this means is that somehow, sometime, the needle has gone clockwise all the way round the dial, over 120 mph, full circle, and fetched up right around and below the pin. No wonder it can't now register correct speeds.

So there's an obvious question: how the **** do I get the needle to rotate anticlockwise back round the dial so that it comes to rest at zero (9 o'clock position) but on the upper side of the pin? I have just tried with a magnet, but that doesn't work.

Is there some way of making the needle re-set itself into the correct position on the dial (short of reversing the vehicle at over 100mph!!). Since my Jeep is a 93, and the speedo is driven by sensor and wiring, not a drive-cable, might there be some electrical/electronic trick of switching the wires from the VSS, reversing polarity, or whatever, to get the needle to jump back round?

As always, any advice would be welcome!

Sounds like you definitely have a short somewhere. Try this: have someone in your jeep with the ignition in the on position. Get under there with a pair of gloves and start wiggling the wiring harness for the sensor. If i'm right, they should see the needle moving as you get closer to the short.

Actually, doing 120 forward or backward will get the same result with an electronic speedo. It just sees pulses, it doesn't know which way it's spinning. No real way to fake it out, either.

You might make it be able to pull back down around by doing 120 and hoping it comes back down off the stop, then slow down and get it back to where it should be, but what I'd do is pull the clear plastic panel off and just spin it back by hand. It's not a geared motor, iirc it's just two crossed coils and a magnetic cup, so as long as you go slow enough that it doesn't bend/spin the shaft because of the fluid damping or whatever, it should just come back down no problem.

Worst case, you may just need a new gauge cluster. They are super common at the junkyard, any 91-95 and maybe 96 ones should fit yours.

Most likely it’s water/humidity accumulated in the VSS connector. I had the same symptoms after driving in a very heavy rain. Problem would come back every time it rained. I unplugged the connector, cleaned it and used some WD40 to take care of the problem. It has been good for few months now.
If that doesn’t work, it’s probably your VSS or its wires shorting somewhere.
Don’t worry about the needle/dash. It should come back to normal after the fix.

Thanks for those replies. Incidentally I was joking about reversing at 120mph.... Years ago I did see someone play around with a cable-driven speedo by connecting the other end of the cable to a power-drill! I'm no electrician, but I realise that with an electronic one it's all about pulses, a coil and a magnetic field (hence my fruitless attempt to swing the needle back round by putting a magnet against the gauge-glass....).

Seems as if the most useful next step is to fiddle with the wiring and connectors, clean them up and try the WD40 routine (it's quite possible that the long cold damp Scottish winter has got at the VSS connections). Then I'll just see if I can find a way of getting the needle to re-set by wiggling wires etc.

Swapping out the cluster for a junkyard one isn't really an option: I'm a great believer in junkyard parts and recycling, but XJs from the 1990s are as rare as hen's teeth in UK junkyards these days.

To each his own but WD40 is not considered to be of much use as a dielectric or long term lubricant. Just my thought.

Been to Scotland once and would almost trade winters (not quite) for the chance to come back. I know my wife would trade a couple of really cold winters to do so.

Good luck with your '93!