Speedometer connection

[bmohan55]

How exactly is the speedometer cable held in the sending unit in the tranny? My speedo works from stop up to 40 mph or so then it drops to 0. I am able to pull the cable out of the sleeve while still connected to the gauge (oiled it well while out). I've also dissconnected it at the tranny (fun with the O/D in the way) and examined and oiled that end. I believe that the cable is slipping out of the sending unit as the rotations increase.
According to my Green Bible (1963 edition, assume it's the same for my '72 truck) it appears to be a bit involved in getting to the speedo sending unit.

thanks,
Bob

[Terrys]

By "sending unit" I assume you are refering to the helical speedo drive gear and plastic worm gear. They do eventually wear out, but, more likely, your speedo head is tired out. There is a spinning disc with a magnet attached.and it is coupled magnetically to the speedo needle. The magnet looses enough magnetism so it no longer pulls the needle as the disc spins faster.
Replacing the plastic gear requires dissassembly of the back end of the transfer case.

[bmohan55]

Yes, I was refering to the drive gear, I'm at work and couldn't remember the exact term. So it's not indicative of a problem that the end that goes into the drive gear pulls out easily?

From what you are saying by replacing the gauge I should solve the problem, correct?

Thanks
Bob

[Jeff Aronson]

The cable is just a pressure fit into the sending unit housed in the transmission. As you're well aware, it is a bear to get at the three tiny screws that hold the plate onto the transmission housing - especially with an overdrive. I know from painful experience.

When you pulled the end of the cable out of the housing, how square were the end corners? If they're rounded at all, they will spin at that end under load. The same would hold true for the speedometer head end, too. If they feel square and sharp at their edges, then, as suggested, the problem is probably in the speedometer itself.

Try this test. Undo the cable from the back of the speedometer and expose it to your feel or view. Start the car and slowly move it forward. You should feel the cable turn rapidly. If it's turning then the problem is less likely to be at the transmission end, but at the speedometer end.

In 500,000 + miles on my Series Rover, I've gone through at least 3 speedometers. All have been rebuildable. As noted above, they do have components that can wear out.

Jeff

[bmohan55]

Thanks, the tranny end of the cable was flattened.

I'll try your test. BTW any tricks on pulling the speedo out, my "Bible" is for an SII. Must I dissconnect all wires to the dash or can I manage to just wiggle out the speedo itself?

Well I suppose it's easier to replace the speedo than to tear into the drive unit!

Thanks,
Bob

[TeriAnn]

The cable is just a pressure fit into the sending unit housed in the transmission. As you're well aware, it is a bear to get at the three tiny screws that hold the plate onto the transmission housing

Jeff

I replaced those tiny bolts with allen head screws a decade or two ago. A long allen driver gets them in and out easily. Of course, I don't & didn't have an overdrive in the way

[Jeff Aronson]

TerriAnne, that's a great idea. I should have done the same one of the two times I've had to replace the cable. The overdrive does complicate the whole thing; without one, it's just a fiddly job. I had to use a magnetized screwdriver and a dab of grease to hold the screw head to the screwdriver as I lifted it into place. The only good thing was that it made for a humorous story in the Rovers North News.

As for the speedometer itself, it comes out fairly easily. When you remove the 6 screws and nuts that hold the fascia to the bulkhead, you'll see that the speedometer is held on to two long, thin studs by a couple of small nuts. When you remove them, two brackets that hold the speedo to the front of the fascia will come off - they're just a press fit.

The bulbs will pull right out of the speedometer, so you don't have to remove any wiring. You won't need to take the whole thing off very far - just tilt the top of it down towards the shift lever and you can push the speedo forward and out.

Jeff

[Daurie]

Ah ha.. the allen head is an excellent idea.. even with an OD unit in the way I bet a ball hex driver would do the trick nicely. :thumb-up: