Speedometer Issue Project 2a

I figured I would install a new cable to my speedometer and see how fast I was travelling. With the chevy 283 in and the firewall massaged to allow it to fit, the new speedo cable will not connect to speedometer straight on, due to the massaging for the distributor clearance, so I left it loose. no needle movement during the test drive so I figured it was snafu, then I noticed it was removing mileage as I drove.
So I figured the speedo gear in the transfer case has to be installed backwards. I was gonna pull the emergency brake housing off and see. The PO had bought a rebuilt D18 with a teralow installed from Herm.

Anyone had this before? I never have in my 40yrs of jeep wrenching.

 

Christine?

 

Haven't encountered that before, but that just about has to be the problem, it is a spiral cut gear and could easily be put in backwards. It is not hard to correct when the unit is out of the vehicle but a bear to get at once it is installed.

May be able to just put a jack under the crossmember, unbolt it and lower it enough to get in there, which is the only way I can get my big hands in there to install the speedometer cable.

The cable fitting does need to be tightened or you will get jerky motion on the speedometer.

 

If not mistaken all IH D18 speedo cables enter the rear bearing cap from the driver side. All jeep D18 have cable entering from passenger side.
I seem to recall that IH cable spins opposite of jeep.
Is that what you have ?

 

going to remove both gears to check out

 

Also I should mention not only that the Jeep D18 gears enter the opposite side of the rear bearing cap; but also that the driven gear sets above the drive gear. I forget if IH driven sets above or below the drive gear. That positioning also effects the direction of Speedo cable rotation.
They both use them Stewart Warner drive and driven gear sets.

 

No reason to remove both gears. The driven gear cannot be backwards, it is the drive gear you need to check and that means you have to pull the yoke, pull out the gear and see if it was put in backwards.

 

It’s possible yet the pressed on driven gear is seldom if ever removed from it’s shaft.
And even if the driven gear was flipped on its shaft I don’t expect it could possibly mesh back onto the drive gear because the helix angles would be opposed.
If the drive gear is reversed I don’t believe the driven gear can possibly be meshed to fit with the driver.
If you take it apart then by all means identify the numbers seen on both the drive and driven gears so we know what your working with. These gears only work in certain matched sets.

 

Ken is more knowledgeable on parts like this than I am, and it has been a couple months since I was inside mine so the mental picture I had of the driven gear may be wrong. I have a tail housing with the gears from a Pickup I'll have to go down to the barn and study it a little.

 

Well, with all of these intelligent replies, I feel like a dufus!
When you said “odometer running backwards” my first thought was the Stephen King novel “Christine”.
I hope these guys can help get you squared away, and I hope my comment can be forgiven!

 

Flipping the drive gear over won't change the pitch direction. It would have to be cut with the opposite pitch to turn the driven gear the other way.

Here's a Ford speedo gear I had sitting around for an example. Rubber band on one side:


Flip it around and the pitch is still the same direction:


International parts seem like they might be the most likely cause.

 

International speedo gears have the same helix cut in the gears as Jeep. While IH rear output housings do have the speedo cable connection on the opposite side from Jeep, one exits below the centerline while the other is above the centerline so no direction change. As was said, even if the the drive gear was installed backward the direction of drive does not change. However, if not installed correctly the mesh of the gears can be effected so can effect the speedometer operation.

 

Ahh, so not international parts either. Interesting problem to say the least.

 

For additional reference, I found a picture of a scout tail housing. Indeed the gears are meshed the same way, it's just rotated over a bit:

 

Yeah Nick clearly explained what I was thinking. I knew he would have the correct answer.
Also, Fireballs pic shows the unusual rear bearing cap detail. Plus Fireball also shows how flipping the drive gear makes no difference.
In fact if one does flip the drive gear; I seam to recall that the driven gear can no longer be engaged to it.

I was mainly grasping for straws trying to figure how the speedo cable could turn backwards.

So Jeff this one continues as a mystery !
But you are correct that IF and WHEN the cable turns backward; then the odometer numbers are reduced.
Just don’t try and reset the odometer by spinning the cable backwards. Eventually it will destroy the odometer.

 

My gut told me that it couldn't be the driven gear flipped over but I wanted to get ideas from the masses. I recall that my cable was pointing to the passenger side, another test drive with a video camera is required to help figure this out. Thanks for your replies

 

Very interesting mystery. I am now wondering if the odd behavior has anything to do with the loose and not straight on connection at the speedometer. My thinking of this is if the end of the cable is not fully engaged it may only be skipping on one side of the speedometer drive.

 

First of all, went to the post office to mail some jeep goodies today, 15 or so miles and recorded a couple of videos of the speedometer during the trip. Tail housing correct for willys, pic of the odometer shows yesterdays mileage, videos show todays odometer mileage. Videos show decreasing mileage.





Any other ideas?

 

Try and localize them problem.

Disconnect speed cable.
Tape the end to dash so you can watch it.
Is it turning nonstop and consistent or erratic ?
Which direction looking down onto the speedo end of cable. It should be smoothly spinning counter clockwise.
Otherwise if you have a spare speedo you could try swapping them to determine if the speedo is at fault.

 

Not the speedo. You need to search out a stewart warner reversing rotation adapter or the like. I used to have this problem all the time years ago with log trucks that would swap transmissions. Back then S/W sold a lot of those reverse drives which kept you from having to replace the speedo cable core to the opposite twist to keep the oil pushed down instead of pushing up and into your speedo and damaging it.