1989 Jeep Comanche Six Speed Transmission Swap - Six Shooter, Round IIPosted in Project Vehicles on November 20, 2008
In the first part of this six-speed swap story, we showed you how we bolted an '06 NSG370 six-speed transmission and NV241OR transfer case into our '89 Comanche. The actual bolting in of the transmission and getting the truck running again went fairly easily.
The idea for this installment of the swap was going to involve finishing it off, using junkyard-sourced Jeep parts for not only a clean, factory look, but for a swap that wouldn't break the bank. Well, let's just say we got the parts installed.
It turns out that getting a mechanical speedometer to read off an electric sending unit without going to the aftermarket is harder than we'd ever imagined it would be. And, after spending about 300 bucks on various and sundry junkyard parts trying to make it work, not to mention enough time to swap the stock transmission back into the Jeep if we wanted to, we had to go to press with this story.
The issues we had with this swap all stem from the fact that the Rubicon transfer case doesn't have any provisions for a mechanical speedometer, and the '87-'90 Comanches and Cherokees run on a mechanical speedometer. If you are doing this swap on a '91-and-up Jeep, which we figure most of you will be, you won't have half the problems we encountered.
At the beginning of this project, when it was still just an idea, we were going to swap a GPS speedometer into the factory cluster after ripping the stock speedometer out. Then we decided that for someone who paid 500 bucks for an '87-'90 truck, a $500 speedometer might not be a good idea.
Even from the start we didn't want to trash all the factory gauges by going to a complete aftermarket array. It just added too much money to this swap. So, we moved on to the idea of using an electric motor to drive the stock mechanical speedometer. Availability simply wasn't there when we started this swap, and we were confident we could save a buck by going at it our way, so we didn't look too closely into it.
Now, with about $300 of burnt or non-functional electrical gauges and sending units in the trash, we wish we'd gone with one of our first two options. If you have an '87-'90 Jeep, be it a Wrangler (which also uses the mechanical speedometer), a Cherokee, or a Comanche, don't do what we did. Just keep your stock gauge cluster.
As of this writing, there isn't a GPS speedometer that would exactly replace the stock unit. GPS speedometers are big in boats and often don't feature odometers. They are just coming into the automotive realm with odometers, trip odometers, and other things that we need. Autometer makes a few units, but most of them have a white face with white rings; Nordskog has a couple of black-face offerings, and while none matches exactly, all would be better than what we ended up doing to all of those poor gauges and sending units.
Terf now makes an electronic to mechanical speedometer adapter. When we started this project, the unit was unavailable. Jaguars That Run also has such a unit to drive a mechanical speedometer from an electronic signal. Either one would have been a better option than the route we took.