If you swap both axles, you will lose the speedometer signal. I suppose you could machine tone rings onto the donor axles, but I personally never looked into that, nor wanted to incur that expense. The solution is to run speedo off the transfer case. This can be done if you have the 242, or 231 like me. Your 242 does not have a speedo port, so get a rear speedo housing that does and swap it. Find the right speedo gear to match your gearing/tire size, and you’re set. Courtesy of Mallcrawlin, here is a link explaining the general concept of wiring your new speedo gear (starting at post #5): [MC link]
. There are a few other links out there (MtnMarc has some good info in his build thread), but be careful -- Chrysler used different wire colors for different model years, so you need to verify with the FSM or by multimeter which are the applicable wires. What I'm saying is, disregard the wire colors that others have referenced because unfortunately, its not that simple.
At some point, I may make a separate thread but for now a few tips: you can use any of the four speedo sensors to accomplish this task, but most use the left rear since it makes routing the wires easier and neater; the speed sensor wire at the wheel has 2 wires -- 12v supply and 5v signal -- figure out which is which with a multimeter or correct
year FSM, and splice into your "new" speedo sensor accordingly (your new speed sensor has 3 wires (power (12v), ground (middle wire), and signal (5v)); once the new sensor is spliced into the existing rear sensor, you move up to the front at the ABS harness/CAB -- using your correct year FSM, find the wires at the ABS harness for vehicle speed sensor (VSS) and the left rear speed sensor signal
(assuming you used the left rear wheel sensor), splice these two wires together at the harness BEFORE the wires enter the plug (leave the other halves of the vss wire and left speed signal wires cut and unattached at the plug); turn key to "on" position and verify you have speed by turning by hand the speedo gear; if you did everything correctly, the speedo will move in relation to your spinning of the gear; solder the wires, shrink wrap, etc and otherwise button everything else back up. Note: you need to have the ABS plug connected in order to complete circuitry.
You will lose ABS if you swap both axles. Solution = pull the ABS fuse and don’t be a pu55y. Bye bye ABS pump and wires.
For the most part, 70’s axles will have front disc brakes and rear drums. There are several kits (aftermarket and junkyard sourced) to convert the rear to disc. I will run rear drums for now. If you run rear drums, you will have to install the correct proportioning valve for the brake booster. A vehicle with rear discs requires more fluid than one with drums and would send too much fluid to the back wheel cylinders. As an interesting note, one should not automatically assume disc brakes will stop better than drums. In terms of sheer stopping power, drums have the advantage. However, by the time you factor in brake fade, complexity of parts, cost, etc, disc brakes do present an appealing option.
The e-brake cables from the donor axle can be reused. Shorten and then simply hook back up to the bracket that is located underneath the rear seat.
To plumb everything in, I picked up a proportioning valve made by Wildwood. This is perfect for front disc/rear drum set-ups. A simple twist of the valve will give you more/less rear brake. Existing lines fit in to the new prop valve. You will have to swap fittings supplied with the kit for the new prop valve connections due to Jeep using metric fittings. The front electrical plug is not used -- you can either let it go or swap out for a plug fitting. The existing lines will have to be shortened, bent, etc. to properly fit the new valve. We fabbed a simple bracket for the new prop valve that bolts to the master cylinder studs. Here's a pic:
Pull the ABS wires and e-brake cables. These are accessed under the rear seat. Both ABS cables have pigtails under the carpet, and the e-brake cables are right there under the carpet as well. Rear ABS/E-brake cables removed: