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Limited slip differentials are a more affordable way to get better rear end traction on most surfaces and in most driving conditions. However, in extreme cases such as rock-crawling or climbing very uneven and steep obstacles which could result in a rear tire having little to no traction, a locking differential provides the best solution in order to overcome the obstacle with the least potential for damage. Damage could be caused either by excessive wheel speed which could result in drivetrain damage, or excessive vehicle speed, which could result in loss of control, leading to undercarriage damage, body damage, and/or drivetrain damage. A very tight LSD could potentially cause some handling/cornering issues on pavement. If you do little to no rock-crawling, the LSD could be a satisfactory option. In my case, the effort/expense of pulling the third member, repacking the clutch pack to increase the breakaway torque, then reassembling it, was not worth the risk of discovering that it still might still not provide enough performance benefit for my style of 4-wheeling. It is for this reason that I opted to just go all-in with an ARB air locker. My R50 is air-lockable both rear and front, but it took a decade of wheeling for me to get to that point. Every driver's situation is different, so the approach to mods I would recommend is to run the trails you enjoy, get lots of seat time to learn how to drive within the vehicle capabilities, learn to choose good lines, and plan your vehicle upgrade path accordingly. Tires are probably one of the most important things to start with, with a lift being next. I would prioritize recovery equipment above drivetrain mods. A locking diff or tight LSD may only give you the ability to get you stuck further down the trail.

I'm pretty happy with the LSD in mine, but I'm not climbing any trail class ladders with it. An LSD is just an open diff with clutches jammed in behind the spider gears to make them harder to turn, so if you're looking to build a rock crawler that'll spend half the trip with a wheel in the air, the LSD will probably disappoint you. Short of that, and on a budget, LSD is good, or at least a hell of a lot better than an open diff. The R50 LSDs were pretty nerfed, possibly for stability reasons (the WD21 LSD does make it pretty easy to get the rear end to step out in the snow). Hawairish did a great writeup on how to repack them to make them useful. Sounds like there's a limit to how tight you can go before you start breaking stuff. If I was going to throw money at my diffs, I'd leave the rear LSD alone and put a ratcheting or air locker up front. But, yeah, some of us is poor, and my truck needs a lot of things more than it needs a front locker I might use once every couple of years. I don't think I've had it properly stuck since I put a decent set of tires on it.

Good solid advice, the only real way to figure out how to build and upgraded your R50 is to test it in the areas that it will be used the most. For example my R50 build is geared towards camping and some moderate Off-Roading. Lately I too have been throwing around the idea of installing an ARB Locker in the future. Chris.

The service manuals confirm what you've found with the wiring. The '87 manual shows the white wire from the tach going through a 2.2k ohm resistor to the + side of the coil. The '90 manual shows the white wire going to the computer, then a white/green wire going from the computer, through the same 2.2k resistor, again to the + side of the coil. So, yeah, sounds like the TBI system runs the tach right off the coil, while the MPFI runs it off a signal generated (or at least modified in some way) by the computer. If you're married to/stuck with the '87 cluster, you could cut the white wire from the computer to the tach, tape up the end going to the computer, and splice the end going to the tach into the white/green wire. That would give the TBI tach the signal it expects. Or, if you'd rather modify the cluster than hack up the harness, you may be able to swap just the tach from the MPFI cluster into the TBI cluster. The drawings of the clusters in the two manuals are not quite identical, but they are very close. I would not be surprised if the tachs interchanged mechanically. I would however be a little nervous about swapping the plastic needle from one to the other to make the tach look at home (I'm assuming the '87 is orange and the '91 is white). If the tach itself is the same between the two clusters, but has different control circuitry, and that circuitry is easily separated from the tach, maybe you could just swap that circuitry from one tach to the other and leave the rest alone. If that pans out, you could basically convert the TBI tach to an MPFI tach, and get the job done without hacking up the harness or prying on a 36-year-old plastic tach needle. Or, yeah, if you don't mind the look of the '91 cluster, save yourself some screwing around and just huck that in there.

My LSD has been sufficient on wet/dry trails and some snow, but I don't do rock climbing.