The front differential project.

Twice I had broken the front ring gear on my Mega Runner. That's at least once too many. I had not been abusing it. Nothing special. Just tackling the same obstacles as anyone else did with their trucks. It still broke.

It was easy to understand what was going on. Strong engine and big wheels. The front diff in a 4Runner is not known to be overdimensioned. Since I had converted my 4Runner to a Mega Runner, it just could not take the strong torque applied to it. I slowly started to wonder what to do to improve the front diff. The following ideas came to my mind.

  1. Installation of a front locker. This should be a unit that would be stronger than the original differential. I had been told that one reason for the ring gear to brake, was that the original diff carrier is to weak, and that under heavy load the carrier may flex, which of course will allow the pinion to climb on the ring gear. This could be one explanation to the broken ring gears.
  2. To find some heavy duty pair of ring gear and pinion.
  3. To be even more careful when driving off-road. If possible, to Thread even Lighter. :-)

The more I thought of it, the more I was convinced that this would become a big project. The installation of a front locker in a 4Runner with IFS and ADD means a lot of modifications. The consequences from this mod' are many and important. The following plan slowly crystalised:

  1. Installation of a True-Track locker in the front. The True-Track is not a full locker, as the ARB locker that I had already installed in the rear. It is what they call a Torsen Diff. Torsen diffs are built to work well in front, without giving any (or at least very little) steering resistance. By the way, this is what you find on the Hummer, so it cannot be that bad.
    The True-Track, sold by amongst others NorthWest OffRoad Specialities (NWOR), is supposed to be very strong and resistant to flexing. That's what I was looking for.
    2. Richmond Gear logo.
  2. New ring gear and pinion from Richmond Gear. I'm not sure if they are so much stronger than the original pieces from Toyota. At least they are said to be extra heavy duty. We'll see.
  3. Re-gearing from the original 4.55:1 (9*41) to 4.88:1 (8*39) should also improve the strength. Having 39 teeth on the ring gear should be stronger than having 41. Each tooth will be wider and thereby stronger. Admittedly, the teeth on the pinion will be weaker, but so far I have never broken any pinion. Only ring gears. (For a while I did even consider going to 5.29:1, but was adviced not to, by the Downey people. They told me that it would make the pinion too weak instead.)
  4. Well, re-gearing in front will of course mean that I have to do the same thing in the rear. Just to avoid strange behaviours when engaging the 4x4. Like folding the truck or something like that. :-) A simple matter of a rear re-build.
  5. Installing a front locker in an ADD diff is not a good solution. Since, in 4x2, the right wheel shaft is always rotating with the wheel, the left wheel shaft is disconnected and the diff is not rotating at all, the locker will have a lot to do to make sure that both wheels turn at the same speed (!!). Not very good for the locker. So, the ADD has to go. In reality this means to block the ADD in engaged mode.
    I am not the first to remove the ADD functionality. It has been done by others. So it's a proven technique.
  6. Blocking out the ADD means that the wheel shafts, rotating with the wheels, will turn the front diff and thereby the front drive shaft even in 4x2. Not what I wanted. So, I had to mount free-wheel hubs on the front wheels. I chose the manual hubs from Warn. Of course I chose their premium hubs, looking for the strongest possible result.

So, from a broken ring gear, this became quite a big project. But, I also expect to gain quite a lot from it:

  1. An automatic front locker is not too bad.
  2. Re-gearing both front and rear means that I will re-gain the loss in torque that I experienced from having mounted bigger tires. (I am running 33*12.5*15 BF Goodrich AT or MT, depending on where I am.) It will also mean that the forward progress will be slower on first low. This is good both for nature and truck. (The Marlin Crawler keeps popping up in my mind, but I will have to leave that to a future project. ;-)
  3. Manual hubs means that my wheel shafts will not rotate in 4x2, as they do with the ADD system. This should reduce wearing and improve gas mileage.
  4. I just hope that the new setup will be strong enough for the torque that I put on it...

Current progress:

  1. In December 1997, I mounted the manual hubs from Warn.
  2. During January 1998, I built a complete front axle from an old broken one that I had laying around. It's now equipped with 4.88 gears from Richmond Gear and a True-Track. Of course, all bearings and joints are brand new.
  3. In early March, 1998, I mounted the complete front axle, including a True-Track, on the truck. I also 'disabled' the ADD system by blocking it in an engaged mode.
  4. In April, 1998, I finally re-geared the rear differential. The rear now has 4.88 gears, just as in the front.
  5. Project is finished.

Next steps:

  1. Try it off-road.

Back to my Mega Runner.



Author: Me.

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