So how much more power did you get from switching to the 4.88's ive got 35s and im still stock gears, but 6th gear on the hi way finally feels right did your hi way mpg get hurt from the 4.88s? Good info on the spacer

 

Hope this cures your rear diff woes Ace. I will call you soon about stuff.

 

wow... that does sound expensive. But, you probably saved someone else the agony in the future. So, thanks for posting this info up.

Curious about the power difference with the 4.88 gears as well.

 

Yeah I remember discussing this with you in Moab. I think I mentioned East Coast Gear Supply, as the place to get you straightened out. Hopefully you won't have to revisit your rear dif, anytime in the near future.
I still believe the best gear combination for the FJ is the 4.56's , unless you do nothing but trail driving and crawling. Even with the 4.56's and 315/75/16's, my gear ratio is slightly lower than stock. I think that makes the best combination. It gives you slightly lower gearing for highway power, but keeps less money flying out of your wallet for gas. If you pull a really heavy trailer
( for the FJ) 4.88's would seem to work well, as long as you don't want to make time, on the highway. The 4.88's probably get you about 2700 rpms at 70
I think I may be at about 2300 with 4.56's
Acre, you can probably verify that with your experience.
thanks
Don

 

2300rpm@70mph with 4.56's is close enough to stock for me!

Unless I was driving a 4banger... 2700 would suck for daily driving. I think I'll stick with 4.56 when the time comes. Thanks!

 

I'm going to get 4.56's installed around the first of the year, what is it costing to get this done, parts and labor?

Thanks

 

can you put 4.56s on the 6mts without a new carrier or is that only for the 4.88s?

 

On the 6MT you do not need a new carrier up to 4.88 It already has taller gear than the 5AT and thus a larger carrier.

 

I agree with don...i went to the nitro 4.56 over a year ago, and NO problems to date. they work great with 35x12.5x17, and when i make the switch to the 37's, i cant see any issues.

 

Thanks FJinCO

 

This post was mostly done to warn others of the kind of pitfalls that can come up with a gear change (or any other significant mod). Overall I am pleased with the 4.88s. Mileage dropped about 2 MPG but this can't be blamed on the gears alone as turning the 35" BFGs takes more fuel too. I tow a 3300 LB travel trailer most days as it is my full-time home and the 4.88s are just right for that, allowing me to tow comfortably in 5th gear with auto trans, at least on the flats. If I were not towing as much as I do I would have gone with 4.56s.

More power? Of course but it's hard to say how much. It is a lot quicker off the line and does much better at rock crawling. Highway RPM is around 2200 in 5th at 65 MPH. Gear swap caused speedo to read exactly 10% off.

Another point in my decision to go with 4.88s was my truck is set up as an expedition rig and is very close to GVW with all the stuff I carry.

Alan

 

Just say no to crush sleeves. Another thing is, if the installer overtightens the pinion nut, then the sleeve becomes too short, thus more play than needed.

I just completed a re-gear on mine and went 4.56. (315/75/16 KM2's). I got the set from justdifferentials.com and started off with the mini-rebuild kit. Before I was done I wound up getting the master rebuild kit which included the pinion bearings. Their kits come with the solid spacers instead of the crush-sleeve type. Pinion bearings are hard to salvage upon removal and it is recommended that you go ahead and order new ones. Mine were all simply worn out, including the front diff bearings.

My only glitch is that now I have a "VSC Off" dash light permanently. I'm sure it's a sensor wire, but not sure which one. Anyone have some insight on this?

 

No changes in any of my lights, A-track or locker operation after the swap.

 

Turns out my ADD switch/motor crapped out. It was causing the VSC light to come on because it had "locked" the collar on the front axle connecting the diff to the front drive shaft. The t-case was still in 2HI, so no real damage to anything, but when parts aren't where they should be, the sensors go haywire.

Now I just have to figure out how to fix the ADD and the additional problem of why I'm not getting power at the ADD switch. Ughh.

 

The crush sleeve is the adjusting method to set the bearing pre-load. Generally this sleeve is very robust and takes a lot of torque to crush "down". In most cases the crush sleeve should not be re-used, only replaced. Sometimes the new sleeve is the solid tube spacer. The solid spacer requires shimming to set the pre-load and is therefore an iterative process and takes longer, so poorly trained techs will take a short cut and re-use the crush sleeve or install it improperly. The other thing is that no mattter which style you use, the pinion gear depth is set independently of the bearing pre-load, so I would wager that was done incorrectly also. How unfortunate

 

Excellent, thanks Lee! I was not looking forward to dropping the coin on a new ADD after just spending all that $$$ for the gears. Tracing the power interruption will be the next challenge.

[update] my buddy just soldered the connections on his spare "bad" ADD actuator and now we have a good one we can install. I'll pull mine off and do the same thing and see if this fixes it. He's been studying the diagram and thinks that the ECU/tcase won't send 12v power to the ADD if it is not working properly. Thus why we have 12V at the fuse panel but not the wiring connector above the diff. Will keep y'all posted.

 

The newly soldered ADD switch worked perfectly. Thanks again Lee for the thorough article.

 

Good deal Rick; you're welcome! Thanks for the feedback.

 

notice brass lead on the right is not touching the vertical lead coming in from the wiring harness.

 

notice brass lead on the right is not touching the vertical lead coming in from the wiring harness.

Exactly how mine were also. Amazing to me that Toyota thought a press-fit connection was OK there. Easier and cheaper to assemble I guess.

 

Did you use Moab 4X4 in Grand Junction for the gear swap?

 

Alan had it swapped in Moab.