Differential Compatiblity and Regearing Help

I have a 1999 Taco, 2.7l, manual tranny. Door code is A02 meaning I have 3.58 gears. I bough the truck with 30/9.5/R15 tires and it's now wearing 265/75/R16s. I live in a hilly area and do a fair bit of towing and hauling (ranch truck, so firewood, water, feed, etc. Lots of heavy stuff.) I don't do any wheeling, just driving on muddy, snowy, and uneven terrain.

I want to re-gear to 4.10, but have questions and I'm having a tough time finding info about what's involved. I'm on a budget but only want to put quality in the truck, so looking for the best bang-for-buck option.

Should I buy a pre-built 3rd member from ECGS, or rebuild a used OEM 3rd member? Can I use a 4runner, etc. diff or does it need to be from a Tacoma? Do I have 7.5", 8", or 8.4" in the back? Should I add a locker, or is that unnecessary? Who makes good quality gears?

Thanks!

 

I have the same set up as you and will be regearing soon to 4:56. I don't know why but every 4:10 gears I see cost more then 4:56 and 4:88. Getting a built 3rd member from ECGS will be probably your best bet. I'm assuming you don't have a rear elocker so you would have a 8.4 rear diff. You'll have to do the front as well which is a 7.5 clamshell ifs. I'm going with Nitro gears when I do mine.

As far as lockers go. It depends on what you want to do with the truck. If you heavy off road with rocks...definitely. If you're like me and only mild off road then it's not needed. I can't justify the cost for lockers for what I do.

 

Yes, I see that 4:10 costs more usually. I don't want to give up too much top-end because I often have to drive freeway miles to get to the feed mill, etc.

I don't have an e-locker, it's an open rear. I don't do any wheeling, nor plan to.

So any Toyota 8.4" 3rd member should work? Like if I buy a front/rear 3rd member pair off another vehicle (like a 4runner) and have them rebuilt, that should work as long as they're the same size as mine?

 

As far as I know any Toyota 8.4 rear diff 3rd member will work. That's my understanding from my research on doing mine. Maybe someone will chime in if I'm wrong.

 

I was in a similar situation. The 3.58s made it impossible to maintain 5th gear on the highway on a windy day. I went the cheap route and bought some junkyard 4.56 diffs off car-part. I'm in both diffs for 400 all together. Im still about 12% over geared but the 4.56s compliment my 33s perfectly.

Of note, while 4.10s are expensive to buy as gear's and set up, 4.10s are probably the most common diff I see in junkyards by far. Any 7.5 front diff, even from a 4runner should fit but an 8.4 will only be found in a tacoma tundra or t100 iirc.

-One caveat: not all 7.5 fronts are set up with ADD. I have manual hubs which is a bit less common

 

Did you rebuild the diffs before installing them on your truck? If there were low mileage (whatever that is for gears and bearings) you could just drop them in, but did you inspect bearings and ring/pinion gear patterns?

 

I'm going to be honest with you. Everything I've done so far with my truck could have been done better or at least more professionally. I'm currently running a ford ranger middle leaf as an add-a leaf and recently made my own top plate spacer out of HDPE- aka a plastic cutting board. I offer no advice. That being said, I didn't rebuild the diffs or have them taken apart to be inspected, I just threw them in. I did clean them out as best as I could and followed new diff break in procedure. I've spent quite a bit in 80-90w gear oil but have had sucess. No rumbling or any noise of any kind so far (it's been about 2k miles since install)

Keep in mind my situation is probably very different then most - I bought my truck with 244k on the odo and near any part I found would have less miles. I found a 4.56 diff with 74k on it at a junkyard in CO. They were closing and only wanted 150 for the diff plus 50 in shipping. I had a mechanic friend give it a 2 cent once over; nothing appeared off according to him. I cleaned the he'll out of it and threw it in.

I understand I was taking a gamble and was prepared to have at least a spare diff to rebuild if the diff turned out to be bad. Same story for the front diff. With manual hubs one would presume the diff saw less action than the miles would imply but who really knows?

As with all things, your mileage will vary.

 

My truck currently:

 

Looks just like my truck!