4.56 front diff

So, the first can of worms I'm getting into this year is re-gearing my 97 to 4.56. The truck currently has 3.58 from the factory which makes it a complete joy to operate on mountain roads. I'm also the first one to shift in 4low.

I ended up finding a used front diff on eBay to kick off the project. I chose to buy the front diff used with the ratio I want because it's really only going to see a couple hundred miles a year and I'd like to get this done inexpensively and used saved money elsewhere. The truck my new diff came from had manual hubs, so presumably the unit I received is new enough inside and not completely clapped out from spinning for 300,000 miles.. The donor truck had a door code of B04A.

First thing I do on the bench is turn the input shaft 4 times while watching a marker on the axle output turn. After 4 turns, the marker lands in the same-ish spot. I would expect 4.5 turns on the input shaft for this to happen.

I also turned the input shaft 41 times and my marker ended up in the same spot. This is where I think a 4.10 diff would land.

I continued to turn the input shaft 45 times and my marker also ended up in the same spot?

I'm confused now. Do I need to crack this unit open and count teeth? Anything else I should do to this diff before installing it in my truck?

 

Agreed, that looks like 4.10 in your video. Triple-check and make sure that nothing is dragging--in other words, make sure the two sides are spinning at the same rate.

From what I know (mostly based on internet research with a bit of inspecting trucks at the junkyard), 4.56 gears were only installed with 4-cylinder engines and automatic transmissions. An A/T with manual hubs seems like an odd combination to me--the combo did exist, but I don't think it was common. A 4-cylinder A/T with manual hubs seems especially rare.

Manual hubs would be much more common with 4.10, 4.30, or 3.XX ratios.

It might be worth cracking it open to verify the gear set, but I'd contact the seller first. Opening the diff could complicate the return/refund process if it comes to that.

 

4.56 was a very rare gear ratio on 1st gen 4x4 tacomas. It was slightly more common on 3rd gen 4Runners, but that wouldn’t have manual hubs.

Best way to check is to do what you are doing, but put a piece of tape like a flag and record a video. That way you can count the rotations afterwards. Normally I would say rotate the axle shaft 10 times, but that might be difficult.