1st Gen (4x4) Rear Diff Question

Hey all!

I had the rear end of my Tacoma up today for a couple things, and noticed something that seemed off to me.

So, truck (5spd) in Neutral, e-brake off, front wheels on ground, rear axle on jack stands.

When I was spinning the passenger side rear wheel, it made the drivers side wheel spin in the opposite direction- this is obviously expected.

However, when spinning the drivers side wheel, it didn’t cause the passenger side wheel to rotate at all. The driveshaft was spinning, but the passenger side wheel remained still. I did get a little movement out of it when I started spinning the drivers side wheel very fast, but not much.

If I spin the driveshaft by hand, both wheels spin (in opposite directions), again, as I would expect.

Is my diff secretly fucked? Am I essentially running on one-wheel drive? I don’t know enough about how differentials work to make any sense of this. It’s totally silent and the fluid was perfectly clean last time I changed it (~2k miles ago). No bad diff sounds while driving or otherwise.

 

Perfectly fine. That is how a open diff works.

 

change ur balljoints

 

Whew. That’s a relief.
What is the explanation for it behaving differently when you spin the passenger wheel vs the driver side? I was previously under the impression that whichever side you spin, the other side should spin the opposite way.

Done bro. Did that first thing I bought the truck, lol. I know you were being facetious but I know I tend to be a bit paranoid.

 

Put it in gear, then each side turning will result in the other side turning the opposite direction

 

I’ll give that a shot tomorrow, just so I can try and wrap my head around it. I mean that makes sense and all, but differentials in general have always been kind of hard to grasp for me. Idk, maybe I’m just dumb. I can rebuild a motor but I don’t understand how a differential works.
Still though, why did the passenger side wheel rotate the drivers side when it was in neutral? Is there something about the gearing that makes that work when in neutral?

 

It's fine. A tiny little bit of brake drag can cause that to happen.

Like suggested, put it in gear. It'll then behave just as you are expecting it to.

 

It just depends on where the friction is because your test allows for multiple outputs because you are driving one input with 2 free outputs. If you spin a wheel and *hold* the driveshaft you will get opposite rotation in the opposing wheel (no ring gear rotation all differential rotation). If you spin the wheel and *hold* the opposing wheel you get rotation of the driveshaft (some ring gear rotation and some differential rotation). If you spin both rear wheels equally you get driveshaft rotation again (all ring gear, no differential rotation).

So when you only spin one wheel with the other items free then the friction at each will determine how the forces balance and what ends up getting driven.

Also, when you spin the driveshaft the wheels will not rotate in opposite directions. Turning the driveshaft is ring gear rotation so it drives both wheels the same direction and any differential action allows speed differences but can't drive them in opposite directions.