How to CONFIRM both differential ratios, front and rear.

[eightynine4x4]

This is getting confusing. Maybe I can boil it down to a few simple statements for clarity.

1. There is no special relationship between front and rear druve shafts. Either can turn independently of the other. When you put the transfer case in 4-hi or 4-lo, it will engage the front shaft and everything will be fine.

2. Turning one wheel or axle shaft and seeing the other side turn the opposite direction is normal for an "open" differential. That is how they work. Turning the driveshaft and seeing this behavior is also normal.

3. When we say "open" differential, we are talking about one that does not have a limited slip assembly or differential lock assembly installed. Do not confuse this with engaging the transfer case or engaging/disengaging (locking) the hubs at the wheels. All totally separate assemblies and events.

4. Gear ratio is "inpututput". Ie; you turn the drive shaft or pinion X.X turns to get 1 revolution of the axle shaft or wheel. As you found, 4.10 turns of the driver shaft = 1 wheel revolution. Therefore, 4.10 ratio.

5. The differential gears are always engaged from input to output.

6. You manually or electrically shift the transfer case to engage or disengage the front drive shaft to attain 4-hi, 4-lo or 2-hi operation of the transfer case.

7. The hubs, engage or disengage independently from everything else. Either manually by you Turning a knob on each hub. Or automatically though mechanical design of the hub. Or by use of vacuum or electrical devices designed to do it. Or, in some layer vehicles or modified vehicles, the hubs are permanently engaged.

Thank you for this! All checks out to me, makes sense. I really appreciate the run down, it’s very helpful for a new guy. I think i feel comfortable now regarding the balancing concerns. I think i understand what sections of my truck are self cohesive and need to remain fastened together the same, and what is all separate and unrelated.

I’ve got my front shaft out and everything was marked before hand, and my front diff is fully unbolted (including the pinch bolt) but it sure is not wanting to budge haha. I spent a good 20 minutes trying different approaches to separating it from the beam but it’s just not moving in the slightest. I suppose the RTV is doing it’s job!

Pop thr cover off the rear and see what it says on the ring gear. If the truck drives in 4x4 without breaking itself.. you'll know the front matches the rear.

Don't worry about losing the fluid.. probably due for fresh lube anyhow.

Yeah i don’t see how i could have used 4x4 without grinding/strain issues if my rear wasn’t also 4.10.
I opened up the rear diff and did the axle seals just a year or two ago, so I’d rather not open it back up again haha.