Understanding the front axle assembly

I have the stock front axle assembly...and, I have some questions.

When the truck is moving in 2wd, what front axle parts are moving?

Driver's side axle, passenger outer axle...right?

What in the differential is moving? Is the passenger intermediate axle moving?

Roy

 

There are random things spinning based on what has the least resistance. Normally you would just be spinning the spider gears in the diff, and the driveshaft would not spin. Ring and pinion and driveshaft my slowly rotate based on friction.

 

Great. How about the passenger's intermediate shaft?

 

From what I can remember (it’s been a hot minute since I’ve rebuilt the Front axle on the Gen 1) the intermediate shaft DOES rotate with the pax side axle though no power is transferred TO that axle unless the 4wd selector/coupler is engaged.

I found this out the hard way when the spider gears in the front end somehow were shaved clean. Never knew I had an issue except that I had a good 4 or 5 tanks of fuel that were netting me 400+ miles a tank. Hahaha.

Well, that AND my 4wd wasn’t working.
Rebuilt with a new front end (2001) and added spider trax lockers to the front and back difs. That little truck was unstoppable

 

OK. So, the moving drivers axle, moves the spider gears, which cause the intermediate shaft to rotate. Is that right?

 

If the driveshaft is not spinning then the intermediate shaft is spinning backwards due to the spider gears turning, but the ring and pinion is stationary. Odds are, everything is slightly turning just there is no load on anything.

 

OK, here is my next question.

Say, the axle is locked but the transfer case is not sending power to the front drive shaft. I know this is not a normal situation.

But, the question is, what's turning in the front axle assembly then? Will the front axle "feel" like it does in normal 4x4 mode (kind-of resistant to turning at low speed)?

 

If the axle is locked, I’m guessing you mean not an actual locker, but the disconnect, then the whole front axle assemble and driveshaft is turning. Lots of drag, but should steer almost normal as the spider gears would allow for differential of tire speed, and the drive shaft isn’t turning with the transfer case.

 

That is right...I am just talking stock parts.

Thanks for the help with this. With an open diff, I was just not understanding the importance of the stock axle-unlock feature. But, you are suggesting, I think, that is is actually not that important. Right?

It is not like the manual locking hubs which kept the axles from spinning.

 

The whole point is for it to reduce drag and increase MPG. Locking hubs are the ultimate drag reducing option, but they require you to get out and lock them and who wants to do that

It’s a lot of drag having the front locked. My 88’ 4Runner in 2wd with the hubs locked feels like I lost 30hp

 

Humm. But, where is that drag coming from?

Without power to the front drive shaft, there seems to be the same amount of stuff turning with and without the ADD locked. No?

4 CV joints, spider gears, the bearings in the diff which support the inboard end of the axles...all moving whether or not the ADD is locked.

 

The difference is they are not fighting each other. With 250ish hp not a huge deal. My 05’ Cummins has no hubs or disconnect, yet it has 610tq so it doesn’t really care if the whole front end is turning. However, if you are a manufacture and trying to get eco credits for mpg across your entire fleet, fractions of a mpg matter.

 

No. He's saying on his 4x4 4runner with manuals hubs locked (turned on), with the transfer case in 2wd hi it still had significant drag.

It'd be 4x CV's, outer intermediate shaft bearing and carrier bearings (and case/spider gears). Plus the weight (inertia) of these getting up to speed (like a lightweight flywheel vs a stock one).

If there's enough drag the pinion gear/bearings and driveshaft will also be turning, even if not engaged inside the transfer case.

 

I know it’s for gen2 but same concepts:

https://youtu.be/47m7QAPrpsI

 

Good explanation of the system in that video. That's exactly how my '01 worked when I was rebuilding it last year. Since the 4wd stuff was all out of sync, I spent some time playing with both actuators and seeing what moved when each one was engaged.
Facinating.

 

Wow...heck of a video.