diffs for dummies

Hi all,
I need a remedial course in differentials.
I have a 1999 SR5 xtra cab 5MT 4WD. No RR locker button. aluminum stock wheels with no apparent hub locking function.

My understanding is that I have an open rear diff.

When 4WD is engaged, I *thought* the front diff was open as well. But, I notice pretty heavy resistance when in 4WD and wheels are turned to full lock. This suggests to me that the diff is locked (or no front diff?).

Before baring my ignorance for all to see here, I looked at the owner's manual that describes the "automatic disconnecting differential," but gives a piss poor description of it, so I'm no smarter as a result. Near as I can tell, it's just a fancy term for the center diff (which is hardly automatic since you actuate it with a shift lever).

Appreciate your explanations. If you decide to abuse my intelligence, at least make it funny.
Cheers,
JV

 

It binds because the front and rear drive shafts are locked at the transfer case. The front and rear diffs are open

 

You should only be using 4wd while the truck is on lower traction surfaces that will allow some of that binding to be released more easily. If you're trying tight turns on high traction surfaces (dry pavement, dry concrete, etc...) the tires can't slip as easily, and you run some risk of damaging the transfer case.

There are two main types of 4wd systems on these trucks. "J-Shift" and "Push Button"- which in the context of this question aren't important, but just as a good to know. When 4wd is activated in either system, the transfer case "connects" the front ds, power or vacuum is sent to the front diff actuator, which connects the front driveline together with the front drive shaft, to receive power from the transfer case. The transfer case does not have a differential. Power is equally sent to the front and rear. This is the reason for the binding you're experiencing. The front wheels are trying to travel at a different rate than the rear wheels.

 

Ive noticed the difference with the push button 4wd button and the shifter 4wd. what is the difference, and why did they have 2 different methods of doing it? it seems like you know more than I do/can find. I would think my 95 would have the "older" j shifter technology but it has the push button. maybe it was an option? last question. is there a way I can look up my vin or something to see all the options I have in my specific vehicle or is that something you cant do? thanks

 

The j-shifter is more mechanical than the push button. There might be some slight internal differences, but basically, the push button system uses an actuator to move the internal bits around, while the j-shifter uses the shifter.

 

I don't have a 2 lo. Im assuming the shifter doesn't have a 2 lo?

 

No one in a 1st Gen has a 2Lo. But those with manual hubs can unlock their hubs and engage 4Lo and thereby access 2Lo

 

very helpful; thanks. Makes sense that the binding is at the transfer case.

 

Or anyone who does the 'ol grey wire mod- they have access to 2lo as well. Effectively allowing independent control of the transfer case gearing, and 4wd actuator, which are otherwise coupled together.

 

Isn't the grey wire mod for using the factory locker in 2wd/4hi, not for 2-lo

 

Yea I realized there were other situations that could achieve 2Lo as soon as I typed that. A buddy of mine pulls his 4wd fuse to get 2Lo via the Jshift in the 4Lo position in his '98 with ADD hubs.

 

That's a good point. I'd imagine there is something similar to do that for non locker equipped trucks