Front Wheels Turning but not Drive Shaft

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This was discussed briefly on a previous thread but I'd start fresh. I have a 97 locked w/149K. After returning from Moab on Sunday and the truck sitting in the driveway a few hours, I tried to move it into the garage. Big time sluggish behavior, similar to low tranny fluid or e-brake on. I pushed they truck into the garage and jacked up the front axle. Both wheels turned with ease but the front drive did not move. I would think this would be a mechanical issue with the front diff but I have ruled out a possible sensor problem in the t-case/tranny. The FSM shows a "No.1 Vehicle Speed Sensor" in the t-case and a "No. 2 Speed Sensor" in the tranny...possible cause?

I had Precision 4:88 gears installed about 2 months ago. There is no grinding, leakage, or any external indication that there is a problem with the front axle or tranfer case. It drove home from Moab great and got 13.9 mpg. I disconnected the battery to reset the computer with no success. Another stange indicator is the speedo moves to 100mph with the key in the run position/not running and with the truck running.

I am looking for ideas. Thanks. Doug
 
jacking the front axle off the ground and being able to rotate both tires easily isn't any thing to be concerned about.

Now, if they both rotate in unison when only turning one than that is something to be concerned about. Then you have some sort of mechanical failure and need to dig deeper.
 
Landtank,
I thought when you raise the front axle and the rear axle is on the ground and the truck in in Park, the front wheels should not be able to turn. No? Wouldn't the t-case need to be in neutral for the front wheel to turn? Sorry if this is elementry and I am in preschool.

They easily turn...one turned forward and other backward.

Thanks. Doug
 
I pushed they truck into the garage and jacked up the front axle. Both wheels turned with ease but the front drive did not move.


You need to be more precise here.

If when rotating one tire, neither the front driveshaft nor the other tire moves, then you indeed have a front end problem. Normal behavior in that situation should be:

1) With diff open: Either the other tire rotates in the opposite direction or the drivshaft rotates (or a bit of both).

2) With diff locked: Both tires rotate in unison and driveshaft must rotate as well.

Curtis
 
Quick note...

With the truck in park and a wheel in the air, and the parking brake off (or faulty - common) these trucks can roll.

Never trust the parking brake. Use good chock blocks.

IMHO YMMV
 
Landtank,
I thought when you raise the front axle and the rear axle is on the ground and the truck in in Park, the front wheels should not be able to turn. No? Wouldn't the t-case need to be in neutral for the front wheel to turn? Sorry if this is elementry and I am in preschool.

They easily turn...one turned forward and other backward.

Thanks. Doug

That's exacty what should happen. What you're seeing is the differential doing its job. If you locked the front diff in the same situation, the front wheels would not turn unless the transfer case was in neutral.
 
x2... With it unlocked, the spider gears are spinning around in the carrier. IE, the wheels will turn in opposite directions, but the ring gear will not spin... That means the pinon won't spin and your driveshaft will not spin.

Now, lock in your front locker and jack the front tires up with the rear on the ground and you shouldn't be able to spin the tires... They will just move back and forth a bit.
 
Thanks all for straighting me out. I'm used to wrenching a 68 camaro with a posi. I need to turn my focus on the t-case and transmission. I also need to jumper my True Speed Calibrator per Truck Monkeys suggestion. I think the tranny is trying to start in Drive in lieu of First. There is not bogging down in Reverse.
 
Thinking about this, the lack of power could be driveline related if the front or rear were disconnected somewhere. I.e. worn flange, missing u joint, ? The 'weak moving' effect would have been as the VC in the TC was doing it's job in that scenario.

Vehicle well chocked. (Opposite corner from working on)
Transfer case in Neutral.
Front, rear and center lockers turned off.
Lift ONE tire off the ground 1"
Turn the tire. The drive shaft should rotate.
Repeat on all 4 corners.

Next, lock the center differential (either by switch or placing transfer in low.)
Repeat the above test. The wheels should not be able to turn more than bit.

When was the last time you greased the U joints? Does the engine sound/feel right/healthy?
 

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