This is my first time posting here and I need to say that I am not a mechanic but enjoy tinkering. I have a 2000 blazer that I am building for my son. I have a stupid question; When I have the *** end jacked up off the ground and put the tranny in neutral, the back tires rotate forward. Is this normal or does it indicate a problem?

 

Is the engine off or on?

Are they both rotating at the same rate and in the same direction?
Is one rotating forward and one backward?
While the wheels are rotating is the driveshaft also rotating?

 

Yes the engine is running and both the wheels rotate forward

 

Sorry Christine I should answer you question completely
Engine is running
Both wheels are rotating in the same direction however not quite as fast as when in drive
I will need to check the driveshaft but can only assume it is also rotating

 

I have not done such a test before, or at least for a very long time. But my guess is that it might be some artifact of the hydraulic pressure from the fluid in the automatic transmission that is causing this. As the owner of a local transmission shop told me; any automatic transmission is basically a big fluid pump. The important thing is that there are no gear to gear connections; i.e. no mechanical connections to between the driveshaft and the rest of the gears in the transmission.

I'm guessing that you could stop its rotation if you wanted while it was in neutral. Right?

And I also probably don't need to tell you to be very careful when putting any vehicle into gear while it is on jackstands.

 

That's normal. Parasitic drag. The torque converter into and thru the transmission is either fluid coupled or fluid and gears and due to viscosity of the trans oil, the engine rotation is sent thru the trans. If a manual trans similar, the gears may be disengaged but one shaft turning transmits torque to the other from fluid drag.

There should not be enough to move the vehicle on level ground. Also idle too high worsens the problem. My 95 S10 sometimes will move a little in neutral on flat ground. It has a factory Remanufactured trans.

This happens on 4x4s with the front axle unlocked- The np2500 transfer case in my Blazer rotates the front shaft while driving. can see it turn with the shift boots removed.

my personal test (not necessarily recommended for everyone) is " can I stop it by hand?

Front d.s yes, rear by holding the rear wheel

Do that with due caution, never allow loose clothing near rotating parts.

 

Thanks Christine I will have to check this

 

Thanks Dave I will see if I can stop it by hand