i have a 2001 blazer 2dr. 4x4 with 72k and im having troubles with my 4 wheel drive. when im in 4hi and my truck goes into overdrive there is a low humming/vibration. i thought it may have been the t-case so i replaced the fluid because i didnt know when the previous owner had done or done it at all. replacingthe fluid didnt make it any better.

any thoughts or tips would be greatly appreciated

thnx

 

driveline out of balance, orbad U-joint. Thats alot of rotating mass going if you are gettin up into overdrive in 4 hi. do you need 4 hi that often as to be runnin down the highway in overdrive?

 

would the drive shaft need to be balanced? how much are new u joints?

 

The driveshaft should not need to be rebalanced unless it is severely corroded (probably should replace it), the weight fell off, or if it somehow got bent (something which you should know happened).

As far as the u-joints, the joints themselves are fairly economical. The replacement can be a pain though.

 

ive noticed that it does it while in 4hi but when its in auto 4x4 it doesnt do it so im thinking its somthing in the front end. am i headed in the righ direction. because in auto doesnt the frent driveshaft turn but the axles arent spinning??

 

anyone????????

 

If you are in AUTO4wd, the front axle may or may not be engaged. This would seem to lead me to believe that it is either in the diff itself, or one of the outer drive shafts. Although I suppose it could be in the front driveshaft itself, but only manifests itself when the front axle is engaged (power being actually transferred).

These front drive shafts have a rather odd joint in the back of them that can dry rot and go bad. You should be able to assess the condition of this joint just by pulling on it from under the truck. You also can simply look into the cup portion of the joint looking from the front of the driveshaft back towards the transfer case.

 

thanks for the reply, i'll put her up on the lift and see what we got and ill get back to you

thanks again...