Hello,

I have a 2001 4X4 Blazer with an auto trans that now makes a noise when driving in 4Hi. I'm pretty sure the sound is coming from the rear. Regardless of the smoothness of the surface, it makes a sounds like I am driving over a bump. When I go back to 2wd, there is no noise. Back in 4Hi, the noise comes back. It's just a sound you hear when you drive over a bump.

Sorry but I can't describe it any better. I am searching the forum now for any similar posts but so far I have not found any.

If anyone has any ideas about what the problem may be, I would appreciate hearing from you.

Thank You

a clunk?

Are all 4 tires the same size? Are they the same brand? And are the fronts worn worse then the rear or visa-versa? I have seen where mismatched tires cause noise when driving in 4wd.

All 4 tires are the same brand and size and are relatively new. The sound could be a clunk (or a thump).

Thank you for your replies.

Do this with a helper: put a chaulk mark on all 4 tires in the same place, then slowly drive the truck forward until one chaulk mark (lets say the LF) comes back to the same spot. Then take a look at the rest of the marks, this will tell you if one or more tires are not the same diameter. I have seen some economy tires not be the same diameter. this is just an easy check and will tell you for sure if it the tires or not. Other then this, the only thing I really can think of is maybe the chain in the t-case is streached and jumping teeth, I just replaced a t-case last week for this problem. DO the tire thing though and let me know, if you cannot tell after 1 revolution, try 5 or 6 revolutions and that will make the difference more obvious. It is a very easy test and will tell you allot!!

Are you driving in 4hi on dry roads?

Korey: Thank you for the reply and the suggestion. I will try it and let you know.

Hanr3: Thank you for your reply. I never drive in 4Hi on dry roads.

Again, thank you both for your posts.