97 gmc sierra making a loud humming noise!

[Bambito]

When I accelerate it gets louder. 30 to 40 mph is the worst. I almost don't hear anything at 60. It is definatly coming from the front. I just had the tranny rebuilt a year ago. Any thoughts? Thanks guys

[Macgyver55]

Front hub and bearing without much question.

[Scott K]

+1

[Bambito]

Kinda what I thought. How much am I looking at to have a mechanic shop fix it? Thanks guys!

[Macgyver55]

Depends somewhat on the quality of bearing you use. A premium one is about 200 at Napa and the standard grade one is about 125 . Add 150 or so labor depending on where you take it and it should be 275 on the bottom end and maybe 400 or so on the high end.

[efgh]

You never said if this is a 2 or 4 wheel drive, If its 4 wheel drive make sure both hubs are locked out. If one is locked in the other out the dif. will make a real loud hum. If its a 2 wheel drive the above posters got it pegged.

[Bambito]

Thanks magyver...it is 4 wheel drive. I have put over 100,000 miles on it and never replaced bearings. I sure hope it's not something to do with dif. Mine is push button 4 wheel drive so how could one lock and the other not?

[Macgyver55]

Does it make the noise all the time, or only in 4wd?

If it only makes the noise while in 4wd then it is possible it is a bearing in the front differential, if not then again the hub and bearing assembly is the most likely.

I'm not quite sure what you are asking about one locking and not the other.

[efgh]

When the veical is changed from 4 wheel drive to 2 wheel drive the front hubs in center of the rim, or wheel unlock, the axle, the dif. and the drive shaft do not turn then. The hubs lock and unlock automaticly. After a period of time rust and dryed grease will freeze one up and it will either be locked in or unlocked all the time. When one is locked and one unlocked the diff. will be spinning 2 times as fast as normal. We had this happen on a trip up north, the oil in the diff. got so hot it started to smoke before could figger out what was wrong. It got so hot it ruined the seals in the diff. I changed the auto hubs to manual lock outs.

[Macgyver55]

What you are saying can be true of older vehicles that used manual or auto locking hubs. There are however no manual or automatic "hubs" on this vehicle, the locking and unlocking occurs in the front differential.

Both front axles are live and turning all the time, but do unlock from the differential.