Gear grinding type noise Need some help
 

I am hearing a grinding gear kind of noise. Sounds like its up in the front. Occurs loudest when I decelerate and changes in pitch from high to low as the vehicle slows down. I can feel it vibrate on the floor. It's not affected in any way by my turning. When I press the gas the sound seems to lessen or perhaps disappear. When I drive in reverse there seems to be a clunking sound and the reverse motion is not smooth.

Any thoughts?...and with your thought can you suggest what I should pay a mechanic to have it fixed?

Thanks.

Could be any number of things but possibly easiest thing to check 1st are the driveshaft joints? If they start to break up they can make a fearsome noise.

Maybe flex plate?

Heffty: if your Blazer is a 4wd, it is probably the front differential is slightly engaging. The gear grinding noise you hear is just that.
Is it a 4wd?

Yes it is a 4x4. I thought that might be the problem too...and it may very well be but I'm not sure. I put it in 4x4 high but the sound didn't go away. Then I put it in 4x4 low and back into 4x4high then to 2x4 to see if I could get whatever is in there moving around a bit. But the problem still exists.

I had a similar issue....my transfer case turned out to be the culprit. When I was driving it sounded like it was coming from the front diff....but when I got it up in the air, put it in drive and could listen from underneath, it was coming from the transfer case.

Of course being the idiot I am...I left it. Then winter came and i needed 4 wheel drive.

Well the lets jusst say it got real loud and a new transfer case from the wreckers was installed.

how much is a new transfer case?

Check your front differentials gear oil too, mine mad a nice loud whine when it was low

The problem is the rear differential. There is a leak that is visible and that is where the grinding sound is coming from. I jacked the vehicle up, put it in drive and then with a metal rod I put it on the diff as the wheels spun. Grind Grind Grind in there going on. So now I guess I either have a big job ahead of me or I just lay the Blazer to rest and move on. A mechanic said he'd put a new one in for $1000 including parts/labour. The 1999 blazer has 255,000km on it now, so if I do put money in it, what's going to go next? How much will that cost? Also...the blazer is a pig on gas as we all know and I mostly do city driving. The fiancée figures we should just buy a chev cobalt or something like that. I suppose I could always try to go to the wreckers and find a rear end to replace mine with...but I'm an electrician, not a mechanic so that task seems time consuming and daunting.

Any suggestions?