[dslemaire]

97 Chevy Suburban 1500 4wd just started grinding noise under hard acceleration or under load from underneath. Maybe transfer case or transmission area?

If I let up on the gas it stops immediately. Once I'm driving it sounds perfectly normal. Transmission operates normal. Shifting transfer case to and from 4wd is normal.


This one really has me baffled as driving down the road it seems normal. I only get the noise with a hard acceleration. Sounds like gears slipping or grinding.

Checked all the u-joints which I greased a couple days ago and they're all tight. Output shaft seems tight at the driveshaft. No leaks except the transfer case is dripping some oil slowly, but hard to tell from where as it's coming from above.

Swerving on the road seems to eliminate any wheel bearings as I can't reproduce it that way.

It almost sounds like gears grinding momentarily and when I let up it goes away. And I checked with the AC off, so it's not that.

This all just started at the end of a 800 mile drive yesterday.

I'm in upstate NY for my sons college graduation and I hope we don't get stuck far from home!

Any help or ideas would be greatly appreciated!!!

 

[MrShorty]

Just an idea to throw out there, I don't know if this will apply or not. Under hard acceleration (epecially with a solid axle with leaf springs) you can get a phenomenon known as axle wrap. Basically the torque causes the axle to tilt up (or is it down, can never remember) more than usual, which changes the geometry at the driveshaft/differential connection. Where your grinding seems to only occur under hard acceleration, I'd go back to that rear u-joint and make sure it's ok (I have seen u-joints where the bearings were dry and starting to rust, but they hadn't gotten "loose"). I'd probably also check the pinion bearing as best I could in case it is coming from the pumpkin.

 

[dslemaire]

Turned out to be the chain jumping inside the transfer case. We put in a used one and made it home. But the solinoid in the front differential is not engaging for some reason. It has 12v, but won't seem to kick in.

 

[Beck9018]

Hey, got the same exact problem going on with my 97 Silverado. At first I thought it might be the torque converter, but after reading your post I'm thinking the transfer case could be the problem. Did you end up replacing the whole transfer case or just the chain itself? Thanks.

 

[dslemaire]

Turns out after talking with the trans repair man that it's a common issue with these transfer cases. Apparently the oil pump wears a hole through the top of the case and it starts to slowly leak out the oil. Mine seemed a little wet, but it's hard to say what happened first. The key is regularly checking the transfer case level and if it is leaking to get the leak fixed right away. He said many people think it's a gasket, but it's not the problem.

In my case he could have rebuilt it and would have charged approx $900 and 3 days. I was on a trip for my sons graduation and had to be home on Monday and it was Friday afternoon. So they put in a used one for about $700. He had a guy come in and work into the night to finish it for us which was amazing. So I picked it up the next day and then drove home that weekend.

Next time I see any oil on the case, I'm going to take care of it right away. I think he said there is a mod they can do to prevent the problem next time around.

But don't put it off to long. He said eventually the chain keeps slipping or something break and then it can get more expensive with parts flying around.

I also had them change the trans oil just to be sure it was all ok.

It could have been worse.