Hi guys,

First time here. Lots of great info on this forum

I have a 97 F150 Extended cab 4 x 4, 4.6L, automatic and have a strange intermittent noise from the drivetrain.

I can be driving for 2 or 3 months and hear nothing. All of a sudden a low whining sound comes up while driving. It appears to start at most any speed. Usually, I just let off the gas and it quits. Won't hear it again for 2 or 3 months.

I did have it start one time and it wouldn't stop, though. I limped home at 30 mph. I shut the truck off and started it again, but it still did it - from 0 mph. It did nothing when the engine was revved, only when the truck began to move. It almost sounds like it's trying to drive in 4W low. It gets higher pitched as the truck rolls faster (30-40 mph is as fast as I felt comfortable driving with the noise).

I took it to my mechanic and he drove it for a bit... so he heard the noise. When he drove it onto the lift, it quit (this was last Nov). Hasn't done it again until the other day.

My mechanic didn't tear into anything, but I had him replace the oils in the front and rear end, as well as the transfer case. Nothing unusual as far as filings / bits go. He checked all that he could without charging major $$, but couldn't figure it out.

I've read some other posts that talked about their trucks getting stuck in 4W low and needing to replace a "Mod-Asy", but they *started* in 4W low. I didn't. I think I've only used the 4W low once. BTW --- I've had the truck for a little over a year.

*That's the best way I can describe the sound; as though it's trying to run in 4W low...

Any suggestions / similar problems??

Thanks !

-Steve

 

First of all you did not mention how many miles are on the truck. But being a 97, I would have to guess about 125,000. The sounds you are describing sounds a lot to me like the rear end gear whine. If it is still happening intermittently, then I would say that there is a bearing going bad in the rear diff. The rear because you said that if you are on the gas then you hear it and not when you let off of the gas. If it is happening all of the time now then I would say it is bad gear mesh. If you trust your mechanic, then I would have him check out the backlash in the rear diff. This only requires removing the cover and setting up a dial indicator, not too much time. The other option, and if I'm right then you have an 8.8 rear, the 8.8 is good for wearing out the outer axle bearings. When your mech. has the diff cover off, pull the C-clips and pull the axle shafts out. If there is a worn spot on the axle shaft just inside the seal area then you need new outer bearings, and maybe axle shafts.
All I can think of for now.

Hope this helps

Steck

 

Hi Steck,

Thanks for the info. You were very close on the miles - 126,000. I don't know at the moment what the rear end is, but I'll find out when I take it to the mech.

I haven't been able to tell whether the sound was coming from the rear end or front end (I need to be standing beside the truck while someone else drives it), but I'll do as you suggest and have my mech check the rear end.

I'll let you know what I find out

Thanks again.

-Steve