For the past 6 months I've had a drivetrain noise that I can't find. The truck is a 1993 F-150 with 302, E4OD and elecric Warn 1356 transfer case. It sounds like a low frequency gear noise that seems loudest when braking. I can't really describe it, but it might be he sound you would get if you had a very noisy chain drive. It seemed less noticeable if I braked with the parking brake. I thought it was front differential noise since the auto hubs weren't always releasing, but after I put in manual hubs, I had the same noise. I then marked the front driveline and front axles with pieces of tape and found that they turned a little even in 2WD. So I then thought I had drag on the front axles and was turning the front driveline even when the hubs weren't locked. So I then took the front end apart and replaced the spindle bearings and the two outer axle u-joints. One was very stiff and the other was frozen. The inner u-joint on the right side was a little stiff, but after putting some oil on it, it rotates fine. I should replace it, but it flexes the least of the joints, so it hopefully will last the witner. I also replaced the front driveline u-joints at the same time. But after all th is, the noise was still there. It seems to be getting louder and I could wait until something fails, but I hate to let it fail when it wants to since it's winter here in MN and it's too cold to get stranded away from the garage where I can fix it. I also hear a high pitched whine when driving at low speeds, but think that might be related to the transmission. It's done that since the day I got it.

So here are my thoughts. I might have a transmission problem, but I've never heard a transmission make that type of sound. And, it shifts fine. Or I might have a transfer case problem. 2WD and 4WD (high and low) work fine. The noise is the same in 2WD and both 4WD high and low range. The chain in the transfer case could be the source of the noise. What does a transfer case sound like when the oil pump starts spinning. I understand that the ridges wear off the case and the oil pump can spin and not lubricate the gears. Or I could have a noisy rear differential, but the noise does't sound like it is high enough frequency for a noisy rear end. A last possibility is bad front wheel bearings. I've had the front end apart so many times and checked the bearings each time and they look fine. I've cleaned and regreased them twice just in case.

I will probably try to run some rubber tubing to near the transfer case and the differential and use it like a stethascope and see if I can hear where the noise is coming from.

Any ideas of what else I can check or what the problem might be? Sorry for the long post, but I've tried everything I can think of and can't find it.

Thanks for any help,

Fred