I am hoping to get some ideas and suggestions for a problem I am having with my 2002 1500 HD 6.0L 4L80E 4x4. It seems to be a unique problems based on several hours of internet searching to find a similar case. I can not find a one that matches the symptoms exactly, and I could use some help figuring this out.
First some history: The truck has 240,000. I am the 3rd owner. I do not know if the transmission has ever been rebuilt. I use the truck only occasionally for weekend up north trips, and plowing my driveway. I put about 5,000 miles or less per year on it. Sometimes it will go a week or two without being driven at all. Last year I had one of the front brake lines rust through during a return trip from up north and lost the majority of my braking. I used mostly engine braking by downshifting the trans, and the little bit of assist that the rear brakes still provided, along with some very slow and cautious driving to get it home. I think that part may be relevant to my current issue.
Then I had another issue that may have some relevance with the transfer case to transmission mounting bolts that came loose, and allowed the transfer case to be supported by the transmission output shaft and drive shaft. It was like this for approximately 300 - 400 miles (another up north trip) before I was able to find it and fix it. I can elaborate on this if needed, but it seemed like when I pulled the transfer case the rear output shaft on the transmission had more play (up down, side to side play) than I would have thought it should. I did some work inside the transfer case and put it all back in, and it was working great again on several short around town trips post transfer case repair.
Then on another trip up north when I was on the freeway, I let up on the gas to drop some speed due to some congestion ahead, and I heard this noise that sounded like gears whirring really fast, and I had no engine braking at all, but my engine RPMS'* dropped about 200-300 RPM in conjunction with this noise. The engine did not miss, sputter, or anything like that, just dropped RPM'* like it was being put under a load. When I tapped the gas again (even a light tap, like 2% on the TPS) the noise stopped virtually instantly. I drove it a good 400-500 miles like this trying to avoid the noise as much as possible by using a bit of accelerator even when I was braking to finish out my trip and get it home. (Note, most of those 400-500 miles were highway and two lane blacktop without much need to stop, not city driving).
When I got home I tried to diagnose it a bit better. I hooked it up to my AutoEnginuity scan tool and checked on a few things that I could think of and based on some googling. I could verify Torque converter application and lockup in 3rd and OD like it should, verify the brake was not falsely activating, verify that the TCC unlocked and stayed unlocked when I let up on the gas to coast, and the whole time this noise was present.
I tried playing around with some things, and noticed that if I put the Transmission in Neutral before the noise starts (it takes about 3 seconds from the time you let your foot off the gas until it starts, pretty consistently) that it wont make the noise. But if it makes the noise first and I try to shift to Neutral it wont stop unless I apply some gas. I noticed the pitch of the noise changes if I shift from OD to 3, 2, or 1. It gets notably faster with each downshift. When I get down to 1 I notice the ever so slightest hint of some engine braking remaining, but it is almost too insignificant to mention.
That'* about the extent of what I have figured out so far. The truck still runs, drives, and shifts through all the gears perfectly. If you did not have to stop or coast you would not think anything was wrong at all. I did check the transmission dipstick, and noticed what was probably some gray clutch material suspended in still red fluid, with a slight off odor. Not burnt, but not fresh either. The trans fluid was just changed less than 5,000 miles ago, so it should have been perfect. I have not pulled the pan yet, I suspect I will find more of the same clutch material.
I am thinking a trans rebuilt may be on the agenda, but I would like to know what I should expect to find before digging in. Is this something I can drive with for awhile, will it cause some catastrophic damage to something else if I continue to drive it like this? What is causing the high pitch gear winding noise? I am guessing the clutch material is from the clutch responsible for engine braking, but how critical is that to overall transmission function? Is there something else I could or should test that would help provide more understanding to what is going on?
I know that is a lot of info, maybe confusing and possibly conflicting. I did not have an editor
so please ask questions if anything is unclear or could use more info.
Thanks for any help,