Wah Wah Wah in Overdrive

[Bisho]

I recently started getting a droning between 45-60 mph. It’s there when I’m essentially maintaining speed. If I’m accelerating or decelerating it not there. It goes away if I click off overdrive. Other than the droning, everything else is the same as it’s been the last 100k miles. It shifts fine. I’ve done a complete fluid exchange a couple times, most recently in the last 10k miles.

Am I getting ready to do a rebuild on the transmission?

 

[OEMGUY0720]

If the symptom is coming from the OD function, we can isolate the troubleshooting in that area first. If the mechanical aspect of the transmission appears to function as designed, you likely have a good transmission. I would assume there was no material on the AT drain plug/ATF when you drained it recently?

 

[Bisho]

If the symptom is coming from the OD function, we can isolate the troubleshooting in that area first. If the mechanical aspect of the transmission appears to function as designed, you likely have a good transmission. I would assume there was no material on the AT drain plug/ATF when you drained it recently?

Correct - no material. Isn’t the OD integral to the transmission?

 

[MongooseGA]

Do you have any clunking on/off throttle while at road speed?

My first thought would be to check the U-joints. They'll rumble or whine differently with different amounts of load on them, which might be the reason you feel a difference with OD on or off.

 

[Bisho]

Do you have any clunking on/off throttle while at road speed?

My first thought would be to check the U-joints. They'll rumble or whine differently with different amounts of load on them, which might be the reason you feel a difference with OD on or off.

I don’t get the clunking, but I do have a new set of ujoints waiting at home. I was thinking that OD on/off has a constant output from the driveshafts and would rule out ujoints, but now that you say that I suppose the load does change. I just can’t replicate the drone with OD off. I hope you’re right.

We’re headed home the next couple days from GA, so I’ll redo the ujoints and hopefully that does the trick.

 

[OEMGUY0720]

Correct - no material. Isn’t the OD integral to the transmission?

It is, and the OD switch is connected to an electric solenoid found in the valve body and can be serviced/replaced if that is indeed the culprit. I have seen a few threads from the 80 section that may share similar symptoms as yours.

 

[Bisho]

I started changing the spider bearings in the driveshafts. This is a much bigger PITA than I expected. I've had to take a cutoff wheel to 3 out of 10 dustcaps thus far, because I can get on side off, but the other will not start straight going back out and starts to maul the inner bore. Working in the Texas heat here I gave up after 10, so 6 more to go when I can get back to it.

I also discovered transmission fluid on the bottom half of the transfer case, so it appears the rear output shaft seal on the transmission has gone out. I replaced it about 70k miles ago when I redid the transfer case seals, but I had to use an off brand one because it wasn't planned. New OEM on the way now, but yay, I get to pull the transfer case.

 

[Bisho]

So, the new ujoints made it better, but not solved. I’ll regrease them next weekend after they settle in and we’ll see what happens. I’ll make a trip to Discount Tire and have the balance checked, it can’t hurt.

 

[mdcoa]

I started changing the spider bearings in the driveshafts. This is a much bigger PITA than I expected. I've had to take a cutoff wheel to 3 out of 10 dustcaps thus far, because I can get on side off, but the other will not start straight going back out and starts to maul the inner bore. Working in the Texas heat here I gave up after 10, so 6 more to go when I can get back to it.

I also discovered transmission fluid on the bottom half of the transfer case, so it appears the rear output shaft seal on the transmission has gone out. I replaced it about 70k miles ago when I redid the transfer case seals, but I had to use an off brand one because it wasn't planned. New OEM on the way now, but yay, I get to pull the transfer case.

Looks like you have a bunch of options for driveshaft shops in your area—I take pride in doing my own work but put driveshafts, CVs, and alignments in a “I’ll pay a pro with the right stuff to do it in 10 minutes” category…I accidentally pulled apart a CV axle on our old Volvo and, after many hours trying to source a boot and figure out how the dang thing went together (in the course of which I destroyed the boot), I finally took it to a time-capsule of a drivetrain shop, which reassembled and rebooted it in literally 10 minutes and charged me like $30 all-in. YMMV, but might be worth pondering…

 

[Bisho]

Looks like you have a bunch of options for driveshaft shops in your area—I take pride in doing my own work but put driveshafts, CVs, and alignments in a “I’ll pay a pro with the right stuff to do it in 10 minutes” category…I accidentally pulled apart a CV axle on our old Volvo and, after many hours trying to source a boot and figure out how the dang thing went together (in the course of which I destroyed the boot), I finally took it to a time-capsule of a drivetrain shop, which reassembled and rebooted it in literally 10 minutes and charged me like $30 all-in. YMMV, but might be worth pondering…

Well, all done now. I had to cut off 4 of the 12 dust caps. Those suckers are very hard.

For me, half the hobby is maintaining the truck. It’s not my only LC, so I’m rarely in a rush, and my street cred on fixing things will make me that much more valuable during the zombie apocalypse.