Ok Turbo-Hydramatic gurus, I've got a puzzle for you. Picking up my daughter from school today, while cruising slowly, I heard an annoying squeaking noise from under the car. This only occurs when the car is in motion, so it's nice and quite while at idle, both in gear and in neutral. So I immediately thought 'wheels', 'brakes', 'differential', etc...

Jacked up and checked each wheel, thinking it was a brake dragging, and all wheels are spinning without any issues, so I went the next step - differential. No noises there, either.

Rearend elevated, in neutral with the engine off, when I turn the driveshaft, I can hear a squeaking sound inside my Th400. It's definitely inside the transmission because I placed my ear on the pan, and it's definitely inside. When I turn the driveshaft in reverse, it's completely quiet, but in the other direction, it squeaks pretty loud.

It just started this today, and I'd rather fix it before it turns into something expensive.

The trans fluid looks perfect with no odors. The u-joints look great, no signs of deterioration or lateral movement. I'm guessing it's something in the TH400 tailshaft, where the driveshaft yoke inserts deep into the end of the TH400, but that's just a guess.

Any ideas would be much appreciated (Thanks).

 

The only time I ever had a sqeek like that under the car it turned out to be a ujoint that was dry and starting to powder the needle bearings.

 

Are there grease fittings on the u-joints ?
If there are, grease them. If not replace them with ones that are "greaseable".

 

+1.

 

More likely is a dry or bad front u-joint. The proximity of that u-joint to the trans is probably why it sounds like it's coming from the pan.

 

Your hearing the roller clutch overrunning. Completly normal. There are 2 roller clutches in a TH400, the low/reverse roller clutch and the intermediate sprag. The low/reverse locks whenever the car is moving forward, and freewheels in reverse. The intermediate sprag locks in 2nd, and freewheels (overruns) in 3rd gear.

 

X3 u-joint.Nick

 

Strangely, the sound has now disappeared. Regardless, I bought a grease gun and will lube those u-joints. Thanks again for the words of wisdom

 

If you haven't changed the ujoints in a while, I would just go ahead and do it. They aren't very expensive.