Les

I've picked up a mild vibration at high speed only and I'm trying to hunt it down since I want to get back out to the dragstrip this fall. It's not enough to feel but you can hear it as if harmonics are out of synch. I know it's normal to have a small amount of movement at the trans tailshaft when the driveshaft is not hooked up. Today I checked for play with the driveshaft in place and at the tailshaft I found a slight amount of up/down/sideways play that can be seen and felt, along with a slight clicking sound.

Question #1- How much play, if any, is acceptable there?

Also, my TH 400 has the heavy duty case, which has a larger fluid capacity and is approx. 1-2" longer than the standard TH 400 if memory serves. Many years but not many miles ago when I installed it, I remember the guy at the driveshaft place shortened the yoke that slips over the tailshaft rather than the shaft itself so that it would fit with the longer trans. In a conversation with a different shop years later, this topic came up and that guy said he would replace the cut yoke with a new one since there wasn't enough yoke extending over the tailshaft to be safe. He said that then the driveshaft should be cut to length.

Question #2- Was the first guy or the second guy correct?

Question #3- If the second guy was correct, where's a good source for a top quality yoke to connect the front of my driveshaft to my TH 400 tailshaft?

Thanks for any info you guys can provide.

Shark Racer

I'd much rather cut the driveshaft than the yoke. You want as much spline engagement as possible. You may be seeing a little bit of wear on the trans output shaft, but I doubt it.

When you disconnect the driveshaft and slip the yoke in a bit more does the play go away?

Inland Empire, Strange, Moser, TCI all sell yokes that are probably great.

Les

There's no doubt that more engagement is better. What I can't remember, or find any info about, is how much had to come off of that yoke to allow me to install the driveshaft. It could have been less than an inch. If I can figure that out I should be able to determine if it's enough to be significant. I know it wasn't much but it's been too many years since then to be sure just how much.

I'm pretty sure if there's any wear it'll be in the bushing for the tailshaft itself. I'm trying to gather more info before disconnecting the driveshaft. Thanks for the info.

Shark Racer

Do you mean play in the mount bushing or in the output shaft seal?

cv67

Had a harmonic type sound as you speak of. Like a roaring or driving over smal rumble strips goes away on decel. That kind of noise?
Was the pinion bearing races and bearings were scored
And I mean so slightly you couldnt even tell unless you really really looked.
Have some slop in my tailshaft bushing if that helps. Car drives great.
Trans guy says dont even worry about it. When it leaks..

Les

Thanks for the info. I had the rear end disassembled for inspection maybe 3000-4000 miles ago by a carefully selected shop with a great reputation. They said it literally looked brand new throughout and buttoned it back up. It had been rebuilt by another reputable shop many years, but not many miles, prior. I had made a fair number of 1/4 passes since that rebuild and wanted to make sure it was OK. The original shop had gone out of business due to retirement. Point being, I'll keep your suggestion in mind but for now I plan to eliminate other possibilities first.

Just a bit more history on the car. Only a few thousand miles ago all the U-joints were replaced with Spicer solids. Those are not likely to be the problem.

Here's a vid that was taken recently. If you listen closely you can hear the vibration starting at about 20 seconds.

larrywalk

Typically, my transmission reference books call for a maximum bushing clearance of .008" (yoke to bushing). It is difficult to get a good clearance measurement by pushing up and down on the yoke because the yoke is splined to the trans output shaft and that's not going to want to move much. Another way to get after the problem is to disconnect the front of the driveshaft and pull out the yoke for a measurement. Measure the unworn diameter of the yoke with a micrometer and compare that with the portion that wears against the bushing. If you find more than a few of thousandths of wear on the yoke, chances are that the bushing is worn enough to require replacement along with the yoke.

cv67

Hopefully your pinion is fine.

My parts were all brand new just sat for 10 yrs.
Even turning the yoke with the gears in seemed perfect.
Wasnt til a 2nd guy turned it over with his ear to it going reeeeeal slow with teh gears OUT he thought he picked up on something
Once it was taken apart the pitting was there.
I was shocked it hardly looks like anything still have them in a bag lol.


Shoot for the tailshaft first let us know.

Les

Good info- thanks. I don't own a micrometer but I know where I can borrow one. Depending on what I can figure out regarding the amount of yoke that's engaged with the tailshaft, I may be getting a new yoke to improve that anyway.
Wow, that 2nd guy must have had some good and experienced ears. Thanks again. I'll start digging hard into this on Monday and once I've figured out more about my situation I'll update this thread.