A833 23-spline tranny and drivetrain vibration - culprit found, need help

[moparedtn]

Greetings y'all.
In the next step of the long-term resurrection of my '68 GTX, I'm on to the next problem now that the basics are all in place and functioning - finally. Thank God.
Car has replacement 440, new clutch (Centerforce) etc. and a replacement "donor" 23-spline.
Driveshaft is stock. Rear end is a fresh rebuilt 8 3/4 with 3.55 and SureGrip.

Anyways, at speeds over 70mph and under load, a fairly heavy vibration occurs and just gets worse with more speed. If I lift, it goes away. If I push in the clutch and/or pull it out of gear at that speed, the vibration goes away. It isn't in the engine or clutch or in wheels.

This is telling me there's a possible problem with the u-joints - or even in the tailshaft housing, so I got under the car and checked things out.
Rear u-joint checked out fine, but I took it loose and reinstalled it 180 just in case I had installed it "clocked wrong" before.

Grabbed the driveshaft yoke at the rear of the tranny and Bingo - there's quite a noticeable amount of slop here. I had replaced the seal on the transmission when I got it, but the actual condition of the transmission was a total unknown before.
It shifts really nice and it's a quiet unit, but this slop at the output is almost definitely the cause of the vibration.
Is there just a bushing that needs replaced in there? Is this something I can do?
Or is there more to it?

 

[Zeppelin264]

There is a tail shaft bushing in there. Requires a special tool to remove it in the car. Otherwise you need to remove the tail shaft and tap it out.

I bought the tool and did mine. Took like 10 mins. Similar vibrations and it did help but didn't totally eliminate my issue. I've got drive line angle problems.

Any trans shop should be able to do it pretty quick. Everyone around here wanted a premium so I just bought the tool instead and did it myself.

 

[Zeppelin264]

Here is the tool. I called this guy up and he gave me a discount on it. There are 2 versions of this tool, so make sure if you decide to buy it that you get the right one.

727's share the same bushing as a th400, th350, 4l80, 4l60, C6 etc... The smaller tool is for like C4's etc..

http://www.handsontools.com/Atec-T-...MIle3_wq-T1QIVgxKBCh3CLg4DEAQYBCABEgJnjfD_BwE

 

[Beekeeper]

Ed, I have the tools to replace the tailshaft bushing. The last bushing I bought was at Holston auto parts (napa)

 

[moparedtn]

Ed, I have the tools to replace the tailshaft bushing. The last bushing I bought was at Holston auto parts (napa)

Oh man, seriously? I know we've talked about it before, but could you be possibly bribed into coming over for a visit?
If you've done this work before, man, that would be a Godsend!

 

[66Satellite47]

Not sure what you mean by "clocking". I've never had an issue with 180* change at the rear U joint making a difference. I have been under the impression that "clocking" refers to the slip yoke fixed position vs the pinion flange connecting flange. Those should be aligned, correct? I have a buddy that had the same problem as you, that "clocking" was 90* off. Cured the vibration.

 

[Beekeeper]

Oh man, seriously? I know we've talked about it before, but could you be possibly bribed into coming over for a visit?
If you've done this work before, man, that would be a Godsend!

I don't mind coming over to give you a hand with it. I have done this a few times I get off work at 5:30 pm i'll pm you my phone number give me a call and we will set it up

 

[AR67GTX]

You also need to look at the yoke as it can be worn in the bushing area also and contributing to the slop in addition to the bushing. The bushing takes the brunt of the wear as it's softer but I have a couple nicely worn, grooved yokes out in the garage due to slop. A sloppy bushing and yoke will definitely cause vibration.

 

[66Satellite47]

One other thing to double check is what may have caused the bushing/slip yoke wear. Is the driveshaft the "proper length"?? I've always been amazed by the LACK of wear in my output bushings(727).

 

[moparedtn]

Not sure what you mean by "clocking". I've never had an issue with 180* change at the rear U joint making a difference. I have been under the impression that "clocking" refers to the slip yoke fixed position vs the pinion flange connecting flange. Those should be aligned, correct? I have a buddy that had the same problem as you, that "clocking" was 90* off. Cured the vibration.

I don't quite understand? I've never paid any attention to the slip yoke vs. axle yoke angle. I assume if it's an untouched factory driveshaft, that relationship is whatever it came as, right?
Yeah, I figured it wasn't going to do anything to rotate the rear one 180 and reinstall, but what the heck, I already had the car up in the air and was under there, so...
I just remember the manual talking about marking the driveshaft and pinion flange before taking it out (and of course, I didn't, back when I had the car all apart).

 

[moparedtn]

I don't mind coming over to give you a hand with it. I have done this a few times I get off work at 5:30 pm i'll pm you my phone number give me a call and we will set it up

PM returned.

 

[moparedtn]

One other thing to double check is what may have caused the bushing/slip yoke wear. Is the driveshaft the "proper length"?? I've always been amazed by the LACK of wear in my output bushings(727).

Remember, this engine is "new" to the car, as is this transmission - and the tranny is "new" to the driveshaft, which has remained with the car since I bought it over six years ago, along with the rear end.
Less than 25 miles on the combination to date, still haven't really driven it much except locally due to other issues recently corrected.
In fact, the only parts that have remained from my previous setup (that had no such vibration) is the bellhousing and driveshaft; everything else is new to the car.
This one is a long time coming, most of which has been well documented right here on FBBO in previous threads.

 

[moparedtn]

You also need to look at the yoke as it can be worn in the bushing area also and contributing to the slop in addition to the bushing. The bushing takes the brunt of the wear as it's softer but I have a couple nicely worn, grooved yokes out in the garage due to slop. A sloppy bushing and yoke will definitely cause vibration.

Thanks. Yep, thought about that too. Nothing like that is visible to my old nekked eye, but that doesn't mean it's not there. We'll definitely check that out closely when we get it all apart to do the bushing.
I'm pretty sure my driveshaft is ok (given previous engine/trans setups not having this issue) and yes, I'm going to get the bushing rectified pronto so that it doesn't become an issue.

 

[moparedtn]

It's this critter here, right?
http://www.brewersperformance.com/proddetail.asp?prod=TB85-62

 

[Beekeeper]

It's this critter here, right?
http://www.brewersperformance.com/proddetail.asp?prod=TB85-62
View attachment 491158

That's it

 

[66Satellite47]

One other thing to consider is if the crank and input shaft are correctly in line (centered). A slight offset there may create the vibration. Offset dowels for the bellhousing/block correct this.

 

[Zeppelin264]

Now, the classic debate. Which way does that oiling hole go?

 

[Beekeeper]

The oil hole lines up with a slight Vee notch in the tail shaft

 

[moparedtn]

One other thing to consider is if the crank and input shaft are correctly in line (centered). A slight offset there may create the vibration. Offset dowels for the bellhousing/block correct this.

Yessir, went through all that when different engine was mated to my original 11" bellhousing, then married to all new Centerforce clutch stuff.
Brewer's was extremely helpful with all that and as it turned out, my stuff was pretty darn true all the way.
Love this Dual Friction clutch setup. It's pretty amazing.
Thanks!

 

[moparedtn]

Now, the classic debate. Which way does that oiling hole go?

The oil hole lines up with a slight Vee notch in the tail shaft

12 o'clock?
Heh, I'll learn that when Beekeeper comes over to help me, I reckon.