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I don’t see how a larger diameter driveshaft would change the pinion angles if nothing was changed
The thought process is that both your shafts shake.
I am not suggesting it is easy to check or adjust, but my understanding is if the angles are not equal and minimal there are weird velocities at the universal joints that can cause shakes.
 

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This is where trans spacer shims go (shown on my T56). 2 came with the car/4L60E. I added the 2nd one back after measuring DL angle with just the 1 shown



what the shims look like



You could make your own out of 1/8" steel bar stock if you don't have any
 

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While in there with the shims, replace the rubber trans mount too. If it's original, and these vibrations have been happening for a long while, I'm sure it's shot. That alone could cause problems.

Back in the day when I did 3.42 gears on my 9C1, I got bad vibrations above a certain speed. I tried to have it balanced, but was told it would never work well for higher gear ratios due to its length, resonance and interaction with the B-Body chassis. I had also read that's why the Impala SS is speed limited to around 154 MPH (I think that was mentioned in the ISS Technical Archives). I'll see if I can find a link. 3.73 gears could hit a harmonic at a lower speed.

Anyways, since the early days, the recommendation has always been something that's not steel. Wayyy back in the day, I got in on a group purchase for an aluminum MMC version which solved the problem and I never looked back. The company at the time sold two versions. A stock length and one that was slightly longer (3/4"???) if you wanted to center your axle with new control arms.

Edit: it may also be a good idea to check everything again. Check the output shaft of the trans. Bushing wear, etc. Vibrations have a way of wearing things out quickly. I completely grenaded a tail housing on an old Mopar in short time because I ignored the vibrations too long. The trans shop told me the yoke bushing was no longer a bushing. LOL. I still have the tail housing as a spectacular catastrophic failure trophy. And a lesson not to ignore these things.
 

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Discussion Starter · #25 ·
OP

This is where trans spacer shims go (shown on my T56). 2 came with the car/4L60E. I added the 2nd one back after measuring DL angle with just the 1 shown



what the shims look like



You could make your own out of 1/8" steel bar stock if you don't have any
This was installed Saturday after racking my brain trying to find the reason for the vibration. 2 shims were on the original. The vibration didn’t improve or get worse with or without the original shims.
 

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Discussion Starter · #26 ·
While in there with the shims, replace the rubber trans mount too. If it's original, and these vibrations have been happening for a long while, I'm sure it's shot. That alone could cause problems.
Back in the day when I did 3.42 gears on my 9C1, I got bad vibrations above a certain speed. I tried to have it balanced, but was told it would never work well for higher gear ratios due to its length, resonance and interaction with the B-Body chassis. I had also read that's why the Impala SS is speed limited to around 154 MPH (I think that was mentioned in the ISS Technical Archives). I'll see if I can find a link. 3.73 gears could hit a harmonic at a lower speed.



Anyways, since the early days, the recommendation has always been something that's not steel. Wayyy back in the day, I got in on a group purchase for an aluminum MMC version which solved the problem and I never looked back. The company at the time sold two versions. A stock length and one that was slightly longer (3/4"???) if you wanted to center your axle with new control arms.
This is what scares me. But he asked all the right questions about the vehicle, tire size, transmission, HP, etc. He came highly recommended from several people I know. Tried using local because of previous issues with a out of state driveshaft company
But I’ve done the calculations on critical speed and even had a math wiz double check it. It checks out for length and the two materials I think he used.
I didn’t go with aluminum because I had one in the past from the “driveshaft shop” for a 5th gen camaro and it vibrated at certain speeds. It’s a long story but that’s the main reason.

Edit: it may also be a good idea to check everything again. Check the output shaft of the trans. Bushing wear, etc. Vibrations have a way of wearing things out quickly. I completely grenaded a tail housing on an old Mopar in short time because I ignored the vibrations too long. The trans shop told me the yoke bushing was no longer a bushing. LOL. I still have the tail housing as a spectacular catastrophic failure trophy. And a lesson not to ignore these things.
New 1350 pinion yoke, U joint , tail shaft bushing, seals, and pinion nut will be here Thursday so I’ll replace all that as well.
Thanks for the help.
 

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This thread reminds me that I need to go and grab the driveshaft out of the Crown Vic cop car I found being parted out.

I hope you get this sorted out because vibrations are annoying. My dad ignored one and kept doing high speed runs until one day the shaft decided it had enough and left the car. It didn't want to be alone so it brought part of the T5 transmission with it.
 

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Discussion Starter · #28 ·
This thread reminds me that I need to go and grab the driveshaft out of the Crown Vic cop car I found being parted out.

I hope you get this sorted out because vibrations are annoying. My dad ignored one and kept doing high speed runs until one day the shaft decided it had enough and left the car. It didn't want to be alone so it brought part of the T5 transmission with it.
This thread reminds me that I need to go and grab the driveshaft out of the Crown Vic cop car I found being parted out.

I hope you get this sorted out because vibrations are annoying. My dad ignored one and kept doing high speed runs until one day the shaft decided it had enough and left the car. It didn't want to be alone so it brought part of the T5 transmission with it.
If I can’t figure it out by this weekend. I’m taking it back and getting a refund.
 
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Discussion Starter · #29 ·
Finally had a chance to get to work on this thing. I mic’d the original slip yoke and the new one. New one is a few thousands smaller in diameter. Not sure if that’s an issue.
But the new shaft was eating away at the tailshaft. Had aluminum shavings behind the seal in the tailshaft. Cleaned it up, replaced bushing and seal. The slip yoke looks trashed. I can feel a ridge where it looks like it got hot.
 

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I agree with @95wagon , whomever assembled that transmission used the wrong tail shaft bushing. The correct one is this:
Yellow Wood Household hardware Gas Auto part

Material property Tool Gas Wood Metal

It’s 15/16” wide. When installed, it should overhang the bushing mount by about 1/16” on both ends. No other 4L60E bushing is even in the ball park, so it must have come from another transmission make/model. That’s why you got the wear you did. Given the correct bushing, can you file down any high spots and reuse the yoke?
 

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Shows I am out of touch with this.
I thought it was too narrow.
Google shows GM teflon coated ones now ?
What exactly is that part of the yoke rubbing on?
It looks like that area would be inside of the bushing .
[ confused imoji ]
 

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Discussion Starter · #34 ·
Shows I am out of touch with this.
I thought it was too narrow.
Google shows GM teflon coated ones now ?
What exactly is that part of the yoke rubbing on?
It looks like that area would be inside of the bushing .
[ confused imoji ]
I agree with @95wagon , whomever assembled that transmission used the wrong tail shaft bushing. The correct one is this:
View attachment 208279
View attachment 208280
It’s 15/16” wide. When installed, it should overhang the bushing mount by about 1/16” on both ends. No other 4L60E bushing is even in the ball park, so it must have come from another transmission make/model. That’s why you got the wear you did. Given the correct bushing, can you file down any high spots and reuse the yoke?
I was mistaken. Just measured it and it’s .995 on my micrometer. The new one looks similar to the one you posted and has Alto stamped in it. I never measured it before I put it in. It was a kit from Summit.
I hit the yoke with some 120 and 320 emory cloth. Then hit it with some 600 paper. Can still feel ridges with my nail. Kinda hesitant to use it. Still have to swap out my 3r yoke for the 1350 I bought.
It’s just confusing as heck that the stock driveshaft works but this new one doesn’t.
The yoke looks like it was cocked in the tailshaft and riding on the outer side of bushing and case. The shavings were from the case at the bushing.
 

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Heard of ,never seen personally, cheap yokes that are mis machined with either or
Splines
Bearing surface
Cup area
Not all true to each other.
Rudimentary measure to try and check , spline to od .
Maybe the yoke is crap ?
 

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Discussion Starter · #37 ·
Heard of ,never seen personally, cheap yokes that are mis machined with either or
Splines
Bearing surface
Cup area
Not all true to each other.
Rudimentary measure to try and check , spline to od .
Maybe the yoke is crap ?
The new slip yoke OD was 3 thousandths smaller than the stock slip yoke. Can’t find any manufacturer marks on the slip yoke. Driveshaft had neapco at the slip side and spicer at the pinion side. Not sure if that matters.
 

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If the tail housing is still off , can you put the slip yoke on the tail shaft and measure from bearing surface of yoke down to the spline ?
Possibly dial indicators on shaft and yoke at the same time , then turn by hand ?
 

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Discussion Starter · #39 ·
If the tail housing is still off , can you put the slip yoke on the tail shaft and measure from bearing surface of yoke down to the spline ?
Possibly dial indicators on shaft and yoke at the same time , then turn by hand ?
I’ll take the take it back off tomorrow and give it a shot and report back.
 
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