700r4 shake?

[Bloodhound1981]

I'll make sure to tag @NickTransmissions for this one.

So I've been chasing a driveline shake that starts at around 68mph and gets better over 75 or so. It comes back at about 85mph. This is my 1981 C-10, second frame-off build in the thirty-something years I've owned it. The motor is a new crate Chevy Performance vortec 350, the transmission is a 1990 Corvette 700R4 with about 20,000 miles original miles on it (tailshaft swapped out with a Camaro one), a Vigilante lockup converter, and a 12 bolt rear. While chasing this shake, I have replaced the driveshaft with a new aluminum one and a new yoke. The rear end is all new, with new axles, bearings, 4.10 ring and pinion, and Eaton Trutrac. I have rebalanced the wheels/tires, they are dead on. The alignment is perfect, and the shake is not in the steering wheel, but defintiely more under the cab floor.

When in 4th gear and converter locked up, while shaking, if I put the trans in neutral, it still happens. So after all that, is there anything in presumably the rear section of the 700R4 that can cause a driveline shake? I am totally out of ideas at this point.

 

[legopnuematic]

Tailshaft/slip yoke bushing? Output shaft bearing?

Just a swag.

 

[Scott91370]

You have a lot of stuff listed and even say rear end is all new. How about u-joints? I know it's obvious but worth asking.

 

[NickTransmissions]

I'll make sure to tag @NickTransmissions for this one.

So I've been chasing a driveline shake that starts at around 68mph and gets better over 75 or so. It comes back at about 85mph. This is my 1981 C-10, second frame-off build in the thirty-something years I've owned it. The motor is a new crate Chevy Performance vortec 350, the transmission is a 1990 Corvette 700R4 with about 20,000 miles original miles on it (tailshaft swapped out with a Camaro one), a Vigilante lockup converter, and a 12 bolt rear. While chasing this shake, I have replaced the driveshaft with a new aluminum one and a new yoke. The rear end is all new, with new axles, bearings, 4.10 ring and pinion, and Eaton Trutrac. I have rebalanced the wheels/tires, they are dead on. The alignment is perfect, and the shake is not in the steering wheel, but defintiely more under the cab floor.

When in 4th gear and converter locked up, while shaking, if I put the trans in neutral, it still happens. So after all that, is there anything in presumably the rear section of the 700R4 that can cause a driveline shake? I am totally out of ideas at this point.

Check trans rear mount...If worn, can cause vibrations, even in neutral (but not common). If the vibration is very high frequency, I'd suspect rear end, specifically worn pinion bearings or pinion depth just slightly off. I know you said the rear end was new but the couple instances where high frequency vibrations were present and driveshaft/u-joints were good, the rear end was the culprit.

 

[Bloodhound1981]

You have a lot of stuff listed and even say rear end is all new. How about u-joints? I know it's obvious but worth asking.

Yes all new u-joints, and all new everything in the rear end.

 

[Bloodhound1981]

Check trans rear mount...If worn, can cause vibrations, even in neutral (but not common). If the vibration is very high frequency, I'd suspect rear end, specifically worn pinion bearings or pinion depth just slightly off. I know you said the rear end was new but the couple instances where high frequency vibrations were present and driveshaft/u-joints were good, the rear end was the culprit.

Trans mount is new. In fact the cross member is new too. Same vibration before and after. It's definitely not a high frequency vibration, I wish it was something I could accurately copy on camera. It's as if I had a rear tire out of balance, yet I don't. Literally everything in the rear end is new, and no change. I was originally thinking somehow it was related to torque converter/flexplate balancing, but I don't think that fits my symptoms.

 

[TotalyHucked]

Have you verified your driveshaft angles? If they're not right, they can cause similar symptoms and it would be speed related

 

[Bloodhound1981]

Tailshaft/slip yoke bushing? Output shaft bearing?

Just a swag.

Could be? Speedmaster has this replacement tail shaft with new bushing and needle bearings, worth a shot?

GM Turbo 700R4 Aluminum Tailhousing with Needle Bearing

OverviewThese Speedmaster tailshaft housings are designed five times stronger and more ridged than stock because they are made from aircraft grade aluminum alloy, thicker walls, and more gusseting than any other manufacturers. And they also include a roller bearing at the end of the tailshaft...

www.speedmaster79.com

 

[Bloodhound1981]

Have you verified your driveshaft angles? If they're not right, they can cause similar symptoms and it would be speed related

Yes I checked just last night using the Tremec app, assuming it's accurate it says I am within spec. So frustrating!

 

[Sad Sack]

Does this truck have a carrier / center bearing, I see no mention of it.

"Symptoms of a bad carrier bearing include vibrations or shaking in the vehicle, especially at higher speeds, and unusual noises like rumbling or whirling sounds during acceleration. If left unaddressed, these issues can lead to further damage in the driveline components."

 

[Bloodhound1981]

Have you verified your driveshaft angles? If they're not right, they can cause similar symptoms and it would be speed related

I didn't trust the Tremec app using my phone so I went and got a digital angle finder, I think you are on to something here! From my initial check, I think my u-joint angle at the rear end pinion is way off. I need to take another round of measurements to verify, but this looks like my trans is sloped down at 5 degrees, the driveshaft is sloped down at 3 degrees, and the pinion is sloped DOWN at almost 4 degrees. Shouldn't the pinion be sloped UP if the trans is sloped down? At matching angles?

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[Ricko1966]

Yes if you draw an imaginary line through the transfer case from end to end of the truckand beyond,and Imaginary lines through the differentials front to rear of the truck and beyond. All the lines should be parallel.

 

[Bloodhound1981]

I should have taken a moment to think about the fact that the gauge was showing a 3.9 degree downward slope for the pinon, in relation to the driveshaft side to the pinion. So of course, the pinion is correctly pointed up 3.9 degrees. Duhhh.

I shimmed the transmission crossmember up a little to 4.4 degrees. Took it for a ride, no change. This mystery will never die....

 

[legopnuematic]

Could be? Speedmaster has this replacement tail shaft with new bushing and needle bearings, worth a shot?

GM Turbo 700R4 Aluminum Tailhousing with Needle Bearing

OverviewThese Speedmaster tailshaft housings are designed five times stronger and more ridged than stock because they are made from aircraft grade aluminum alloy, thicker walls, and more gusseting than any other manufacturers. And they also include a roller bearing at the end of the tailshaft...

www.speedmaster79.com

I don't think a needle bearing unit would be necessary (didn't even know that was a thing), you can get a new bushing and seal for sub $20. Not a big deal to R&R the bushing and seal.

Pull the driveshaft from the rear yoke and give the slip yoke at the trans a wiggle and see how much movement you have and see if it slides in and out freely.

Easy to check too is the phasing of the u joints/yokes. I would hope your aluminum driveshaft is made right, but who knows. Easy enough to pop the angle finder on.

 

[Bloodhound1981]

I don't think a needle bearing unit would be necessary (didn't even know that was a thing), you can get a new bushing and seal for sub $20. Not a big deal to R&R the bushing and seal.

Pull the driveshaft from the rear yoke and give the slip yoke at the trans a wiggle and see how much movement you have and see if it slides in and out freely.

Easy to check too is the phasing of the u joints/yokes. I would hope your aluminum driveshaft is made right, but who knows. Easy enough to pop the angle finder on.

Turns out the needle bearing tailshaft is for F-bodys and doesn't have the transmission mount on the bottom anyways, so that's out. I am going to get a bushing and replace it, I will check the yoke for play before that. This shake was happening before the full rear end rebuild, and before I got the aluminum driveshaft made. At this point I would pay someone a whole lot to diagnose this, in OD in lockup at 60mph it drives so smooth...until 67 and this shake starts. So aggravating.

The driveshaft...

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