SBC T56 driveline vibration?

[Squag27]

1 degree different isn't going to induce a vibration. You need to be in the multiple 3+ range to begin to get anything.

Your locations measuring are a little innacurate due to casting draft but close enough to rule anything super wrong there.

How do your U joints feel? Can you see any wear offset to the slip yoke on the OD?

U joints are brand new actually. Everyone and their mother told me to check the driveshaft so it's been gone through several times by a local shop.

That's within the window of the working angles you would want: 2.2° - 1.0° = 1.2° difference since the driveshaft is higher in the front vs. rear. There is still room for decreasing that target if you're still sensing vibrations but you def seem to be within range. I'm assuming the numbers were pulled w/full weight on the chassis? Confirm your trans number by comparing w/the crank pulley.

Now.... Keep in mind that angles on joints are impacted on both the vertical & horizontal plains. Verify your C/L of the trans output shaft vs. the C/L of the pinion using the frame rails for reference. You'll want a similar tight dimension there as well. This is often over looked yet it's a common issue to have the rear not centered.

I had considered that there could be an issue in the horizontal plane but I don't have a great way to check that without a lift. I did check these with the car under the ground as well.


Out of curiosity, have any of you guys had an issue running a standard 3.5" steel driveshaft? My G-body is an El Camino so it is a little longer than most but the shop also claims that PST says I need a 4" aluminum shaft to make everything shake out with critical speed as well. The reason I'm asking is that the vibration is worst at 75-85mph and then smooths out at higher speeds, which lends to the idea of it being an issue with 1/2 critical speed of the shaft.

 

[scoti]

U joints are brand new actually. Everyone and their mother told me to check the driveshaft so it's been gone through several times by a local shop.


I had considered that there could be an issue in the horizontal plane but I don't have a great way to check that without a lift. I did check these with the car under the ground as well.


Out of curiosity, have any of you guys had an issue running a standard 3.5" steel driveshaft? My G-body is an El Camino so it is a little longer than most but the shop also claims that PST says I need a 4" aluminum shaft to make everything shake out with critical speed as well. The reason I'm asking is that the vibration is worst at 75-85mph and then smooths out at higher speeds, which lends to the idea of it being an issue with 1/2 critical speed of the shaft.

ElCo's were single shaft vehicles from GM. Current driveshaft balance was verified as good?

The OE driveshafts were not exactly HD so any upgrade there is good. But once you start going to larger OD's on the shaft, your tunnel clearance diminishes (a concern on lowered vehicles).

 

[Squag27]

The driveshaft has been balanced several times but the shop thinks there's still something wrong with it. I'm also concerned with diminished clearances on a 4 inch shaft, especially if hauling anything heavy in the bed on occasion. I've had the rear end rebuilt with new bearings throughout on the chance that's the cause and even put the car in gear with the rear end jacked up to see if I could find the source of the noise with a stethoscope. Asides from simply throwing more money at the problem, I'm not sure how to proceed at this point.

 

[scoti]

The driveshaft has been balanced several times but the shop thinks there's still something wrong with it. I'm also concerned with diminished clearances on a 4 inch shaft, especially if hauling anything heavy in the bed on occasion. I've had the rear end rebuilt with new bearings throughout on the chance that's the cause and even put the car in gear with the rear end jacked up to see if I could find the source of the noise with a stethoscope. Asides from simply throwing more money at the problem, I'm not sure how to proceed at this point.

Per my comments, you can probably tell I've enjoyed an extended stay in this rabbit hole. If you do opt for replacing the d-shaft w/something beefier, consider getting a Double Cardan Joint when you do it. It's an extra expense but typically eliminates the driveline vibrations commonly noticed in OD applications (OD apps are more sensitive to this issue).

My C10 exploits 'require' a 2pc driveline to minimize issues. Problem is, piecing together a quality 2pc driveline & carrier bearing isn't cheap. And, after you spend all that money you can still need a DBL Cardan style u-joint (more $$) because "extreme dropped trucks are a compromise". My logic said If I'm spending >/= $700 for a fresh balanced assembly that still might need the extra help of the DBL Cardan joint, I'll trim some sheet metal to clearance as needed, run a 1pc. drive-shaft, & adjust the working angles as much as possible for $150. Worst case scenario I still have to add the DBL Cardan joint but still be @ less than half the cost/complexity for the 2pc/carrier bearing set-up.

But the extreme dropped trucks are a different type of set-up. The linked info below is more inline w/these g-body's. It's an excellent read start to finish w/some very informative tech sh*t but for stuff specifically related to this 'OD manual trans vibration' topic start @ pg10 post #200:
https://www.pro-touring.com/threads/40904-1970-GTO-Version-2-0

 

[Squag27]

Per my comments, you can probably tell I've enjoyed an extended stay in this rabbit hole. If you do opt for replacing the d-shaft w/something beefier, consider getting a Double Cardan Joint when you do it. It's an extra expense but typically eliminates the driveline vibrations commonly noticed in OD applications (OD apps are more sensitive to this issue).

My C10 exploits 'require' a 2pc driveline to minimize issues. Problem is, piecing together a quality 2pc driveline & carrier bearing isn't cheap. And, after you spend all that money you can still need a DBL Cardan style u-joint (more $$) because "extreme dropped trucks are a compromise". My logic said If I'm spending >/= $700 for a fresh balanced assembly that still might need the extra help of the DBL Cardan joint, I'll trim some sheet metal to clearance as needed, run a 1pc. drive-shaft, & adjust the working angles as much as possible for $150. Worst case scenario I still have to add the DBL Cardan joint but still be @ less than half the cost/complexity for the 2pc/carrier bearing set-up.

But the extreme dropped trucks are a different type of set-up. The linked info below is more inline w/these g-body's. It's an excellent read start to finish w/some very informative tech sh*t but for stuff specifically related to this 'OD manual trans vibration' topic start @ pg10 post #200:
https://www.pro-touring.com/threads/40904-1970-GTO-Version-2-0

Hey I'm appreciative of anyone who'll listen to me whine about my '80s Chevy not driving as smooth as a new car. I've never heard of a Double Cardan U joint but that's certainly wild looking. Reading about the GTO in the link you posted was pretty interesting in where he put his angles to get a smooth ride though. I'll have to keep going through the thread further.

 

[ostrich]

Hey I'm appreciative of anyone who'll listen to me whine about my '80s Chevy not driving as smooth as a new car. I've never heard of a Double Cardan U joint but that's certainly wild looking. Reading about the GTO in the link you posted was pretty interesting in where he put his angles to get a smooth ride though. I'll have to keep going through the thread further.

By the look of it your angles should be fine. I did replace my driveshaft in my Camaro when I had my vibration issues, even though the driveshaft in it was balanced, U joints were on the newer side. Didn't fix my issue. From your pics I see you have a poly transmission mount, I had the same in mine, motor mounts were rubber, so I went back to a rubber OEM transmission mount (3rd gen Camaro) $15. Best $15 I spent on my issue. Not saying it will fix it, but for $15 and 15mins of work?

 

[81cutlass]

If your driveshaft is eliminated and angles are likely not a problem you have a fun one 🙂

Has the same shop looked at the driveshaft every time? Can you put a dial indicator on the shaft itself when it's in the car, trans in neutral and wheels off the ground at ride right and see if you have runout? It's possible that the driveshaft could be in balance on their machine and has runout on the car.

 

[Squag27]

By the look of it your angles should be fine. I did replace my driveshaft in my Camaro when I had my vibration issues, even though the driveshaft in it was balanced, U joints were on the newer side. Didn't fix my issue. From your pics I see you have a poly transmission mount, I had the same in mine, motor mounts were rubber, so I went back to a rubber OEM transmission mount (3rd gen Camaro) $15. Best $15 I spent on my issue. Not saying it will fix it, but for $15 and 15mins of work?

I actually have a rubber mount but I think I had to modify it or something last time I looked in order to make it work with the crossmember I have.

If your driveshaft is eliminated and angles are likely not a problem you have a fun one 🙂

Has the same shop looked at the driveshaft every time? Can you put a dial indicator on the shaft itself when it's in the car, trans in neutral and wheels off the ground at ride right and see if you have runout? It's possible that the driveshaft could be in balance on their machine and has runout on the car.

This is actually a really good idea. I have a nice dial indicator so I'll have to check this.

 

[Squag27]

So I got around to checking the runout on the driveshaft, seems to be +/- .014 at it's worst which as I understand it is in spec.

 

[64nailhead]

You need to measure off from the u-joints/yokes.

81cutlass He is correct, with 2-2.5 degrees in either direction is not going to cause an issue. Be sure you are measuring with the weight the vehicle being supported by the tires and the car is not being held in place by a parking brake, gear or any driveline component. This is most easily done on a drive on lift.