SBC T56 driveline vibration?

[Squag27]

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.

The car is tall enough that I can squeeze under it to check the driveline angles without jacking it up any and the car was in neutral as well.
Checking runout from the u-joints would indicate more runout from the pinion yoke/ trans output shaft than the driveshaft itself wouldn't it?

 

[64nailhead]

The car is tall enough that I can squeeze under it to check the driveline angles without jacking it up any and the car was in neutral as well.
Checking runout from the u-joints would indicate more runout from the pinion yoke/ trans output shaft than the driveshaft itself wouldn't it?

Driveshaft angle is almost a non issue unless you have 20+" wheels installed. The only reason it's a non issue is that you would have to have something really whacky going on to have a driveshaft angle that's causing the problem.

To answer your question directly, the yoke/u-joints identify the true driveline angles of the engine/trans angle and differential angle. Have you been measuring the driveshaft angle?

Lastly, you must be built Gumby to fit under the car with it on the ground.

 

[Squag27]

Driveshaft angle is almost a non issue unless you have 20+" wheels installed. The only reason it's a non issue is that you would have to have something really whacky going on to have a driveshaft angle that's causing the problem.

To answer your question directly, the yoke/u-joints identify the true driveline angles of the engine/trans angle and differential angle. Have you been measuring the driveshaft angle?

Lastly, you must be built Gumby to fit under the car with it on the ground.

Well I'm not a teenager anymore so I prefer to keep my cars at stock height. That paired with the reasonably tall tire and occasional trip to the gym helps me squeeze at least enough to reach the driveshaft.

As far as the driveshaft angle. I've measured it at both yokes as well as the driveshaft itself being that all three angles are needed. The front slip yoke measures the same as the flat on the trans which is why I didn't post up that.

 

[Texas82GP]

Well I'm not a teenager anymore so I prefer to keep my cars at stock height. That paired with the reasonably tall tire and occasional trip to the gym helps me squeeze at least enough to reach the driveshaft.

As far as the driveshaft angle. I've measured it at both yokes as well as the driveshaft itself being that all three angles are needed. The front slip yoke measures the same as the flat on the trans which is why I didn't post up that.

My dad and I chased a vibration in his car (1962 Ford Galaxie) for a long time. In the end, it turned out to be poorly balance rear brake drums. I ended up balancing the drums with stick-on lead weight, using an old school bubble balancer. I'm not saying it is your problem but I wanted to throw that out there.

When did the vibration manifest? When you did the swap? Did you do other work at the same time? It's sounding like it's not a driveline angle problem. I've bought a few driveshafts from Denny's in Buffalo, NY and had them shipped all the way to Houston. It's not cheap and they are always busy, so you have to be patient, but the quality is exceptional.

 

[Squag27]

My dad and I chased a vibration in his car (1962 Ford Galaxie) for a long time. In the end, it turned out to be poorly balance rear brake drums. I ended up balancing the drums with stick-on lead weight, using an old school bubble balancer. I'm not saying it is your problem but I wanted to throw that out there.

When did the vibration manifest? When you did the swap? Did you do other work at the same time? It's sounding like it's not a driveline angle problem. I've bought a few driveshafts from Denny's in Buffalo, NY and had them shipped all the way to Houston. It's not cheap and they are always busy, so you have to be patient, but the quality is exceptional.

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The car has always had a vibration as long as I've owned it but it's changed in pitch and frequency as I've changed different things on it. It came to a head though when I rebuilt the trans and, shortly after, the rear end that the vibration turned to a droning high frequency vibration.
To answer your other suggestion though, I actually pulled the wheels and brake rotors off the rear and ran it on jackstands to see if it made a difference and it didn't. I took the driveshaft to a different shop to have it balanced again and if that doesn't work I think I'm going to take the car to a different shop up in Gainesville and leave it with them.

 

[64nailhead]

I typed a long response and my cat decided he didn't want you to see it.

I was only picking in my previous response. And I feel like a teenager, sometimes, despite being 35 years removed.


I'm curious what the 2nd driveline shop tells you about the driveshaft.

I read in one of your earlier posts that someone discussed critical speed and such regarding diameter, and that a 4" aluminum shaft would resolve your issue - that is straight up 100% hog wash. These types try to convince you that they are performing brain surgery with laser tools when in fact they are stitching up a paper cut with an old needle and thread. You are no where near a critical speed issue with a 3", 3.5" or 4" shaft in G-body.



You mentioned that the vibration gets worse when coasting. Is that only between 75-80 or do you get a vibration at other speeds when coasting?

 

[Squag27]

I typed a long response and my cat decided he didn't want you to see it.

I was only picking in my previous response. And I feel like a teenager, sometimes, despite being 35 years removed.


I'm curious what the 2nd driveline shop tells you about the driveshaft.

I read in one of your earlier posts that someone discussed critical speed and such regarding diameter, and that a 4" aluminum shaft would resolve your issue - that is straight up 100% hog wash. These types try to convince you that they are performing brain surgery with laser tools when in fact they are stitching up a paper cut with an old needle and thread. You are no where near a critical speed issue with a 3", 3.5" or 4" shaft in G-body.



You mentioned that the vibration gets worse when coasting. Is that only between 75-80 or do you get a vibration at other speeds when coasting?

No harm no foul, sarcasm tends to be my default setting. The second driveshaft shop said the driveshaft measured pretty much in spec and that they didn't think that was the source of the vibration. What I've been told, and have done the math on mine as well is that 75-85 is around where the 1/2 critical speed of the shaft is which could lend credence to the vibration. Much like you I'm not sold that the driveshaft is the issue though. If I can ever get a T56 shim kit I can fix up my spare trans to slap it in and test if that's the problem. Otherwise it's got to be a rear end issue, despite it having been gone through several times.
The vibration on coasting can be felt coming on around 65 and up into the low 100s but it's mild enough to not really be an issue outside of the 75-85 range.

 

[black_aerocoupe]

Set up an oscilloscope app on your phone. The speed of it the vibration(s) can be determined and you can narrow it down to driveline speed or axle speed.

The T56 is not as likely to be a source of vibration, but you should verify there's basically no play at the yoke to bushing. The F-body and GTO extension housing bushing is a challenging one to get right if you're DIY changing it.