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Discussion Starter #1
Well I picked up this 65 nova late last yr and finally took it on it first cruise few days ago.
Once I get above 35 mph I start getting a really bad vibration all through the car on any amount of throttle. Let off the throttle and it lessens but doesnt go away 100%.
It's got brand new wheels and tires that I just but on this month. So that's not the vibration problem.
Car does have a 8.5 rear end from god knows what that has been cut down. I took some measurements of the angles let me know what you think.
20200523_203518.jpg
 

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Mike - 74 Nova Baltimore, MD
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Did you take these measurements with the weight of the vehicle on the front and rear suspension?

For a mostly street driven car, I was under the belief that the best driveline angle would be with the transmission yoke angle and the rear end yoke angle parallel to each other... and the driveshaft offset by 0.5°- 3° from the front and rear yoke angles for best U-joint wear.
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In your scenario (transmission -3° front to back / driveshaft -5° front to back / rear end +6° front to back) ... for a mostly street driven car, I would try to lift/wedge the rear end pinion upwards towards the transmission tunnel so the pinion yoke angle was -2.5° to -3° front to back. Lifting the rear pinion may also change the driveshaft angle to -4° front to back > and that would still work out fine.

NOTE: For a mostly strip/drag race car, the rear end pinion can be angled a little lower than the transmission pinion angle, since the engine torque under load (racing) will most likely lift the front of the rear pinion yoke some (but how much really depends on the type of rear suspension and traction aids that are being used).
 

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The rear axle pinion being down 6° could well be the problem. You want the pinion angle to mirror the trans angle, equal but opposite while under power, which would be your pinion being 3° UP. your pinion at 6° DOWN is a 9° difference....too much.
Since this is a leaf spring car, you have to allow some for the fact that the springs will wind up and the axle will rotate up a few degrees when power is applied, so the basic setting on your set-up needs to ne right around 0(zero)° to 1° UP unless this is a high powered drag car, and then it might need to be between zero and 2 to 3° down.
In any case, your 6° down is way too much.
You can get spring wedges to go between the spring perch and the main leaf to change this without welding, it's how drag racers tune theirs..

All angle measurements have to be taken with the car's rear weight sitting on the axle...either put the up with axle on jackstands to hold the car up or do it over a pit or drive-on lift so the car is sitting on the axles.
When you jack the car up and let the rear end hang, pinion angle will drop drastically.

II is also likely someone messed up the drive shaft when fitting the 8.5" rear axle swap. I would consider it highly suspect if it is just a shortened stock or jubnkyard OEM shaft, less suspect if it is aftermarket made shaft.
Have you got a dial indicator and magnetic base?? Need it to check run-out at both ends of the shaft, and the center of the shaft, to see if driveshaft is straight and not bent, and the ends welded in on center..
 

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holy poo that's some bit of knowledge shared here. I have had a vibration problem in my '74 but it was the brakes heating and trying to stop the car without me applying them, Good luck. The guys here really know their stuff on these cars.
 

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Discussion Starter #6 (Edited)
Thanks guys, lots of great info

When I took these measurements I placed the car on Jack stands. Two under the rear axles and two under the front control arms. And tried to make the car as level as possible. Summit has 6* wedges. Do you think that would be enough?
 

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Mike - 74 Nova Baltimore, MD
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I agree with Ericnova that the leaf springs are going to wrap-up a few degrees (therefore changing the pinion angle) when power is applied during acceleration.... but I think the amount of leaf spring wrap-up during steady cruising would be minimal.

I guess it all depends on how you plan to operate the car for the majority of time it is driven.
A compromise for both acceleration and cruising would be setting the pinion angle about 1° to 2° lower than parallel to trans yoke angle.... so the 6° wedge gets you pretty darn close.

I found an image of your rear suspension set-up from your Introductory post.
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It looks like you have mono-leaf springs with some traction bars that are mounted to the rear axle spring perches.
Something additional things to consider....
  • Your traction bars are going to help control spring wrap-up to some extent.
  • If you insert an angled wedge between the top of the spring and the spring perch to raise the pinion angle, you might also need to insert an other angled wedge between the traction bar mounting plate and the bottom of the spring to maintain the current angle/spacing of the traction bars.
 

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Yep, I agree with the last two posts.

Watch you driveshaft yoke at the transmission, when you angle the pinion up with the 6° wedges it is going to push the driveshaft forward....make sure you don't run out of travel and bottom the yoke out and that it has adequate travel remaining....if it ever jams solid to the trans it will hurt or kill the trans or the driveshaft...or both. Can make an expensive mess.
 

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You should be good then, because it is too far out now....that may be a contributor to your vibration. Spec is 3/4-1" at ride height.
 

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Discussion Starter #12
Yeah I agree, I've had about 5 driveshafts made over the past 30 yrs and I've always ran the yolks about 1" out the back of the trans. This is a fairly new built shaft as I have the receipt for it when I bought the car.
 

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There are many other things that could contribute to the vibration. You eliminated wheels and tires, but what about differential, wheel bearings, brakes, transmission, etc? Just thinking since this was the cars maiden voyage, there are a lot of gremlins in new builds, it could still be many other things. I wouldn't think the drive shaft angles you have would create that vibration. I was under the understanding bad angles would create premature wear on the ujoints, but not on your first drive surely. I don't know, but I would put it back up on jack stands and get some help, and run it and look and listen. My best guess is its something else.
 

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Discussion Starter #15
I'm pretty sure it has to do with something in the driveline like the pinion angle, cuz the vibration changes when your on and off the throttle.
 

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I've found this video from Dana/Spicer corp can explain a lot to people about what actually happens when you've got driveline angles off more than 5°. Few people realize that a driveshaft running even on perfectly acceptable angles does not turn at a steady speed....it will only have a stead speed if everything is in a perfectly straight line with no angles at all.

Notice why angles have to be equal and opposite to get a steady speed at the pinion .
 

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There are many other things that could contribute to the vibration. You eliminated wheels and tires, but what about differential, wheel bearings, brakes, transmission, etc? Just thinking since this was the cars maiden voyage, there are a lot of gremlins in new builds, it could still be many other things. I wouldn't think the drive shaft angles you have would create that vibration. I was under the understanding bad angles would create premature wear on the ujoints, but not on your first drive surely. I don't know, but I would put it back up on jack stands and get some help, and run it and look and listen. My best guess is its something else.
He has an 11* working angle on his rear u-joint. This is about 9* too much. No way it will not shake the car apart.
 

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Well I picked up this 65 nova late last yr and finally took it on it first cruise few days ago.
Once I get above 35 mph I start getting a really bad vibration all through the car on any amount of throttle. Let off the throttle and it lessens but doesnt go away 100%.
It's got brand new wheels and tires that I just but on this month. So that's not the vibration problem.
Car does have a 8.5 rear end from god knows what that has been cut down. I took some measurements of the angles let me know what you think.
View attachment 405066
The transmission should be flush no angle and the piñon street car should only be a 3 to 4 degree angle . If it’s more and it looks like it way to much of an angel built many Nova just my opinion . Plus make sure the drive line is balanced .And the Toque converter can also be coming apart and can cause this . Plus you could have a wrong flex plate on it and all of the can make the whole car do this . Jack up the back end of the car and put it on jack stands up let it idle in gear and watch everything . Hope this helps . Good luck Diane
 

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Discussion Starter #20
Car is at chassis shop as of this morning, they said the one of the weights in rear of driveshaft did fall off probably from the bad vibration of the rear end being so far off. They pulled the rear out and are moving the spring perches, so I'll know more tomorrow night.
 
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