Vibration right off idle

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At rest on my 4 post lift with the weight of the car on all 4 tires.
Try to keep the angles between 2-2.5 degrees and you should be good to go.

I have the car on ramps and it's level, so good there. Sorry, but are you saying keep both the pinion and the trans at 2-2.5*? And is that in both directions?
 
I have the car on ramps and it's level, so good there. Sorry, but are you saying keep both the pinion and the trans at 2-2.5*? And is that in both directions?
Set the trans so it is pointing up +2.5 degrees
Set the rearend pinion so it is down -2.5 degrees
Negitive or positive 2 to 2.5 is just a range to shot for.
 
Look at the trans on the right 904
Then look at the overdrive trans on the left at how much longer it is than stock.

Screenshot_20210410-203807_Chrome.jpg


Being your overdrive trans is longer, you end up with a shorter driveshaft and in the process it steepens your driveline angles.

What is the tailshaft angle right now, car sitting level, and no shims at the tail shaft mount? 2° Negative ????

Now measure the rear pinion angle, what is that, 2° Positive ???

This is the senario you want with Negative degrees at the tail shaft and Positive degrees at the pinion shaft.

Raising and shimming the trans tail higher is going the wrong way, giving you too sharp of a driveshaft to tailshaft angle.

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Let's see what your angle degree measurements are to start with.
 
Ever notice how the carb is always level, but the drivetrain is tilted down in the back? And the manifold is angled about 3 degrees? You tilt the motor/trans down in the back about 3 degrees, and the pinion up 3 degrees. That article was written by a person who really doesn't understand driveshaft angles. Read his last post about Sunbeam Tigers. Driveshafts don't know the angles of the two units they are connecting, so up, down, left, right; don't matter to a driveshaft; only the overall angle; measured from any perspective.
 
Sorry, guys. I missed these updates. All I have read is that you want what @George Jets is saying. (trans (-) and pinion (+) the same measurement to offset each other.

So in my case: trans is -2.5* so my pinion needs to be at +2.5. Currently my pinion is -3.9*

So if I roll the pinion up +6.5* that will give me a pinion angle of + 2.6 (-3.9+6.5).

If the pinion rolls up 2* under power. Then I can subtract 2* from my shim. So I need to roll the pinion up 4.5*.

Totalling .6* at rest and 2.6 under power.
 
Look at the trans on the right 904
Then look at the overdrive trans on the left at how much longer it is than stock.

View attachment 1715721665

Being your overdrive trans is longer, you end up with a shorter driveshaft and in the process it steepens your driveline angles.

What is the tailshaft angle right now, car sitting level, and no shims at the tail shaft mount? 2° Negative ????

Now measure the rear pinion angle, what is that, 2° Positive ???

This is the senario you want with Negative degrees at the tail shaft and Positive degrees at the pinion shaft.

Raising and shimming the trans tail higher is going the wrong way, giving you too sharp of a driveshaft to tailshaft angle.

_________

Let's see what your angle degree measurements are to start with.
He posted them already. U absolutely do not want the pinion higher than the trans. The way u describe it he would have 4* positive. Kim
 
Sorry, guys. I missed these updates. All I have read is that you want what @George Jets is saying. (trans (-) and pinion (+) the same measurement to offset each other.

So in my case: trans is -2.5* so my pinion needs to be at +2.5. Currently my pinion is -3.9*

So if I roll the pinion up +6.5* that will give me a pinion angle of + 2.6 (-3.9+6.5).

If the pinion rolls up 2* under power. Then I can subtract 2* from my shim. So I need to roll the pinion up 4.5*.

Totalling .6* at rest and 2.6 under power.
No no no no no
 
Ok, coming back to this. I bought a poky trans mount, which raised the trans up and I checked the angles with the Tremec app and all green. Woo hoo.

Now after test driving, the same rythmic vibration is there, but very slight. When the Overdrive kicks on it goes away?
 
Im back
The driveshaft and yokes do not know or care if you are in or out of overdrive.
If your road speed remains the same and the vibration changes or goes away when the trans shifts into overdrive IMO you likely have an internal trans or engine issue causing the vibration.
 
Im back
The driveshaft and yokes do not know or care if you are in or out of overdrive.
If your road speed remains the same and the vibration changes or goes away when the trans shifts into overdrive IMO you likely have an internal trans or engine issue causing the vibration.

Well the speed does change. The OD kicks in about 45. The speed where the vibration is felt is cruising at about 35.

I'm going to turn off the OD and manually run it in each gear for further diag. One thing is for sure, raising the trans up made a SIGNIFICANT difference.
 
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These Driveshaft angles are like talking camshaft grinds with people . . .
 
Ok... So how did that happen? It's a factory 8.75 with espo springs and things 6 leaf springs. I never changes the perches...
 
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