Driveline and Pinion Angles

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Wvbuzzmaster

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Just installed my new Espo +2” leaf springs. My pinion angle just got worse... no fault of Espo. Previous owner matched perch angle of the 7-1/4 he took out (supposedly) cause it was a B body 8-3/4. So I will be chasing some driveline angles throughout because the transmission to driveshaft angle goes upward (don’t ask how cause I don’t know). Car is 1972 Duster swapped from slant 6/904 to 340/727. So its using swap mounts for the engine to K frame. Using a 73 spool trans mount but I bought a 72 trans mount to swap in so easier to shim transmission.

So before I start shimming rear axle how many degrees of pinion angle does everyone have? Im about 5 degrees down at the front currently. I know all cars are different and rake affects that angle. Anyway, considering going with 6 degree shims and them with raising back of transmission that might work?? I’m confused... maybe.
 
5 down compared to what?? Where is the engine/ trans centerline angle at this point?
 
Transmission angles down, driveshaft angles up off the transmission, but downward to the pinion, which is nosed down.
 
When I finished my transmission driveline conversion I double checked it with this tremec app. It’s easy to use and lets you know if your inside or outside a good angle range. Every car’s a little bit different. As 67dart273 said...you need to know your engine/transmission centerline angle to establish any base line changes. Lots of good info here for sure. Use the search tool and get ready to read. Good luck.

https://www.tremec.com/menu/tremec-toolbox-app/
upload_2020-3-6_0-13-24-png-png.png
 
Ya, i downloaded the tremec app, favorite app ever. Sadly my car is so screwed up my eyesight is more right. Cause first angle was in the green but it is going the wrong way... the others are red...
 
Transmission angles down, driveshaft angles up off the transmission, but downward to the pinion, which is nosed down.

THIS MAKES NO SENSE WHAT IS the engine/ transmission centerline compared to level?

What the driveshaft is doing does not mean squat. You want the pinion in relation to the crank/ transmission centerline. So you measure that compared to level. You measure the pinion compared to level. And you figure out how many degrees down the pinion is compared to the crank/ transmission.

You want those two shafts parallel or close to that when under hard acceleration.

The only time the drive shaft means squat is when you have a jacked up 4x4 or a "dump truck"
 
Transmission angles down, driveshaft angles up off the transmission, but downward to the pinion, which is nosed down.
Whatever the engine/transmission center line angle is, is a must know. The pinion should be within 2 degrees of this angle to be acceptable for a general street car if I remember right. The pinion will rotate up when under load to decrease this difference. Smarter guys than me may chime in but for sure run a “pinion angle” search to increase your knowledge base.
 
I had all the angles on the tremec app but forgot to screenshot it so I lost that and the car is not parked at my house cause Dad has a 2 post lift and I don’t so it’s there.

memory serves me the engine and trans are 4 degrees tail down, driveshaft 2 degrees, and pinion 5 degrees nose down.

in tremec app I know angle one was around 2 degrees and angle two around 7 degrees
 
If the trans/ engine center is "down" the pinion should be up by comparison under that condition.. Take the engine "down" angle and "in your mind" bring it to level. The pinion at rest MUST be "down" from there. When the pinion moves under power it goes nowhere but up.

This diagram is INcorrect "at rest" but would be correct under acceleration. "At rest" in this example, the pinion needs at least another 1 1/2--2* down, so that under power it swings up

Drive%20line%20angle.jpg
 
1. With the vehicle's weight resting on its suspension, make the pinion parallel to the transmission as a base-line.
2. Point the pinion 2 degrees downward from the base-line and weld (or shim) the perches. The result is a stock, 2 degree negative pinion angle.
 
Transmission angles down, driveshaft angles up off the transmission, but downward to the pinion, which is nosed down.

This ^^^^^^ and that's why it gets a little confusing.
 
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