Pinion angle question

[fred29406]

There are a million posts about pinion angles and they all seem to contradict each other. I need some help- recently swapped out my original drivetrain on my 73 Blazer for a 383 crate motor and 4L60E transmission. After installation the rear differential was at 18 degrees pointing up with the transmission at 2. Very bad. Added shims to get the differential down and now driveshaft is too short. Added an 8 inch slip yoke to the driveshaft, lowered the tail of the transmission a bit and now the slip yoke measures 4.2 and the u joint on the differential measures 5.7. So I’m within 2 degrees, that’s good right? The driveshaft sits at a pretty high angle though- but that shouldn’t matter as long as everything clears right? Thanks in advance.

 

[shock88]

ideally you want the angles to match with a single u joint driveshaft. it’s not so much of how high of an angle the pinion is from level, it’s the difference of angle between the pinion and driveshaft. So even if ur pinion is 15° from level that’s ok. You just want the angle of the driveshaft to be say 18° so there’s only a 3° difference. and same with the trans output. If that’s at 2°, u want the driveshaft to be at roughly 5° so there’s only a 3° difference. It’s not a perfect world with these lifted trucks, so u might not get it perfect

 

[fred29406]

Ok so to be clear- the angle from the yoke to the driveshaft should be within 3 degrees, and the differential ujoint to the driveshaft near 3 degrees, but they don’t need to be equal front to back?

 

[shock88]

Ok so to be clear- the angle from the yoke to the driveshaft should be within 3 degrees, and the differential ujoint to the driveshaft near 3 degrees, but they don’t need to be equal front to back?

yup exactly! in a perfect ideal world, the pinion will point up say 2° up and driveshaft will be at 5° and same with the trans output. But that only really happens on cars where the height of the difference of the pinion and trans is close. These trucks are a different animal, especially modified.

 

[HankScorpio]

Stop. You didn't say what kind of driveshaft you have.

A driveshaft with a double cardan joint at the transmission end will want the pinion pointed straight at the transmission, matching angles isn't required.
A standard straight driveshaft with single u-joints on each end will want the transmission angle and pinion angle to match. If the trans is 5 degrees down then the pinion should be 5 degrees up.

Also, if you shim the trans down to help with the rear driveshaft angle it makes the front driveshaft angle worse.

 

[HankScorpio]

 

[Wes Harden]

Not sure Op can see this. Up load to gallery, then pist insert in thread. Everyone should be able to see.

View attachment 502798

 

[muddybuddy]

A picture of your setup would be worth a thousand words.

The info on pinion angles is not contradictory, there are different types, which essentially require the opposite approach. If you apply the cv shaft approach to a non cv shaft or vice versa, you will have horrible results and rip your hair out.

 

[Blue85]

There are a million posts about pinion angles and they all seem to contradict each other.

No, this means you're not understanding the different types of setups.

the rear differential was at 18 degrees pointing up with the transmission at 2. Very bad. Added shims to get the differential down and now driveshaft is too short. Added an 8 inch slip yoke to the driveshaft, lowered the tail of the transmission a bit and now the slip yoke measures 4.2 and the u joint on the differential measures 5.7. So I’m within 2 degrees, that’s good right? The driveshaft sits at a pretty high angle though- but that shouldn’t matter as long as everything clears right? Thanks in advance.

You put in 12 degrees of shim on the axle? How is the spring pack center pin routed through this? How did you lower the transmission? Spacers between the frame and crossmember? A longer slip yoke (and the other 2 things I just mentioned) is not recommended due to added stress on the tailshaft of the transfer case and a worse balance overall. Plus, you're increasing the angle between the slip yoke and the driveshaft, which makes it more likely to bind and wear out the seal/bushing.

How did you start at 18 degrees on the pinion? Shackle flip? How much lift does it have? It sounds like where you started it was good for a C/V joint. If the U-joints have more than about 10, maybe 12 degrees in them, the driveshaft probably won't run completely smooth.

 

[fred29406]

Stop. You didn't say what kind of driveshaft you have.

A driveshaft with a double cardan joint at the transmission end will want the pinion pointed straight at the transmission, matching angles isn't required.
A standard straight driveshaft with single u-joints on each end will want the transmission angle and pinion angle to match. If the trans is 5 degrees down then the pinion should be 5 degrees up.

Also, if you shim the trans down to help with the rear driveshaft angle it makes the front driveshaft angle worse.

Ok I have 2 u joints. After working today the rest at the diff is 2 degrees difference between the pinion and the driveshaft Front angle between the yoke and the driveshaft is still 8 degrees. Does it matter if the differential points up and the front angle points down?