Transmission - Pinion alignment with Mild PB DM

[jerimy75]

Just wanted to check with everyone here on my process and results of setting the horizontal alignment of my transmission and pinion/axle. Here are the specifics:

Mild PM DM front and rear
SBC and 700R4
Chevy 12 Bolt rear end

I am putting new perches on the axle so I can correctly adjust the vertical pinion angle. I centered the axle in the frame the best as I could by dropping a vertical line down from the outside of the frame rail (PB notch). To double check I pulled diagonal measurements from rivets on either side of the frame to the center of the pinion and the dimensions didn't match. I did some additional measurements and realized that the pinion is offset to the passenger side 1-inch. I did some research on here and learned the offset is standard.

Here are my questions:

1. is there a better way to center the axle housing in the frame?
2. should I still center the transmission between the frame rails?
3. is this horizontal offset going to require any special attention when I set my pinion and transmission angles? In general I plan on using the PB suggested angles of transmission down at 6 degrees and first driveline at 5 degrees with the pinion at 5 degrees.


Thanks in advance for your input folks!

[crazy longhorn]

Porter can probably explain it better than any of us here? I ? the 5-6 degree down on the engine /trans, old school tried to tell us 3-4 degrees down on the eng/trans, on a rod or racer. Porter has set up many lowered(slammed) cars/trucks, & is well respected here You should check with him, & post back here? Old school as I am, if I am shown a better way...I learned a new trick! Longhorn

[fleetsidelarry]

jerimy. if I understand correctly, you have a 2-piece drive shaft? ("...and first driveline at 5 degrees...") if so, and if I understand the Spicer manual correctly, then you are fine with what you are planning IF the rear shaft angle is not excessive.

I'd find the actual centerline of the axle housing by measuring end-to-end or backing plate-to-backing plate and attach the perches.

and I'd keep the engine/tranny in the center and parallel with the frame.

[jerimy75]

Ok gents (and ladies), here is my experience in setting up my rear axle, transmission, and driveline. Thanks goes out to PB, n2billet, and Drive Line Service Sacramento for their input. If someone sees an error in my method please don't hesitate to let me know!

Givens:

1. PB Mild DM with ride height set at 7-inches
2. Assumed 28-inch wheel and tire combo
3. 700r4 Tranny


1. To locate the rear axle I started by dropping a plumb line down from the outside edge of the upper crossmember at the frame notch (the outside edge of the upper bag mount plate steel) to the centerline of the axle on both sides. I got these measurements as close as possible, then pulled angle measurements from the rear of the frame and front bend mounts to the centerline of the backing plate mounting plate to try and get it as square as possible. With the lower shock bar mounted to the trailing arms, I tacked the axle perches to the trailing arms so they would not move and centered the trailing arms on the rear axle by measuring from the axle backing plate mounts on each side to the perches. I then tightened the U-bolts snug enough to keep the axle from rotating as I adjusted my pinion angle (see below).

2. PB provided some angles for the transmission, first shaft, second shaft, and pinion. I started with their recommended transmission angle of -4* and pinion at 0* to get the measurement for the 2 pc driveshaft. The driveline shop provided some good recommendations for angles and their recommendations were in line with the Spicer/Dana Installation Manual that is floating around here on the forum. By shimming the carrier bearing up 2 5/8" I set the first shaft of the driveline at -3* (within 1* to 1.5* of the transmission as recommended by the DL shop and the Spicer manual). With a 3 inch shaft this gives me about 1/4" clearance from the top hoop of the trailing arm crossmember. I then set the pinion based on recommendations from the DL shop and manual to +3* (equal and opposite of, or as some people say parallel with the first shaft). This resulted in a second shaft angle of +3*.

So there you have it. Not sure if I will have any vibration and it will likely be a few years until I know, but that's the method and angles I used in setting up my 2 piece driveline. I may have left some things out, so please don't hesitate to ask if you have a question.

Thanks!

[fleetsidelarry]

sounds good, jerimy75, thanks for the update. if I understand correctly, you are saying the pinion, rear shaft, and front shaft are all set at 3° (front higher than rear each part). if so, your driveline is not just parallel but actually in a straight line relative to the ground. viewed from the ground, this would mean that the rear and center u-joints wouldn't have any working angle. viewed from above, however, the offset pinion provides even these u-joints with some angle so you should be good. a little trigonometry would tell you what that angle is, all you need is the driveshaft length, the amount of offset of the pinion and: http://www.engineersedge.com/calcula...solution_1.htm
use the calculator to solve for angle B, with c= rear driveshaft length and b= pinion offset

[jerimy75]

Fleetside - Actually the first shaft and the pinion are parallel but on different planes than eachother when viewed from the side. The first staft is -3* (down, sloping down to the rear), the second shaft is +3* (up, sloping up to the rear), and the pinion is -3* (the pinion is facing up towards the front of the vehicle).

***I just realized that my post from last night was incorrect. I said the pinion was +3* when it really is -3*, sorry guys! Can I edit my original post so I don't mislead people?***

So yes looking from the side of the vehicle I do have working angles. But as you indicated I also have a slight angle between the carrier bearing and pinion in plan view (viewed from above the vehicle). The resultant is a compound angle, I know, I'm just hoping it's not too severe and causes vibration. Thanks for the link, I'm an engineer but it's still nice to have calculators like that. That said, I don't know that I care what the offset angle is, I can't change it (unless I get a new axle) so it is what it is.

Thanks again!

[jkeating1]

Thank you for the detail! I will be at the point of locating my trans tail crossmember/mount soon (and hopefully NOT relocating my carrier bearing). This will be helpful. Please continue to post as you progress.

[fleetsidelarry]

just a note. the rear shaft u-joint operating angles are going to be 6° not counting any compounding. whether that's a problem or not remains to be seen. the Spicer Manual recommends that joint angles be kept under 3.

but sometimes you got to do what you got to do when building, and compromise somewhere.