CELEBRATING 20 YEARS!

How do you measure the angle of the drive shaft between the trans and the differential?
If the tans has a down angle should the diff have an up angle?
It would seam like the distance from the ground ( or some reference point) to the ends of the trans and diff should be the same to get a straight line between the two.
Are there any diagrams that show how this is measured to help me understand.
I have read a few things about this but the more I read the more confused I get.
I think I need a lot of pictures to get this thru my thick head.
Keith

Keith, check with SSLance or SickSpeedMonte- Bernie Duplan and good luck!!

I never worry about the angle of the actual driveshaft, I just try to get the angle of the trans tailshaft and pinion yoke the same/parallel. This puts both u-joints operating at the same angle and eliminates vibration.

Using a digital angle finder like you can pick up at Harbor freight, the easiest place to measure the trans side is on the harmonic balancer. You have to make sure the meter is exactly perpendicular to the ground to get accurate measurement. Mine for example, the engine/trans is pointed 3.5 degrees down toward the back.

For the pinion side it is easier if you remove driveshaft from yoke so you have a flat surface to put angle finder on. I have mine set so pinion yoke is pointed 3.5 degrees up toward the front. This puts the trans output and pinion yoke exactly parallel so U-joints operate at exactly same speed during most circumstances. The angle of the driveshaft itself is irrelevant.

The angle of the drivetrain is irrelevant to the angle of the ground. It's the angle of the engine/trans to the angle of the pinion that is important. The angle of the driveshaft is only important if the vehicle has it's ride height greatly increased like on a 4x4.

Engine/trans angle will be in the area of 3 1/2 as Lance said, maybe plus or minus a 1/2 degree depending the rack of the car. Several places to pull the engine trans angle, damper face is one, oil pan rail, starter mounting surface. I made a precise block of steel that fits into the u-joint cap at the front of the driveshaft to get engine/trans. But my driveshaft is not stock,
I do pull the driveshaft and measure angle off the face of the pinion yoke.

As for pinion angle I run 1 degree less pinion angle than engine/trans. So 3 1/2 engine trans and 2 1/2 UP pinion angle. Under hard acceleration my pinion will climb 1/2 to 1 degree possible.
How much pinion angle to run depends on what bushings are in the rear suspension. Rubber will deflect much more than poly and solid joints have close to zero deflection. Under hard acceleration the rear will climb, rotate upwards at the pinion, and this changes the pinion angle. Less deflection of the joints, less climb.
Ideally under very hard accel the drivetrain will be a straight line which reduces power low to the u-joints. But street cars don't need to worry about obtaining that.

I would shoot for about 1 degree less pinion than engine trans angle.

Do you have adjustable UCA or LCAs?
Is this a problem with vibration at highway speeds?
Bob

Yes adjustable upper and lower control arms. I believe they are UMI control arms, maybe ride tech.
I do not notice a problem, but I did repacae the differancel with a Moser 12 bolt and would realy like to make sure I have the angle right
Keith

Good, makes adjusting, dialing in, a new rear much easier.

Looking back through your posts and build you've been pretty busy with changing most everything in the chassis. From experience doing the same thing i find once you throw all those new parts from a whole lot of different venders on the car you need to insure they all correct out of the box. The LCA should be equal length and so should the UCAs before pinion and thrust adjustments are done.

I had Global rear non adjustable LCA for years and changed over to a Spohn adjustable. The Global length was 18 13/16" out of the box and the Spohn were 18 5/8", stock length is supposed to be 19 1/4". The UCAs are Edelbrock adjustable bought 20 years ago. When the Spohn LCA went in the UCAs were pulled and adjusted so they are equal length. Forget what they measured at that time but stock is said to be 11 1/4".

With all four links set pinion angle can be checked. Adjusting the UCAs equally to rough in pinion angle, LCA are not touched for this. Next is the alignmnet rack and set thrust angle by only adjusting the LCAs. Once done it's back to double checking the pinion angle and adjusting it equally on each UCA. The LCA isn't touched. Next front end alignment will verify whether the thrust angle is still good.

Most will say the rear in the car is not centered in the frame, fat tires will rub one side of the frame. Some will try to adjust the UCAs to move it left or right, not a good idea IMO. Different lengths of UCAs effects how the car leaves when launched, it will go left or right depending on arm length. Drag racers use adj arms to dial out those tendencies.

Pinion angle and thrust angle are two very important things to adjust especially when a non stock rear with all non stock arms are installed. After spending thousands to put some really good parts in the rear the 75 bucks spent on the alignment rack to know the rears thrust, toe, camber angles are good to go is money well spent. Never take for granted that what came out of the box is correct. Double check everything.

Couple years ago bought a Intercomp digital angle gauge for the front suspension relocation project. One of the most useful tool I've bought recently. Had one of those plastic angle gauges prior, have no idea where it is anymore, might have trashed it.
https://www.intercompracing.com/digital-angle-gauge-p-99.html

On tremec's website there is an APP to download that will allow your phone to be a angle gauge.
https://tremec.com/menu/tremec-toolbox-app/

Keith, nice build, keep us posted, I like seeing the progress.
Bob