The Stovebolt Site Forums The Shop Area Driveline pinion angle

How important is pinion angle? What are the downsides of too much or not enough pinion angle other than excessive U-joint wear?


Weeds

technically there is no such thing as too little pinion angle. That would mean perfect shaft pinion alignment. Unless of course it was achieved by increasing the front shaft angle.

In addition to U-joint wear, too much pinion angle will cause a "lumpy" turning of the drive shaft causing the pinion to cyclically speed up and slow down 4 times per revolution and a loss of power due to increased friction at the acute u-jount angles.

The pinion angle will change as the axle moves up and down. The correct angle will be the best compromise that can be had. Think, compressed, +3 degrees, Unloaded, -3 degrees. And how to set? Get as close as you can. Set with the truck unloaded. Then check with it loaded.

I just went through this with my truck. I had done a transmission swap, followed by an engine swap, followed by a rear axle swap, and always had a persistent vibration. Turns out the pinion was at 2 degrees up compared to the transmission. A cheap set of 2 degree wedges has nearly eliminated the vibration. If the angle is off, it is better to be off in the downward direction. As torque is applied, the pinion will rotate upward.

Way back when I had a lifted Blazer and even with rear end wedges it still sat at 7 degrees. I replaced u-joints about every 10K. If I didn't change them religiously they would break for sure.

You need to know what angle the engine/transmission is at, and have the pinion angle set at the same angle +/- 1 degree.
Carl

52 carl. How do I find the engine/transmission angle. Do I level the carb mounting pad and go from there?


weeds

Do you have a cheap protractor level?

Easiest way to measure transmission and rear axle angles is as follows

Remove the driveshaft

Turn the transmission yoke so that both holes line up vertically

Place a piece of straight pipe about 1 foot long in the yoke, making sure the pipe seats in the yoke.

Place your protractor level on the pipe and measure the angle

Do the same for the rear axle

Please note, it is best to do this when the truck is sitting on all 4 tires.

If you are still confused, there are several videos on youtube describing the procedure. You don't need a digital level that costs several hundred dollars. A cheap $10 plastic gravity protractor level will work fine.

Hey bigbadswingdaddy, I like your tip for checking the pinion angle of the rear axle, but to do the same for the engine/transmission angle, it would require removal of the u-joint from the front yoke. Not so much fun. Just fine though if he hasn't already installed the u-joint, or has an extra yoke laying around. There should be a level surface somewhere on the transmission to gauge off of?
Carl

The starter housing is parallel to the drive train.

However, when setting your engine mounts you are correct that the carb mount should be level. That will put the drive train a few degrees down. I'm assuming you are setting the engine to match your existing pinion shaft. Find the angle of the pinion shaft then set the engine to the same angle, measured at the starter housing.

Big bad, Cletis and Carl, Thanks for the advice. You guys are always ready with solutions and I appreciate it.


Weeds

Cletis, I am running a 283. is the starter mounting pad parallel to the driveline or 90 degrees to it. As usual I'm totally confused. Do I take the starter off and put the protractor on the mounting pad to read the angle?

Starter mount is exactly parallel to the yoke when the yoke is vertical. Yes the starter will have to come off. The good news, with the 283, you have an open drive shaft. So pull the drive shaft out and get the measurement from the yoke. Leave the starter for another day.

I have a magnet mount protractor and put it on the valve cover to get the measurement for the engine. I use a floor jack on the transmission and can adjust things up or down as needed with the rear transmission mount.

You could use the starter mounting pad but I used the starter housing and subtracted 90 degrees.

don stocker, Cletis and Big Bad. I have the drive shaft out the starter is off and the engine and trans is out. I am doing the Scott Danforth front cross member/ S10 IFS and with this arrangement the 283 and TH350 sits down in the engine bay lower. as a result I have to raise the engine up thus changing the pinion angle. With the previous front crossmember(84 GMC 1/2T) I had to lower the transmission to get a good pinion angle.Worked good. no vibration and a highway ratio but wore out front tires to beat He double toothpicks.Also when turning a corner the steering wheel would not return to the neutral position. Danforths crossmember should correct the tire wear and alignment problems.Too cold to work now but hope to have it ready by spring. I really miss not being able to drive it. Nice rig.



Weeds

Weeds, I'm sure you'll have a FEW days when the sun will shine and you'll be in the shop.
You are right about the engine sitting lower in the frame. I've experienced it a couple times myself. On my 37 it set the fan real low and I had some heating issue's to deal with because the fan was so low...and I could run a big fan for a couple reasons.
I know you have it figured out and looking forward to your progress reports.

(hope the Pontiac is coming along to)