The Stovebolt Site Forums The Shop Area The HiPo Shop Final check before welding...

I've searched and read everything I can about pinion angles on this site and others, but I'd like to get a few opinions before I weld on new axle seats. Ok great ones, here's where I'm at with installing a '79 rear axle under my '63.

I removed the old axle (intact), replaced trailing arm bushings, cleaned everything up, installed 3" drop springs, went through the new (to me) '79 rear end, fabricated a new panhard bar bracket for the frame and all parts are cleaned, painted (except the axle tube), and ready for almost final installation to set the pinion angle and tack the axle seats in place. Before I do any welding on the axle I have a few questions...

The angle of the motor/tranny as measured with an angle finder at the starter housing is -2 degrees (i.e. pointed slightly down). It is my intention to set the rear end pinion angle at +2 degrees (i.e. pointed slightly up). When I do this the truck will be sitting on all four wheels in a mostly level garage. Sound about right?

I have measured everything I can think of to get the rearend centered between the frame rails and for the life of me I can't satisfy myself that it is right. I've measure the distance between the trailing arms and the pumpkin to make sure that they are the same and about the same as what was on the old axle (compensating for the difference between old v. new pumpkin). I've measured from the inside of the tire (at ride height) to the outside of the frame to make sure that it is the same. I've measured from the inside of the fender to the outside of the tire. Here's the problem...with the measurement the same on each side from the inside of the tire to the outside of the frame I have less fender clearance on the passenger side than on the driver's side.

My gut tells me the problem is that the bed is not sitting on the truck straight (which wouldn't suprise me). Any thoughts?

I was told to set the pinon angle on our 53 1/2 ton to between +2 to 3 degrees. When we had the front end aligned, the mechanic checked it and said it was right on the money. I had the same problem with our bed. The axle was centered and it still was closer on the passanger side. I guess either I don't have the bed centered or the cross member holes were nevered centered by the factory. Frank

Sounds like you have the right idea.
If you ever have any questions about pinion angle and driveshafts they will be answered here, I suggest you skim through the entire thing, and read the part that looks like your setup.
http://www.roadranger.com/Roadrange...=Installation%20Guide&Language=en_US

For your setup you will need the pinion centerline and engine / transmission centerline to be parallel.
You can't talk about the pinion angle without also knowing the engine centerline angle. It is the relationship between these two angles that is key, one without the other means nothing. However if the u-joint angles get large you have a problem, but in a stock situation this won't happen. Read the Spicer manual so you understand how u-joints and driveshafts work...

To center the rear I would first center the ends of the trailing arm brackets on the axle by measuring from a machined surface at the end of the axle tube on each side. Usually the backside of the flange the backing plate bolts to is machined, or check to see that that flange is the same thickness both sides and you can still measure from it if it is not machined.
While trying to make the left and right side measurements the same make the center of bracket to center of bracket the same measurement as the original was.

Once that is tacked in place, and even finished welded you can center the rear axle in the frame by adjusting the location or length of the panhard bar. I would drop a straight edge down both sides of the frame and make the distance from frame to backing plate on both sides the same at ride height.

The location of the bed, fenders, and tire all have a pretty slack tolerances. You need to pull all measurements from accurate preferably machined surfaces and the frame.

Grigg

Thanks guys...

This was also discussed in the Engine/Driveline Forum recently as I just had to re-do mine truck because of "abuse"!! I might add that my 37 is like yours as far as how the bed sits on the frame or is centered. I can tell a small difference when I wash it and run my hands around the edge of tires. My truck tracks and drives good and the front end man says it was a good job on what I did. We have to remember, or at least in my case, that some farmer has loaded, unloaded, probably ran over several cows and even tree's with the truck twisting the cab, body and frame in all directions. After over 60 years of "work" I figure mine is pretty good!

Texmo, can i throw my two cents in here on the pinon angle? When setting the pinon angle start like you said with the truck on all fours and at ride height. After you have that done to set the pinon angle make sure the plane of the manifold is level. now you can check the pinon angle at the tail shaft of the transmission. If it is down 3 degrees or what every then the rear end needs to be up the same amount.. BUT!! if you're using leaf springs they say to go at least 1 degree less than the trans. because as the motor puts power to the rear end the rear wants to roll up and then the angle will be the same front and rear.. does this make sence to you? Not knowing if your truck is lowered in the front or up will have something to do with all of this also.. you said something about putting it up 2 degrees is this because the truck sits higher in the front?? Wayne

Wayne,
My truck has 2" drop coil springs in the front and 3" drop coil springs in the rear...it sits just about level (measured at the top of the bed rail and the seat of my pants). The motor is tilted slightly down and I have now welded the axle seats on such that the pinion is tilted slightly up.

Texmo,
Sounds good so far, just remember that you want the tail shaft and the pinon to be parallel under load, or as close as you can get it.. With that you shouldn't have any problems...

With coil springs you won't have the axle wrap that leaf springs do, so just set the angles equal and you will be golden.