Another pinion angle Question

[forestb]

What pinion angle should I be looking for on my 62, single drive shaft, short bed, C10, with a 5 inch rear drop?

[PGSigns]

The pinion angle needs to be set based on the angle of your engine. The angle of the rear and the angle of the engine need to b measured with the weight on the wheels. With 5 inch springs in the back of my 66 I have about 2 degrees of shims under my rear end perches.
Jimmy

[SkinnyG]

General rule of thumb is to match the angle of the engine/trans.

If the transmission output shaft is 5° down, then the pinion should be 5° up, so they are parallel to each other.

I like to go a degree shallower on the pinion, to allow for any compliance in the rear suspension.

It is also a good idea to have the trans output higher than the differential pinion, so the rear u-joint is not at some unusual operating angle. In my '61 (and my '77), I raised the transmission considerably to make sure the driveshaft sloped down.

[forestb]

So if the transmission pinion angle is 5 degrees. You would set the differential to around 4 degrees? Should I assume that the differential is usually lower than the transmission output shaft? So the transmission output shaft should be pointing down and the differential should be pointing up?

I have heard that it is not good to have everything perfectly parallel.

[SkinnyG]

You want a u-joint operating angle around 1° to 3°. That means that the transmission perfectly inline with the driveshaft perfectly inline to the pinion is a problem - the bearings in the u-joints don't "move" and the u-joints fail.

A u-joint operating angle greater than 3° can cause vibration.

A significant difference between the front u-joint operating angle and the rear u-joint operating angle can cause a vibration.

On my truck, just looking at it wrong causes a vibration.

The differential is -usually- lower than the trans output shaft, unless you are significantly lowered. My '61 is. My '77 had the trans and pinion at the same height until I raised the trans.

Carrying a load changes the ride height which will change the pinion angle.

Leaf springs change the pinion angle all over the place, and are a pain to set right - you have to find the best compromise.

Yes, I would set it at 4°, but I would also keep my mind open to the possibility of having to shim it to what it wants once it's on the road.

[forestb]

Ok thanks guys. I am planning on checking all of my angles this weekend and I will let you know what I come up with.

[forestb]

So I tried to check my pinion angle while sitting on the ground. I don’t think I can trust my measurements though the ground was not exactly level and I had to use the bottom of the transmission pan to check that angle because I could not reach the tail shaft. With that being said the differential pinion angle was 5 degrees and the transmission pinion angle was 1 degree. I am going to take it to a shop this week that has a lift that lifts the truck from the tires instead of the frame. That should give me a better measurement and will allow me to measure from the tail shaft. I was hoping to fix it by lowering the end of the tail shaft but if it goes any lower the drive shaft will make contact with my energy break mechanism.

[SkinnyG]

You can have the truck up in the air, but you must support the rear axle on stands. The truck does not have to be level - the angles relate only to each other, not "earth" or "gravity".

Don't trust the trans pan, but you CAN measure off the engine pulley (measuring off vertical: 85° off vertical is 5° off horizontal).

I'm assuming the trans is pointing down. Is the pinion 5° up (pointing towards the trans) or 5° down (pointing to the ground)?

If the shop is any good, they're going to need to know the angle of the driveshaft as well.

[forestb]

When I measured the truck was almost level. Do to the slope of the ground. Usually I have a pretty good rake. With that being said it’s hard to say if the differential would be pointing to the ground or up to the transmission and visa versa. With the vehicle about level the 5 degrees is with the differential pointing up towards the transmission and the transmission pointing down towards the ground. I assumed that having the truck on non level ground would change the wait distribution. At any rate I will check it on the lift. The shop I am taking it to is only letting me use the lift to take measurements and nothing else. Should I measure the driveshaft angle also?

[bigmoe]

The truck should be sitting fairly level with weight on the wheels. I find the easiest place to measure engine angle is on the front pulley. Just put something flat on the front surface to rest your angle finder on. They say 3 degrees down motor and 3 degrees up at the rear is ideal but you've got some leeway. I think my truck is closer to 5. The rear pinion angle changes as the rear suspension moves.

[forestb]

I have a pretty good rake. When you say level do you mean the frame should be level or the ground should be level that it is sitting on?

[bigmoe]

Originally Posted by forestb

I have a pretty good rake. When you say level do you mean the frame should be level or the ground should be level that it is sitting on?

Ground level

[forestb]

So the knows of the differential is pointed up 5 degrees and the transmission tail shaft is pointing down between 0 degrees and one degree. The angle of the drive shaft is pointing down toward the rear of the truck is 1 degree.

We tried lowering the tail shaft of the transmission a little but the drive shaft got a little to close to the parking break mechanism. So I think what I need to do is add a 4 degree shim in order to get the angle of the differential to be around 0 degrees.

[mongocanfly]

You dont want all zeros..u-joints wont last...you may try raising the engine to get the needed angles..

[forestb]

If my truck has a good rake than it is not actually all zeroes is it? If the angle of the transmission is the same as the angle of the differential than if any vehicle had a rake that was the opposite angle than it would be all zeros. I not trying to be argumentative. I am just looking for clarity.

[SkinnyG]

The angle of the vehicle is essentially irrelevant.

What matters is that the angle of the transmission and the angle of the pinion match. If the trans is pointing down 1° (pointing at earth, not sky), the pinion should be pointing up (at sky, not earth) at 1°. Essentially the two centerlines should be parallel to each other. Like this: \ _ \

Having said all that....

I have been chasing vibration in my lowered '77 squarebody for years, and am currently finding the least vibration ever with the trans down 4.5° and the pinion also down (not up!) at 1° like this: \ _ /. It shouldn't work, but it does. I did have the angles match for a time and it was h-o-r-r-i-b-l-e.

What I've done is matched the u-joint operating angles at either end to be 2.5° each. That is, the angle between the trans and driveshaft is 2.5°, and the angle between the driveshaft and the pinion is 2.5° (but going the opposite way).

Like this:

[forestb]

Ignore

[forestb]

So I added a 4 degree shim to the rear. When I first got it back on the ground it was making a whining noise at lower speeds But by the time I got off the freeway it had stopped. Maybe it was just everything readjusting after being apart. I will not really know if this salved my problem because I only noticed the vibration around 4000 rpms on the dyno.

[SkinnyG]

Give it a week. You'll better know what it's doing by then, as it settles in to reality.