Driveline angle question.

[Lugnutz65]

QUESTION: Front to rear, should a C10 short bed DS be angled up or down in relationship to the tranny output shaft line?

I’ve read that the transmission output shaft should be parallel to the rear axle pinion, but they should not point directly at each other. The DS should have maybe 3 degrees of angle at the u-joint ON EACH END. That way the u-joint can do the “work” it was designed to do.

The rest of the info:
The 1968 C10 short bed I’m working on has a stock rear axle and rear control arms. Currently, a straight line drawn from the 700R4 main shaft would end up beneath the pinion. The angles are equal on each end of the DS but it looks backwards to me.

So here’s the rest of the story.
My son bought a project 1968 C10 short bed.
Prior owner quit half way through.
Currently truck has a fresh 1992 SBC 350 with a 700R4. Engine is not moved forward. Stock engine perches and mounts.
The transmission angle has not yet been set because the crossmember is temporary.
With the truck on the suspension, the driveshaft hangs VERY low inside the “oval” in the rear swing arm crossmember.

[mongocanfly]

If your truck is lowered the trans yoke could possibly be lower than the differential yoke...but the theory is the same..set your pinion angle pointing 3deg up...set your engine/trans angle 3deg down
You want the imaginary centerline of the diff and the engine to be parallel to each other...
Doesn't matter which is on top
And 3deg is just a number to go by...it could be 4 or 5 or even 2 deg....but both need the same angle ...just the diff up and engine down...
What you dont want is the trans yoke pointing straight at the diff yoke....the angle is needed to make the needles in the u-joints rotate

[Lugnutz65]

The pic in my first post shows the DS at the pinion. The DS is at a more horizontal position than the pinion.

Currently, if I draw a line straight out of the pinion, it would end up hitting the tranny ABOVE the tranny yoke. This picture shows a setup exactly OPPOSITE mine.

[mongocanfly]

I'm guessing this is what your seeing...or similar

[mongocanfly]

Is the truck lowered?
Your pic in post 3 shows what I was saying about needing the angle to make u-joints work

[Lugnutz65]

Your diagram in post 4 shows a similar setup to the 68, yes.
The truck is not lowered.

[mongocanfly]

Does the engine and trans sit really low in the truck?....if it was someone else's project I'm wondering how its put together

[Lugnutz65]

It needs new motor mounts but that will not change the angle of the crankshaft/tranny in relation to frame or rear pinion. The PO chopped out the factory bell housing crossmember to fit the 700R4 in there, but never installed a proper crossmember for the tranny. So the tranny only has a temporary support for now. My next task is to install a proper tranny crossmember.

['63GENIII]

I wonder if the lack of the correct crossmember is allowing the tail shaft to hang too low creating the weird pinion - transmission angle relation that you've got going? Might mess around with some wood blocks of varying thickness between the tail shaft and the temp crossmember to mock up the right angle?

After re-reading your first post again and realizing that the truck was originally a manual trans (missing bell housing mounts), I would be looking to see if there is a mount for a carrier bearing. Could it be that it used to have a 2 piece DS which located the center U joint closer to the rear axle? If so, that could be the issue.

Off hand, I wouldn't know what the difference in length is between the manual set up vs the 700r but i would guess that it could be enough to go from a 2 pc to 1 pc DS. Not knowing the previous guys skillset, I might even look into having a reputable driveshaft shop check out your DS.

Nothing worse than a 2500 rpm jump rope .

[Ironangel]

Originally Posted by mongocanfly

If your truck is lowered the trans yoke could possibly be lower than the differential yoke...but the theory is the same..set your pinion angle pointing 3deg up...set your engine/trans angle 3deg down
You want the imaginary centerline of the diff and the engine to be parallel to each other...
Doesn't matter which is on top
And 3deg is just a number to go by...it could be 4 or 5 or even 2 deg....but both need the same angle ...just the diff up and engine down...
What you dont want is the trans yoke pointing straight at the diff yoke....the angle is needed to make the needles in the u-joints rotate

Greg, 3 degrees is a u-joint limit angle. Unless he's using extreme angle u-joints which he is not then 3 degrees is a limit number allowing movement in a + and - for suspension stroke. The OP needs to get his cross member in and bring that tail shaft up to level out the motor and trans. He needs to measure the angles off the yokes and match those angles within 3 degrees. Judging from the pic the pinion is up and the tail shaft is down which is ok as long as neither angle exceeds 3 degrees. Need to know exactly what that pinion angle is so he can set angle on the tail shaft with shims on the cross member. 3 degrees up on the pinion would be ok if he holds 3 degrees down on the tail shaft. Since he's running on stock suspension heights and stock motor mounts, he should be golden as long as the rear axle and suspension hasn't been changed. That said, his pic appears to show that pinion in an up or positive angle? Like you I was wondering if the truck has been lowered or was once a two piece drive shaft truck at one time?

[Lugnutz65]

I have the good fortune of owning three trucks with the same exact suspension set up. All three trucks are short bed trucks with original suspension. The pinion on all three trucks points up towards the floor of the bed. As you are aware, these trucks have brackets welded to the rear axle tubes. That makes changing the angle of the pinion impossible unless you change the brackets. Lowering the rear of the truck with lowering springs does make the pinion angle more horizontal, but this truck has factory suspension.

I mocked up a crossmember for the transmission yesterday. I will be able to make the transmission angle parallel to the pinion angle.

What had me perplexed was the cartoon diagram I posted earlier. It shows a drive shaft that angles downward from front to rear. That part is correct. In the drawing, if you draw a straight line out of the transmission towards the rear axle, that line will come out ABOVE the pinion, instead of below the pinion. In all three of my trucks, the pinion is pointed upward towards the bed. If you draw a straight line from the transmission main shaft towards the back of the truck, it will end up below the pinion instead of above the pinion.

I will sit down soon and draw diagrams to show my setup since photos are often difficult to interpret.

[Lugnutz65]

This drawing may not be exactly to scale but it’s really close.
These are on a stock 1965 suspension.

[Ironangel]

Originally Posted by Lugnutz65

I have the good fortune of owning three trucks with the same exact suspension set up. All three trucks are short bed trucks with original suspension. The pinion on all three trucks points up towards the floor of the bed. As you are aware, these trucks have brackets welded to the rear axle tubes. That makes changing the angle of the pinion impossible unless you change the brackets. Lowering the rear of the truck with lowering springs does make the pinion angle more horizontal, but this truck has factory suspension.

I marked up a crossmember for the transmission yesterday. I will Be able to make the transmission angle parallel to the pinion angle.

If you draw a straight line from the transmission main shaft towards the back of the truck, it will end up below the pinion instead of above the pinion.

The pinion angle can be changed using wedge shaped shims. Only you can know if the pinion angle has been changed due to any number of possibilities, we cannot. And yes, the last two sentences in your comment above is what you want. It was my understanding that short beds had factory two piece drive shafts? All three of your trucks have factory single piece drive shafts? In any case, keeping the tail shaft parallel to the pinion shaft with no greater than 3 degrees at either yoke and you should be golden...The key is matching those shaft angles (output and pinion) so those u-joints work evenly and cancel each other out.

[Ironangel]

Originally Posted by Lugnutz65

This drawing may not be exactly to scale but it’s really close.
These are on a stock 1965 suspension.

That's perfect! Both angles identical to give a 3 degree+ plus a 3 degree - for a 6 degree dead nuts goal! Button that baby up! As long as the shaft is balanced...

[Lugnutz65]

Originally Posted by Ironangel

That's perfect! Both angles identical to give a 3 degree+ plus a 3 degree - for a 6 degree dead nuts goal! Button that baby up! As long as the shaft is balanced...

But you hopefully see what had me confused . . . The diagram I posted in post#3 shows the angles opposite to what I actually have. So I thought I needed to do a lot of correction.

[Ironangel]

Originally Posted by Lugnutz65

But you hopefully see what had me confused . . . The diagram I posted in post#3 shows the angles opposite to what I actually have. So I thought I needed to do a lot of correction.

I think it would have worked either way...All good and let know how it feels at speed...Good luck! PS. Hell, I confuse myself all the time! :P

[Keith Seymore]

Equal and opposite is what you want.

(Frame angle and driveshaft angle relative to the ground don't matter. The truck could be upside down and the U joint working angles remain the same).*

Normally we pitch the pinion nose down (relative to the shaft) because it will climb during acceleration due to leaf spring wind up. Since you have a control arm suspension that will not happen.

K

*other than the fact that the weight wouldn't be on the wheels

[mongocanfly]

Here is what we shoot for when setting one up
Rear diff angle measured on pinion yoke +3deg
Trans angle measured on tailshaft -3deg
This creates 2 parallel lines between pinion and crankshaft centerline
That will cancel each other out

[mongocanfly]

This is always a good video that shows what happens when it's not right...
https://m.youtube.com/watch?v=Idk3BVDVHq4

[mongocanfly]

Iron angel...I'm not referring to operating angle when I say 3deg...I'm referencing the yoke angle
Here is a driveline working angle calculator
If you put 3deg down on driving member (trans)
And 3deg up on driven member (pinion)
And 4deg down slope on driveshaft
It gives you a working angle of 1

https://spicerparts.com/calculators/...gle-calculator

[Daaaanz67]

Originally Posted by mongocanfly

Here is what we shoot for when setting one up
Rear diff angle measured on pinion yoke +3deg
Trans angle measured on tailshaft -3deg
This creates 2 parallel lines between pinion and crankshaft centerline
That will cancel each other out

When taking these measurements, does the frame have to be level? Other words can I just put the truck up on jack stands front and rear to take the measurements?
What happens when you put a carrier bearing in this picture and let’s say you raise and lower the bearing. How will it effect the angles?
What would the working angles need to be at each joint so it will cancel itself out when it reaches the differential?
Since you guys are on this subject I figured I would ask. My truck is experiencing some vibration. 69 c10 LB with 2piece shaft. It’s lowered 4/6.
Thanks for any input you may have.

[Lugnutz65]

My 1963, 1965 and 1968 2WD short bed trucks all have the same rear swing arm suspension and 12 bolt rear axle. Each of them have the snout of the diff pointing up towards the sky rather than towards the ground. I believe that is the way they all were. The tail shaft of the tranny points towards the ground. The drive shaft is tilted down 4* from front to back. The angles are equal and opposite as shown in my post #12.

For comparison, here are pictures of my 1992 Toyota pickup with leaf springs. The snout of the diff points towards the ground and the angles at each end of the DS are opposite and equal BUT OPPOSITE of the angles on my C10.

[mongocanfly]

daaanz..
you can put the truck on jackstands but the suspension needs to be carrying the weight of the truck
a carrier bearing in a 2pc driveshaft adds a little complication to it but its just math to get it correct...
you need to determine the operating angles
I'm just throwing these angle numbers out there..they are not meant to be what yours is or isnt

1st is determine operating angles of the trans and the 1st driveshaft..
say you trans is pointing down at 3deg and the down angle of the 1st driveshaft is 2deg...subtract 2 from 3 and this gives you a 1st operating angle of 1deg..

then you need to determine the operating angle between the 1st and 2nd driveshaft..
your 1st shaft is down 2deg and your 2nd shaft is down 3deg.. add the 2 and 3 and your 2nd operating angle would be 5deg

then take the 1st operating angle and subtract it from the 2nd operating angle..
it would be 1-5 = -4...don't worry about the neg mark ..the working angle is 4,
so now the final ujoint angle needs to be 4deg as well to cancel out the other 4deg

[Daaaanz67]

Ok thanks Mongo, I’ll give this a try. What if the second shaft goes upwards because of the 6 inch drop, would I add instead of subtract? My carrier bearing is mounted on the bottom of the cross member. I usually see most carriers bearings mounted on the top side of the cross member.

[mongocanfly]

The angles dont care which way they are...its all about the angles canceling each other out...but with drop things change...got any pics of your setup?