The Stovebolt Site Forums The Shop Area Engine Shop Driveline Angle

I am installing a 12 bolt rear in my 51 half-ton. The truck is torn apart down to the frame. I will be installing a 235 in the stock location so that algle remains stock. I could only estimate the needed differential angle at this point which I may have to do.

Can anyone tell me that they have done this before. If so, what angle did you mount the spring pads on the rear end. I think that I have heard that the nose should be angled 5 degrees up. My thanks to anyone who can help me not reinvent the wheel here.

what i did and trust me i'm no rocket scientist,was to level out the carb part of the intake to 0 deg. with a angle finder(3.99 at harbor freight) .next put the angle finder on the block where the starter bolts so its nice and flat,it read - 3 deg.(downard tilt) so with the weight of the truck on the springs i put the angle finder on the flat part of the yoke on the rearend and brought it up to + 3 deg. so everything is lined up. then welded it up.theres always shims to fine tune it if need be ......................dave

Whatever your down is on the engine should be the same on the up at the rear yoke. It could be 2 degrees or like David said 3 degrees, whatever toots your horn.

centerline on the trans pinion and differential pinion should be parallel. Most driveline shops reccommend a max of three degrees for a high speed shaft. More angle is allowed for slower shafts. For example, 11.5 degrees is ok for a shaft that only turns 1500 rpm max.

Good info!
This Tech Tip has more of the same: http://www.stovebolt.com/techtips/driveline/setup/index.html

The important thing in this situation is:
Rule #2 -- Universal joint operating angles on each end of a driveshaft should always be equal within 1 degree of each other.
(from the tech tip, and ultimately from the Spicer Driveline manual)

Grigg

David, I put a 56 pumpkin in my panel but I'm not at the point of welding it down. Would you share with me how you welded yours down? I know we should not weld on the spring itself since its heat treated/sensitive so what are my options? I will probably be at this point early spring...maybe!
Thanks for any help.....from anyone.

Usually you have a spring pad on the axle, then u-bolts clamp the springs to the axle and tight to this seat. Here is a poor picture, but may give you the idea: http://rides.webshots.com/photo/2651856980080251109LSnfpj
Welding the spring seat to the axle tubes is where you can adjust the pinion angle.
Or if the spring pads are already in the right position center to center, but the wrong angle, and you don't want to move them you can make a shim like this to correct for the pinion angle.
http://rides.webshots.com/photo/1484200068080251109FlXuOW

Grigg

Nice project truck.
Take a good picture of the doors as someone here has a pretty good collection of AD DOOR ART.
We put a 12 bolt in my rear end of the 51. i also spaced it back (towards the rear) about 2-1/2'' and wished I done it 3''. the vendors sell the 1-1/2'' kit. I MAY BE WRONG BUT your total angle per one side can't be more than 1-2 degrees, shooting for that total of 3 degrees.
http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=Scan1_0001-1.jpg this is how we did ours, drill a hole for the spring bolt to center on. this is it, all done e/w sway bar.
http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=2748800-R1-045-21.jpg
see CCP: http://www.classicperform.com/Store/1947_59_Trucks/4754RCK.htm it spaces the tires in the wheel well better.
west sac driveline service:
http://www.dlssac.com/php/trig.php
other sites
http://www.carcraft.com/howto/91758/index.html
http://www.streetrodderweb.com/tech/0203sr_drive_shaft_angles/index.html
http://www.buickperformance.com/Pinion.htm a good article 'the straight scoop'
http://www.carcraft.com/howto/91758/index.html
'''''''' Sometimes corrections need to be made at the front of the vehicle to ensure that the engine and trans are sitting in the proper location. According to Currie, the average car crafter [font:Comic Sans MS]should strive for between 1 and 3 degrees between the tailshaft of the transmission and driveshaft, and 1 to 3 degrees between the driveshaft and pinion. Furthermore, the two angles should be nearly equal (between 1 and 3 degrees), but always opposite (see crude diagram). ''''''. NOT 3 degrees at each end!
B-4 you weld it in consider what you may wish to install under the bed in the future ..... i.e. new power brake system, gas tank, either on one side or where the spare tire should really be located (or two) exhaust system, crossover ( dual pipes), spare tire or an extra tool storage system. anything else???
food for thought;

Would you share with me how you welded yours down? I know we should not weld on the spring itself since its heat treated/sensitive so what are my options? as grigg said,you dont weld on the spring.the spring perches sit on the springs themselves and the axle tubes sit in the spring perches.this is where the adjusting takes place. this is how i did it.center it up side to side then snug up the u- bolts.with the weiht of the truck on the springs and the cheapo angle finder on the yoke of the rear end put a floor jack under the front of the yoke and slowly raised it til i got my + 3 deg. then tightened it down.jacked up the rear of the truck,jack stands under the framerails,removed the wheels.and tacked welded all 4 corners of the spring perches.unbolted the u-bolts,flipped over the rear end and welded it up solid.once again this is my understanding of how this thing works and how i did mine.also as said if the 56 rear already has the spring perches installed andits centered and you just need to adjust the angleyou can buy shims in degreed increments that slide under the front of the spring perch and spring to raise the angle or slide under the rear to lower the angle.if the 56 rear is not centered or has the wrong size perches you will need to cut and grind the old ones off.and install new ones to get it correct.thats what i had to do with mine.as i installed a later model 12 bolt under mine. hope this helps.....................dave

Thanks for all the replies. David, you came pretty close to the most direct answer. Do you know if your pads and the yoke on your setup are essentially 93 degrees apart. If I could sit your axle flat on it's pads, the yoke on the front would measure 3 degrees up? I am hoping to install all of this before I have the cab and bed installed on the frame. I will of course measure the downward angle of the engine/transmission. I have read the tech articles and think I understand it all, I was just looking for someone with a stock engine setup who has been through this. Again, thanks to all for the help and pointers.

You can't look at one truck and then decide what the driveline angles on another need to be. It may get you in the ball park, but the specs say you need your angles to be the same within 1 degree, you could be off several from one truck to another depending on weight, spring size, worn out springs...

Just take your measurements and make it work out for your truck.
If you don't have the truck assembled, put it in loose, without welding the spring pads, then assuming you won't be driving in in the mean time, once the cab and bed are in place fine tune the angle and weld them in place.
Or get it close as you can, weld them, and when the truck is complete plan to double check and use shims to adjust if needed.

Grigg

Thanks Grigg, I agree, that I will have to find it out for myaself. However, if the factory had put in an open driveline, all the axles would have been built with the same geometry, based on the angle the engine / trans were mounted. I can find the trans angle relative to the frame, once I get my engine here from Nebraska. If the rear axle were to move verticly, without changing angle as the springs compress, then it wouldn't matter if the springs are sagging or not. However, my placement of the axle along the arc of the spring will matter. I think that I am going to use the kit that moves the axle 1.5 inches back. It looks like it will better center the wheel in the opening. Because the spring is an arc, I will need to place it and measure for myself for the best result. Otherwise, I would be confident that anyone mounting a rear axle on stock springs in the same way with a stock motor mount would have the same angles. AS you say, I can always add shims if I have to.

Carolines Truck,

Thanks for all the links and info. You have some nice pictures of your truck.