Just finished installing a rear leaf spring kit from Engineering Chassis on my 51 Pontiac - everything bolted up great - highly recommend this kit for those thinking of doing the conversion. I do have a couple of question on finding the correct spot for the rear axle. I'm replacing the original with a 10 bolt of out a 98 Jimmy and completing to an open driveshaft. 1. I'm planning on centering the axle by measuring the distance from the end of the shaft tubes to the new leaf springs and making sure they are equal distances. There has been body work done previously on the car so I'm not comfortable on using the body panels as a reference. Prior to welding the new blocks in place I will check distance to the panels to make sure there is no big difference. Am I on the correct path, or is there a better way to center the axle ??? 2. Everything I read it seems about 3 - 3.5 pinion angle is recommended. What is the best way to go about setting this angle ?? Do I need to get the car sitting on the ground with the wheels on its own weight, or can I do this on jack stands to make it easier ?? I know I can get shims to adjust if needed but wish to get it as close as possible on the first try. Thanks much for any advise offered !!!!
Your pinion angle should be the same as the angle of the trans output or as I set them 1-2 degrees below, the rule of thumb is same angle in as out. I usually put the U bolts on the assembly and snug them up, level the frame and measure the 2 angles (trans output and pinion) then rotate the axle till its right and weld it to the saddles.
Basically you want the u-joint angles at both ends of the driveshaft to cancel each other. Put the car up on stands under the rear axle and as close as you can to the front axle. This should put your rear suspension travel about where it is at ride height. You need to have a drive shaft in or simulate one with a piece of tube or even a string line between the two u-joints. You can use a digital level or a machinist's protractor for the next step. Get an angle from level on the engine, the driveshaft and the pinion. From this you can get a deflection angle on each u-joint. For instance your engine should be approx 3* down to the rear. If the drive shaft runs 1* down to the rear the deflection is 2* (3 minus 1). Theoretically you want to match that deflection angle with the rear u-joint. You can leave the u-bolts loose and play with rotating the pinion up or down 'till you find a happy medium. You'll want the pinion down in relation to the driveshaft normally to get this right in a street car. Also I would leave an extra degree of deflection down in the rear u-joint with leaf springs because the pinion will rise under acceleration. You have to keep rechecking the drive shaft angle and refigure the deflection as you rotate the rear because everything changes as you move the pinion up and down. Hope this helps, Rick
Update - I've got things located (not welded yet though) and this is what I've ended up with. The trans output shaft is on a 4.5 degree down slope so I've adjusted the the pinion angle to the same 4.5. The resulting angle of the drive shaft to output shaft/pinion will be about 2.5 degrees. Is this suitable ?? Next step is to get the driveshaft re-lengthend - its about 6" too short. How do you measure the correct shaft length ?? I know its center to center on the u-joints, but far out do you put the yoke on the trans output shaft prior to measuring ?? I've got about 3" of travel overall. Thanks much !!!
the drive shaft shop I use asks for the measurement form the center of the rear yoke on the rear end to the back of the output shaft of the transmission with the front yoke removed. They calculate the yoke length and movement. They want this measurement with the rear axle at ride height not hanging free. They have done 20+ driveshafts for me this way and Never had a problem.
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