I was doing some searching to find some info on drive shaft alignments and found this article. I found it helpful so I thought I would share.
Two-Piece Driveshaft Technology
Both designs may or may not use a carrier bearing depending on your specific application. Parameters that will determine the type of carrier bearing (pedestal or U-bracket style) you use will depend on the space available, among other things. Consult your driveshaft specialist to determine what type of joint and support bearing your driveshaft requires.
When setting up a one-piece driveshaft, all the experts agree that the engine and transmission should be set in the chassis with the rear approximately 3 degrees below horizontal (a magnetic protractor can be used to check this angle). In the rear, the angle of the rear-end pinion will be set to 3 degrees above horizontal. When the car is finished with all the weight added you should recheck the pinion angle. If any added weight has changed the pinion angle, correct it. Leaf spring-equipped vehicles can be adjusted with shims available from alignment shops, and on four-link-equipped vehicles, the links are designed to be adjusted to dial in a perfect pinion angle.
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Angle setup for two-piece shafts is similar to the one-piece. All three working angles should add up to zero. The easiest way to do this is to mount the front shaft section so it has zero degrees through the joint at the transmission. The rear shaft may then be treated as if it were a single shaft. Sometimes this is not possible and all three angles must be juggled to arrive at zero. It is a good idea to allow for some up and down adjustment at the center support mount so the angles may be tuned as necessary once the car is driven. Vehicles that do not have the proper angles set in the driveline components will experience pulsations that will cause vibration in seats, mirrors, gearshift levers, and other miscellaneous parts. These pulsations can also destroy transmission clutch packs,tailshaft housings, rear-end bearings, gear sets, and axles. Another concern in this area is a compound angle that comes about if the centerline of the differential is not in direct line with the centerline of the engine and transmission. Luckily most rodders are visual conscious when setting up the rear-end and use housings with the pumpkin centered perfectly in the center of the vehicle. Pay equal attention to avoid any compound angles while setting up the engine/trans relationship to the rear-end. Setting up the components right from the beginning can save a lot of frustration and costly repairs down the road.
Once the components have been properly set up on both ends it's time to measure for your new driveshaft. When it came time to figure out each of the two-piece shafts’ lengths, Frick states, "There is no hard and fast law governing shaft lengths. It is customary, though, to divide the overall length 40-percent front and 60-percent rear. Our experience with motor home manufacturers has taught us not to make either shaft, especially the front shaft, shorter than 18 inches. Available cross members, frame obstacles, and U-joint angle cancellation will all play their part in dividing up the span. “Both Denny's Drive shafts and Inland Empire Driveline make this process easy with detailed instructions and order forms on their Web sites. What you'll need to know is what type of transmission you are using (for slip yoke spline application) and what size U-joint you are using at the third member yoke. When making your measurements, the vehicle must be on the ground at operating height (jacking up the vehicle will change your dimensions). Measuring for a two-piece drive shaft is similar to measuring for a one-piece unit. The major difference involves noting the location of the carrier bearing for the driveshaft joint if one is being used.
Jason
Good drive-train/drive-shaft alignment article.
That is a good article but contains a glaring error or two. The article states:
"Another concern in this area is a compound angle that comes about if the centerline of the differential is not in direct line with the centerline of the engine and transmission. Luckily most rodders are visual conscious when setting up the rear-end and use housings with the pumpkin centered perfectly in the center of the vehicle."
It is important to note that this is not critical as it says and is actually incorrect. The centerline of the differential and the centerline of the engine and transmission do not need to be in a direct line and rarely are in vehicles when manufactured. What is critical is that the centerline of the differential and the centerline of the engine and transmission are PARALLEL. That is to say that you should check the angles side to side just as you do top to bottom and they should also equal zero. A really important and apparently missing point in the article is also that there must be some driveline angle as all too often inexperienced builders will aim centerline of the engine and transmission at the centerline of the differential and have no angles at all. This will cause premature bearing failure. The 3 degree figure that is cited in the article is a guide but remember that ideals are not always atainable and if you have 5 degrees on the centerline of the engine and transmission you need to set the rear at 5 degrees as well so the final number is still zero. I would point out that Ford had some great exampls of ideals not always working and the best in my mind are 58-66 Thunderbirds. These cars had a different angle from the fullsize cars and because of this the intake manifold carb flanges were at the wrong angles (they used the same intakes except on tri-power cars). To fix this problem Ford had to use wedge shaped carb spacers on Tbirds to allow the carbs to sit properly on the odd angled engines. Hawkrod
"Another concern in this area is a compound angle that comes about if the centerline of the differential is not in direct line with the centerline of the engine and transmission. Luckily most rodders are visual conscious when setting up the rear-end and use housings with the pumpkin centered perfectly in the center of the vehicle."
It is important to note that this is not critical as it says and is actually incorrect. The centerline of the differential and the centerline of the engine and transmission do not need to be in a direct line and rarely are in vehicles when manufactured. What is critical is that the centerline of the differential and the centerline of the engine and transmission are PARALLEL. That is to say that you should check the angles side to side just as you do top to bottom and they should also equal zero. A really important and apparently missing point in the article is also that there must be some driveline angle as all too often inexperienced builders will aim centerline of the engine and transmission at the centerline of the differential and have no angles at all. This will cause premature bearing failure. The 3 degree figure that is cited in the article is a guide but remember that ideals are not always atainable and if you have 5 degrees on the centerline of the engine and transmission you need to set the rear at 5 degrees as well so the final number is still zero. I would point out that Ford had some great exampls of ideals not always working and the best in my mind are 58-66 Thunderbirds. These cars had a different angle from the fullsize cars and because of this the intake manifold carb flanges were at the wrong angles (they used the same intakes except on tri-power cars). To fix this problem Ford had to use wedge shaped carb spacers on Tbirds to allow the carbs to sit properly on the odd angled engines. Hawkrod
Thanks Hawkrod. Will be a big help.
Great points that they did not mention. I'm going to throw out there suggestion about mounting the front drive-shaft in line with the engine. As you mentioned and I have learned in the past it is a good idea for every u-joint to have somewhat of an angle. I first wondered if it were possible to end up back at zero with two different length shafts but I just tried it on a flat surface, a wood block, and two pieces of different length flat stock and it worked fine.
My flat surface on the top of the block of wood was 1 degree. (A pinion and engine would be more but 1 deg. worked for my playing/testing)
The front shorter shaft was 5 degrees adding 4 degrees
The rear longer shaft was 8 degrees adding 3 degrees
Then down to the top of the 1 degree flat surface and that's my negative angle -7 degrees
4 + 3 + -7 = 0
Great points that they did not mention. I'm going to throw out there suggestion about mounting the front drive-shaft in line with the engine. As you mentioned and I have learned in the past it is a good idea for every u-joint to have somewhat of an angle. I first wondered if it were possible to end up back at zero with two different length shafts but I just tried it on a flat surface, a wood block, and two pieces of different length flat stock and it worked fine.
My flat surface on the top of the block of wood was 1 degree. (A pinion and engine would be more but 1 deg. worked for my playing/testing)
The front shorter shaft was 5 degrees adding 4 degrees
The rear longer shaft was 8 degrees adding 3 degrees
Then down to the top of the 1 degree flat surface and that's my negative angle -7 degrees
4 + 3 + -7 = 0