I have located the engine where it needs to sit on the frame. I've bolted up the transmission to the engine. With everything in place, the body sitting on the frame, no gl***., & various other missing stuff, I'm trying to figure out. the angle of the drive shaft to the rear end. As it sits right now the center line of the rear shaft of the transmission is 17- 3/4" off the floor. The center line of the rear end flange is 11-3/4" off the floor, for a 6" drop. Total distance between the two points is. 51-1/2". I still have room to drop the tail end of the transmission down. a little bit, but this gets me to my quandary. How do I make sense of it all and nail these parts into their final position? This is the frame with the missing X member. I plan to construct a new X replacement similar to the pic below. I want to have the body off while I do this. Of course when I lift the body, the rear springs unwrap and add an additional 4"between the rear end and frame... My brain hurts. Is a 6" drop over a mere 51-1/2" too steep? I still need to add in a yoke and two universals. What's the secret formula?
So I’m reading a lot about pinion angles. I get it. But.. if I’m striving for 1-3 degrees of angle, don’t I need to know my final ride height first? The weight of the body+ gl***+ every thing else will settle the rear leafs and change the pinion angle in relation to the transmission, which does not move in relation to the frame. More weight = less pinion angle. Then, if I decide to lower the car ( definite possibility)the angle changes again…
If you research universal joint they are made to work thru a 22* arc. (11* up to 11* down) If you want to see real punishment of a u-joint go to You Tube and search “rear suspension IMCA modified rear end movement.” You will never get to anything a racer does… If the joint are parallel you should be fine just grease the ever 10,000 miles or so.
First get one of these, Next thing is your trans pointing up or down? Should be down. It's all about parallel angles. If your trans points down 5 degrees from level, your pinion needs to point UP 5 degrees
The goal in setting up the vehicle is to have both angle A and angle B be the same (parallel). If they are the same and within the 11 degree working angle that ujoints prefer, the system will work very well and will be in sync. You asked about the weight on the car causing the angles to change. The answer is yes. But as angle B reduces due to spring compression, Angle A will be reduced by the same amount as the rear of the driveshaft will be raised in relationship to the transmission end equalizing the angle. Axle wrap can very angle B but is generally a temporary condition and unless the axle wrap is extreme, it should not cause a failure. When the angles are not the same, it causes the ujoints bind at different times and this creates harmonics in the drive line which will cause premature wear and possibly failure. Some say it is desired to have some angle on both ends and not have the everything in a straight line. This is to allow the roller bearings in the joints to continuously move and stay lubricated.
You could put it together with the spring pads not welded to the axle tubes until all the weight is on the car then set your pinion angle and weld away
The main/output shaft on the transmission and the pinion shaft angle have to be parallel as this drawing that I snagged off the net a few years ago shows. That is correct pinion angle. That makes the static between transmission shaft and drive shaft and drive shaft and pinion shaft match. Damned few corectly built hot rods have enough height difference to cause issues with the U joints as far as how much angle the U joint is working with. I've never seen one that was built right where he centerline of the crank, and the shafts in the trans were angled up at the rear of the trans. If that is the case you most likely have done something wrong from the get go. Plus forget that BS from the old drag racers down at the spit and whittle club who tell you that yo uhave to angle the pinion down because it will "raise up with torque" they were the doumb ****s who were always breaking U joints on the starting line back in the day and we would have to wait until their car as pushed out of the way again and the broken pieces swept up.
The only time the pinion should point down is if the transmission was pointing up. The critical geometry in drive shafts is the ujoints being parallel with each other just like they are in the above example. You can go further and delve into joint timing and keeping the joints in phase. Having the pinion pointed at the transmission and that joint square to the shaft while the trans joint is angled down is a larger problem.
I am unaware of the engine you are installing but I can tell you I installed a SBC/TH350 in a 38 Olds, a car very similar to yours. Disregard ride height and focus on the expected "rake" of the ch***is once the car is complete. Prop the ch***is up so the angle of the car (when viewed from the side) is what you are shooting for once completed. Nose down? Level? Tail down? Your choice. Again, this is all about expected angle of ch***is once complete, NOT actual ride height. With the ch***is at the expected "rake" that you are shooting for (and keeping in mind that you really don't want the lowest part of your car to be your oil pan and you must also take into consideration any firewall clearance issues), place an inclinometer/angle finder on the carb pad of your intake manifold (I used a Edelbrock Performer single four for example). Level the carb pad using your angle finder. Generally, SBC carb intakes have the carb angled meaning the carb (once installed) and the center line of the crank are not parallel (when viewed from the side). By leveling the carb pad, the front of your engine will be slightly up and the trans will be slightly down (when viewing the crank center line from the side), the engine and trans will NOT be level as the engine and trans, unlike your drawing, will be pointing down at the back, not up. You have now correctly located the engine and trans in the ch***is. With the car finished and the ch***is at (or close to) your expected "rake", your engine will be situated such that the carb pad on the intake is level. Again, this has nothing to do with ride height. Once your ch***is angle is set and the engine is installed such that the carb PAD is level, you have now correctly located your engine/trans. You can offset them both slightly if needed for steering clearance or possibly exhaust clearance but they both MUST be in line with the center line of the ch***is (when viewed from the top). As for the rear end ... as someone else mentioned, bolt the rear end in place on the leaf springs but do not weld the spring pads onto the rear housing until the car is complete and all of the weight is on the suspension. Unless you are building a 4WD Monster Truck out of your '39 Pontiac, you will be just fine. Many cars came from the factory with offset engines and offset pinions. There is nothing wrong with centering your engine/trans in your car and connecting them to an offset rear end as long as the engine/trans centerline follows the centerline of the ch***is. Do NOT center the engine (just the engine) in the rails then "swing" the trans mount to line up with an offset rear end. If the engine is centered in the ch***is, so should the trans. If you offset one, you need to offset both. As for setting the final pinion angle and welding the pads, if the trans output shaft is 3 degrees down, set your housing so the pinion is 3 degrees up and you are good to go. Edit: Do NOT worry about driveshaft angle. Correctly locate the engine/trans in the ch***is, install the rear end on the leaf springs without welding the pads to the housing, finish the car. Once finished and the weight is on the suspension and you've adjusted your pinion angle to work with the engine/trans angle, you can now complete the car with the installation of a driveshaft. Its angle will be determined by the location of your engine and the ride height at the back of the car. It really isn't an angle you need to bother worrying about at this time or ever. The ch***is setup will determine that angle and, as suggested earlier, unless you are building a 4WD Monster, you should not have any issues.
There are quite a a few videos that show the pinion twisting upwards under acceleration with a leaf sprung vehicle , it's no joke . Is it necessary to compensate for that with your initial drive line angles , probably not , unless you're drag racing without a ladder or ******* bar .
Thanks for all the insight. I do not envision this car ever seeing a hole shot or enough acceleration to worry about axle wrap. At worst I’ll toss in some old school traction bars. I think I’ve got a starting point now. It’s all about finding the correct terminology to search for, and “pinion angle” is the winner. Searching this term gets me a lot of good info to start this effort.
Another thing to consider is how much the pinion angle changes throughout the suspension travel. If a 4 bar is setup wrong the angle can change drastically.
I set up angles at ride heigt Needs more pinion angle if using parallel leafs. Try to keep em less than 3* but then add more on the rear if parallel leafs are used
BORNTOLOZE, thats about the best write up on pinion angle I have seen. It's all the information needed without all the ****. Only thing I would add is, the engine/trans can be moved off center in the frame for clearance issues as long as it's parallel to the frame and relative close to center.
Although a gentle 1-3 degree angle is good, it wont hurt anything if it's more angle either. What's utmost importance is the trans and rear pinion angles cancel each other. So if both trans and pinion were dead level then the driveline wont care if they're 3 degrees or 6 degrees. I own a couple inexpensive dial angle finder and also a digital angle finder. Put the angle finder on a spot that matches the transmission output shaft, and pinion and see how the two compare. If they don't match up, then adjust the trans mount, or pinion angle until they cancel each other.
The Jalopy Journal
