Setting up the model A frame for my 31 sedan. 3in drop in front, wheels are 6.00 in front and 8.20 on rear. I have the rear end set at 3 degrees down and carb base level. I was told to do it like this. From doing a search I confirmed this is a drag race application. I'm putting something together for the street. What effect will it have on the car's driving? Do I need to bring the rear end to 3 degrees up since it's what everyone recommends for a street application or will I be fine with what I have. Sorry, I know it's been beat like a dead horse. I did a search, but I just could not find the answer I was looking for. Thank you guys.
The correct procedure is to have the vehicle/ch***is on the ground (or on a 4 post hoist) with all the weight on it, the correct wheels/tires and at the desired ride height. At this point the engine/trans should be mounted so the carb mounting surface is level. Now measure the angle the trans output shaft is pointing down and adjust the rear end so it is pointing up the same amount of degrees (not too exceed a maximum of 3-3 1/2 degrees) For drag racing you can point the rear end down to compensate for rear end wrap under launch but this is not suitable for the street and will cause driveline noise and stress on the u-joints. For the street the rear end should be pointing up the same amount of degrees the trans is pointing down.
It is this simple: If you have leaf springs in the rear, set the rear 1 degree down in the rear (from the 3 shown above: i.e. set it to 2 degrees), to compensate for spring wrap, under load. Enough said.
There are so many variables on setting pinion angle that it becomes a SWAG instead of a science. 3 degrees down with the ch***is at ride height should be OK as long as the driveshaft is a normal length. In applications where the shaft is about a foot long the angle between u-joints will be a problem, with a 50" shaft the angle doesn't much matter for a street application. I have found that with fairly soft suspension that would be desirable for a good street rod you need the 3 degrees for spring wrap even under normal stop and go driving. Here again the variables raise their ugly head, a four bar setup stays the same but paralell leaf springs will let the rear end twist. Bottom line, 3 degrees should be OK.
Yup, except it IS science. I am over 300 ch***is setups in, for street, track, drag, 4x4, running 2,3,4,5-links, bags, coils, torsion bars, elastomers, 2,3,4,6-wheels, 4-30 inches of wheel travel. Parallel (3-down/3-up), or within 2 degrees of parallel, for a 2-joint shaft, is the way to go. Now, if you drive shaft is so short, and the tail shaft and differential yokes are so far out of plane that your drive shaft's slope is near, or over 20 degrees, you should NOT be running a 2-joint shaft.
Gimpy, what's your recommendation on a solid mounted axle for a '60ish altered? 9" ford with the pinion centered and a SBC/powerglide at the other end. Sorry, forgot the shaft length. I don't have a solid number, but I'm guessing 18-24 inches.
Aproximatly how much slope? Or, how far apart are the yokes, and how much are they apart in vertical distance? So long as the driveshaft slope is not too much, the same rules hold true. Parallel yokes. You may want your carburetor(s) level, so your intake manifold may be what governs the angle, unless you want to shim. I would, however, make sure that the angle is at least 1 degree, in order that the grease is circulated in the joints. Without this, they don't last too long.
How can I get all of the weight on the wheels/ground without my rear suspension together? I'm ready to set my pinion angle and tack my ladder bar mounts and spring perches... currently the rear of the frame is on jack stands at a height that puts the rear end about three inches below my 32' frame (as per the ladder bar instructions). Thoughts? Thanks!
1. Set your frame at the desired ride height and rake. 2. Set your engine/trans at an angle that gets you a level carb base. 3. Measure the downward angle of the output flange on the trans. 4. Set the rear axle pinion to that same exact angle, only UPward. 5. Grin and enjoy.
The only thing that matters is the angle between the trans and the rearend, as gimpy's pic shows. The angle can be up/down or left/right or some combination in between. A lot of rearend actually are not centered due to pinion offset. The U-joint does not know if the angle is any direction, just the total operating angle. Keep them the same at both ends, and the yokes in phase, angle around 3 degrees, and you will have no problems.
That image works for one that the rrear is below the engine. For one that the rear is above reverse it as long as the angle is the same.
rotate the picture so that the driveshaft is horizontal, then it IS the pinion angle. ain't geometry wonderful?
This is the part I'm working on - "setting it" doesn't seem accurate with respect to where it will actually sit once its fully sprung with body and drive train weight on it. My current plan is to mount the rear spring to the frame, and suspend the ch***is with the ends of the spring on jack stands at the height they'll be at once perched on the rear axle. Then I can weigh the car with equivalent body, drive train, misc weight and have an idea of when the "height and rake" will be. Thoughts? I want to do this before tacking in my motor mounts too, as the rake of the frame will change with these weights and spring rates added to the equitation. Thanks...
I've always welded my coilover/ladder bar 4 link brackets etc to the rear end on the bench. Set it to the 3 degress and weld her up. Unless I'm missing something having weight on the rear end shouldn't change the pinion angle but would apply to the transmission which is governed by the frame.
That makes sense - but I haven't determined my pinion angle yet because I don't have a solid frame angle to base my zero degree carb plate angle (which will give me my ****** output angle, which will give me my pinion angle). As most have said, I'm probably overthinking this. Probably safe for a street car to set the rear at 3 degrees and go from there. Thanks for the input.
Apologies for the thread hijack, but here's an updated question. With the carb plate level (buick 215 w/ saginaw 4 spd), the output angle from the ****** is 5.5 degrees. According to my research, this seems to be more than the average. Should I set the motor mounts to accommodate a forward tilt of the carb plate to make things easier on the u-joints? The center line of the pinion sits about two inches higher than the ****** output, what are your recommendations for pinion angles and motor placement? Thanks...
That is quite the tilt, although 2.5 degrees over average is not the end of the world. If you can get it back to 3 or even 2 (in your case), that might be better on the u-joints. Then set the rear axle to that. The basic idea is to not have the angle between the imaginary line of the output shaft and the drive shaft, and as well, the pinion and the drive shaft, not be too harsh, and the slope of the shaft too steep. The sharper the angle, the shorter the u-joint life, and increasing the likelihood of vibration. As I also build 4x4 stuff, it is not unusual to have a situation where a comfortable angle cannot be achieved on a rear drive shaft. It can never be accomplished with a front shaft. For that application, 3-joint shaft would be in order. Your application is not unlike the front of a 4x4 rig, flipped over. Unlike a 4x4, you can get away with a regular shaft, as long as your angles are not sharp, or your drive shaft slope too steep. If it were too steep, or you were running radius arms (or similar) with bags, you might need the 3-joint shaft. I run one in my A, with radius arms, and bags.
Thanks for all of the input, and again, appologies for the thread jack. New question - what would be considered "too steep" of an angle? I've put arrows on here to illustrate the pinion and drive shaft output angle - both are 3 degrees. With my rear end sitting a few inches about the ****** output, will this be within the working angles of my future driveshaft? Thanks for the education. Rear end brackets and just tacked in place and can be moved without too much drama.
You're fine. you have parallel components with equal 3* ujoint angles on the shaft connecting them. Weld it.
The problem with the parallel center line design is angle change with rear end movement. If you use the pinion down design, the realative angles do not change as much. Most rears are set up so the pivot about a point towards the front of the car. When the back of the car goes down, all the angles change.The pinion down design has no angle change if the pivot point is exactly in the middle of the driveshaft. All the parallel design is trying to do is make the included angles at the joints the same. The angles can be both up, both down, or parallel. The joints don't care. I prefer the back of the engine down and the pinion down. It is harder to set up as you must measure the angle of the engine and the driveshaft and find the angle between them, Then do the same at the rear. Moving the rear will change the driveshaft angle and you will have to determine the new front angle and adjust the rear to match. You have to be fairly precise but it is the best design.
so just to verify, do all the rules to applying proper pinion angle still go even if the rear axle sits level or heigher than the eng/trans. ? sorry i know im beating a dead ho**** on the subject here but just wanna make sure
Doesn't matter if the engine is above or below the pinion as long as you follow the rules for the parallelism of pinion and engine centerlines and don't exceed minimum/maximum angles. Bob
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