So, if you're doing a frame up restoration and getting rid of the stock suspension and drive train then what are the proper steps of rebuilding it? More specifically, I've redone my front suspension on my 54 chevy truck frame and now need to install motor/trans and weld up the rear trailing arm suspension. I'm not sure what comes first. I'm being told engine and trans need to be mounted first so I can set the pinon angle at least 3 degrees down after leveling off the frame. Others have mentioned the rear suspension/axle need to be installed first so I can establish ride height before laying in the engine/trans. Although, won't I need the weight of the engine/trans to get to ride height? It seems like a double-edge sword in which one install needs to be done before the other. Or, maybe I'm just clueless. haha...In any case, any info would be greatly appreciated.
You are not doing a "frame up restoration", you are building a hot rod (or something similar). And setting the pinion angle down 3 degrees is not going to work if your motor is not installed at the same angle. You need to set the frame at the height that you want it making allowances for suspension travel, ground clearance etc. If you don't plan on changing any of the suspension parameters you can cobble up something to let the motor and trans sit on the frame in roughly the correct location and that will determine your frame height (at least at the front). You also need to know what diameter rear tires you are going to run as that will determine the actual pinion height which has some relevance in the big picture. The motor can be mounted at what ever angle is appropriate. If it has an angled carb base on the intake it is usually a good idea to keep that level with the ground plane or close to it. Do a search here on the HAMB re pinion/driveshaft angles and educate yourself as to what is actually going to work. Your "at least 3 degrees down" most likely came from someone running a leaf spring drag race car and in that case the nose down pinion is to compensate for spring wind up. With your rear trailing arm (truck arm style?) package any compression of the rear suspension will simply increase the nose down pinion angle (by a small amount) depending on the length of the trailing arms. Is sounds as if you need to rear a few hot rod "How To" books before you get in over your head. Roo
I always get my wheels and tires that I am going to run and then set my stance that want to end up with. You can make up sliding rods with pit pins to simulate the springs . Make sure you have a known reference point to pull your measurements from so your car ends up square and tracks true. A guy brought me a car that he had built to check and the rear was an inch and a half off from being square. Luckily there was enough adjustment in the 4 link bars . Otherwise I would have had to do some major surgery.
I was wiring a friend's Model A full fendered Coupe, all new, on a TCI frame. 350/TH400, 8" rear. Car was finish painted, (black) but rear axle ass'y sat too far back in fender wells. Coil overs and Hairpins on rear, fully adjustable (and plenty of threads for adjustment) This guy would NOT let me correct the problem. Some people...
As I most often have to get the engine and transmission to fit between a radiator and a firewall, and under a tunnel, I set those first. I set the chassis level, and the engine/trans down at 3º. If the radiator and firewall are not as much of a concern, make sure that your fan, if you are running a mechanical one, can reach the radiator, with no, or a minimal spacer. Beyond that, you will need to have a good idea of what you want the lowest point in the chassis to be. I always try to put the engine and transmission as low in the chassis as can be accomplished. Depending on what rear trailing arms you are using, you may be able to simply clamp on to the rear axle for now. If not, set the pinion angle at 3º to the ground, and lightly tack the brackets on, in a few locations. That will allow you to set up the chassis. Yes, ALL of the weight needs to be on the chassis to set up ride height, and final pinion angle. This is not debatable, unless you are a chassis shop that is recreating a chassis that you have already built several times before. Setting the pinion angle is about dead-last, and it would be 3º UP.
Don't take the three degrees as gospel. The only gospel in the driveshaft is that the input angle needs to match the output angle in the opposite direction. It might be two degrees, or four, or five, or seven. It doesn't even care which one is pointing uphill, and which is pointing downhill. Just as long as they are opposite like in Gimpy's drawing.
Opposite direction is not gospel. Keeping the angles the same, or as close to the same as possible, is gospel. As long as the angles are the same, they can both point up, both point down, or be opposite. The second configuration in the image below, known as a "W" configuration, is what the setup is called when both angles are the same direction.. Not normally used in our hobby, but in odd cases where you have to do it, it works as well as the top configuration does.
Thanks a lot for the info everyone. I really appreciate it. A few more questions please: 1. What's the reason for the "3 degree down" on the trans yoke? 2. Would the engine/trans final angle change if I my ride height was raked down in the front vs. level? 3. If my design required a two piece driveshaft would the engine/trans still need to be raked down or kept level?
Good post Gimpy, but why do you always try to put the engine/trans as low in the chassis as possible?
'Cause I'm an incorrigible road-racer. The lower the heaviest bits are in the chassis, the lower the center-of-gravity, and the better the handling.
1. A traditional carburetor pad is at 3°. Tilting the engine and trans down makes for better floor clearance, and shallower driveline operation angles. 2. The angles are relational. The crankshaft centerline and the pinion centerline need to maintain parallelism, regardless of chassis rake. 3. Can of worms. You don't have a long enough chassis to justify a two-piece driveshaft. You don't want to go here.
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