First time big build and have a conundrum I can’t wrap my head around. I am at the point of mounting my rear axle in my Model A. I will be using aftermarket perch mounts, stock spring, on top of a late model Ford axle. My question, I know you set the pinion angle in relation to the crank/output shaft angle and at ride height but how does one do this with no rear axle to have the car at ride height? Compound this with no engine mounted since that too I believe needs to be mounted at ride height with the carb level. Do I level the frame and lock in that with wheels and all the frame will sit level and purchase tires accordingly? Is this the time to make that choice, pick wheel size and determine the sit and work off where that would set the frame angle in relation to the ground? I realize that four bars or ladder bars allow some adjustment of the angle but with the stock spring and perches in my head these need to be mounted in a way that take away that adjustment really, correct? Bit of a chicken and the egg situation going on in my head! Might be over thinking this but figure get some advice before laying a single bead to mount anything!
You really need the components you intend to use. And remember, the frame will not be level when the car is finished. It will be on a rake. So either set the frame up on the rake, or compensate with the angles.
Leave the mounts loose on the axle but bolt everything together and finish the car. Once ***embled, you adjust the angle then weld the perches. To be totally accurate, add p***enger weight to the seats so the car is at its " as driven " weight.
Yep, do a search here for "pinion angle" and you can see that it's a common topic and the answers so far have you covered.
Carb level to the ground is not really necessary. Most guys will set the engine so I engine centerline has a degree or so rake to the back at ride height, but if you have an extreme rake I wouldn’t worry about it. On an A frame I’d probably just give it two degrees down in back from the frame top and call it good. Then you can mount the axle to correspond.
Sounds like you're headed for a lot of Redo through your build. Most builders start with something to build from or at least some of the pieces to build with and a pretty good idea where they want to end up.
Don't be overthinking it yet. It's practically the last detail that you will dial in. The angle isn't set to the ch***is or the pavement. The pinion angle is set to compliment whatever angle you will have at the front end of the driveshaft. If somewhere in the middle of your build you want to mock up the drive line, use temporary clamps on the rear axle, for example, and only weld after you have established the load weight, spring compression height, etc., etc.
Thank you all for the replies. I will take the tack and work through it advice for sure. I of course have a vision and nearly all the parts and pieces for the build just felt stuck at this cross road what the order of operations should be. I will be running the aforementioned 8.8 mounted with PJ crossmember and ladder bars and aftermarket weld on spring perches. For motor, SBC pretty much stock mated to a Muncie 4 speed. I am going for about this low, not dragging , and same size front and rear tires similar to the picture.
It doesn't matter how the frame sits when you measure pinion angle. It can be slightly up or down, and that wont mean a thing. What really matters is the axle, and engine/trans are in place, and the angle at the pinion is exactly opposite of the angle at the trans output. If your frame was perfectly level, or nose down 5 degrees wont change the fact the pinion needs to be opposite angle of the trans to cancel out driveline vibration.
IMO, make it the last thing you do. Put everything on it that's going to be and stay there-get max weight of the critter on the tires-then set the angle. No redo then.
I’ve saved that for last In a pro shop that was set in the frame jig. But from known experience of them doing this many times. Ride height vs level. The angle in relation to another part will be the same for both. 2-3 degree rake is kinda normal for a “hot rod”. 2-3 degrees of angle on the intake during the build with the ch***is level will get ya close to zero degrees on the intake at ride height with the “normal” rake.
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