Advice on this this setup? In attempting to locate an SBC engine /2004r tranny into the 1939 Poncho frame, I’m attempting to find that “sweet spot”. I’ve raised the engine to keep the oil pan even with or above the forward frame saddle for obvious reasons. I added 2” lowering blocks in the rear, which should raise the axle in relation to the transmission. I set the engine at 3.5 degrees to match the pinion angle. I currently have the engine nested on wooden blocks and a temporary trans support before committing to welding in the engine mounts. I used a length of PVC to mock up the driveshaft and give me a rough idea of that angle, which comes in somewhere around 10-11 degrees. My concern is the driveshaft angle. The frame is leveled and supported on jacks, which allows the rear end to dangle. I have no way to know or simulate the weight of a complete car sitting on its wheels. It just “looks” like an awful steep drop on the driveshaft down to the pinion. With the short wheelbase on this car, I’m not seeing any way to lessen that angle… so.. am I overthinking this? I know people but SBCs into old narrow frame, fat fender cars frequently. Take a look at the pics and toss in your opinions, thoughts, ideas, criticisms, …whatever. I just want this project to start moving forward again.
Just a couple of observations. Once on the tires most cars have 2 or 3 degrees of frame rake due to suspension or tires. So that will change the engine reading with the frame now level. For the driveshaft you really need to get all four tires on the ground. Then you can attempt to guess what the final outcome might be by compressing the rear springs a few inches either by weight or heavy duty rachet straps. But you won't really know until the car is complete and on the ground. Then you can rotate the rear axle in the spring pads if needed.
In the mid 70's I was "sorta" where you are. I had a SBC/four speed going in the 38 Chevy that I still have. I had little to go on but if my memory serves me correctly ( at 80 that is suspect I placed the engine with the plugs about even with the top of the frame. I must have eyeballed the angle?? I mounted a 57 Chevy rear axle in the same position as the original axle (which pushed it too far forward appearance wise). I drove it that way for ten years and twenty thousand miles with no problems. The car sat from 85 to 2010 when I was able to get back on it. I fussed a lot getting the driveshaft angles just right with the Tremech app (https://www.tremec.com/menu/tremec-toolbox-app/) BUT I welded the spring pads on the narrowed nine inch Ford without having weight on the tires. I ended up modifying my home made lowering blocks to "wedge" the driveline angles to the correct numbers. Good luck.
U-joints need an angle to “work” properly. Rear leaf springs wrap on every start changing the angle along with bumps in the road. without traction bars. They can work thru a 22* arc. Always be careful when angling the 3rd member as it can affect oiling. It’s best to try and simulate the original manufacturer positions when doing a power train swap. Original installation vehicles with a enclosed drive are so what confusing do to fact of no rear u-joint and what appears to be angle rear the open ones do not have….Good luck
Without the rear axle at proper ride height setting angle is difficult and having it dangle at full extension as pictured means little. I usually finalize the angle later when the expected weight is on all of the suspension and then weld the mounts on the rear axle. An alternative is to put the springs in a hydraulic press which can provide a height at a certain pressure to approximate expected weight and then do the measurements and math to see where it is expected to end up.
Set engine and trans first so they fit the frame and body. Keep the crank centerline kinda parallel to the main part of the frame, or maybe up a degree or so in the front. Not really as important as you are thinking. Then you can adjust the rear axle so the angle matches the crank and trans output. Either reweld the spring mounts on the axle, or use some tapered shims. But ALL the weight of the car will need to be on the tires to be able to fine tune the rear axle. Actual angles in comparison to the ground are kinda meaningless.
Drive shaft angles are relative to the engine and rear. Not the floor When I set one up I set the chassis at ride height. Even if using leafs. I will set the rear end and front spindle at my desired height. if using a carb I’ll put the intake level. then set the pinions theoretical angle Most leaf sprung rears have more pinion angle due to the action of the springs when in motion. The pinion moves in an arc and up and down. The current chassis we are doing we set the chassis at the ride height we determined by setting the vehicle at ride height and measured frame to floor distance. Spindle height and rear end height are determined by tire diameter. if running a 28 inch rear tire, 14 inches is the theoretical axle center line. (Yes tires compress with weight) Do the same for spindle height. This allows you to figure out where the chassis will sit height wise. As far as angles. You don’t know where the rear will be with no weight on it but you can build it to where you want it to be
It may be the way the pic is, but it looks like the transmission is also level? How level is the carb base plate? It looks to me that the trans mount needs to drop about an inch.
The Jalopy Journal
