So I set all of this up so that everything is basically in a straight line. Engine is 2.3 degrees down, pumkin is 2.3 degrees up, and the driveshaft is perfectly in line. Do you think I should rotate the pumkin down a degree or so? Or leave it?
Pinion should be at least 3 degrees nose down... This makes the needle bearings in the U-joint rotate....
"equal and opposite" was always the rule i read. You got that, should be o.k. 2-3 degrees seem standard.
2 things to consider. 1. Pinion and Transmission output shaft should be PARALLEL. It looks like you are there. 2. The driveshaft should be have at least 1 deg of angle between it and the pinion / transmission. This allows the U-Joint bearings to move as Hemihotrod66 alluded to. However, the rear suspension is always moving when you are driving, unless you only drive on glass smooth roads, so the conventional thinking about needing an included angle is a bit overdone.
After the chassis is loaded with the full assembled weight it will be time to revisit pinion angles. Any needed adjustments can be made then but without assembly you could set an estimated amount of weight distributed on the chassis now to simulate final ride pinion angles. Beautiful chassis construction!
I’m no engineer, but I’d shoot for the trans and rear having equal but opposite angles like you have before messing the alignment trying to make the joints “work the grease”.
Sounds good to me but I think it's best to know where the diff is at ride height, fully loaded. But I just don't know how you do that during construction. Maybe it doesn't matter that much as long as you start out ok?
I'd either leave it as you have it, assuming you can make minor adjustments later to the length of the lower bars.
It appears to me that your trans, driveshaft and pinion form a straight line. The image/chart above describes that as being "OK". As mentioned though, some difference between the driveshaft and the trans/pinion is 'better' in order to get the U-joints working/moving. That being said, the difference can be found if the pinion is offset in the chassis. When viewed from above, is your trans perfectly in line with your pinion (centered engine/centered pinion) or is there some offset there?
I spent some time in a pit with new Ford trucks rolling over me at one every minute. I saw a shit ton of trucks that the shaft was dead level, straight out of the trans into the rear end. I think the roller bearings must rotate when the suspension goes up and down. Just a guess.
The general rule of ‘3 degrees’ and parallel for trans and pinion assumes a driveshaft angle of zero degrees. Driveshaft angle is taken into account along with the trans and pinion angles to arrive at the angle at each u-joint, which is what the ‘3 degrees’ generalization refers to (it IS a generalization). Spicer has a nice tool to calculate such things: https://spicerparts.com/calculators/driveline-operating-angle-calculator Your current angles are fine, but need to be finalized with the car at ride height. John
It is at ride height now. Any weight from the body will be compensated for when I tighten up the springs.
That’s some beautiful work there, sir. I can’t tell from the picture if there is a slight side-to-side angle in the driveline - if so, that counts too. John
Watch a YouTube of a dirt track modified rear end movement camera and you will never worry or think of a U-Joint again..
Everything is offset about 1.5 inches to the passenger side with the rear diff a bit more. Beauty of a straight 6.
Just another tool I find very helpful. Before the body is lowered on to the chassis it is easy to position a line laser from a suitable height mounted on a tripod. This allows you to very accurately pinpoint center of or offset of each component. The front cross member, engine damper/ centerline, transmission output shaft, driveshaft yoke, rear axle position/ squareness will all be visible at the same time in relation to where everything should be. It is just an easy way to fine tune the driveline alignment. There is nothing wrong with having offsets but they need to be consistant from one end of the drive train to the other, to minimize possible unwanted vibration. The same + or - pinion angles apply when viewing from a side view perspective or from above. I don't know of a better way to do this without some very sophisticated equipment. Once the body is mounted, it will be much more difficult.
This is a commonly held misconception. No offset is required in a driveshaft that is attached to a moving suspension element. If the differential center section were fixed-mount like a Jag or a Corvette, then no angle would decrease u-joint life. The normal function of suspension articulation is more than enough to distribute lubrication.
I actually used a string line to set everything off of. However mixing and matching axles, engine mounts/crossmembers the drive line sort of "is what it is". The 8.8 is out of a 94 crown vic, with an offset diff. The front cross member is a 2004 crown vic (which has offset motor mounts) and lastly the inline six crank is offset to one side compared to it's mounts.
I'm sure you are aware that the offset in the rear can be solved by using another short axle (pass. side i think) in place of the long one. Have to cut/weld the housing but no big deal and it centers the pinion perfectly. I did this to an 8.8 in a coupe, works great.