help with driveshaft and pinion angle

[Macdaddy1]

PSGsigns

Ok thanks. I would like to change the springs in the back to 3 inch lowering springs. I guess I will remove the old ones and jack the rear up and take some measures. I am still confused why isin't the measure more correct with the wheels on and the weight distributed with springs than with wheels off and no springs for weight distribution?

[PGSigns]

Here is the point. You need to get your driveline in place and sorted out before you have the truck 100% assembled. Thats the only time all the weight is on the suspension. So by pulling the springs and raising the rear suspension to a point close to where it will be (plus or minus and inch) you have something to actually get a measurement off of that is meaningful. Right now you are trying to match the engine angle to a rear end angle at a place it will never be when the truck is finished, So pull the springs and raise the rear end up till you have about 6 inches from the frame to the rear end. You will see two things happened. First the pinion angle changes several degrees and the rear end has moved side to side as the track bar swung through the arc. You may find the rear is not in the center measuring from the backing plates to the frame. That is why the make adjustable track bars is to correct this. The longer track bars like the early classics super track bar move the rear housing less side to side due to the longer length. The next thing you will see is that the pinion angle has changed several degrees.
When doing this kind of engine swap it is important to get the engine in the correct alignment and at an angle in relation to the frame that is good. Most swaps I shoot for two to three degrees down compared to the frame and that works well as a lot of cars or trucks have a couple of degrees of rake front to back. This sets the engine close to level at the final ride height so things like carbs sit level. Once you have that relationship sorted and locked down then you can adjust the pinion angle to match at you desired ride height. Have been building cars this way for more than 35 years and it works.
Jimmy

[Macdaddy1]

OK, Will do it this weekend and take a bunch of pics. Do I remove the shocks to? Should I leave the back tires on or measure the frame height with the tires then take tires off and set frame at that height on jack stands?

[PGSigns]

pull the wheels and set the frame on good jack stands and level it side to side if you can. Then you can put a jack under the rear and pull the springs. Take some measurements as you go so you can see the change.
Jimmy

[Macdaddy1]

PSGsigns

As instructed I removed springs and shocks and jacked it up to within 6 inches of frame and measured the pinion angle. I temporarily set the trans angle at 3.2 and the pinion angle came out to be 3.9. Would that be acceptable or do i need to alter the trans angle to 3.9? By the way I really really appreciate all of your help as this is all new to me but i am enjoying all of it. I just don't want to make to many mistakes. Also, The damn angle gauge only reads vertical axis so I cannot measure the trans and diff to see if it is parallel. Any suggestions?

[mongocanfly]

before digital came along all we used was a sweep gauge to check angles..
as long as your within 1 degree you should be fine....but I still wouldn't commit to anything til you get the body and drivetrain back on the frame...
not sure what you mean by vertical axis...

[The Rocknrod]

I have one of those digital units. I now use my old sweep dial unit so I dont have to fool around with what the digital doesnt do. https://www.harborfreight.com/media/...mage_17440.jpg

[PGSigns]

What is the angle of the engine compared to the frame? When you lower these trucks it changes the pinion angle as you see in the measurements you got today. Thats close to 6 degrees of change. Get the engine in the frame at a good angle and then adjust the pinion as needed when your done with the truck. That is the best way to do it. That way you know the engine is correct in relation to the frame and when you get it all done and decide on final ride height shim the pinion as needed. When I got my 66 to where I wanted it height wise I measured the angles and since I have 1 1/2" blocks in it machined the tops to correct the pinion angle. What I had you do today was to show you how the pinion angle changes as the ride height changes.
Jimmy

[Macdaddy1]

OK will do. Once again thanks for all of your help.

[62chevy302]

Hey PG I see you asked him what is the angle of the engine in relation to the frame. What should it be? I would think he needs to find out how level his frame will set at ride height to determine how his engine needs to sit in the frame.

[PGSigns]

Most cars and trucks sit with just a couple of degrees of rake. Doing it the way I suggested will get you a starting point no matter what you end up with on a final ride height. One thing I have learned is we tend to change things up as we go on a build. Having the engine in a good place in relation to the frame allows for changes and does not hem you into a specific height that may or may not work when the truck finally comes together.
Jimmy