My 9-Inch rear housing is hung in my '51. Everything lined up perfectly, using a '68 F100 rear end. My question is, What should the angle of the center section be to the ground ? Should it be perfectly 90 degrees, or off kilter a little pointing up or pointing down. I'm up to 3 shims (using from the old rear end), and I'm still not perfectly 90 degrees from with the ground. Any pics of this ? Thank you !!

 

It needs to be at the same angle plane as the engine/trans. Typically, they tilt down 3 degrees, and the pinion will point up 3 degrees to match. Don't worry about pinion angle until you know what your powertrain angle is, first.

 

Wayne gave you some great information. If your 9 inch already has the leaf spring perches welded on and matches the frame width spacing, you could use shims to correct the pinion angle to the drive line and engine angle. I just did this last summer and got a lot of confusing information on You Tube. Finally I found this calculator on Spicer's web site, and I thought it worked pretty good and gave me enough information that I could use a little math to determine how many degrees of a shim I needed.

https://spicerparts.com/calculators/...gle-calculator

 

A simple magnetic angle indicator is a great help with this project that doesn't cost a lot.

 

https://jniolon.classicpickup.com/dr...nephasing.html

j

 

While Wayne's info is correct the picture is very deceptive to a lot of folks because in probably almost all cases the engine sits higher in the frame than the rear differential. John's link show a better perspective to it. The centerline of the crankshaft is usually at or above frame height due to the mounting while the rear diff is usually below the frame height. So in Wayne's picture if the diff line was below the crank line it would be a more real world look for folks who are trying to look at their vehicle and make the mental correlation between what they are being told and what they are looking at.

To the OP, I went and looked at some of your earlier post to determine where your at in your build. Why I did this is I believe your doing a few things out order for what you are basically building from scratch. All new suspension, front and rear, on a truck that is not assembled, has no established ride height, no engine/trans installed, etc. and your asking about rear shocks and pinion angle. Those types of things can not accurately be determined until after your chassis is assembled and weighted. So don't worry about pinion angle or shock length/mounting until later. You do not need items like that, which would likely need to be changed again. Clamp the diff to the springs with U bolts and continue working. After you truck has a body and engine/trans installed determining ride height you can set pinion angle, measure for shocks and all the little things. Just my .02 that may not be worth anything to you but I feel your putting the cart before the horse on some things. Good luck.

 

I am putting a 9" into my 51 Mercury M1. I am only swapping the rear end, still has the original engine/trans. My question is what should I expect for the pinion angle? I know I will have to use the angle gauge to see where it is at, but being it is a factory Ford rear end (from a 70 F100) with the spring perchs still welded in the original locations, the engine/trans is still in the original position, should it be at the correct angle or will I still need shims?
I have read a lot of posts on here about this, so I think I am getting a little "information overload".....
I welcome and appreciate all comments, thank you.

 

I am thinking you will need to actually install or mock up your new replacement rear end and take your engine and your new pinion measurements at ride height. Measure your engine down tilt on the crank damper pully, then measure your new rear end pinion angle. Hopefully they are both close around 2 to 3 degrees and complementary to each other.
Or maybe try to match the new axle's pinion angle to the old one. Add shims between the leaf springs and axle pads on the replacement axle to get the pinion angle you need.

EDIT:
Shims come in varying degree angle. I've seen 2, 4, 6, 8, even 10 degrees. Unless you grind off the perchs and re-weld new ones on, if using shims you may not get the pinion angle dead on exact. But all the research I did on this last summer seemed to indicate 0.5 to 1 degree was exceptable. I looked at many, many YouTubes on this subject and everyone says something a little different about this. Not trying to be an expert here, but just from my experience go back up to Wayne's post, look at his diagram and just see if you could match your '70 rear's upward angle to your engine's downward angle. If the rears' upward angle doesn't match, then try adding the shims to correct it. It's a lot of bolting, and un bolting parts, jacking up and down the rear end, jacking up and down the truck, checking the pinion angle at ride height, etc. But once you are done it will be worth it. At least it was for me as a PO installed a Dana 60 with no correction at all. And I got rid of a lot of annoying vibrations at different road speeds.
There is probably better ideas and advice out there. It's just what happened to work for me.
If you are looking for shims. Summit Racing is one source. You may also need longer heads on your leaf spring center bolts with shims.

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Being another FORD diff has no bearing on anything as far as what your asking, different chassis, ride heights, suspension,everything. So you will need to check it all upon final assembly as stated by Hooler.

 

Thanks for the advise and tips. Having to do that is the conclusion I came to after all the reading. The hardest part for me is knowing that I can not have everything planned out and have all the exact pieces and parts before I start! (I am working that though) I have acquired all the items that I think I will need, except the shims. I know that I will use shims where needed, I do not want to remove and reweld the spring perch pads. Now there are two things that I can not plan for until I get it bolted in-- shock mounting and pinion angle.
Here in northern Minnesota there is still too much snow to get the pickup from the storage building into the shop. I plan on starting this rear end swap as soon as I can get it into the shop. I am sure I will be looking for more tips as I move forward.

 

I have the 9" installed! When I let it down from the lift and have it sitting at ride height on its own weight, the pinion angle is 11 (the shaft is pointing up) and the engine angle is 3. These measurements are using a digital angle indicator and measured several times. After all the reading, I believe I need 8 degree of shim and a longer spring pin. My driveshaft needs to be 1.125 inches longer to sit at the same place on the trans as it did with the old rear end. I had already talked to the local driveline specialty shop about the driveshaft and that is no problem at all.
My question is: do others agree that 8 degree of shim would be recommended?

 

You need to have the suspension loaded to figure it out properly. Pinion angle, simplest way I can explain it, you are adjusting a static value so that the angle is ideal in a dynamic state. Basically, you are putting it where it will be in the "sweet spot" while driving/under load. During acceleration with a leaf spring suspension, the pinion will "nose up" relative to its position at rest. You are setting the pinion angle at rest, so that when the pinion noses up during acceleration, it is as straight as possible relative to the driveshaft angle. So, having the suspension loaded at ride height dor your base measurements is crucial, so you have an accurate starting point. In a perfect world, the transmission tailshaft and pinion would be perfectly aligned, with zero angle. Since this is not possible in practical use, you are setting it up so that everything is within a good operating range while accelerating/decelerating and as the suspension articulates. Hopefully I've explained it well enough that it makes sense. Sometimes it's hard to put what's in my brain into words.

 

When I did the measurements the wheels were on and it was sitting at ride height, and on its own weight. The pics are just as I was doing the swap. At only 90 horsepower how much would it move during acceleration or at cruising?

 

It's not just the 90 hp, it's the multiplication of torque through both the transmission and the rearend gears, applied to a couple of thousand pounds of vehicle that is stationary. It's going to move, add in suspension movement as weight transfers to the rear during acceleration and movement of the suspension as it goes over road irregularities.

 

In your situation where you engine and tailshaft points down 3 degrees and your rear ends pinion points up 11 degrees. Then I would say, yes! You would need 8 degree shims. But I have had only one go around with this. My pinion angle was not as steep as yours. But corrected it the same way you are, and it came out great!