Pinion angle relative to frame?

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Idaho

Idaho

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I'm about to weld perches onto my 8.8 diff. This is being done before the engine and tranny are in and I want to get my pinion angle roughly set. I've read a bunch of threads and articles. I've not found what I need to do it.

What I need to know is the typical angle between the engine/tranny and the frame since I can't measure the actual angle. The number I see for this angle is 2 degrees down, but it seems this is in reference to the ground. Presumably this is for a car in factory configuration. If the frame is level to the ground from the factory then the 2 degree number can be used.

I'd like to use the rocker as a reference. Does anyone know, in factory configuration, what the rocker angle in reference to ground is?

(I know angles will change somewhat when the drivetrain is installed. I plan to tack the perches and do a final check after the car is complete.)

(I know how to set the angle once I can reference from the rocker.)
 
Factory A body stuff the pinion pointed up 5* when perches are level.
 
Interesting. Maybe the snubber explains how that works.
Still need angle referenced to frame.
 
turn rear upside down on jack stands level pinion yoke.Then lay on spring perches measure center bolt distance and level .Will be close.Can not use a body line angle reletive to stance
 
What you want is the transmission/ crank centerline -- and the pinion parallel under full throttle.

I realize that with different springs this works out, well, "different"

An accepted starting place is 2.5* down from crank centerline. THIS IS NOT (necessarily) the same as the body "level." (Look at a typical intake manifold---the carb is not "tilted forward," the rest of the manifold is, rather, "tilted back.")
 
I had to redo my pinion angle because when I would drive the car it would wine. I took the rearend out, cut the perches off, put the rearend back in the car. I bolted it all back together and left with the perches loose on the housing and left the U bolts just a little loose so I could wiggle it around and let the car back down on the tires to load the suspension. Make sure the car is sitting how it will be when you are driving. Measure the angle of the transmission. I set my rearend pinion angle 4 degrees down from the angle of the transmission. My trans output was 1* down so I put the rearend pinion down 5*. Once the rearend is set in place tack the mounts to the axle. Then remove it and weld it all up. After I did this my rear axle wine was gone.
 
jockeyshift said:
turn rear upside down on jack stands level pinion yoke.Then lay on spring perches measure center bolt distance and level .Will be close.Can not use a body line angle reletive to stance
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That may work out fine, but I want to be more sure of what I'm doing. I can set the car close to its final stance. The engine/trans will be in factory position. If I know the typical factory angle between the engine/trans and rocker I believe I can indeed use that to get the pinion close.

Knowing typical engine/trans angle to ground (2 degrees down) helps but is not enough since it changes with stance and I don't know how my stance compares to factory.

Typical rocker angle to ground will give me what I need.

67Dart273 What you want is the transmission/ crank centerline -- and the pinion parallel under full throttle.

I realize that with different springs this works out, well, "different"

An accepted starting place is 2.5* down from crank centerline. THIS IS NOT (necessarily) the same as the body "level." (Look at a typical intake manifold---the carb is not "tilted forward," the rest of the manifold is, rather, "tilted back.")
Click to expand...
Based on the typical engine/trans being 2 degrees down relative to ground, and typical power wrap for a leaf spring car being 4 to 5 degrees with engine HP in the 400 range, if I were at factory rake angle I would set it at 2 to 3 degrees down relative to ground so it would be parallel under load.

With an altered rear suspension, the 2.5 number could be incorrect. I think my rear may be a bit lower than factory, so my engine/trans angle might be more like 3 to 4 degrees down. Knowing typical rocker angle to ground will allow me to make an adjustment.

duster360 I had to redo my pinion angle because when I would drive the car it would wine. I took the rearend out, cut the perches off, put the rearend back in the car. I bolted it all back together and left with the perches loose on the housing and left the U bolts just a little loose so I could wiggle it around and let the car back down on the tires to load the suspension. Make sure the car is sitting how it will be when you are driving. Measure the angle of the transmission. I set my rearend pinion angle 4 degrees down from the angle of the transmission. My trans output was 1* down so I put the rearend pinion down 5*. Once the rearend is set in place tack the mounts to the axle. Then remove it and weld it all up. After I did this my rear axle wine was gone.
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Exactly what I want to avoid. I think you forgot I have no drive train in the car :) I will be just tacking to start regardless.

If someone with a factory setup (springs in good condition and front not turned way up or down, car on level hard surace) could measure the rocker angle I'd be off to the races. Funny part in all this is I suspect the difference may be only a degree or so.

This pic shows my stance without torsion bars in. The front will be up a couple inches. If necessary I'll guess I'm a degree low on the back and set the pinion at 1.5 degrees down.
 

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I set mine per Denny's Drive Shafts. With the rockers level, both the trans and rear are three degrees down. I have two left 3000# SS springs in a heavy car, so it doesn't sit high.
 
CUDA69 said:
I set mine per Denny's Drive Shafts. With the rockers level, both the trans and rear are three degrees down. I have two left 3000# SS springs in a heavy car, so it doesn't sit high.
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You get the prize for the first to give info on drivetrain angle relative to the frame/rocker. :cheers: Thanks!

Supershafts Set the motor and trans at 0 and then do the same for the pin
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You got me with that one.
1) The drivetrain will be sit at the factory angle.
2) I have no drivetrain... :)
 
Of course that was with the car's weight on the suspension. It looks like you simulated the front height so it should work out.
 
Honestly - I'd tack them and do it when the drivetrain is in. You need the trans output angle and on every car that will be slightly different. Seeing that you're installing them anyway, why not do it once at the right angle? Otherwise you may end up needing to run 1 or 2° shims after remeasuring after the engine and trans are in.
 
You don't even need to tack 'em. Just assemble it all with the U bolts "snug." Don't put lube in the axle, and buy some flare plugs so you can plug off the brake lines. When you get it so that it can sit on it's own with engine/ trans in, measure it up and then tack it. Then just jack it up, pull the U bolts and ties, and flop the axle upside down in the springs and weld it right there in the car.

Or spend 5 more minutes and drop the rear shackles so you can slide it out and get to it.
 
From post #7

... I will be just tacking to start regardless.
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Based on prior threads on this topic I knew the conversation would be interesting :)
Thanks to all for the input. I have the info I need for tacking purposes.
 
crackedback said:
Factory A body stuff the pinion pointed up 5* when perches are level.
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This is correct and would get you close if you were building an 8.75 mopar. Since you are building a 8.8 ford rear , there is no way of knowing what you will end up with unless you install the engine and tranny first. Any other method is a gamble. Never heard of anyone using the rockers as a reference point. Forty year old sheetmetal is probably not the best place to measure driveline angles to.
 
I don't understand why the type of rear axle would affect pinion angle..........................
 
I don't know how others do it but we get the car sitting level on all four wheels with everything in it engine, transmission, complete body and interior ( if you don't have everything ready to install weigh everything on each side and add that amount of weight to each side. So just put sand bags or battery's on the driver side and pass. side so the ride height is were it should be with the weight in it) now depending on automatic or stick decides pinion angle on an automatic we put 1-2 degrees down pinion but in a stick 3-5 degrees what you are looking for is on full acceleration the pinion should move up to a zero angle with the transmission output shaft if you have to much pinion down you will wear out u-joints quickly and have a bad vibration at highway speeds if you have too much pinion up angle you wear pinion bearings and u-joints and on hard acceleration you could put the drive shaft out of the back of the transmission on the extreme side of the problem. the best advise I can give you is take your time and make sure the pinion angle is what is best for you and your driving. If you need more help PM me I'll see what I can do to help.
 
forphorty said:
This is correct and would get you close if you were building an 8.75 mopar. Since you are building a 8.8 ford rear , there is no way of knowing what you will end up with unless you install the engine and tranny first. Any other method is a gamble. Never heard of anyone using the rockers as a reference point. Forty year old sheetmetal is probably not the best place to measure driveline angles to.
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I'm certainly no expert, but in my non expert opinion, if the rockers are not straight, I'm not ready to worry about pinion angle :D

67Dart273 I don't understand why the type of rear axle would affect pinion angle..........................
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I'm puzzled too. In fact the 5 degree up thing is baffling to me.

hemi446 I don't know how others do it but we get the car sitting level on all four wheels with everything in it engine, transmission, complete body and interior ( if you don't have everything ready to install weigh everything on each side and add that amount of weight to each side. So just put sand bags or battery's on the driver side and pass. side so the ride height is were it should be with the weight in it) now depending on automatic or stick decides pinion angle on an automatic we put 1-2 degrees down pinion but in a stick 3-5 degrees what you are looking for is on full acceleration the pinion should move up to a zero angle with the transmission output shaft if you have to much pinion down you will wear out u-joints quickly and have a bad vibration at highway speeds if you have too much pinion up angle you wear pinion bearings and u-joints and on hard acceleration you could put the drive shaft out of the back of the transmission on the extreme side of the problem. the best advise I can give you is take your time and make sure the pinion angle is what is best for you and your driving. If you need more help PM me I'll see what I can do to help.
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I do appreciate the help and concern. The reality is I'm just going to tack it, and get it right after everything is done.

My purpose for now it see the results of my spring relocation and rear leaf slider install, and make it a roller. The initial setting is not going to matter much, but it would be cool to get it right. It's also a learning session.
 
the REALITY is you're making a really STUPID mistake tacking it in before the motor and trans are in. just bolt the damn thing in for now, there is no REASON to tack it.
 
How do you answer a question which has no definitive answer?

On the 5 up perch angle, look at the spring mount locations, they will give you a clue about why it's at that angle from the factory.
 
Yes I thought about that after. 5 up from level perches does not mean 5 up from level ground. In their installed position, the perches must have some downward angle.
 
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