Adding Pinion Angle Shims - Tell Me If This Sounds Correct, Please

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MobileCustoms

MobileCustoms

You can twist perceptions, reality won't budge
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Just finishing my install of a Gear Vendors Overdrive and checking my driveline angles to make sure I end up with the correct specs under load.
First photo shows about 4.5 to 5 degrees down on the output of the overdrive and about 5 degrees up on the pinion angle.
I ordered some 3 degree shims from Doctor Diff to put under the perches on my 8 3/34 rearend which has the ESPO +1" leaf springs and an adjustable pinion snubber which is currently almost touching the floor pan since I flipped my front spring hangers upside down to lower the rearend a bit. I will cut the pinion snubber down so it has some clearance.

3 Questions:
1. Adding the 3 degree shims to bring the pinion angle down should wind up leaving my pinion angle me about 2.5 degrees down from center, at rest. does this sound right? Or will that be too much for mainly a street car and possibly cause a vibration at cruise speeds?

2. Before I measure for my driveshaft, I am installing some 3/8" shim blocks in the front spring hangers in order to move the rearend back a little to help center the larger tires in the wheel opening better.
This shouldn't really affect the pinion angle at all, or very very little, correct?

3. How much room should I leave between the pinion snubber and floor pan? My combo is a 340/416 stroker with 540 ft/lbs torque and 520 horse on the engine dyno. Currently running 3.73 gears but switching to 4.10 gears with the overdrive unit installed. Tires are 295/55/15 drag radials, so it hooks pretty well. This is mainly a street car but hoping to get it to the track on occasion once I have things dialed in better.

-Thanks for any input!

-Doug

20240621_120003.jpg

20240621_120040.jpg


Here's how I have the car sitting, all jackstands under suspension.

20240616_231918.jpg
 
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Depending on your springs, I think 2 1/2° down is about right. I have angle shims on my car to get the nose about 5° down, but it's primarily a strip car, with ss springs.
I personally throw every pinion snubber in the trash. If it's close enough to the floor to actually DO something, it wrecks the ride, and beats up the floor of the car. In the case of my car, the rear rises leaving the starting line, and the snubber becomes dead weight, waving in the breeze, six inches away from doing anything. Hence, round file.
 
MobileCustoms said:
Just finishing my install of a Gear Vendors Overdrive and checking my driveline angles to make sure I end up with the correct specs under load.
First photo shows about 4.5 to 5 degrees down on the output of the overdrive and about 5 degrees up on the pinion angle.
I ordered some 3 degree shims from Doctor Diff to put under the perches on my 8 3/34 rearend which has the ESPO +1" leaf springs and an adjustable pinion snubber which is currently almost touching the floor pan since I flipped my front spring hangers upside down to lower the rearend a bit. I will cut the pinion snubber down so it has some clearance.

3 Questions:
1. Adding the 3 degree shims to bring the pinion angle down should wind up leaving my pinion angle me about 2.5 degrees down from center, at rest. does this sound right? Or will that be too much for mainly a street car and possibly cause a vibration at cruise speeds?

2. Before I measure for my driveshaft, I am installing some 3/8" shim blocks in the front spring hangers in order to move the rearend back a little to help center the larger tires in the wheel opening better.
This shouldn't really affect the pinion angle at all, or very very little, correct?

3. How much room should I leave between the pinion snubber and floor pan? My combo is a 340/416 stroker with 540 ft/lbs torque and 520 horse on the engine dyno. Currently running 3.73 gears but switching to 4.10 gears with the overdrive unit installed. Tires are 295/55/15 drag radials, so it hooks pretty well. This is mainly a street car but hoping to get it to the track on occasion once I have things dialed in better.

-Thanks for any input!

-Doug

View attachment 1716265502
View attachment 1716265503

Here's how I have the car sitting, all jackstands under suspension.

View attachment 1716265522
Click to expand...

When your GV is as high as possible, it seems to me that you want just a bit less than the same opposite at the differential.
Lets say you have 4.5 down on the GV, then you want 2-3 degrees up at the diff.
Then when under load the diff comes up a little more making the angles about perfect for cancellation of vibration.

This is the way I do it anyway.
One of the GV’s I did on a 71 Dart, we raised a section of the floor under the bench seat 2 inches because the guy didn’t want to change angles at the rear end.
That came out about perfect.
 
Pinion angle terms are critical to be on the same page, using the same terms. I agree with Trailbeast, and want to make things clear. If your o.d. is tipped down 5° from level, front to rear, then ideal for the pinion gear is 5° up from level. To get it to be there under load, somewhere around 2° static lower the the example 5° up, is what I would shoot for.
There is a whole raft of pinion angle talk, both here and B-bodies. A search should bring most of it up.
 
This all sounds exactly like what I described (or tried to) in my original post, so I will go with the 3 degree shims as planned. Maybe my post was a little sketchy, but I thought I included all the details. My trans angle is basically down 5 and the pinion is up 5.
3 degree shims should bring it to 2 degrees down from center at rest.
Thanks guys. I'll post an update when it's done!
 
U r thinking wrong. U need the pinion 3* lower than the end of the gear vendors. If your gv is really -5* down u need the pinion down 3* more than the gv. So the pinion needs to be at -8*. Go to the Doctor Diff website it all there. Kim
 
oldkimmer said:
U r thinking wrong. U need the pinion 3* lower than the end of the gear vendors. If your gv is really -5* down u need the pinion down 3* more than the gv. So the pinion needs to be at -8*. Go to the Doctor Diff website it all there. Kim
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I believe you are not correct. If the trans is down X degrees, then the pinion needs to up the same amount of degrees under full load, to cancel each other out, from everything I have read.
 
MobileCustoms said:
I believe you are not correct. If the trans is down X degrees, then the pinion needs to up the same amount of degrees under full load, to cancel each other out, from everything I have read.
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Did u read on doctor diffs site? Never in my life have I set a pinion higher than the trans. But try it your way. Kim
 
What Greg (TB) said

The way I read what you are contemplating, you have the two shafts parallel WITHOUT load. You want the two parallel UNDER load. So if the trans is 5 down (sounds like a lot, I agree with Greg, TB, I'd try and raise that) then you want the pinion down maybe 2 from the trans. So under torque, as the springs flex and the pinion comes up. they are roughly parallel

THIS is a quote from DrDiff

"



Pinion angle is the relationship between the transmission centerline and the pinion centerline, not to the driveshaft and not to the ground.
Ideally, the pinion should become relatively parallel to the transmission as the pinion wraps up under power. This is how U-joints are designed to run.
When the vehicle is resting on its suspension, make the pinion parallel to the transmission as a base line, then tip the pinion downward 2 degrees (for a street car). This is referred to as 2 degree negative pinion angle."
 
This is all explained very clearly in the MP suspension manual. For like 50 years now. lol
 
RustyRatRod said:
This is all explained very clearly in the MP suspension manual. For like 50 years now. lol
Click to expand...
Well, you know I'm a little stoopid, right? LOL
I think I did a bad job of using the right words to explain my measurements. So I just raised the car back up with jack stands under the front and rear suspension and re-measured everything as it sits now with the 3 degree shims installed so that they dropped the pinion angle downward.
I made this drawing to hopefully show what I did better. Tell me if this makes sense and if it sounds like I'm in the ballpark. According to my gonkulations, if my pinion angle comes up 2.6 degrees under load, then that should net me close to 0 degrees under load, which would make the transmission centerline nd pinion centerline end up parallel to each other when under load, right?
I'm still learning everyday and am not too proud to admit when I'm wrong, or stoopid... or both.
Edit: I know I spelled "Plane" wrong. But I'm too lazy to correct my drawing here and too dumb to spell it right in the first place.
@DoctorDiff

Pinion-Angle-Measurements.jpg


Pinion-angles-under-load.jpg
 
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Forget about the drive shaft. It has nothing to do with the trans and pinion angles. Get them right and the ds angles will be right. Measure the angles at the gov and the pinion. What are they?
 
oldkimmer said:
Forget about the drive shaft. It has nothing to do with the trans and pinion angles. Get them right and the ds angles will be right. Measure the angles at the gov and the pinion. What are they?
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Those measurements were in my first post. GV was 4.5-5 degrees down and pinion was 5 up with the angle finder. Isn't this what one would need in order to cancel each other out for the least vibration at under a full load? Because that's what I find from many sources. So then adding shims to bring the pinion down 2-3 degrees under no load is what I shoot for, right? When the pinion comes up under a load it gets it as close to zero as possible. Right now, with the shims added, my pinion angle is down 2.6 degrees lower than the output shaft on the overdrive unit under no load.
 
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Based on those numbers, it's fine. Run it.

My only question would be are you positive the engine oil pan rail is perfectly parallel to the transmission output shaft centerline?
 
mopowers said:
Based on those numbers, it's fine. Run it.

My only question would be are you positive the engine oil pan rail is perfectly parallel to the transmission output shaft centerline?
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I always thought and have seen that the pan rails are parallel to the crankshaft, which is parallel to the trans output shaft. I've measured it from both the output shaft and the pan rails with the same readings. I don't think I'm totally dumb, but some of the responses here (not yours) sure make me wonder. LOL
I don't have all the books but feel like I've done my best to research multiple sources before posting here. Just trying to make it right as best as I can and learn.
 
JMO, I would measure off the output shaft if it is sticking out from the gear vendors. Not sure if anyone else mentioned that. If the yoke doesn't have a flat surface machined into it, I would not use it to obtain the trans angle. Whatever the trans angle measures, down 3*, you want the pinion UP 3* for prallel state, then roll it down to obtain the "roll up" variance. Your math approach looks correct.

Dr Diffs parallel comment is when the vehicle is under power. Static you want the pinion to be down slightly as it will "roll up" under power. It's why they put pinion snubbers on cars, to plant the tires using the rotational/roll up forces under acceleration. I agree with the other poster, I use snubbers as door stops to allow a breeze in the shop, save the environment a little and not in a landfill.

I've worked on some drag cars that had stupid levels of pinion down in them. Most passenger cars are good in the 1-3* down range. 2* down is a good starting point for a street driven car. More power in the engine, roll the pinion down a smidge more. Too much and you may induce vibration. It's a balancing act.

Your diagrams, pinion on most passewnger cars is lower than the output shaft level. Driveshaft almost always points down going to rear of vehicle.

Pinion angle is where you get 10 bazzilion answers and none of the right... LOL That's sarcasm for the few that want to start in on it! Looks like you got it.
 
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crackedback said:
JMO, I would measure off the output shaft if it is sticking out from the gear vendors. Not sure if anyone else mentioned that. If the yoke doesn't have a flat surface machined into it, I would not use it to obtain the trans angle. Whatever the trans angle measures, down 3*, you want the pinion UP 3* for prallel state, then roll it down to obtain the "roll up" variance. Your math approach looks correct.

Dr Diffs parallel comment is when the vehicle is under power. Static you want the pinion to be down slightly as it will "roll up" under power. It's why they put pinion snubbers on cars, to plant the tires using the rotational/roll up forces under acceleration.

I've worked on some drag cars that had stupid levels of pinion down in them. Most passenger cars are good in the 1-3* down range. 2* down is a good starting point for a street driven car. More power in the engine, roll the pinion down a smidge more. Too much and you may induce vibration. It's a balancing act.

Your diagrams, pinion on most passewnger cars is lower than the output shaft level. Driveshaft almost always points down going to rear of vehicle.

Pinion angle is where you get 10 bazzilion answers and none of the right... LOL Looks like you got it.
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Thank you for thoroughly reading my info and replying. I did measure it on the ouput yoke previously, as stated. Now the driveshaft is in and a test drive felt good. There is definitely no shortage of opinions. Still ready to make changes, if needed. I aint cocky.
 
crackedback said:
Whatever the trans angle measures, down 3*, you want the pinion UP 3* for prallel state, then roll it down to obtain the "roll up" variance. Your math approach looks correct.
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^^^ This! Don't overthink it. Make the pinion parallel to the trans and rotate it down 2-3*. Yours is good. Run it!
 
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