Pinion Angle? Do I have this right before I cut it up?

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Minnesota Muscle

Minnesota Muscle

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The previous owner installed SS springs on my '67 barracuda. I just rebuilt the 8 3/4 and decided to check the pinion angle as it didn't look right. I haven't driven it down the road more then a 1/4 mile as I've been busy doing other repairs. So I don't know if it has any vibration at speed. Here are the measurements taken with a harbor freight angle gauge. The vehicle is on it's wheels and is primarily a drag car.

Measuring off of the output shaft of the trans, I have 2 degree downward angle from ground parallel (negative 2*). The yoke on the rear differential has an upward angle of 4 degrees from parallel to the ground (positive 4*).

If I understand this all correctly, while under load, my pinion angle should be parallel to my trans angle. So if my trans angle is -2*, my pinion angle should be +2* under load. Which would mean when set correctly aiming for a 5* downward static (they say 5* to 7*), I should have a static pinion angle of -3*???

With a current setup of +4*, it's clear I will have to cut the perches off and reweld them correct? As I'm told shims past 4* aren't safe, let alone the 7* I would have to move it.

So before I cut it all up tomorrow, tell me if I'm understanding this right?

Thanks a ton!

MM
 
https://www.tremec.com/menu/tremec-toolbox-app/

https://www.tremec.com/anexos/Literature/Driveline-Angle-Finder_Instructions.pdf

Take a look at this app and down load it to your phone. Follow the instructions to see if you're close.
If you run a search here you'll find tons of info and probably figure it out pretty quickly.
It sounds based on your numbers you might have some work to do.
Some pics of your driveline with the angles you have might help others understand just what you're looking at. I'm curious to see what you have and how you make out. Good luck.
 
Subscribed!
I don't get your problem, if your trans is down 2 and the rear is up 4, why can't you shim the rear down 2 and have what you want (-2 and +2)?
 
Isn't it possible to lose 1 or 2 or more degrees under load?...bringing him back out of the acceptable range? Could shim down 4* first and see where it is.
 
The Mopar Performance Suspension Manual is another great resource....IF you can locate one.
 
67dartgtgo said:
https://www.tremec.com/menu/tremec-toolbox-app/

https://www.tremec.com/anexos/Literature/Driveline-Angle-Finder_Instructions.pdf

Take a look at this app and down load it to your phone. Follow the instructions to see if you're close.
If you run a search here you'll find tons of info and probably figure it out pretty quickly.
It sounds based on your numbers you might have some work to do.
Some pics of your driveline with the angles you have might help others understand just what you're looking at. I'm curious to see what you have and how you make out. Good luck.
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Thanks for the response. I suppose I should have prefaced my post with what I've done for research. I've been reading and searching through the forums most of the day to get a handle on driveline angles and how it all works.

I did download that app. It was very inconsistent and didn't reflect what I was seeing manually measuring with this angle gauge. Might have been my phone. Plus, when the numbers were "incorrect" according to the app, it didn't help you understand why, it just says the numbers are not within working perimeters.

Here are a few pictures. This is how dozens of posts have said to take a measurement by. The gauge is new and pretty crudely simple so I trust what it's telling me.

PXL_20220427_021655016.jpg


PXL_20220427_021619799.jpg
 
12many said:
I like to keep it simple: trans is down 2°
Pinion is up 4°
If you were Using shims:

2° Shims = will put the pinion parallel with the trans.

Increasing things for the strip:

4° shims = will put the pinion 2° down from the trans. That’s better.

6° shims would put it down 4° down from the trans

Need to determine the driveshaft angles as pinion angle is changed, as then you get the working angles. That’s really important
Strike a happy medium, weld em up.
Click to expand...

Thank you, that simplifies what I was trying to say. From everything I've read, 5* to 7* down angle should be utilized for launching drag applications. Such as this. So if I wanted to get it to 5* down, I would need a 7* shim, OR cut the perches and relocate which is what I'm going to do, just need to get confirmation I'm understanding it all like I think I am before I do
 
Yes, the 5-7 degree figure is for hot street and drag cars for hard launches. BUT that is the pinion that needs to be 5-7 degrees DOWN from the drive shaft angle, so that's not necessarily 5-7 degree working angle if that makes sense. It's all in the MP manual. But that's hot street and drag, so unless you're going that way, you should set it up normally. I always still go a little further down at the pinion with "any" type performance build. It helps give the rear suspension more lift on acceleration, which plants the tires.
 
RustyRatRod said:
Yes, the 5-7 degree figure is for hot street and drag cars for hard launches. BUT that is the pinion that needs to be 5-7 degrees DOWN from the drive shaft angle, so that's not necessarily 5-7 degree working angle if that makes sense. It's all in the MP manual. But that's hot street and drag, so unless you're going that way, you should set it up normally. I always still go a little further down at the pinion with "any" type performance build. It helps give the rear suspension more lift on acceleration, which plants the tires.
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So NOT 5 to 7 degrees down from parallel of trans output? Here I was thinking the 5-7 figure was how much further down from trans angle you should be while the vehicle is static.

If thats right and it's based off of pinion angle to driveshaft angle, why bother knowing what the trans angle is when figuring out how far to point the pinion down? Man thats confusing to write.
 
Minnesota Muscle said:
So NOT 5 to 7 degrees down from parallel of trans output? Here I was thinking the 5-7 figure was how much further down from trans angle you should be while the vehicle is static.
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No, that would be WAY too far down and that hangs people up sometimes. It's clear as a bell in the MP manual and people spout 5-7 down as gospel......and it is, sorta, but it's referring to 5-7 down FROM the angle of the drive shaft, not the transmission shaft. When I set one up from scratch, I set the perches on the rear housing with the pinion 5 degrees down. Normally, that gets it so close it usually doesn't need any shims if everything else is right.

Of course, there's always different applications, so it's all dependent on "WHAT" you're doing.
 
Measuring the tailshaft as you are doing is not accurate. See if you can get on something on the block, even the trans pan is likely more accurate than the tail shaft. The shaft is unsupported as you are showing it
 
I jut ran out to the shop and threw the driveshaft in the car and took a reading. The static driveshaft angle is 0.75* up.
 
67Dart273 said:
Measuring the tailshaft as you are doing is not accurate. See if you can get on something on the block, even the trans pan is likely more accurate than the tail shaft. The shaft is unsupported as you are showing it
Click to expand...
I did measure off of multiple points, including off of the crank pully face and it was all within half a degree, and that could have been me. Thanks for the thought though.
 
RustyRatRod said:
No, that would be WAY too far down and that hangs people up sometimes. It's clear as a bell in the MP manual and people spout 5-7 down as gospel......and it is, sorta, but it's referring to 5-7 down FROM the angle of the drive shaft, not the transmission shaft. When I set one up from scratch, I set the perches on the rear housing with the pinion 5 degrees down. Normally, that gets it so close it usually doesn't need any shims if everything else is right.

Of course, there's always different applications, so it's all dependent on "WHAT" you're doing.
Click to expand...

So even though I'm showing only ".75 of a degree up" right now, as I rotate the pinion down, my driveshaft angle should change too. So its a moving target to get those correct numbers?
 
Minnesota Muscle said:
So even though I'm showing only ".75 of a degree up" right now, as I rotate the pinion down, my driveshaft angle should change too. So its a moving target to get those correct numbers?
Click to expand...
Yup. I don't shoot for same/same at static. I figure out what I'm gonna be doing most and shoot for same/same there. That's the part that's really not printed anywhere. Shooting for equal numbers static means on acceleration you're going more negative then you probably should. So I always put the pinion 1-2 degrees further down, more if I'm racing. 5-7 down from the drive shaft is the racing spec, and I use 2-4 down from the drive shaft on the street. It usually works out fine. Every now and then you run into somethin stupid, but not often.
 
So this is the stuff that drives me bonkers. There are loads of threads and posts that will come out right and contradict what your saying. That driveshaft angle doesn't matter and its all about trans output shaft angle and pinion angle. See post 14 and 18 in this thread linked below to see what I mean. Others who appear to know what they are saying, claim to come down 5* off of the trans output angle and that will give you your pinion static angle. Which your saying will be way to low. I did read in very few publications the mention of needing to know the driveshaft angle, so I'm not willing to ignore what your saying.

Our fist track day is tomorrow. I'm quickly watching it slip away by not coming up with a definitive answer. I do appreciate all the dialog though.

pinion angle
 
Minnesota Muscle said:
So this is the stuff that drives me bonkers. There are loads of threads and posts that will come out right and contradict what your saying. That driveshaft angle doesn't matter and its all about trans output shaft angle and pinion angle. See post 14 and 18 in this thread linked below to see what I mean. Others who appear to know what they are saying, claim to come down 5* off of the trans output angle and that will give you your pinion static angle. Which your saying will be way to low. I did read in very few publications the mention of needing to know the driveshaft angle, so I'm not willing to ignore what your saying.

Our fist track day is tomorrow. I'm quickly watching it slip away by not coming up with a definitive answer. I do appreciate all the dialog though.

pinion angle
Click to expand...
You're not understanding. "Whatever" the pinion angle reads is "down" compared to the drive shaft angle. As I've made mention many times, the MP suspension manual explains it very well.
 
When the car squats and the axle wraps up; all the angle relationships change. The only angle that stays constant is the crank (except when it comes to traction). Leaf springs are notorious for massive upward pinion angles under load, and four links are considered the opposite. The sad truth is; only a video camera aimed at the pinion will tell you the whole story. But even if your trans/pinion angles are perfect under load, how they got there will dictate how well the tires plant.
 
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