Driveline angles

-
A

Abodysrule

FABO Gold Member
FABO Gold Member
Joined
Jan 30, 2018
Messages
416
Reaction score
141
Location
California
As I understand it, the engine/tranny tilt angle and the pinion angle should be equal, i.e. the two axis should be parallel and the U joint operating angles should not exceed 3 degrees ideally.

That all said, I see mopar enthusiasts using some pinion angle (preload?) to account for the rise of the pinion under load. That is, put the pinion angle a bit below parallel to the output shaft so that when it rises under load, it becomes parallel to the output shaft or close to it. Some in fact, determine this preload angle based on horse power, more hp means more preload angle (apparently this is derived from empirical observations).

OK, so I measured my output shaft angle and the engine/tranny is sloped downward (from front to back) 3.4 degrees. The pinion is sloped downward (from front to back) .6 degrees. My driveshaft slopes downward 2 degrees. Using Spicer's driveline operating angle calculator, see pic below, gives me equal operating angles at each U joint of 1.4 degrees. This seems fine, I don't have any vibrations of which I'm aware. My inclination is to leave it alone, but....

Questions:

1. should I shim the axle regardless, say with a 2.5 degree shim so that the output shaft and pinion are parallel at rest?

2. My engine puts out 375 hp at the crank, does that change your answer to question 1?

1.png
 
Let me preface this with my situation: I have 2° shims on my superstock springs to tip the nose of the pinion down a bit more (I forget exactly, somewhere around 5° down).
But I've got somewhere around 500 hp, and slicks, so....
For your situation: you are good, don't mess with it!
 
You DO NOT want the pinion and output shaft parallel at rest on a leaf spring car with no traction devices on it.
 
crackedback said:
You DO NOT want the pinion and output shaft parallel at rest on a leaf spring car with no traction devices on it.
Click to expand...
I love instructions that come on stone tablets from a higher authority...

But why is this true? :)
 
Like this shows.
Note on the spring wrap diagram how the diff is twisted.
Clamping leafs so they don’t separate so much can help.

IMG_5671.jpeg
 
warning: Not being a smart ***!!!
is that true when you are just driving? (I really want to know...)
 
RustyRatRod said:
No vibration = Don't eff with it.
Click to expand...
Ok, so when would he see vibration? Only under acceleration? Cruising? High speed? I am curious as to how the driveline angle being too high or low will present itself when driving. Experience out there?

RGAZ
 
RGAZ said:
Ok, so when would he see vibration? Only under acceleration? Cruising? High speed? I am curious as to how the driveline angle being too high or low will present itself when driving. Experience out there?

RGAZ
Click to expand...
You could see vibration any time the drive line is out of phase or out of the range of accepted angles. Here's a decent video.
 
Nice, thanks. So from that video, my takeaway is if the phasing is correct and the angles are parallel, there is no vibration felt. If there is a small difference in parallel the vibration would be felt all the time and get worse the faster you drive. It would be constant and never come and go, right? I also would surmise that the vibration would be in phase with the speed of the driveshaft. (vibration cycle changes with speed of shaft).

This is good info, I always wondered why some people would immediately know its a driveline problem and not just alignment or something else. This makes sense.

Thanks,
RGAZ
 
67Dart273 said:
Watch especially, the second half. 'hard acell



Click to expand...

Holy cow, that angle changes a ton. That is just crazy when I am setting up for a ~3Deg downangle and it flexes way more than that up and down. OF course the Caltracs eliminate that I see.

Good videos.

Thanks
RGAZ
 
RGAZ said:
Nice, thanks. So from that video, my takeaway is if the phasing is correct and the angles are parallel, there is no vibration felt. If there is a small difference in parallel the vibration would be felt all the time and get worse the faster you drive. It would be constant and never come and go, right? I also would surmise that the vibration would be in phase with the speed of the driveshaft. (vibration cycle changes with speed of shaft).

This is good info, I always wondered why some people would immediately know its a driveline problem and not just alignment or something else. This makes sense.

Thanks,
RGAZ
Click to expand...
Meh, sorta. There's a range of which you get no vibration. In other words, if it's "close enough" you're ok. That "close enough" varies so it's best to get it as close as you can. It has to have that range, because as you saw in the video Del posted, the driveline angle is constantly changing while the vehicle is in motion.
 
RustyRatRod said:
Meh, sorta. There's a range of which you get no vibration. In other words, if it's "close enough" you're ok. That "close enough" varies so it's best to get it as close as you can. It has to have that range, because as you saw in the video Del posted, the driveline angle is constantly changing while the vehicle is in motion.
Click to expand...
I get it. What it tells me is that my crappy worn out stock leaf springs (that are essentially flat almost inverse) that I installed my 8.75 rear on are probably allowing crazy motion. Good thing my ESPO's just arrived.

I will have to check the angles again after I get the ESPO's installed, that was the reason for my questions.

RGAZ
 
RGAZ said:
I get it. What it tells me is that my crappy worn out stock leaf springs (that are essentially flat almost inverse) that I installed my 8.75 rear on are probably allowing crazy motion. Good thing my ESPO's just arrived.

I will have to check the angles again after I get the ESPO's installed, that was the reason for my questions.

RGAZ
Click to expand...
Yup, that's entirely possible.
 
Abodysrule said:
That's my inclination, if it ain't broke, don't fix it....just getting the temperature of the driveline crowd.
Click to expand...
The angles you described are ideal if they hold for normal driving/cruise and they improve/reduce the running angle as the trans and the pinion under load because both angles are reduced. The joint is strongest when the driveshaft is at the same angle as the pinion (i.e., zero angle difference between them. I use hellwig traction springs for a different application. They clamp to the front and are curved to resist the axle rotation much better than extra leafs and are adjustable and much cheaper than caltracs. They also stiffen the ride a bit. I don't know if they make them for this but they could probably be adapted.
 
The driveshaft angle is a red herring. The two angles you need to know are the transmission output shaft angle and the differential pinion angle.
 
H22A4 said:
The driveshaft angle is a red herring. The two angles you need to know are the transmission output shaft angle and the differential pinion angle.
Click to expand...
I've never observed that. I've set up many vehicles through the years. Set them up correctly according to various driveline diagrams. If it was a Mopar, I went right by the Mopar suspension manual. Same with my current 64 Valiant. The end all be all is, if you follow correct instructions, you will not have an issue.
 
The drive shaft angle isn't a red herring per se, you need it to calculate the operating angles. Driveshafts of different length, will have different angles, so for example, if your pinion and tail shaft angles are parallel, but the pinion and tail shaft heights differ greatly, and your drive shaft is really short, you may have an operating angle that is unacceptable.
 
You must log in or register to reply here.
-

Back
Top