pinion angle

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trudysduster

trudysduster

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I was sitting on my stool looking in at the rear end with the tire off and it hit me. I think my rear end is sitting up too high. I drove a semi all my life and know a little about pinion angles and vibrations. I would guess the pinion should be pointing down a little so when it is under a load it would be up almost level. I would say this pinion is about an inch or so higher than level just sitting. I dont have any guages or tools to measure this but I would guess this is not right. could someone give me their input on this. Thanks,Bill
 
When the MP suspension manual talks about "nose down" it is not speaking relative to the ground. It means nose down in relation to the drive shaft angle. What is actually being measured is the u joint "working angle" which is the difference between the drive shaft angle and pinion angle. As usual, Mopar makes it easier to understand. Much in the same way they made camshaft degreeing much easier using their 180* degree wheel. If you have a copy of the MP suspension manual, it is all there. If not, I highly recommend it. The ninth edition is the latest print. Mancini's regularly runs them on sale for 10 dollars. Very good deal.

Oh and the only tool you need for measurement is a four dollar angle finder.

http://www.harborfreight.com/dial-gauge-angle-finder-34214.html
 
There is a small carpenter level now with a angle degree finder on it.you lay it on the flat side were the snub-er goes and turn the dial and it tells you the degree.
 
That's great info & threads, thank you. I'm guessing everything is different with a 4 bar rear end suspenion. 4 bar is new to me and it looks like the pinion shaft angle moves very little if at all when the rear end moves up and down. Staying relitivly fixed. It also looks like I can adjust the rear end to just about anything I wish. I've been told that installing a A518 is tight in the 69 Valiant. I may be limited on the angle the transmission out put shaft is going to be by how much clearance I get in the transmission tunnel and from cutting the frame part of the transmission cross member. I would rather not cut or modify the floor at all. Only as a last resort. Is there any pit falls you might think of? Does the same advice apply to leaf spring suspensions? Thanks
 

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I was dusting off some old books and found Mopar Chassies, Carroll Shelby's speed secrets (P/N: P4349341) Like winning the lotto. I scanned the pages related the drive shaft alignment but, the files are way to big to post here. If you want, PM me with your e-mail and I will be happy to send pages 94 through 95. I'm going to ask the computer wiz at work if she can pdf the whole thing. Might cost me a lunch :happy1:
 
StrokerScamp said:
When the MP suspension manual talks about "nose down" it is not speaking relative to the ground. It means nose down in relation to the drive shaft angle. What is actually being measured is the u joint "working angle" which is the difference between the drive shaft angle and pinion angle. l
Click to expand...

I FIND THIS TO BE INCORRECT (or at least poorly written)

That article "almost" ignores the angle at the transmission, and talks about shimming the transmission mount, which in most cases is not necessary. It implies that the transmission shaft must be level with ground, which is also not necessary

The ONLY THING that a driveshaft "cares about" is that the two angles --the one at the gearbox, and the one at the rear axle-- ARE BOTH EQUAL UNDER ACCELERATION or nearly so.

Here's a pretty good explanation. The only flaw in this article is that they do not allow for "fudge factor", that is, the pinion MOVING UP under hard acceleration.

http://www.hotrodhotline.com/md/html/drive_shaft_harmonics.php

The one important statement is:

Under hard acceleration, the CENTERLINES of the transmission output shaft and the rear axle pinion must be PARALLEL or nearly so.
 
Well I thought I had it right with my trans/pinion angle but maybe not?

Am 3 degree down on trans and 3 degree down on pinion. Reset factory leafs no caltracs or bars and about 450 hp.

I have banked on about 6 degree of pinion rotation on hard acceleration to be at zero? Too much? Bring it back to zero at the pinion? Any help much appreciated.

Good vid from GT falcon on PA....

[ame="http://www.youtube.com/watch?v=JsdT57d4w20"]Falcon XY GTHO Group Nc racecar diff pinion & spring windup under acceleration & braking - YouTube[/ame]
 
Henry, I am gonna tell what I had to do with mine. I know the book tells you this and that but it didnt work for me. I had put shim in mine from 1 degree to 3 degree and even stacked them, turned them around after setting it to where the dial said it should be. Now this is a hillbilly way of doin it but it worked. I had to put new perches on mine because when I had the rearend sent out to Moser Engineering and had it cut down I ASSUMED they put it back where it should be............not. So I took the new perches and put them under the rearend and set the angle where it should be with the dial and I locked down the u bolts. I didnt weld it. I ran the car to see if there was a vibration. If there was I brought it back, loosened the u bolts and adjusted it and took it out again. After about the 3rd time, I didnt feel the vibration. I then took it out again and got in it pretty hard to see if it vibrated when under acceleration. I had to adjust it down just a little. when I got it to where it didnt vibrate under acceleration or on the interstate or during deceleration, I came back, spot welded it. I pulled the rearend out and finished welding it the proper way. It may not be the correct way to do it but a friend of mine who works at a truck spring shop told me to either do it that way or bring it in the shop and they would set it up for $375.00. I chose this way and it worked for me. I had put a different engine tranny and rearend in mine though. Maybe you wont have to do it like this but I had to.
 
The angle of the dangle is directly proportional to the heat of the meat....
 
I just set mine a few months ago. I called cal trac and this is what they told me. I had them dummy it up for me.

1.) the car has to be on its tires in full driving weight.
2.) find the degree of slope on the engine and trans. I measured off the front of the harmonic balancer. my engine tilled down in the rear 2*
3.) they told me that i needed to anticipate 3-5* of rotation upward on the pinion snout under load.
4.) you want your engine/trans center line to run paralled with the differental yoke center line under full load.
5.) so i set my rear diff angle upward @ 2* then subtracted the 3-5* ( i chose 4*) so it was set at 2* down.

every car is different, but the pinion angle relates to the angle of the engine and trans.
 
trudysduster said:
Henry, I am gonna tell what I had to do with mine. I know the book tells you this and that but it didnt work for me. I had put shim in mine from 1 degree to 3 degree and even stacked them, turned them around after setting it to where the dial said it should be. Now this is a hillbilly way of doin it but it worked. I had to put new perches on mine because when I had the rearend sent out to Moser Engineering and had it cut down I ASSUMED they put it back where it should be............not. So I took the new perches and put them under the rearend and set the angle where it should be with the dial and I locked down the u bolts. I didnt weld it. I ran the car to see if there was a vibration. If there was I brought it back, loosened the u bolts and adjusted it and took it out again. After about the 3rd time, I didnt feel the vibration. I then took it out again and got in it pretty hard to see if it vibrated when under acceleration. I had to adjust it down just a little. when I got it to where it didnt vibrate under acceleration or on the interstate or during deceleration, I came back, spot welded it. I pulled the rearend out and finished welding it the proper way. It may not be the correct way to do it but a friend of mine who works at a truck spring shop told me to either do it that way or bring it in the shop and they would set it up for $375.00. I chose this way and it worked for me. I had put a different engine tranny and rearend in mine though. Maybe you wont have to do it like this but I had to.
Click to expand...

You're lucky you didn't drive your pinion into the floor pan and break a U-joint/driveshaft with the U bolts holding the rear in place. If it worked, great...

The angle that you see the pinion when sitting static has nothing to do with setting proper pinion angle. The angle is not relative to the ground. Like Younggun mentioned and how he set it, it's relative to the engine trans angle. Usually on street driven stuff, you don't want angles greater than about -3.
 
Im gonna need this advice too. I have a 7.25 rear out of my dart parts car. Im narrowing a c body 8.75 rear to fit my 67 cuda. Couldent i copy the angle of the spring perches are welded onto the dart rearend onto my narrowed c body rear. I mean if the stock angle on the dart rear worked, shouldent it work with my barracuda on a shortened 8.75 rear? I plan on running leaf springs that should lower the car about 2 inches, plus 2 inch drop spindles in front. Im not sure how this will affect pinion angle, or alignment with the driveshaft , and transmission.

Good idea, bad idea? Any suggestions?
 
lower car on wheels: Absolute angle of trans output shaft (eg. 2 {down}) should equal down angle of static pinion (in negative number eg. -3) +5 for wrap up of leaf springs. And the only one of these you can vary is the static pinion angle with shims available in 1,3 and 5 degrees from a 4X4 shop. So as it has been said, you want to MAKE the final rear pinion angle (-3) + spring wrap (+5) + angle of trans yoke (-2) to equal 0 at full torque....or just parallel to the output shaft of the trans adding variable 5 for spring wrap. The 5 is also a variable, depending on what leafs you have and also what suspension you have. You DONT want it to be 0 at cruise or you will wear out your U-joints as there will be no roller action to distribute the load against the bearing race, sounds wrong but that is what has been written. driveshaft angles have little to do with it unless they are nearing their max deflection rates as in a 4X4...EZ?
 
pishta
So is the 5 degrees true for SS springs as well? I'm going to start over on my angles. Bad vibes from 5K up in high gear only. So if I have 1 degree down on the 904 output shaft and 3 degrees up on the pinion what should my shims be. This is not u-joint angle measurement. I measured on the pinion yoke. Do I need 6 degrees down on the pinion? What about the pinion snubber
Thanks,
 
blewbyoutobad said:
pishta
So is the 5 degrees true for SS springs as well? I'm going to start over on my angles. Bad vibes from 5K up in high gear only. So if I have 1 degree down on the 904 output shaft and 3 degrees up on the pinion what should my shims be. This is not u-joint angle measurement. I measured on the pinion yoke. Do I need 6 degrees down on the pinion? What about the pinion snubber
Thanks,
Click to expand...

Right now you have a 2* up angle which is BAD!

If the output shaft is 1* down, the pinion needs to be 1* UP to be a 0 angle.

If you want a 5* down pinion angle, you'd roll the pinion down so it's at 4* below level.

I've had a SS spring car need 9* down... 5* is not a bad place to start. You likely wont find a 7* shim to correct the current angle issue. The locator pin won't engage the perches, too short.
 
I know this is an old thread but still useful. I am confused here

Drive Shaft Harmonics

If you read through this it says the transmission should be a degree or 2 down (compared to the ground with the assumption the car is on a level surface). Then measure the rear axel and it should be up a degree or two.. I thought this alignment should be only when the car is under acceleration, so in reality it should be pointing down a couple degrees so when it winds up it is a couple degrees up.
 
Don't believe everything you read on the internet. Make the transmission output shaft and pinion parallel, then roll the pinon down 2-4 (or whatever you want) degrees and weld the perches. Boom - done.
 
mopowers said:
Don't believe everything you read on the internet. Make the transmission output shaft and pinion parallel, then roll the pinon down 2-4 (or whatever you want) degrees and weld the perches. Boom - done.
Click to expand...

Ok so I am not crazy.
 
Not crazy. Your trans/engine/crank has its own angle when the weight of the car is on wheels (could be 2* down ((in all probability it has a downward angle)) but it could be 3-4*). Imagine the snout of the pinion coming up under acceleration. In that event, you want your pinion and trans/engine/crank to be parallel. So, if trans/engine/crank are 2*down at rest, I believe you would set your pinion at around 6* down as it will raise the snout up under acceleration 4*(ish) and as a result be parallel with engine/crank/trans.......ya?......no?.....fer sure! I have heard that in a stick car the "hit" is more extreme so if the car sees a bunch of track time, realize that traction will affect the rise of the snout more dramatically, and as a result the pinion snout would be set down a degree or two more. I apologize in advance if I have this all azz-backwards, but I think I have a grip on it (pun intended)
 
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