Register now to get rid of these ads!

Technical pinion angle ?

Discussion in 'Traditional Hot Rods' started by johnrfray, Aug 10, 2019.

  1. almost got this 48 truck ready to roll, thanks for all help. Now to set pinion angle this is what I have tranny down 2 deg shaft at 5 down and diff at 15 up ,, I guess I want to end up with 1 deg
    31Vicky with a hemi likes this.
  2. choptop40
    Joined: Dec 23, 2009
    Posts: 3,521


  3. so this meens that the rear diff hast to be 2 deg up
  4. Ford blue blood
    Joined: Jan 4, 2009
    Posts: 600

    Ford blue blood

    Nope, down 2 degree........
    rockable likes this.
    Register now to get rid of these ads!

  5. ok I will move again put load on wheels and try again
    chryslerfan55 likes this.
  6. 51504bat
    Joined: May 22, 2010
    Posts: 1,326


    Thanks for the diagram, Choptop. Getting ready to install a 302 and AOD with a ranger rear end in my 54 Ranch Wagon and this makes things pretty straight forward.
    chryslerfan55 likes this.
  7. Ks Muleskinner
    Joined: Nov 15, 2014
    Posts: 15

    Ks Muleskinner

    Diff 2 deg UP
    Blues4U and X-cpe like this.
  8. jaw22w
    Joined: Mar 2, 2013
    Posts: 929

    from Indiana

    You really must be very careful with terminology when discussing trans and pinion angles. I know the old trans down 3*, pinion up 3* deal has been around forever, but it is really misleading for someone not familiar with what's going on here. A lot of confusion is caused by this. I think this might very well be the leading question on the HAMB.
    Let's define negative slope as sloping down from front to rear. Positive slope as up from front to rear. Now that old saying becomes "trans down 3*, pinion down 3*", which more clearly explains the desirable, parallel condition. Then the math works to come up with your u joint working angles. It's too bad that old saying ever got started that way.
    EDIT: By the way, that 3* ain't chiseled in stone either.
    chryslerfan55, Montana1 and TagMan like this.
  9. What he said
    jimgoetz likes this.
  10. Mr48chev
    Joined: Dec 28, 2007
    Posts: 26,103


    No it forget up down. That nonsense always throws guys off and screws things up.
    As the diagram that choptop40 showed shows the pinion will be on the same parallel plane as the crankshaft and output shaft of the engine an trans.


    Pinion angle _______________________________ The driveshaft will angle down slightly from the trans in most cases and slightly up from the pinion in most cases causing the pinion to appear to be angled down. Both U joint angles should end up being the same.
    chryslerfan55, Mark Yac and jaw22w like this.
  11. RmK57
    Joined: Dec 31, 2008
    Posts: 1,222


    In a perfect world you may get the ideal angle on both ends but in the end engine placement,rear axle height, trans tunnel is going to dictate where it's going to end up.
    With a mild engine combo I found it's not as critical.
    chryslerfan55 likes this.
  12. Mr48chev
    Joined: Dec 28, 2007
    Posts: 26,103


    If you have a trans tunnel issue you are probably going to have to go to a driveshaft with double cardan joints to compensate. Or modify the tunnel. Either is getting off topic for his question though.
  13. The Shift Wizard
    Joined: Jan 10, 2017
    Posts: 1,668

    The Shift Wizard

    It helps to remember that U-joints are not constant velocity joints. As a U-joint turns a full rotation, it's trying to speed up halfway and then slow down the other half. It's a definite pulse.
    The driveline joints need to be asymmetric so that the speed up and slow down "half turns" of the front and back U-joints are happening together, not fighting against each other........\-------\
    You don't want them symmetric, mirror images.......... \-------/ ...or... /--------\
    This rule applies to left-right horizontal angles as well as up and down (vertical) angles. Once it all clicks in your mind it'll be crystal clear, like learning to tie your shoes, it'll be automatic to you.
    Montana1, Black_Sheep and X-cpe like this.
  14. 1946caddy
    Joined: Dec 18, 2013
    Posts: 1,510

    from washington

  15. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,509


    Are we really doing this again?

    This is the single most covered topic on this board.
  16. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 680

    from Brooks Ky


    Think of it this way: If the car were perfectly level AND the transmission were perfectly level, AND the rear pinion of the rear end were perfectly level (as in the lower diagram) everything would be correct The reason it would be correct is because the pinion is mounted lower than the transmission . That means they operating in parallel planes at different heights from the ground. This allows the U joints to work as they rotate.
    In the normal scheme of things most engines are not parallel to the ground (level) but actually are lower at the rear. Most commonly accepted angle is appx 3 degrees downward. In order to get the Pinion to stay in a "parallel plane", it must be rotated upward 3 degrees.......The result of that move "must not" result in something like the upper diagram. The pinion still needs to be lower than the transmission.
    At this point you have what would be considered as the "best operating condition" when driving.

    Things are not as they seem though, because the torque of your engine will cause your springs to slightly wrap upward and increase the pinion angle beyond the desired 3 degrees. So you may end up with a pinion angle of 5,6,7 degrees. To combat that, you actually want to set the pinion only at maybe 1 degree when stationary with vehicle weight on springs. Then as you drive the springs will wrap and you get the actual 3 degrees you desire.

    Thanks to Choptop40 for the diagram.
    stillrunners and Droopydogg like this.
  17. pitman
    Joined: May 14, 2006
    Posts: 4,746

    from Hampsha

    I choose to run 3° at each shaft end, so that the ujoint brns will rotate & distribute grease. It spreads the fatigue and wear out.
    Have seen brinnelled ujoint surfaces, unsure if high HP, lack of angle, or run dry were to blame.
    Last edited: Aug 16, 2019
    stillrunners and Randall like this.
  18. Sure if measuring from the back side.
  19. The Shift Wizard
    Joined: Jan 10, 2017
    Posts: 1,668

    The Shift Wizard

    No argument about the 3 degrees being a good target. But the greasing seems to happen fairly constantly with the suspension in motion on the road. Even the front U-joint, which is more solidly mounted than the rear, tends to see a little bit of angle change.
    (My apologies for the O/T truck vid.)
  20. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 1,886

    from illinois

    The fact that many on here can't compose a credible sentence, have the vocabulary of a second grader and the reading comprehension skills of a large primate , not to mention basically zero math skills, doesn't add to their ability to describe or understand much of anything even remotely technical ...Yeaa , this is where paying attention in school could have payed off .....
  21. ferus88
    Joined: Apr 16, 2017
    Posts: 42


    jimgoetz likes this.
  22. bewdley96
    Joined: Jan 17, 2011
    Posts: 26

    from UK

    well that's clear as mud lol ,so if your engine pinion is higher than the rear axle and facing down 3deg ,what angle should the axle pinion be at .
  23. seabeecmc
    Joined: Jan 28, 2005
    Posts: 943


    You're correct paying attention in school should have paid off. Ron
    smurftastic and Atwater Mike like this.
  24. Parallel.

    And engines don’t have pinions
  25. rooman
    Joined: Sep 20, 2006
    Posts: 3,803


    The torque of the engine really only comes in to play when the car is launching off the line and for a street car the amount of spring wind up is negligible. And that deal only applies to parallel leaf spring cars not those with ladder bars or any sort of four link. The aim is to have the angles correct with the car as it is driving down the road as that is hopefully the most constant condition. Everything else is transitional for short periods of time. Any sort of suspension displacement (bumps, hard launches, heavy braking) will change the pinion angle with most common forms of rear end location with an equal length parallel four bar providing the least variation.
    And the pinion does not need to be lower than the transmission as the driveshaft does not care whether it is running up hill or down from the transmission output as long as the angles are correct.

    ferus88, RMR&C, X-cpe and 2 others like this.
    Joined: Jul 20, 2006
    Posts: 2,073


    This forum is supposed to help those who have questions. This is a very serious question, it’s not very easy for a lot of people to comprehend it’s principles. Don’t beat those that don’t understand so badly
  27. Russco
    Joined: Nov 27, 2005
    Posts: 4,074

    from Central IL

    I posted that video a couple years ago and that really surprised some people. That pinion is probably moving 5* or more.
    Montana1 and The Shift Wizard like this.
  28. banjeaux bob
    Joined: Aug 31, 2008
    Posts: 5,802

    banjeaux bob
    from alaska

  29. When guys take their spring pack apart and remove leaves, then de arch what’s left, then add in an axle flip with lowering blocks ,,,

    The springs wrap up like wet noodle under mild acceleration.
  30. ^^^^^ You mean the axle doesn't sit static! :rolleyes:;)

Share This Page

Register now to get rid of these ads!


Copyright © 1995-2020 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.