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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: 3,365

    choptop40
    Member

  3. so this meens that the rear diff hast to be 2 deg up
     
  4. Ford blue blood
    Joined: Jan 4, 2009
    Posts: 579

    Ford blue blood
    Member

    Nope, down 2 degree........
     
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  5. ok I will move again put load on wheels and try again
     
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  6. 51504bat
    Joined: May 22, 2010
    Posts: 1,162

    51504bat
    ALLIANCE MEMBER

    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.
     
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  7. Ks Muleskinner
    Joined: Nov 15, 2014
    Posts: 12

    Ks Muleskinner

    Diff 2 deg UP
     
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  8. jaw22w
    Joined: Mar 2, 2013
    Posts: 817

    jaw22w
    Member
    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.
     
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  9. What he said
     
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  10. Mr48chev
    Joined: Dec 28, 2007
    Posts: 25,429

    Mr48chev
    ALLIANCE MEMBER

    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.

    _____________________________engine/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.
     
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  11. RmK57
    Joined: Dec 31, 2008
    Posts: 985

    RmK57
    Member

    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.
     
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  12. Mr48chev
    Joined: Dec 28, 2007
    Posts: 25,429

    Mr48chev
    ALLIANCE MEMBER

    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: 1,370

    The Shift Wizard
    ALLIANCE MEMBER

    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.
     
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  14. 1946caddy
    Joined: Dec 18, 2013
    Posts: 1,479

    1946caddy
    Member
    from washington

  15. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,144

    gimpyshotrods
    Member

    Are we really doing this again?

    This is the single most covered topic on this board.
     
  16. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 279

    ekimneirbo
    Member
    from Brooks Ky

    [​IMG]


    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.
     
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  17. pitman
    Joined: May 14, 2006
    Posts: 4,658

    pitman
    Member
    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
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  18. Sure if measuring from the back side.
     
  19. The Shift Wizard
    Joined: Jan 10, 2017
    Posts: 1,370

    The Shift Wizard
    ALLIANCE MEMBER

    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: 1,657

    2OLD2FAST
    Member
    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: 33

    ferus88

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  22. bewdley96
    Joined: Jan 17, 2011
    Posts: 26

    bewdley96
    Member
    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: 928

    seabeecmc
    ALLIANCE MEMBER

    You're correct paying attention in school should have paid off. Ron
     
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  24. Parallel.

    And engines don’t have pinions
     
  25. rooman
    Joined: Sep 20, 2006
    Posts: 3,689

    rooman
    Member

    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.

    Roo
     
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  26. OLDSMAN
    Joined: Jul 20, 2006
    Posts: 1,821

    OLDSMAN
    Member

    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: 4,065

    Russco
    Member
    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.
     
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  28. banjeaux bob
    Joined: Aug 31, 2008
    Posts: 5,761

    banjeaux bob
    Member
    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:;)
     

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