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- Bob
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Well damn, Now I gotta google plebeian.
- Thread starter
- #229
adding this to thread.
A diff drop doesnāt really maintain oem geometry. It only helps improve CV half shaft angles at full shock extended length. I would keep the extended shock length under 24.3ā and run the ufdu. Better solution for 37-38s if you are pushing things and has a much improved intermediate shaft.
I know I am in the minority here but not a diff drop fan. It is really just a band aid fix that is only minimally effective. Need to really drop diff (2+ inches in many cases) to get back to oem CV angles and then plunge becomes a real concern. Not worth the effort.
first figure shows CV angles as a function of shock displacement during a suspension cycle. Zero shock displacement is at full extension. Oem CV geometry is shown (angles snd plunge). Also shown is a typical aftermarket shock with the extended length of 24.3ā (4WP coilover but many fall into this range including fox and king). Also shown is the 4WP shock with a 1ā spacer increasing effective extended length to 25.3ā.
notice that CV angles significantly increase with increasing shock extended length. This is why the diff drop is considered since it can decrease those angles. Also notice the CV plunge remains fairly tight and less than +/- 3 mm. This is because of the OEM location for inner CV pivot point on half shafts. This point has been located along the line of action between LCA and UCA pivots. Thereby necessarily minimizing CV plunge.
adding a diff drop will move the inner CV pivot point downward and thus begin to effect CV plunge. The question is how much can a diff drop really help CV angles and how bad does plunge get?
second plot shows 24.3ā extended length shock with a 1ā diff drop. Also shows a 25.3ā EL shock with a 2ā diff drop. Notice CV plunge begins to increase as diff drop distance increases. CV limits for plunge are in the +/- 10 mm range. So a 1ā diff drop is still within limits but 2ā is not. Starting to get serious plunge >20 mm. Also notice that it really takes near 2ā of diff drop to get back to stock CV angles.
A diff drop doesnāt really maintain oem geometry. It only helps improve CV half shaft angles at full shock extended length. I would keep the extended shock length under 24.3ā and run the ufdu. Better solution for 37-38s if you are pushing things and has a much improved intermediate shaft.
I know I am in the minority here but not a diff drop fan. It is really just a band aid fix that is only minimally effective. Need to really drop diff (2+ inches in many cases) to get back to oem CV angles and then plunge becomes a real concern. Not worth the effort.
first figure shows CV angles as a function of shock displacement during a suspension cycle. Zero shock displacement is at full extension. Oem CV geometry is shown (angles snd plunge). Also shown is a typical aftermarket shock with the extended length of 24.3ā (4WP coilover but many fall into this range including fox and king). Also shown is the 4WP shock with a 1ā spacer increasing effective extended length to 25.3ā.
notice that CV angles significantly increase with increasing shock extended length. This is why the diff drop is considered since it can decrease those angles. Also notice the CV plunge remains fairly tight and less than +/- 3 mm. This is because of the OEM location for inner CV pivot point on half shafts. This point has been located along the line of action between LCA and UCA pivots. Thereby necessarily minimizing CV plunge.
adding a diff drop will move the inner CV pivot point downward and thus begin to effect CV plunge. The question is how much can a diff drop really help CV angles and how bad does plunge get?
second plot shows 24.3ā extended length shock with a 1ā diff drop. Also shows a 25.3ā EL shock with a 2ā diff drop. Notice CV plunge begins to increase as diff drop distance increases. CV limits for plunge are in the +/- 10 mm range. So a 1ā diff drop is still within limits but 2ā is not. Starting to get serious plunge >20 mm. Also notice that it really takes near 2ā of diff drop to get back to stock CV angles.
Youāre definitely on to something.adding this to thread.
A diff drop doesnāt really maintain oem geometry. It only helps improve CV half shaft angles at full shock extended length. I would keep the extended shock length under 24.3ā and run the ufdu. Better solution for 37-38s if you are pushing things and has a much improved intermediate shaft.
I know I am in the minority here but not a diff drop fan. It is really just a band aid fix that is only minimally effective. Need to really drop diff (2+ inches in many cases) to get back to oem CV angles and then plunge becomes a real concern. Not worth the effort.
first figure shows CV angles as a function of shock displacement during a suspension cycle. Zero shock displacement is at full extension. Oem CV geometry is shown (angles snd plunge). Also shown is a typical aftermarket shock with the extended length of 24.3ā (4WP coilover but many fall into this range including fox and king). Also shown is the 4WP shock with a 1ā spacer increasing effective extended length to 25.3ā.
notice that CV angles significantly increase with increasing shock extended length. This is why the diff drop is considered since it can decrease those angles. Also notice the CV plunge remains fairly tight and less than +/- 3 mm. This is because of the OEM location for inner CV pivot point on half shafts. This point has been located along the line of action between LCA and UCA pivots. Thereby necessarily minimizing CV plunge.
adding a diff drop will move the inner CV pivot point downward and thus begin to effect CV plunge. The question is how much can a diff drop really help CV angles and how bad does plunge get?
second plot shows 24.3ā extended length shock with a 1ā diff drop. Also shows a 25.3ā EL shock with a 2ā diff drop. Notice CV plunge begins to increase as diff drop distance increases. CV limits for plunge are in the +/- 10 mm range. So a 1ā diff drop is still within limits but 2ā is not. Starting to get serious plunge >20 mm. Also notice that it really takes near 2ā of diff drop to get back to stock CV angles.
The big thing that we ran into with the long travel build wasnāt CV angle, but the plunge. The bigger bells with the 32 spline axles helped a teensy bit with angle, but the real gain was the plunge. And even then Vasher locked out the bottom LCAās as it was so close with 17ā of travel that just moving the alignment cams could have caused issues.
- Thread starter
- #231
For reference this was first posted in the following thread. Added here to be thorough.
https://www.bronco6g.com/forum/thre...u-had-any-problems-with-your-cv-axles.136698/
For OEM style CVs, the axles are free to move (not restrained) along their axis (longitudinally). This allows for some misalignment along CV axis as the wheel moves up and down during suspension cycling.
For example, consider the imaginary distance from wheel hub center to the half shaft insertion into FDU. Call this āplungeā. If this distance decreases during a suspension cycle then there is positive plunge. If it increases then negative plunge. If the plunge were rigidly fixed or constrained, then CV would pull apart during negative plunge.
The oem CVs have a maximum allowable angle that is related to plunge. If they operate near zero plunge (+/- <10 mm) then they have the greatest allowable angle. As plunge increases, either pos or neg, their allowable angle decreases. They are fairly symmetric wrt pos or neg plunge. I have seen some actual design plots of the ford oem CV allowable angles vs plunge, 10 mm of plunge is a reasonable limit state and will get you close to 30 deg of angle.
https://www.bronco6g.com/forum/thre...u-had-any-problems-with-your-cv-axles.136698/
For OEM style CVs, the axles are free to move (not restrained) along their axis (longitudinally). This allows for some misalignment along CV axis as the wheel moves up and down during suspension cycling.
For example, consider the imaginary distance from wheel hub center to the half shaft insertion into FDU. Call this āplungeā. If this distance decreases during a suspension cycle then there is positive plunge. If it increases then negative plunge. If the plunge were rigidly fixed or constrained, then CV would pull apart during negative plunge.
The oem CVs have a maximum allowable angle that is related to plunge. If they operate near zero plunge (+/- <10 mm) then they have the greatest allowable angle. As plunge increases, either pos or neg, their allowable angle decreases. They are fairly symmetric wrt pos or neg plunge. I have seen some actual design plots of the ford oem CV allowable angles vs plunge, 10 mm of plunge is a reasonable limit state and will get you close to 30 deg of angle.
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