A diff drop doesn’t 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 24.3” and run the ufdu. Better solution for 37-38s if you are pushing things and has a much improved intermediate shaft.
A 1” diff drop is fine. Even 1.5” is probably ok. Just not a fan since there is diminishing returns with minimal gain. The other two posts are just a long winded way of saying that. I would go a different route.
No I agree with your posts. If I didn't already have one, I wouldn't look at putting one in necessarily. But if it's already there, dunno that I'd go ripping it out either.
Vasher does not screw around.pictures to help gain a visual perspective
He is very thorough. He’d never worked with the 32 spline axles or UFDU so I had to send him the axles and he tore them apart for angle and plunge measurements. He then had me take diligent notes on the FDU placement on the mullet bronco to get as accurate as possible on the center bars being the correct length. It was a process.
A small diff drop (1”) keeps plunge in check (<10 mm) and is no concern. It will reduce CV angles across the board, both at droop and ride height. This is real not koolaid.
My plots came out different.A diff drop doesn’t 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 24.3” 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 24.3” (4WP coilover but many fall into this range including fox and king). Also shown is the 4WP shock with a 1” spacer increasing effective extended length to 25.3”.
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 24.3” extended length shock with a 1” diff drop. Also shows a 25.3” EL shock with a 2” 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 1” diff drop is still within limits but 2” is not. Starting to get serious plunge >20 mm. Also notice that it really takes near 2” of diff drop to get back to stock CV angles.
My plots came out different.
