IRS/Diff/halfshaft angle
 

I thought I posted something similar on here a few days ago but?

Anyway I need a little advice so I can move forward with my chassis.

Using an Infinity Q45 diff and axles with 350Z suspension...does not matter at this point but also 350Z engine and 6 speed.

Setting ride height at 3.5" at bottom of chassis so we will be riding low. My quandry is setting up the diff height. My understanding is that I need to firstly maintain proper driveshaft angles and in order to do that I will have to drop the diff. I currently have it set in a fixture that maintains 3 degrees angle in the halfshafts UP to the diff which is about what OEM is. This setup has the driveshaft running uphill a good bit which I think is bad! Plus I think it is going to put the OEM mounting locations of the upper control arm perilously close to the halfshaft.
So if I drop the diff to get the driveshaft angles correct it has the halfshafts running downhill to the diff...I am guessing 4 degrees.
MAIN QUESTION IS....ARE THE HALFSHAFTS GOING TO BE HAPPY RUNNING DOWNHILL? I am assuming they don't care as long as I don't get them bound up in bump and rebound?

From what I understand, when the car is at rest and at ride height you want the halfshafts level or pointing slightly up towards the diff.

Andrew

Well, that is what I also thought and I started that way and got the diff in a fixture based on the halfshaft angle and pretty much OEM 350Z. Then realized the engine will sit a lot lower and the driveshaft will run uphill to the diff and I guess that is not good...
I can't have it both ways and something is gonna have to run at a different angle...just not sure where to compromise?

Halfshafts at correct OEM angle equals driveshaft running uphill to diff
Driveshaft at correct OEM angle equals halfshafts running downhill to diff

This can't be so difficult as it would be the same proplems racecars would run into with drastically lowered ride heights....It about has to be the halfshafts running downhill to the diff and focus on maintaining proper driveshaft angle...I THINK????

What kind of car are you working on? Can you raise the back of the transmission so that it points at the diff? That will fix your driveline angle problem.

Andrew

At this point I can do just about anything as I just started on the chassis. Tube chassis 240z with 350z engine and 6 speed.
I read that all mfg pretty much drop the rear of the engine about 3 degrees to get the angles or something....if it is not a problem raising the back a little then that would work.

Did a little this morning and with the diff in its OEM position and halfshafts in proper angle...hub in a fixture...I have the following rough measurements.

Crankshaft centerline 11-1/4" (engine at level...if I drop the rear 3* then the trans tail shaft will be approx 2" lower.
Diff pinion centerline 12"

not sure this is enough info as I do not have the tranny yet but do have the dimensions so I can come really close to figuring out the angles and then the driveshaft length and Working angles.

The crankshaft centerline is about the only thing I can't really change...everything else is in play at this time. Lower diff, angle engine...I am just struggling on what to work from.

I kinda think I should lower the diff if it is OK for the halfshafts to run a little downhill to the diff...I think I could get my working angles OK on the driveshaft if I lower the diff. Really this is not much different than the guys that race 350z's...they are all lowered a good amount and they have to have the same issue with the halfshafts running downhill to the diff???????

I will be glad to get this all sorted out...arrrgghh