So I have a spec v tranny with the 4.133 final drive which I think will make my gearing too short for 1st and 6th gear. I've got the transmission apart and it appears that the pinion gear is machined onto the main shaft. Am I correct on that? Courtesy Nissan's parts fiche shows no part number for it.

So if I wanted to go with the 3.812 ratio, I'd have to buy a whole new main shaft and a ring gear?

It also appears that there is no inner race for the main shaft bearing. That the shaft just sits inside directly on the cylinder rollers in the bellhousing side. WTF? I guess this means that if your main shaft bearings go bad, you have to replace the main shaft along with the bearings. Epic FAIL. I guess this means I really need to get the shimming right. OTOH, it appears to be a really stout bearing.

 

Ok, so I was looking through the FSM some more and looks like I was right. D@mmit! That means I'd have to spend $177 for a new main shaft and another $128 for the ring gear which is currently on backorder at courtesy nissan.

I'm also annoyed with the .670 6th gear that the sentra comes with. With .670 6th gear and a 4.133 FD, I'll be at the same RPM in 6th gear as I am in 5th gear now on my 5 speed.

If you want to build the ideal 6 speed tranny, you basically need the HLSD unit from a sentra, a 3.182 ring and pinion gear, an altima/maxima 6th gear, and the synchros from the 07+ Altima.

Even then, I think the .630 6th gear and 3.812 FD is still too short for a hwy econo gear. The 1st gear is also too short for a 4.5 gen Maxima with the 3.812 FD. There's no reason that the VQ couldn't loaf along at 1500rpm @70 mph in our small and lightweight 4th gens.

OTOH, if I extended the red line to 7200 rpm with the 4.133 FD, it would probably be unstoppable as far as performance goes.

 

There's a reason why Nissan went to the 4.1, stick with it.

Look at dynos and powerbands of the motor, the 4.1 makes much better use of it.

But as for the matter at hand... You are correct, you need the main shaft pressed on, pulled off w/ the matching FD.

I want to do this but for the 4.3 FD.... Awww baby....

 

The 6th gen has larger wheels/tires and about 500lb on me too. A broad powerband with a nice flat torque curve doesn't need gearing as aggressive and short as one that is peaky.

 

Only a LS# motor has a broad powerband.

Our 3.5 is small compared to the broad spectrum of motors our there (not honda small, but not LS# broad either).

4.1 is just better overall with only a 100rpm(ish) change higher in 6th gear.

It may only be a handful of MPH, but I think it's crucial on the track.