904 mainshaft

[no substitute]

I see Otto's wants $775 for a 904 mainshaft. Is that trip really necessary for a 3.2 or bigger upgrade, in the interest of the 901's survival (street only)? I bought the intermediate plate on sale years ago so I'm half way there I guess.

[M. Hendrix]

Your problem is going to be driving it cold, gearing, and no burnouts.

The 904 mainshaft doesn't help the transaxle handle the power, it allow taller gearing for 2nd.

The weakness is in the ring-and-pinion.

If you want a gearbox made for that engine, you should just have him build it.. it's going to cost more than your motor, but it won't explode if you drive it right.


M

[Zeke]

Otto's 904 mainshaft is a liitle beefier than the stock 'antique' one. I say antique because any real 904 shaft is gonna be pretty used. I haven't heard of any NOS out there.

The other problem I hear about is 1st gear. It's not in the main cluster, but rather back in the tail with reverse. The billet intemediate plate probably helps out in more ways than one. Helping out 1st gear has to be one of them.

Nevertheless, abuse the throttle in 1st and it will break. This has to do with the mechanical advantage of the ratio as much as anything.

[BURN-BROS]

Why not go with a 915 trans? It adds a little weight, but is engineered for the increased displacement/power.You would probably be out less money too.

[M. Hendrix]

...and be stuck with the worst shift pattern possible.


M

[no substitute]

This doesn't look new, but perhaps they're remanufactured.

[SteveStromberg]

Those are Brand new. They are machined for us by a shop that builds Aerospace stuff.Steve

[no substitute]

Excellent. Thanks to all for the answers.

[Jim Smolka]

The 915's were not that great, 911 with 3.2 had problems, that is why they went with the G50 gearbox in '87.

Currently, I track a 3.2 with a 901 gear box. Just have to be reasonable. No silly burnouts in 1st gear, no slamming gears etc.

However, one of the other weak points is the CVs. Ate one set of 914 CVs, installed a set of 911 CVs, so far, no problems.

IMHO, I would go with a good stock 901 gear box. Even if you destroy it, they are relatively cheap to replace.

[M. Hendrix]

Speaking of CVs, has anyone ever seen a u-joint setup on a Porsche?


M

[Jim Smolka]

I think some early 911's had U-Joints

[JWest]

Some early 911s had Nadella joints. These were u-joints, but had an extra joint to allow extension as the suspension moves.

They were not well loved, and it was common to replace them with CV joints.

[M. Hendrix]

I mean a modified set of honest asskicking u-joints.



There are some sturdy half-shaft designs out there.

M

[BURN-BROS]

the corvettes had troublefree halfshafts,perhaps modified/new flanges for the 914s. Would be a viable mod dont ya think?

[M. Hendrix]

I dunno..

http://www.pim.net/1.2pim.html

M

[JWest]

Originally posted by BURN-BROS
the corvettes had troublefree halfshafts,perhaps modified/new flanges for the 914s. Would be a viable mod dont ya think?

The Corvette uses the halfshaft as a locating member of the suspension and the axle remains the same length through it's travel.

If you did that on a 914, you would bind the suspension.

The options would be to change the design of the 914 suspension and use an axle with u-joints, use a splined slider in the center of the shaft, use Nadella joints, or use CV joints.

CV joints can be had in many sizes and the fairly easy upgrade to 108mm 911 joints over the 100mm 914 joints would probably satisfy most requirements.

[BURN-BROS]

You could incorporate the rubber pieces like the 935s. I forget the name. The outside cv joint does have clearance issues with trailing arms do they not? I am under the impression that we are limited in this area.What are the current remedies/upgrades for this?Does anybody have pics of Nadellas as well?

[JWest]

The 935 used a rubber "guibo".

One remedy is to upgrade to 108mm 911 CVs either using the 911 parts (when going to 5-lug this makes more sense) or using the spacer/adapters that Jim Smolka has. These will fit in the trailing arm.

I've got some pics of Nadellas at home, but here is a quote from Gunnar Racing:

"This car has the original nadella axles, which will be kept in a cabinet. The car will be raced with CV joints (way better, way stronger, way out!!!)."

[BURN-BROS]

Is the 108mm the limit in reguards to clearance within the trailing arm?

[JWest]

I don't know, I've never measured for anything larger.

What transmission do you plan to use? I think you will break a 915 before the larger CV joints.