Baja

Besides gear ratios, what are the differences between a 944 NA 7V LSD transmission and a 951 LSD Transmission?

People doing the LS1 engine swap recommend using the 951 trans but swapping the NA 5th gear, is there a strength difference is the case or gear sets between the two?

admiralkhole

The R&P are stronger (bigger teeth) in the turbo trans. I don't know if the gears in the turbo trans are any stronger, but people run the NA long 5th gear set with good results. I've never heard of one failing.

The turbo s (AOR) box has hardened 1st, 2nd, and input shaft. I think the S2 trans does as well but I'm not 100% sure, someone will correct me if I'm wrong.

Going ls1? I might have a cheap(ish) lsd turbo trans coming up for sale soon.

Baja

I did just pickup another '87 with a blown motor that will be getting an LS1 transplant. Can you PM me the details on your LSD trans you may be selling?

Dimi 944

2nd on that and the S2 AOT LSD transmission also comes with hardened input shaft. I am not sure about the 1st and 2nd gears.

drive135mph

Does anyone know if the LSD unit itself differs between the two trans-axle?

for example if I buy an open 951 trans-axle can i drop in the LSD unit from my LSD 944 trans-axle?

lart951

Yes,

bordin34

To which question?

lart951

You can drop a 944na LSD on a turbo transmission if Iam not mistaken the LSD is the same

drive135mph

Well that makes life easy!

Dougs951S

You can swap them in the sense that it will fit, but an na lsd wont hold up to v8 torque. If you want that gearbox to live, you need a 951 differential. The strength difference isnt minor, the NA diffs are made of glass compared to the turbo diffs which are actually impressively strong if you dont launch or shift hard on them.

odonnell

Even if they were the same, installing it would require lots of labor and precise measurement/trial and error. I remember reading up on the process when I was considering rebuilding my NA trans.

Dimi 944

Hm....I actually disagree based on experience. I have had a LSD units out of NA, 951 and S2 gearboxes and they are identical internally and externally.
I have had two track 951 transmissions converted to LSD with differentials from NA transmissions with no failures.

The important thing is to have the hardened ring, pinion and input shaft, and tranny fluid cooling in place from the in order to have the transmission survive the high torque from the V8.

murrayg

Not really that bad a job at all. All that has to be set when replacing the differential is bearing preload and backlash. This assumes you reuse the original ring gear. The difficult one is pinion depth to set contact patch, but this doesn't need to be done for just a diff change.

KevinGross

The 944S/2/Turbo transmission has a number of differences from the 944 eight-valve, normally aspirated gearbox.
- thicker gears
- later versions have hardened 1st and 2nd gears as cast into the input shaft
- different lubrication paths to fifth gear
- larger pinion gears, most importantly wider roots to the pinion teeth (yes, ratios different too)
- availability of the oil pump and cooler
- different rear needle bearing for input shaft in the diff carrier
- redesigned 3rd/4th floating gears and operating assembly that made it impossible to push the op assy too far onto the floating gear dog teeth (and dislodge the op assy detents)
- minor differences to reverse gear synchronizer
- larger pinion shaft and input shaft bearings

The limited slip differential is dimensionally identical across all versions, but has a number of differences over the years. Most significant was the shift from welding the ring gear mounting flange to the LSD, to a single piece design. I have seen a lot of the early design LSDs crack and fail at the weld, there was a problem with the design. Other changes:
- different steel used for the LSD case, later use what Porsche calls type GGG steel
- AOR versions got 2.5 mm clutch disks and shorter pressure rings, versus 2.0 mm previously
- AOR versions also got moly coating on spider gear cross shafts to address wear problems

There are so many different versions of the open differential used over the years, design changes, that it's impossible to sort them. They do include different spider gear ratios (number of teeth).

I won't address here the differences in the very early MY 82/83 gearboxes since so few of them are out there (other than to say I have the rare parts needed to service them!), and the 83-84 gearboxes with no speedo pickup and diff cover o-ring. There are probably other things I am forgetting...

Kevin
Catellus Engineering

admiralkhole

Thanks Kevin for laying some knowledge on us, time and time again. It is appreciated!