Is it possibly to mix gears between for instance the Na transmission and the S2?
For my applicaton the best ratios would be to use the final drive from an S2 and 1,2,3 gear and 4,5 gear from the row NA transmission.

 

Yes. Reach out to Kevin Gross.

 

With one exception, the gears cannot be swapped between the eight-valve normally aspirated cars' transmissions and the S, S2, and Turbo transmissions. They are dimensionally different: the later models have thicker gears, and the pinion shaft, shift forks, and case are in fact slightly different in length to accommodate.

The exception is fifth gear, which is shares dimensions but flows oil to its needle bearing through a different path. A little machine shop work can change this. I can provide details if helpful.

Van, thanks for the referral.

Kevin
Catellus Engineering

 

You could always run 944S gears, IIRC 1-4 are closer to the NA box than the s2 ratios. 5th is the same as the NA.

 

Thanks for the info! How about the ring and pinion? Can you take that from an S2 and put it into the 8v Na transmission? Is the differential the same in all the transmissions?

I know about the S transmission, i think it has the same gears as the turbo box but the final drive is same as on the 8v na?


The plan is to rebuild an 8v na transmission and put an arftermarket lsd in it. And i would gladly change the final drive from an S2 if that´s possible to avoid failure.

 

You really want to stick with the s/s2/turbo box as its stronger if you have anything besides an 8v in your car. The NA is a lot weaker and will be pretty likely to fail on you in that situation.

 

Yes details would be helpful and appreciated.

 

No, they cannot be swapped. Again it comes down to dimensions. The 944 S/2/Turbo pinion, among other things, is longer than the 944 eight-valve aspiro.

The differentials are the same in terms of dimensions, and you can swap them between the different gearboxes. There are many versions of the open differential that appeared over the years, and the later ones are stronger due to more and better material used for the case of the differential. They weigh more too, which is a slight negative.

The limited slip differentials can also be swapped. There were basically three versions. The earliest had the ring gear flange welded to the case and this weld broke frequently. This was replaced by a single-piece differential case, no weld, in GGG steel, apparently a stronger material. Finally, the version used in the 944 Turbo S shifted to 2.50 mm clutch disks (better heat sinks) vs the 2.00 mm disks, and had moly coating to the cross shafts where the large spider gears rode, to reduce wear.

The way to work against failure is to do two things. First, keep the fluid fresh. Dirt is a poor lubricant and a poor conductor of heat. The hypoid ring / pinion design puts a lot of stress on the gear teeth, a lot of heat generated. Second, get the gearbox serviced by someone who takes the time to properly measure pinion depth, bearing preload, and has all the shims and sized circlips to do the job right. You cannot slap the old shims and circlips back into a rebuild, it doesn't work.

I have many, many clients racing 944 eight valve normally aspiros hard in PCA, SCCA, NASA, etc. and none of them has ever come back to me with a broken pinion. Some of them are running the 4.11 ratio or shorter with narrow pinion tooth roots, which is the critical dimension in terms of strength. It's all about set up and maintenance.

Kevin
Catellus Engineering

 

I have an -83 8v car so i cant really change the whole transmission becouse of the mounts. And if you cant mix the ratios i think the 8v NA trans has the best ratios for my application.

 

Thanks for the info, i appreciate you taking some time answering

Unfortunately i dont live on the same continent as you so i have to find some other expert to do the job.

Then i think it would last for me too, i dont drive the car that much but mostly hard track use. In the future im planning to upgrade to an mildly tuned 2,7l engine with some more hp/tq