3.94 diff help needed fast

SGT BRAD · Post by **SGT BRAD** » Mon Mar 05, 2007 11:51 pm

does anyone know if there is a problem running a 3.94 diff in a std 2gn trans? i have seen the chart that lists the gear ratios as all being the same, and only the diff seems to be different b/w the r/t (3.94) trans and the std neon (3.55) trans. i was thinking of buying a 3.94 diff to install my lsd into prior to my engine swap. help please.
brad

OB · Post by OB » Tue Mar 06, 2007 12:32 am

I was just about to post this same thread. I assume the diff is the only diff (haha) between the two trannies. From what ive heard the gears and everything else are exactly the same. anyone know more about this?

ACR MAN · Post by **ACR MAN** » Wed Mar 07, 2007 12:44 am

The 3.94 final drive ring gear requires a matching pinion gear. On the T350 manual transmission, the pinion gear is built into the output shaft. That means you have to change the output shaft and differential ring gear to get the 3.94 final drive ratio. What's more, there were two different 5th gear ratios on 2001-05 non-Magnum 2.0L neons:

2001-02: 0.81:1 fifth gear

2003-05: 0.72:1 fifth gear

If you happen to have the correct 5th gear in your existing transmission, you won't have to do anything with the input shaft. If your existing 5th gear ratio does not match your new 3.94 FD pinion equipped output shaft, you can swap the 5th gear on the input shaft for the correct matching one. How much do these parts cost? The Mopar list price for the output shaft assembly is over $1000. It is possible to swap the 5th gear cluster on the ouput shaft, but that requires a strong hydraulic press to disassemble and some heat to re-assemble.

Conclusion: Just buy a good used 2001-04 Magnum 3.94 FD / .81 fifth gear transmission assembly, a 2001 PT Cruiser 3.94 FD / .81 fifth gear trans assembly or a 2002-07 PT Cruiser non-turbo 3.94 FD / .72 fifth gear trans assembly.

BTW: The 2000 model year neons had two different T350 transmissions, depending on build date. The early cars had the T350 with the same ratios as the 1995-99 SOHC non-ACR neons. The later 2000 neons had the T350HD (but still with cable-operated clutch) that had different ratios in several gears -- including 2nd 4th and 5th. This is detailed in my transaxle cross-reference chart which is linked in my sig.

SGT BRAD · Post by **SGT BRAD** » Wed Mar 07, 2007 10:19 am

ok so the output shaft would have to be changed to make the 3.94 work with 3.55 tranny. i have an 02 sxt and the gear ratios are listed as the same for the mag and non-mag trannies for 2002. only the diff ratio was changed to 3.94 from 3.55. if i'm correct in reading that the output shaft will have to be changed then this diff is a no-go. i was simply hoping to gain a little lower ratio as well as have the diff ready to go in once i do the motor swap. looks like i'll just stick with the stock diff and install the lsd. thanks.