So what about the T5 "looking" transmission you find out of the vehicle at the salvage yard and it doesn't have a tag or bar-code decal? If you determine that it IS a T5, how are you going to determine WHICH T5 it really is; a .86 OD with the 4.03 1st gear or the .72 OD with the 3.76 1st gear. And maybe it's a Camaro box without a tag or bar-code sticker. It makes a BIG difference if you're trying to lock-in on the differential R&P ratio. The .72 works great with a 3.42-3.90 R&P while the .86 is more applicable with the 2.70's and 3.08's. And I wouldn't count on the yard folks to know!!!
In reality, it's pretty easy if you use the following steps:
1. Put the transmission into 5th gear.
2. Make a crayon mark at the 12 O'clock position on both the front splined (input) shaft and the rear splined (output) shaft.
3. Rotate the OUTPUT shaft 360 degrees and check the INPUT shaft mark to see what part of 360 degrees it rotated.
4. If the INPUT shaft rotated MORE than 270 degrees (3/4 rotation or past the 9:00 position) you've got a .86 box. If it rotates slightly LESS than 270 degrees (about 8:00) it's going to be a .72 box. If it's a Camaro box it'll likely be less than the 8:00 position but more than the 6:00 position or a .63 box. If it WERE (hypothetically)6:00 it would have a .50 ratio.
I've used this little procedure a number of times and have identified several boxes that were offered as .72 (preferred ratio) if you want to use the 3rd generation Camaro 3.42 diff, that turned out to be the .86 OD with the 4.03 (short) 1st gear.
Regardless of which T5 you're hunting this little trick will eliminate the guesswork. Hope this helps.
Dave
