Here's the deal.

I need a T5 transmission for my project car. However, I want one with a .63 5th gear and not the .74 or .83 gearing because I am using a 4.11 rear diff.

Is there anyway to know definitely what the 5th gear is without tearing the transmission apart?

Maybe shift it into 5th and turn the input shaft 1 full turn while measuring the output shaft and see how much it turns?

Shouldn't it turn between 1/2 and 3/4 turn if it is .63 gearing and pretty much exactly 3/4 turn if it is .74 gearing?

That would be correct; for the grocery-cart 5th, 1 turn of the clutch gear = about 5/8 turn of the mainshaft.

You might think you want that gear now since you don't have it, but you don't. Believe it. I screwed up once and put one in my T-5 by accident (came from a core I was scabbing something else out of, and I got the 5ths mixed up). I hated it so bad I actually pulled the transmission and put the right one (.73) back in it the first chance I got. Now granted, my car just has the stock gears in it, which are only 3.73; so maybe the RCH more gear that you have would make a difference. But I highly doubt it. The problem wasn't so much the gear itself, as the STEP between 4th and 5th. It felt like the engine went from "screeeeem" to "lugggg" when I shifted to 5th. Always felt like it needed one in between.

I've never heard of a .83 5th for these cars.

I will be running this trans in my Mazda RX7 w/ 4.11 gearing coupled to a TPI 350.

With a .63 5th gear, I will be running about 2200 rpm at 70 mph.

With a .74 5th gear, I will be up around 2600-2700 rpm at 70 mph.

I think the .83 is available aftermarket in rebuilds.

The .63 geared 5th came in cars with 3.08 rear ends, for reference. Why they put the lower 5th gear with the lower ratio rear end, I'll never know.

i have a g-force t-5 with the .59 5th gear option.. it sucks.. i could run a 4.56 with it if i wanted.. going from 1:1 in 4th to .59:1 in 5th is like shifting 1st to third.. like sofakingdom said, it will be screaming in 4th thug chugging in 5th.. you would be better off getting a t-56.. if you do the gear swap, i bet you will want the factory 5th after a couple months..

I've never heard of a .83 5th for these cars.[/QUOTE]

It's actually .80, and is rumored to have come in some of the 5 speed equipped 1LE cars. TKO performance said he's come across a few of them over the years. They're definitely available from the aftermarket too. Astro Performance and 5 speeds.com both sell the aftermarket .80 fifth gear set for a whopping $200! It's referred to as the Sebring overdrive kit. Apparently it's quite popular with the road racing crowd.

I have a T-5 out of a known 91 1LE car. It has the .73. I can't say that "some" didn't come with some other gear; but knowing mass production techniques as I do, I highly doubt it. Gears are EXPENSIVE to produce, especially in short runs, and I can't feature GM randomly adding extra cost to "some" of an already very limited production run that was already unprofitable, in a way that would not have noticeably increased sales. Which is of course not the same as saying that it didn't happen... only that it's incredibly unlikely.

"A few" aftermarket racing parts that may have found their way into cores are a different matter altogether.

They used that stupid .63 gear ratio in the slow cars to squeeze every last inch per gallon of fuel economy out of those cars that they could. Everything else about them was sacrificed in favor of CAFE. Remember, anybody buying a TBI car, had already established that they were looking for image and not performance; so those people were more likely to accept that kind of compromise.

[QUOTE=sofakingdom;3273900]I have a T-5 out of a known 91 1LE car. It has the .73. I can't say that "some" didn't come with some other gear; but knowing mass production techniques as I do, I highly doubt it. Gears are EXPENSIVE to produce, especially in short runs, and I can't feature GM randomly adding extra cost to "some" of an already very limited production run that was already unprofitable, in a way that would not have noticeably increased sales. Which is of course not the same as saying that it didn't happen... only that it's incredibly unlikely.

Oh believe me Sofa, I won't argue that point at all. I'm highly skeptical on this too. Out of the big three American car builders, GM is the king of interchangeability, and using the same parts on more vehicles to cut production costs. That's why it always cracks me up when someone has an old 60's or 70's SBC, and they say it's a "Vette" motor, like it's something special, and should be set apart from all other SBC's. Alot of times, the only thing that changes when you request a part for a Camaro or Corvette is the price of the part. If you requested the same part for a Caprice or Nova, you end up getting the same part for a cheaper price.