[eatonde]

Can anyone tell me how I can find out what series my carrier is in my differential??
The car is an 82' Cutlass supreme, and I'm almost certain it has 3.08 gears in it now... Not positive, but pretty sure... It's not the V6 Grandma version.... It came factory with sunroof, spoiler, 2 door, 307 TH350.

I have a major mis match going on right now between my cam/stall/gears. The cam is 300/300 dur. : 246/246@.050" : .515/.515 lift..
Converter is a Dacco full competition PP3402 10" 3300-3500 stall
TH400 stage 2 shift kit
AND the problem child stock GM 7.5" rearend

Its getting pretty annoying riding around in 1st & 2nd gear just to keep the R's up high enough to stay off the converter. I want to go to atleast a 373, possibly a 410 gear to help this issue and make the car a LOT more fun to drive.... All the 410's I've seen say Must be used with a carrier that came with atleat a 323-342 stock.
Is there any particular way to tell this w/ out removing the differentail?? Who would sell the right ring and pinion for my car??

[fiscus]

Check your gear ratio by counting the teeth on the ring gear and divide by the number of teeth on the pinion.

There is a way to get a close approximation, put the trans in neutral and jack one wheel off the ground. Count how many times the driveshaft spins for one turn of the tire and divide by two. If you have a posi differential then you will probably not be able to turn one tire while the other is on the ground so you need to lift both rear wheels. In that case do not divide by two.

Richmond makes a 4.10 gear set that fits on the 2 series carrier.

[prostreet6t9]

308 and higher ratio's fit on one carrier.
323 and lower ratio's fit the other carrier.

[eatonde]

Thats kinda wierd, cuz 308 is lower then 323, and 323 is higher then 308... Hows a guy supposed to understand that??

[BUFFALOBILLPATRICK]

Yes, it does sound backwards.

The term "low rear-end" means it's good for "off the line" for low speed acceleration. My 4.56 is called a "low rear-end" the drive shaft turns 4.56 revolutions for each revolution of the rear axles & tires. This has the effect of multiplying the power of the motor by 4.56 This is not good for driving down the freeway as the engine is turning high RPMs, using lots of gas, & wearing out quicker. (that's why I have an overdrive that effectively reduces my 4.56 down to 3.56 in my 6th gear)

A "high rear-end" is good for highway driving (higher speed) & gas mileage & has a low numerical ratio.

BBP

[prostreet6t9]

308 & 276 ratio's fit one carrier
323/342/373/411/456 fit the other carrier

[joe_padavano]

Originally Posted by eatonde

Thats kinda wierd, cuz 308 is lower then 323, and 323 is higher then 308... Hows a guy supposed to understand that??

As noted, the terminology is somewhat backward. The terms "low" and "high" gears actually come from the transmission, where first gear is called low and has a large ratio (like 3:1 or 2.5:1) for torque multiplication off the line. The top gear in the trans (third or fourth) is called high gear and will have a smaller ratio (like 1:1) for top end speed. This same "low" and "high" nomenclature is also used when talking about rear axles. That's why in the earlier post 3.08 and smaller ratios are referred to as "high" and 3.23 and larger ratios are referred to as "low". Of course, just to confuse it further, some people (like me) say "low numerical" gears, which are "high" gears in the normal nomenclature.

Confused further?

[curtis73]

The 2-series carrier fits up to 3.08 (numerically) gears.

The 3-series carrier fits everything numerically higher than 3.08.

They make extra thick gear sets to fit the 2-series carrier, and they also make spacers.

[jimfulco]

Originally Posted by fiscus

Check your gear ratio by counting the teeth on the ring gear and divide by the number of teeth on the pinion.

There is a way to get a close approximation, put the trans in neutral and jack one wheel off the ground. Count how many times the driveshaft spins for one turn of the tire and divide by two.

If you have the cover off the rear end, don't bother trying to count the teeth. Somebody already counted them for you and stamped the numbers into the edge of the ring gear, along with a date code. Four sets of numbers, one or two digits per set. One set should be in the 30's or 40's, and that's the tooth count for the ring gear. Next to that one should be a set that's in the teens (occasionally 9, but not on a GM 7.5" rear), and that's the pinion gear tooth count. The two sets for the date code will also be adjacent to each other.

If you do the turn-a-tire method, you must MULTIPLY by two, but I find it easier to just turn the tire twice using the valve stem for a handle, and starting it at the bottom so I can get the two turns by feel and not take my eyes off the rear u-joint while I'm counting.