determining axle ratios?

[CherryK5]

I'm trying to figure out what my axle ratios are.
the code on my axle is "bb3 g342 2"

I looked for it online and stuff but I can't find it..

 

[4X4HIGH]

The ONLY way to know what ratio for sure is to pull the diff cover and do the math (divide the ring gear by the pinion gear tooth count).

 

[Blue85]

Of course, you don't have to count the teeth, because the numbers are stamped on the side of the ring gear. But if you've already popped the cover, why not count? You probably need to change the gear oil anyway, but if you don't want to drain, clean, form a new gasket, refill, etc. just to check the gear ratio, there are ways to estimate.

Just lift the back end off the ground and rotate the driveshaft by hand. Place some marks (tape, chalk, whatever) on the tire(s) and driveshaft and count revolutions. Go for a lot of revolutions, like 30, to get a decent estimate. If you have a locker, you'll have both wheels spinning. If the diff is open, keep one tire on the ground and divide the number of tire revolutions by 2. Your gear ratio is just the driveshaft revolutions divided by the tire revolutions. Then look for the standard ratio closest to that number.

Or you can use an accurate tach, a GPS and the true tire diameter to do the math.

 

[CherryK5]

If i do it that way i get somewhere around a 3.08 ratio

So if i went from stock tires to 35's what gears should i run?
4.10 or 4.56?

 

[Stomis]

Well 3.08 is a very common gear ration for a blazer so I'd say thats about right.

Gears for 35in tires:

Stick non OD: 3.73s or 4.10s
Stick with OD: 4.56s

Auto non OD: 4.56s
Auto OD: 4.88s or 5.13s

 

[shovelbill80]

no sticker in glove box? i used to mark drive shaft and tire like Blue said, spin tire one revolution and count how many time the driveshaft spins. pretty darn accurate with stock tires......it'll give you final drive ratio with different tires too.

 

[Blue85]

3.08 gears are marginal with tiny tires, bad with 31's, terrible with 33's and awful with 35's. Swap for sure and you'll have a whole new beast on your hands. You want 4.10-4.88 depending on what transmission you have and how you will use the truck. You almost can't go wrong with 4.56. Although you might consider 4.10s since they were available sometimes in stock axles. This brings up the next point...

Sometimes you are ahead by swapping the axles instead of buying and installing R&Ps. Which brings up the next point...

A lot of people here will tell you to move from 1/2-tons to something bigger. But it's your truck, you need to decide what's best.

Anyway, what transmission do you have and what will you use the truck for?

 

[Stomis]

3.08 gears are marginal with tiny tires, bad with 31's, terrible with 33's and awful with 35's. Swap for sure and you'll have a whole new beast on your hands. You want 4.10-4.88 depending on what transmission you have and how you will use the truck. You almost can't go wrong with 4.56. Although you might consider 4.10s since they were available sometimes in stock axles. This brings up the next point...

Sometimes you are ahead by swapping the axles instead of buying and installing R&Ps. Which brings up the next point...

A lot of people here will tell you to move from 1/2-tons to something bigger. But it's your truck, you need to decide what's best.

Anyway, what transmission do you have and what will you use the truck for?

Gears are completely dependent on transmission as said. Thats why I always list a few suggestions based trans. That being said there are far deeper options for factory gears than 4.10s. 4.56s arent that uncommon and some cab and chassis trucks were even 4.88s.

Honestly your best bang for your buck upgrade if you need to regear is CUCV axles. You get 4.56s, a dana 60 front, a detroit locker in the rear and even a front posi in some sets. On top of that they usually have like less than 50,000 miles on them. Theyre plenty strong for tires all the way to about 37s or 38s stock and loads of upgrades are available.

If your on a more conservative budget then 3/4tons (10bolt front, 14bolt rear, 8 lug) can be had for scrap weight usually and with 4.10s. 4.10s are NOT enough gear for an OD auto with 35s though unless maybe you live in kansas.

 

[wheels87k5]

Hey.....Kansas does have 2 hills

Up one and down the other.

 

[CherryK5]

Well i pulled the cover.
2.73's.
If only i had 25's instead of 35's.

Im trading a set of 3.73 10 bolts for a 14 bolt with 4.10's and posi.

That explains why i could cruise at 65mph at 2100 rpm...in 3rd..
FML

 

[CherryK5]

Gears are completely dependent on transmission as said. Thats why I always list a few suggestions based trans. That being said there are far deeper options for factory gears than 4.10s. 4.56s arent that uncommon and some cab and chassis trucks were even 4.88s.

Honestly your best bang for your buck upgrade if you need to regear is CUCV axles. You get 4.56s, a dana 60 front, a detroit locker in the rear and even a front posi in some sets. On top of that they usually have like less than 50,000 miles on them. Theyre plenty strong for tires all the way to about 37s or 38s stock and loads of upgrades are available.

If your on a more conservative budget then 3/4tons (10bolt front, 14bolt rear, 8 lug) can be had for scrap weight usually and with 4.10s. 4.10s are NOT enough gear for an OD auto with 35s though unless maybe you live in kansas.

Eh. 4.10's will do. I cruise at 70 most of the time anyways. And after driving on 2.73's for the last year im fine with anything lower.

Not only that, with the 2.73 i could still roast the tires through 1st gear.
I cant wait to roast em through third.

 

[Stomis]

Well i pulled the cover.
2.73's.
If only i had 25's instead of 35's.

Im trading a set of 3.73 10 bolts for a 14 bolt with 4.10's and posi.

That explains why i could cruise at 65mph at 2100 rpm...in 3rd..
FML

Meh if ya got a cheap line on a 4.10 axle then sure run it but I wouldnt go wasting money on regearing 2 axles just to go 4.10s when you have an OD trans.