Gear ratio identification

[smdk2500]

I don't want to be that guy but you could just pop the cover and look at the stamping on the ring gear and do the math. If your truck is like mine its probably due for a rear end oil change anyway.

 

[TxChevyGuy]

I don't want to be that guy but you could just pop the cover and look at the stamping on the ring gear and do the math. If your truck is like mine its probably due for a rear end oil change anyway.

Unfortunately I just did the diff fluid about 2 weeks ago. I'm trying to find a cam rpm that will work with the gears in it. The ring and pinion looked perfect, but I was hoping for 4.10 gears. Once I get home I'm gonna recount in multiple of tens.

 

[smdk2500]

Unfortunately I just did the diff fluid about 2 weeks ago. I'm trying to find a cam rpm that will work with the gears in it. The ring and pinion looked perfect, but I was hoping for 4.10 gears. Once I get home I'm gonna recount in multiple of tens.

It was just a thought. Not saying that your one of them but Ive known people that dont know that they should change the oil in there let alone know that there is oil in there.

 

[TxChevyGuy]

So I went outside. Jacked up one side of the trucks axle. Ten turns to the wheel. Pinion turned 18.65 times.

So 18.65 pinion rotations ÷ 10 tire rotations = 1.865

1.865 x 2 (for each side of axle I guess) = 3.73

So I have 3.73 gears.

Should of looked while I had the cover off......oh well.

 

[kennythewelder]

So I went outside. Jacked up one side of the trucks axle. Ten turns to the wheel. Pinion turned 18.65 times.

So 18.65 pinion rotations ÷ 10 tire rotations = 1.865

1.865 x 2 (for each side of axle I guess) = 3.73

So I have 3.73 gears.

Should of looked while I had the cover off......oh well.

Now you know you have 373s.

 

[98chevy2500SS]

3:73s still aren't a bad gear ratio, good thing you don't have 3:42s lol.

 

[DerekTheGreat]

3:73s still aren't a bad gear ratio, good thing you don't have 3:42s lol.

Funny, I actually sought out a 3.42 for the wife's truck. Had 3.08's and my truck has 3.73's. We're both very happy with the 3.42 G80 rear end we swapped in a few weeks back. It's better in the city and still good on the expressway. Even she can feel the difference when left in gear and opening it up a bit, moves a lot better and downshifts aren't necessary. ('92 C1500 reg cab long box, 350 five speed)

But I had the same problem TxChevyGuy had. Turns out a decently accurate method is you mark the pinion and passenger side wheel, then spin that wheel two full turns while you or someone else counts the amount of times the pinion rotates. The number of pinion rotations will be an approximate value of your ratio. We were able to verify the donor rear for hers at the yard by RPO's GU6 & G80 but that doesn't mean they weren't swapped at some point. So popped the cover off to verify no one pulled the pin on the gov-bomb and before that we did that same test. Ended up at ~3.5 turns of the pinion. I think GM either put a 3.42 or 3.73 in these trucks so we just assumed it was a 3.42 and that the method isn't exactly dead nuts accurate, but at least gets you to the stadium if you know what I mean.

 

[kennythewelder]

342s do good on a small tire, like the OE size tall. Thats what I have in my 97 with 275/60/15s. Im happy with mine. If I had bigger tires, then yes, I would need lower gears.

 

[98chevy2500SS]

I agree, smaller tires are better with 3:42s, but I was more so saying about a 3/4 ton truck, I wouldn't want 3:42 gears in a 3/4 ton truck.

 

[kennythewelder]

410s in a 3/4 ton, thank you very much. Ha Ha. I used to work with a guy who would put 410s in anything he drove. He said 410s will make a I-6 carbed gas engine run good.