How do identify my gearing????

[lyrikz]

I have a 1971 chevy 2wd shortbox stepside. It has a 12 bolt chevy rear end. I have searched and searched and i cant find out what gears i have in the rear. I tried the turn the tire and count the rotations, but i cant get my damn truck in gear for some reason.. Its been sitting for a few months.

Sooo, is there anyway of telling what gears i have back there?? it is a stock rear end. I looked at the RPO sheet in the glove box and that gives me ZERO info and the options it states dont tell me anything..... I went to a website that gave me a decoder on the RPO, but all the numbers on that rpo sheet dont match up on this decoder...

How do i figure out my rear??? HAHA.....

Thanks guys.

[Longhorn Man]

what engien and tranny were original?
You could always pop the rear diff cover off and count the teeth on the gears. Divide one into the other and you'll know your gear ratio no question about it.
We can look at axle codes, and talk about what was originalwith the original combo... but things get chainged out in 36 years.

[lyrikz]

Hmmm. Original was I-6. 250.

I guess i dont need to know that bad, im getting a cam for my motor and i kinda wanted to know this info... dang..

[Longhorn Man]

a 250 most likely came witha 3 speed manual, which would have been a 3/73.
Again... assuming the gearing/rear end never got swapped out.

[factorystock]

If logic holds true, the SPID ( glove box decal ) should list an optional ratio, but no info if equipped with the standard axle ratio 3.73.

[463]

this site clears up your questions http://www.ringpinion.com/Calculators.aspx

[rick0312]

i had the same question recently...so I pulled the cover...man i am glad I did; nasty lookin inside.(see pic) i cleaned the gears up and then could see the ring gear and pinion cleearly stamped....41 on the ring and 11 on the pinion.(3.73) put a new gasket and cover on and some fresh gear oil. If it has not been changed in a while i would reccomend pulling the cover.

[Longhorn Man]

Originally Posted by factorystock

If logic holds true, the SPID ( glove box decal ) should list an optional ratio, but no info if equipped with the standard axle ratio 3.73.

Standard gear ratio chainges regarding engine and tranny options. So that statement is too general.

I normally do mention that popping the cover is not only the best way to find out whats in there, but a very important service that is more commonly ignored than even brake fluid. That gear oil could be original, could be 10 years old... no tellin.

[factorystock]

Sorry I dont have a link, but check out ebay #200216347601, a 68 c-10. the SPID shows an optional ratio, 3.54 , it is a dana 44, judging by the photo.

[LONGHAIR]

Why does everyone act like pulling the cover is a huge deal? It's 12 bolts that can be removed easily with power tools. They are all right there in the open and on a stock height truck you don't even need to jack it up. A few bucks for a gasket and some lube and you get a look at a very often neglected item, plus you know for sure about your ratio.
This get suggested often and most times the reply is.....Oh, I don't need to know that bad

[lyrikz]

Originally Posted by LONGHAIR

Why does everyone act like pulling the cover is a huge deal? It's 12 bolts that can be removed easily with power tools. They are all right there in the open and on a stock height truck you don't even need to jack it up. A few bucks for a gasket and some lube and you get a look at a very often neglected item, plus you know for sure about your ratio.
This get suggested often and most times the reply is.....Oh, I don't need to know that bad

ahaha... Id rather pull a motor then change diff fluid.. I HAVE NO idea why... Im thinking about that now.....

The smell maybe?? Something subconsciously.. ahah who knows...

[Longhorn Man]

I tend to agree with Jim, (longhair) however, i will also admit to being guilty of the same.
However, let me add this,
At least once every 6 months at work (fleet and diesel repair) we come across a pick up or van with damaged gears and the driver had no clue. We would be doing a oil and gasked on the diff, and see a chipped tooth, odd wear, chunks in the oil.... what ever. These are 5 to 15 year old vehicles. Granted, they get worked harder than the typical truck we own ever did, most of them were scrapped 20 years ago, BUT. it's still a very good idea to take care of this before a gear gets sput out when you are showing off doing a burn out, or traveling up the freeway cruisin at 70 MPH.

[LONGHAIR]

I know what you are saying Andy, but we are talking about trucks that are as much as 40 years old here. While there is a little bit of the "You may really not want to know what is in there" factor, if a guy is curious about ratio...it really is the way to do it. You may be opening a "can of worms", but like you said, it is better to know now, than have a "dramatic failure". Also, as you said, if it is really that bad...it's dead/dieing anyway and this will not speed-up that failure, it might even buy you some time.
Differential lube and brake fluid are probably the most abused/neglected things on any car/truck.....and the lube is far easier to change. It's a half-hour job with no down-side. Anyone who can change their own oil can do it.

[Longhorn Man]

I agree one million percent.