Finding my ratio

[78C10BigTen]

Pretty much that’s if it even still works

Well i drive it every day so id say it does lol. It wont burn out ill tell ya that lol

 

[Honky Kong jr]

So explain gov bomb lol i need to update my knowledge...

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[Honky Kong jr]

Posi fluid

https://www.gamut.com/p/crc-gear-oi...gclsrc=aw.ds&dclid=COXqtYu9ntgCFVMIDAodQj4O3g
This is what I’ve always used and what’s in both my front and rear diff

 

[CSFJ]

Last time I checked, most of the 80/90wieght gear lube has the additive for limited slip already added. It will say on the bottle if it does or doesn't. And, if you have no idea when it was last changed, it's a good idea to change it.

The gear ratio will be on the ring gear like this

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In this instance, you would divide 41 (teeth on ring gear) by the 10 (teeth on pinion) to get a ratio of 4.10

 

[78C10BigTen]

Well once the winter has passed ill get her ass up and have a peek under the cover. I was not aware of that stamping

 

[rpcraft]

Yeah I don't think they started including the RPO code on the glove box label until after 1981 but I could be mistaken. Aside from that they used to put a metal tag on the axle and the only reason it wouldn't be in there is if someone has been in the axle and not put it back.

 

[74propu]

On the right axel tube just to the side of the pumpkin on the top of the tube it is stamped with a code . @RetroC10Sport has a thread on here that tells what the code is . that is how I gound out I had a 12 bolt 4.11 locker in my 86

 

[rpcraft]

Yeah but what might be stamped on the tube is not necessarily guaranteeing someone has not changed the gears and unless you are the original owner who can really say...

 

[rpcraft]

Same thing about the RPO code. The only real method is to open and check the ring info or spin the tire and count the rotations compared to the driveshaft.

 

[78C10BigTen]

Ok anyone with knowledge, i found some casting numbers and googled but got more confused. First pic is 3896839. The second is tough to read but its E198. And the third is GM84. One site says that the E198 is the build date but i cant figure out how.... any help?

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[CSFJ]

I don't think anything cast into the axle is going to give gear information. That same casting will be used for several options. You need to clean (wire wheel, sand, whatever) the build up off the tube, and look for anything actually STAMPED into the tubes. Iirc it would be on one tube or the other, near the diff on the side facing the front of the truck.

 

[78C10BigTen]

Any idea on the suposed build date?

 

[rpcraft]

Don't hold my feet to the fire here but I've never known the axle casting numbers to tell the ratio (sorry to say). The metal stamp tag is usually a small metal tag on one of the bolts of the diff cover but to be honest I think that stopped in the early 80's or somewhere there-about. if that is missing, then you can do one of two things... Open up the diff cover and rotate the ring gear until you can read the markings on the edge of the ring gear. or jack up the rear of the truck to where the rear wheels are off the ground and rotate your wheel and count how many times it rotates compared to one revolution of the driveshaft. I've fogotten the math for what is a 3.08, 3.73, or 4.11 but 3.08 was such a common gear ratio on GM trucks I pretty much always assume that is what it has. Diesel trucks actually may have a numerically lower gear ratio though (I think like 2.70 or something in that range).

To be honest the easier of the two methods may actually be draining and changing the rear diff cover, plus if you are the first person in a while, then it probably needs it worse than most anything on the truck. All you need to do that is a replacement gasket and some silicone and about 3 to 6 bottles of diff/gear oil. Probably 40 bucks worth of materials overall.

 

[78C10BigTen]

Don't hold my feet to the fire here but I've never known the axle casting numbers to tell the ratio (sorry to say). The metal stamp tag is usually a small metal tag on one of the bolts of the diff cover but to be honest I think that stopped in the early 80's or somewhere there-about. if that is missing, then you can do one of two things... Open up the diff cover and rotate the ring gear until you can read the markings on the edge of the ring gear. or jack up the rear of the truck to where the rear wheels are off the ground and rotate your wheel and count how many times it rotates compared to one revolution of the driveshaft. I've fogotten the math for what is a 3.08, 3.73, or 4.11 but 3.08 was such a common gear ratio on GM trucks I pretty much always assume that is what it has. Diesel trucks actually may have a numerically lower gear ratio though (I think like 2.70 or something in that range).

To be honest the easier of the two methods may actually be draining and changing the rear diff cover, plus if you are the first person in a while, then it probably needs it worse than most anything on the truck. All you need to do that is a replacement gasket and some silicone and about 3 to 6 bottles of diff/gear oil. Probably 40 bucks worth of materials overall.

I can tell you honest that ive had it 2 years and ive personally never been in it. So yup most likely the best route. I did just the things to get it on the road with the intentions of doin the rest later but still havent got to "later". Terrible i know

 

[rpcraft]

Also, FWIW, the build date really doesn't change anything across the board. All you need to do is determine what it is... And that can be done my looking at the rear pumpkin and counting the bolts on the Diff cover (for half ton trucks). If you have 10 its a 10 bolt, 12= 12 bolt. If you have the 10 bolt for sure then all you need to change gearing is the setup kit, the knowledge, and the ring and gear. If you have a 12 bolt then it can be a little more complicated because of the 3.73 cutoff on the carrier (if you don't have a 12 bolt don't ask, lol).