Gear change

The rearend in my 83 C20 has 4.56 gears. I think 3.73s might work better in this application and allow for better gas mileage. What whould be the best way to go about this? Is there a proper description to call this rearend such as 12bolt truck? It has a different housing than the passenger car and has big brakes. Are 3.73 gears readily available or would possibly finding a complete rear end assy from the boneyard be cheaper?

 

If you find a good shop you can have a new ring and pinion installed in your truck for a few hundred dollars. The ring and pinion itself shouldn't be too expensive, but it's tricky to install. I prefer to leave it to professionals.
Although it would be cheaper and you could do it yourself, I wouldn't recommend a boneyard rearend since you don't know the condition of the contents, including brakes, bearings, and gears.
You probably have a 12-bolt, just count the bolts on the cover, although I believe there are other differences as well. I would suggest driving it to a rear-end shop and having them tell you what rearend you have and get them to give you a quote on the gear swap.
Jeff
http://www.jeffsclassics.com

 

Actually, I believe it probably had a semi-floating 14 bolt. It has a 9.5" ring gear, and a more rounded housing. I priced ring and pinions for this particular rear end and found they were kinda spendy. Somewhere around $250 just for the parts (install kit included) which is more than you'd pay for something like, say a dana 60. Anyway, I wouldn't try the junk yard approach, and have a shop install the gears for you. There are a few things you have to get just right, like gear lash, and it's worth the money for the peace of mind. 3.73 will also work just fine I'd imagine. Won't suck so much gas either. You might want to find out for sure what your gear ratio is before you swap, because perhaps if you have 4.10 gears now, and want to drop your RPM a lot, 3.73 might not be a big enough change. Going taller than that would seriously cut into towing, hauling power. 3.42 is the next taller ratio I have seen for sale for that rear end. Sorry about the essay I just wrote, but to sum it up, find out what gear ratio you have (count teeth on ring, devide by teeth on pinion), find out what rear end you have (14 bolts on the cover, and semifloating would be the GM 14 bolt 9.5" ring gear, semifloating means that there's no big hub sticking out of the wheel on the end to make it simple) and have a shop put in the new gears when you get them. Good luck.

 

You guys got my curiosity up, so I went out in the cold and foggy weather with a flashlight to take a look at the rearend. There are 14 bolts on the cover housing. I don't mind 4.56 gears its just that in these times of rising gas prices, it could run me broke.

 

MTCK, I'm sure the gears are 4.56. The glovebox sticker says so and I know the original rearend hasn't been out of the truck. Its also a 4-speed manual which I wonder if an RV type cam is too conservative for this, considering on the highway it cruises at over 3,000rpm at 60mph with 31"tall tires.

 

Man, that is wrapped out. I can see why you want to change it. I can imagine it likes to stop at about every gas station it see's. OK, here's a little something that might be helpful; go to http://www.richmondgear.com click on the calculators link, then when that menu comes up, click "street performance" There's a calculator in there that will tell you what RPM you will be running at a certain speed. You enter in your rear end ration and tire size. With 31's and 3.73 gears, you'd be turning about 2400 rpm. Hope that helps.

 

I'm not sure about GM rears, but in Dana there is a different carrier between 3.73 and lower and 4.10 and higher gearsets. That makes the swap potentially more costly if you have to get a new carrier along with new gears. I think the cheapest and easiest way out would be to find a used, complete axle and just bolt it in. If you go that route, try to get the speedometer gears out of the back of the tranny as well. Going from 4.56 to 3.73 will make a big difference in your speedometer and odometer readings.

 

So, who makes the 14bolt rearend? Is it GM or some other maker such as Saginaw? Are these somewhat common that I could find one at a truck junkyard? Is it worth keeping and just changing out the gears, or swapping in a different one?

 

I'm 99% sure that GM makes this rear end. Did you look to see if it's a semi-floater or full-floater? I think they make it either way. I'd keep the rear end you have, and swap the gears, if everything else is OK on it. Don't know what you're getting from the junk yard and there is a LOT of stuff that could go wrong back there that you wouldn't know about until you had it home. Brakes, seals, bearings, gears, ect. So, if yours is OK, just have a shop swap the gears, and that would be the best way to go. Good luck.