Where can I find my rear end gear ratio?

[jbell1]

I've checked the radiator bracket, all it says is a bunch of emissions stuff and speed screws. The door jam part of the door only has tires and tire pressure. It's on a 1985 Chevy c20, 305 (well was a 305), big brake drums if that makes a difference.

[zieg85]

Look at the sticker in the glove box. 

[Blazin]

Or pull the cover. Count the teeth on the pinion gear, and divide them into the teeth on the ring gear.

[jbell1]

Okay thank you guys

[fitz]

Or pull the cover. Count the teeth on the pinion gear, and divide them into the teeth on the ring gear.

As our trucks get older you never know whats been swapped in and out of them.
The older they get the less you can can trust the option code sticker.
In the past month I've run across 2 4x4's that had miss matched gears front/rear.
Like Blazin said, pull the cover.
GM gears will have the teeth count stamped on them. Just divide them out to get your ratio (10 40= 4.10's).     

[jbell1]

Okay well it's been raining here for the past few days so I haven't been able to check the gears but any opinions on what the best ratio would be for a built 350 2 wheel drive truck? I plan on upgrading to a limited slip anyway.

[zieg85]

It depends on what your driving habits are.  In-town truck with no highway use and/or pulling a load 3.73 or 4.10 should be fine.  Highway driving mostly with no loads, 3.42 or a 3.21. Automatic, Automatic Overdrive or manual transmission?  Lots to choose from.  Me personally I like my 3.21 in my 1985 C20. 

[Stewart G Griffin]

It's highly unlikely that the rear gear has been swapped.  It's also highly unlikely that the entire rear axle was swapped (in order to change rear gear).


You can take your vin# to the dealer parts counter and they can look up exactly what gear (among other things) you got.  Probably best to be a chevy or gmc dealer because the others, b and c, may not really want to deal with you as much.

[Lt.Del]

Stew, I think Fitz is correct with his statement.  The older these vehicles get, the more likelihood of having parts interchanged.  I have knonw many of our trucks get the entire axle swapped.  When going to salvage yards, the first things stripped from these trucks are the axles/gears.  Every 73-87 p/u out in the graveyard no longer has its rear gears.

[fitz]

It's highly unlikely that the rear gear has been swapped.  

                                                                                                                                                                                            why is that? Someone already pulled the 305 and installed a built 350. When your dealing with an old modified vehicle anything goes. Keep in mind he is looking to add a limited slip carrier to his axle. In order to buy the correct limited slip unit you must know your gear ratio.

[jbell1]

Okay to take care of any confusion, the truck was bought by my great grandfather in 85 new. Then my father bought the truck from my grandfather with 10k on it bone stock 305 and all, drove it to 30k as a secondary truck until 03, then he parked. He gave me the truck about a year and a half ago, I replaced the gas tank (hole), entire rear brakes (drums to lines), new rocker panels, then a month ago we pulled the 305. Built a 350 from a 350 block 40 over to a 355, flat top pistons, AFR performance heads, hi flow oil pump, edelbrock performer intake edelbrock performer electric choke carb, compression ratio is 9.5:1. nothing was changed on that truck unless it was changed by me the rear gears are the stock ones. oh and replacement distributer cap and 8mm wires haha if that helps

[1979C20]

Built a 350 from a 350 block 40 over to a 355

.030 over is a 355. So you have like a 356.6 at .040 over. Not prudent, just sayin.

[jbell1]

haha sorry

[1979C20]

No need to apologize, haha. And it sounds like a pretty nice build. Is yout truck a manual or auto?

[jbell1]

Yupp its a manual. I checked the glove box sticker and the only things i found that had anything to do with the rear end were that it said it had the standard rear axle and it said this "7.50r-16d TBLS HWY s/I" option number "YWY" have pictures but i need to compress them i will have them tomorrow.