71'AirStrike

Im trying to find out my gear ratio. Where is the gm code stamp located? too much road boogers to see clearley.


thanks
chad

'79ProwlerOrange

i think the 3.55s had it arround the edge of the cover... the 4.11s dont have a stamp.

Gordonm

They should all be stamped. Look on the housing where the cover meets the housing. If you are laying on your back looking straight up at the carrier it should be there. Wish I could draw on your picture. But it is right behind where your bracket for the camber rods are

71'AirStrike

Is is in area A, B , or C (C is "facing" towards the front of the car)



mucho grasas
chad

HEARTBEATUSA

My book shows a '71 w/ the stamp just above the casted gusset on the passenger side
denada

Rowdy Rat

Chad,

It will be in flange that you have marked as "A", but it will be on the bottom side the differential (by the exhaust pipe in your photo). The area is not machined and the stamps tend to be lightly struck, so you'll need to clean the area well and look closely. As Gordon noted, all original differential housings were stamped.

Original differential housings also had a paper tag attached to the machined area that mounts to the crossmember. The tag is white paper with the broadcast code for the differential/ratio in red letters. It can't be seen with the differential in place and is usually in pretty rough shape anyway... Still, it can sometimes be used to identify a particular differential.

Good luck in your numbers search!

Regards,

71'AirStrike

ah HA found it! Much thanks guys!

Here is what I found

AW (space) W (space) 100 (space) E (space) 1

Could you double check the Black Book and Tell me what I got?

There is a heavy coat of what looks,feels like Blue RVT siclone gasket maker. Did GM use that stuff back in 71?
Probally not, wich could mean that the diff had been rebuilt in the past.

thanks again :cheers:

HEARTBEATUSA

code AW: 3.08:1

Rowdy Rat

People say a picture is worth a thousand words...

This is the differential stamp on my '70... Photo taken laying on the ground, looking up.



This particular differential is a 3.70 to 1 ratio for 1970; the format for other years will vary.

1 CFA 1 6 70 W

The first "1" is the shift number (1st shift)

"CFA" is the broadcast code for the gear ratio (3.70 to 1)

The second "1" is the month (January)

The "6" is the day of the month

"70" is the year (1970)

The "W" is the positraction source (Warner Gear)

The format for your '71 will be a bit different. It will begin with two letters for the ratio code, a letter for the axle plant, one to three numbers for the julian day of the year, a letter for the positraction source, and a number for the shift.

Let us know how you make out.

Regards,

71'AirStrike

Thanks Heartbeat and Rowdey! you guys are Da Bomb! (just dont say that at the airport). :jester

Do you know the procedure for marking the driveshaft or something and counting the rotations to vefery the actual gear ratio inside the "pumkin"?

chad


[Modified by 71'AirStrike, 5:40 PM 10/19/2002]

HEARTBEATUSA

ratio # equals the # of turns the driveshaft makes for one complete revolution of the wheels

71'AirStrike

WOO HOO!
you guys just saved me 600 bucks.
I am currrently doing a major rear end rebuild on the vette. I had budgeted on doing a rebuild with the diff and going to a 3.08 ratio.
Well its already at 3.08!
Ill check that off my "to do" list

thanks again

Rowdy Rat

Chad,

Looks as though our last posts crossed paths...

Per my last post, your differential decodes as follows:

AW - Ratio Broadcast Code (3.08 to 1)

W - Axle Plant (Warren Motive)

100 - Julian Assembly Date (100th day of 1971 - April 10, 1971)

E - Positraction Source (Eaton)

1 - Shift Code (1st shift)

Looks to be pretty good for a mid to late build 1971 Corvette.

I'd clean up the differential with some solvent to get the grease, dirt, and other assorted garbage off of it... Which will make spotting any leaks easier. I'd also seriously consider changing the old fluid for new differential lubricant and positraction additive.

Regards,

Chuck Gongloff

Great info, BUT....if you found "blue goo", you know somebody has been in there in the past, and MIGHT have replaced the original 3.08's with ????

Jack the rear of the car up in the air. (be careful, etc.). Mark the driveshaft with a piece of chalk. Mark one rear tire with chalk lets say at 12:00 o'clock. Rotate the tire one revolution, and count the number of times the driveshaft turns. Do this several times to get an average.

3 times???? You've got 3.08's. 4 times???? Probably 4.11's. 3 1/2 times??? Probably 3.55's and so on. I rebuilt the diff in my 69 last winter. Original 3.08's in the original case, etc., BUT I chose to put 3.36 gears in it. SO...if you look at my rear case, it's still stamped AW....but the ratio has been changed. Chuck

Stingray1970

The rear axle identification numbers are stamped on the underside of the rear carrier housing between the rear spring and the rear strut arm bracket.Rowdy Rat shows the correct location

GaryS

Put a piece of tape at the 12 o'clock position on your wheel arch. Put another piece of tape at the 12 o'clock position on that tire. Put another piece of tape on your driveshaft and, finally, a piece of tape on the differential, opposite the tape on the driveshaft. Raise the car, take it out of gear and rotate the tire one full revolution by hand. Have your buddy count the number of times the driveshaft turns. Quick, easy and simple. You should easily see the difference, if you go slowly between 3.08, 3.36, 3.55, etc.
Gary