rear end, SPID, gear ratio question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

miller6t9 · 10-09-2010, 04:02 PM

ok...the SPID shows that my truck came with a G80 Posi-traction rear end (no other rear end options listed), the M49 turbo hydra-matic and the LS9 350 engine. Am I correct to assume the rear end ratio was a 3:73?

Longhorn Man · 10-09-2010, 05:19 PM

nope, the 3.07 gearset was standard with the 350/automatic

chevytruckluver · 10-09-2010, 05:27 PM

Quote:

Originally Posted by miller6t9

Am I correct to assume the rear end ratio was a 3:73?

Never assume anything, you should know better!

Longhorn is right, unless they got changed somewhere along the line

aintmisbehavinn · 10-10-2010, 11:16 PM

If mine is a 307, why does it tach 2200 at 53mph? 350 automatic OEM

Longhorn Man · 10-11-2010, 12:09 AM

i think a 307 was the exception to the rule, i think it may have gotten a 3.73.
However, 'taching out' (to me) indicates redline... 5500 or so RPM... ?
you may have a problem there.

Jacfourteen · 10-11-2010, 01:12 AM

Best thing to do is pull the rear diff cover off to see what you really have. If you haven't ever changed the fluid it is a great time to do so. It is real easy to tell what you got once you are in there. you just wipe off the edge of the ring gear that faces to the rear of the truck and look for some #'s. If it is a 3.73 for example it will say "11-41", this indicates the ring has 41 teeth and the pinion has 11 teeth. Then you just divide the big # by the little #, so it would be 41/11=3.72727... so 3.73. It really doesn't take long to do, I checked 3 rears in the junk yard the other day and it only took 30 minutes (I didn't have to put them back together though

). Good luck!

miller6t9 · 10-11-2010, 08:30 AM

I was looking at the specification list on the '72 brochure (http://www.lov2xlr8.no/brochures/che...v/bilder/9.jpg) and best I could tell the 3:73 was the standard gear and the 3:07 was optional.

OhOneWS6 · 10-11-2010, 01:33 PM

Quote:

Originally Posted by miller6t9

I was looking at the specification list on the '72 brochure (http://www.lov2xlr8.no/brochures/che...v/bilder/9.jpg) and best I could tell the 3:73 was the standard gear and the 3:07 was optional.

There is something strange about that literature. Those are not the GM names for those colors.

cdowns · 10-11-2010, 01:40 PM

if in doubt do your rear a favor and drain the 40yearold sludge out of it clean and fill with new. in the process you can take any guesswork out of the equation and ID your gears and carrier

Longhorn Man · 10-11-2010, 05:15 PM

Quote:

Originally Posted by miller6t9

I was looking at the specification list on the '72 brochure (http://www.lov2xlr8.no/brochures/che...v/bilder/9.jpg) and best I could tell the 3:73 was the standard gear and the 3:07 was optional.

in a base model truck, that is true.
Once you get an optional engine, or tranny, or both, it may include a gearset in the rear as standard with that combination.

68C10HotRod · 10-11-2010, 05:30 PM

Here's a copy of some 71 data that might shed some light.

Of course, I've already found a number of times the "parts" don't always match the SPID. As others have said, checking is always the sure way of knowing.

aintmisbehavinn · 10-11-2010, 07:53 PM

It must be a 3.73 as the original owner quoted, it's not listed anywhere in the codes on the glove box door. I did change the fluid, I'll know for sure when it goes in for a limited slip diff.

10-09-2010, 04:02 PM	#1
miller6t9 Registered User Join Date: Aug 2009 Location: Rockingham, nc Posts: 166	rear end, SPID, gear ratio question ok...the SPID shows that my truck came with a G80 Posi-traction rear end (no other rear end options listed), the M49 turbo hydra-matic and the LS9 350 engine. Am I correct to assume the rear end ratio was a 3:73?

10-09-2010, 05:19 PM	#2
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: rear end, SPID, gear ratio question nope, the 3.07 gearset was standard with the 350/automatic

10-10-2010, 11:16 PM	#4
aintmisbehavinn Registered User Join Date: Dec 2008 Location: Lawrenceville GA Posts: 64	Re: rear end, SPID, gear ratio question If mine is a 307, why does it tach 2200 at 53mph? 350 automatic OEM

10-11-2010, 12:09 AM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: rear end, SPID, gear ratio question i think a 307 was the exception to the rule, i think it may have gotten a 3.73. However, 'taching out' (to me) indicates redline... 5500 or so RPM... ? you may have a problem there.

10-11-2010, 01:12 AM	#6
Jacfourteen Big Red - Now its a SWB! Join Date: Jun 2009 Location: Oroville, Ca Posts: 1,624	Re: rear end, SPID, gear ratio question Best thing to do is pull the rear diff cover off to see what you really have. If you haven't ever changed the fluid it is a great time to do so. It is real easy to tell what you got once you are in there. you just wipe off the edge of the ring gear that faces to the rear of the truck and look for some #'s. If it is a 3.73 for example it will say "11-41", this indicates the ring has 41 teeth and the pinion has 11 teeth. Then you just divide the big # by the little #, so it would be 41/11=3.72727... so 3.73. It really doesn't take long to do, I checked 3 rears in the junk yard the other day and it only took 30 minutes (I didn't have to put them back together though ). Good luck! __________________ 68 3/4 ton (Project)-350 Small Block, .030 over, 10:1 comp, 3998993 heads, C3BX edelbrock intake, comp cams XE268, Holley 670 SA, long tube headers, dual flow 40's, E-fan, Alum rad, currently under the knife getting shortened and bagged build thread 41 3/4 ton (wife's)-flatbed, fully restored to original 01 Tahoe LT 4WD (my daily driver)-Magnaflow Muffler, Rollin on 22's 02 Ford Mustang Convertable (Wife's Car)-Flowmaster 50, Clear corners, Intake, sittin on 18's

10-11-2010, 08:30 AM	#7
miller6t9 Registered User Join Date: Aug 2009 Location: Rockingham, nc Posts: 166	Re: rear end, SPID, gear ratio question I was looking at the specification list on the '72 brochure (http://www.lov2xlr8.no/brochures/che...v/bilder/9.jpg) and best I could tell the 3:73 was the standard gear and the 3:07 was optional.

10-11-2010, 01:40 PM	#9
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: rear end, SPID, gear ratio question if in doubt do your rear a favor and drain the 40yearold sludge out of it clean and fill with new. in the process you can take any guesswork out of the equation and ID your gears and carrier __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

10-11-2010, 05:30 PM	#11
68C10HotRod Registered User Join Date: Feb 2008 Location: Omaha, NE 68144 Posts: 333	Re: rear end, SPID, gear ratio question Here's a copy of some 71 data that might shed some light. Of course, I've already found a number of times the "parts" don't always match the SPID. As others have said, checking is always the sure way of knowing. __________________ Bryan '52 Bel Air 2dr HT - in pieces '68 C10 - 6cyl/4spd REMOVED, LT1/T56 to be installed “Any society that would give up a little liberty to gain a little security will deserve neither and lose both.” - Benjamin Franklin "And those who know what's best for us, Must rise and save us from ourselves" - RUSH lyric (mockery)

10-11-2010, 07:53 PM	#12
aintmisbehavinn Registered User Join Date: Dec 2008 Location: Lawrenceville GA Posts: 64	Re: rear end, SPID, gear ratio question It must be a 3.73 as the original owner quoted, it's not listed anywhere in the codes on the glove box door. I did change the fluid, I'll know for sure when it goes in for a limited slip diff.

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