Spid Rear End Question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Already Gone** · 09-13-2011, 12:18 PM

Here are 2 spid labels. The blue one is from a 71 GMC Burb and the green one is from a 72 Chev Burb. Now I think the 350 engine codes are for the same engine. I always thought the small block burbs came stock with 3:73 rear ends and the big blocks came with 3:08 rears stock. If that is the case why would the one spid show the 3:73 axle and the other not ? The main reason the guy is selling the green one ( with the 3:73's ) is because he says he cant afford to drive it. I guess my question is why is the 3:73 axle printed out on one spid and not the other ?

gcburdic · 09-13-2011, 05:32 PM

Greg...I'm gonna move this to the main board where it'll get more action

Longhorn Man · 09-13-2011, 06:00 PM

small block with an auto or 4 speed got 3.07 gears. 3.73 was if it was a manual 3 speed. So the 3.73 is listed becouse it was not base equipment with that engine/tranny combo.

**Already Gone** · 09-13-2011, 06:04 PM

Quote:

Originally Posted by Longhorn Man

small block with an auto or 4 speed got 3.07 gears. 3.73 was if it was a manual 3 speed. So the 3.73 is listed becouse it was not base equipment with that engine/tranny combo.

Thank You LM

Longhorn Man · 09-13-2011, 09:34 PM

correction... not small block... 350. 307 engines commonly came with the 3.73 gear.

**Already Gone** · 09-13-2011, 10:04 PM

Quote:

Originally Posted by Longhorn Man

correction... not small block... 350. 307 engines commonly came with the 3.73 gear.

That makes sense as the 307 wouldn't be as powerful as the 350 so the lower (3:73) gears would help the driveability of the heavy Burb with a 307.

rsavage · 09-13-2011, 10:14 PM

My '70 2WD Burb came with a 307 and truck 4 speed. It has the 3.07 rear gear and it isn't listed as an option on the SPID.

**Already Gone** · 09-13-2011, 11:43 PM

Quote:

Originally Posted by rsavage

My '70 2WD Burb came with a 307 and truck 4 speed. It has the 3.07 rear gear and it isn't listed as an option on the SPID.

Thinking out loud about this a 307 with the garnny 4 speed should have reasonably good pulling power but the 3 speed autos would be a little sluggish with the 3:07 gears.

rsavage · 09-14-2011, 06:56 AM

I don't know what the ratio for a 3 spd first gear is as compared to the second gear on the 4 speed, but I do know that I never had to use the granny gear to start out when I had the original 4 speed in it. I always used 2nd which is actually felt like a regular first gear.

**special-K** · 09-14-2011, 07:02 AM

I believe the reason that Suburban was ordered with 3.73s is because it also had the optional L78 rubber.

m6z · 09-14-2011, 12:26 PM

While we're on the subject. What would be the typical gearing on a big block 1/2 ton?

Longhorn Man · 09-15-2011, 06:56 PM

3.07 unless optioned otherwise

Vintage Windmills · 09-15-2011, 07:12 PM

While we're still on the subject what about a C20 big block?

Longhorn Man · 09-15-2011, 07:23 PM

C/20 came with the dana rear and 3.54 gearing... again, unless optioned otherwise.

09-13-2011, 12:18 PM	#1
Already Gone 70+ ( Old Skool Club ) Join Date: Nov 2003 Location: Saskatoon, Saskatchewan ,Canada Posts: 9,073	Spid Rear End Question Here are 2 spid labels. The blue one is from a 71 GMC Burb and the green one is from a 72 Chev Burb. Now I think the 350 engine codes are for the same engine. I always thought the small block burbs came stock with 3:73 rear ends and the big blocks came with 3:08 rears stock. If that is the case why would the one spid show the 3:73 axle and the other not ? The main reason the guy is selling the green one ( with the 3:73's ) is because he says he cant afford to drive it. I guess my question is why is the 3:73 axle printed out on one spid and not the other ? Attached Images __________________ 1972 C10 Custom/Deluxe 613 Highlander 406/700R4 1999 White Tahoe LS 4x2 with Z56 Police Package 1992 K1500 GMC Suburban Members I have personally met: MusicMan70 - HeavyD - ChewyChevy67 - StingRay -71SWB4x4 - 67 Burb - DeadheadNM - too much stuff - bc65 - das601 " Circumsatances Do Not Change Responsibility " " The Sky is not the Limit, Your Mind is." Marilyn Monroe .. RIP Charlie Watts 1941 - 2021

09-13-2011, 05:32 PM	#2
gcburdic Restoration Virgin! Join Date: Jan 2008 Location: Huntersville, NC Posts: 8,298	Re: Spid Rear End Question Greg...I'm gonna move this to the main board where it'll get more action __________________ Geoff with a G 1968 Chevy C10 SWB The Mistress 1972 Custom Deluxe C20 Suburban A Suburban Named Isabella 1966 Ford Mustang Mama's High School Graduation Present

09-13-2011, 06:00 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Spid Rear End Question small block with an auto or 4 speed got 3.07 gears. 3.73 was if it was a manual 3 speed. So the 3.73 is listed becouse it was not base equipment with that engine/tranny combo.

09-13-2011, 09:34 PM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Spid Rear End Question correction... not small block... 350. 307 engines commonly came with the 3.73 gear.

09-13-2011, 10:14 PM	#7
rsavage Registered User Join Date: Aug 2009 Location: Alden NY Posts: 2,705	Re: Spid Rear End Question My '70 2WD Burb came with a 307 and truck 4 speed. It has the 3.07 rear gear and it isn't listed as an option on the SPID. __________________ 1961 C1 Corvette 1959 El Camino 350 TPI, 9" 4 w disc 69 Blazer K5 - sold July '20 2021 Durango RT 5.7

09-14-2011, 06:56 AM	#9
rsavage Registered User Join Date: Aug 2009 Location: Alden NY Posts: 2,705	Re: Spid Rear End Question I don't know what the ratio for a 3 spd first gear is as compared to the second gear on the 4 speed, but I do know that I never had to use the granny gear to start out when I had the original 4 speed in it. I always used 2nd which is actually felt like a regular first gear. __________________ 1961 C1 Corvette 1959 El Camino 350 TPI, 9" 4 w disc 69 Blazer K5 - sold July '20 2021 Durango RT 5.7

09-14-2011, 07:02 AM	#10
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,863	Re: Spid Rear End Question I believe the reason that Suburban was ordered with 3.73s is because it also had the optional L78 rubber. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

09-14-2011, 12:26 PM	#11
m6z Registered User Join Date: Aug 2008 Location: Pittsburg, KS Posts: 2,466	Re: Spid Rear End Question While we're on the subject. What would be the typical gearing on a big block 1/2 ton? __________________ Doug Looking for a 67-72 short bed driver.....

09-15-2011, 06:56 PM	#12
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Spid Rear End Question 3.07 unless optioned otherwise

09-15-2011, 07:12 PM	#13
Vintage Windmills Vintage 4x4s Join Date: Sep 2010 Location: Prior Lake, MN Posts: 4,305	Re: Spid Rear End Question While we're still on the subject what about a C20 big block? __________________ 67 GMC K1500 Custom- 305V6 SM420, PTO, Ram Assist, yellow (the outcast) (project period correct upgrades) 67 GMC C2500 351V6 TH400, AC, PS, PB (can't decide what to do with. Update, decided to keep and will restore ) 86 CHV K30 502 th400, apple red NEW 71 CHV K20 350 SM465, ochre (saved work truck) 71 CHV K20 292 SM465, white, tach, PTO, (future project) 72 CHV K20 350 350th, medium blue (project stocker) 01 CHV K2500hd crew, indigo blue ^3 dont run and the others don't see winter either '86 K30 Cummins "Fireside" thread: http://67-72chevytrucks.com/vboard/s...d.php?t=649649 '71 K20 "get driveable" thread: http://67-72chevytrucks.com/vboard/s...d.php?t=590642 '72 K20 Build Thread: http://67-72chevytrucks.com/vboard/s...=493477&page=6

09-15-2011, 07:23 PM	#14
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Spid Rear End Question C/20 came with the dana rear and 3.54 gearing... again, unless optioned otherwise.



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