2.73 Rear Gears?????????
Melting Slicks
Joined: Jan 2000
Posts: 2,386
Likes: 3
From: far, far away
Re: 2.73 Rear Gears????????? (Pacha)
I'm not aware of a 2.73 ever being offered in a stock C3 differential. However, some '81's (including mine), and perhaps some '80's and '82's, came with a 2.72 rear. It's not clear to me exactly what rears came in which cars, but it appears that the 4-speed '81 had a standard axle ratio of 2.72, while the automatic '81 had a standard axle ratio of 2.88. An optional 3.07 was apparently available in both cars. I'm not sure if those numbers are precisely right. I've seen 2.89 instead of 2.88, and 3.08 instead of 3.07, in different books.
I suppose somebody like Richmond gear might offer such a high-speed ratio for your '76, but swapping in a diff from an '80-'82 would be a lot of trouble. Even the struts are different.
Having a 2.72 diff isn't a lot of fun. It makes for a nice cruiser (less than 2500 rpm @ 70 mph without an overdrive), and it gets 24mpg on trips, but just about any car on the street will beat you away from a stoplight, even with a healthy dose of aftermarket horsepower. If I ever have to put any money into the diff in my car, I'm certain I won't put a 2.72 back in it. More likely, a 3.07 or perhaps a 3.55, depending on how much cruising I think I'll do.
:seeya
I suppose somebody like Richmond gear might offer such a high-speed ratio for your '76, but swapping in a diff from an '80-'82 would be a lot of trouble. Even the struts are different.
Having a 2.72 diff isn't a lot of fun. It makes for a nice cruiser (less than 2500 rpm @ 70 mph without an overdrive), and it gets 24mpg on trips, but just about any car on the street will beat you away from a stoplight, even with a healthy dose of aftermarket horsepower. If I ever have to put any money into the diff in my car, I'm certain I won't put a 2.72 back in it. More likely, a 3.07 or perhaps a 3.55, depending on how much cruising I think I'll do.
:seeya
Thread Starter
Instructor
Joined: Dec 1999
Posts: 229
Likes: 1
From: Buenos Aires, Argentina
Re: 2.73 Rear Gears????????? (Pacha)
I have a Th400 with 3.08 rear, but I can´t get used to the auto trannys, so I'am thinking to convert to manual.
I figured that a richmond 5 with 2.73 rear will act as an overdrive, does it???????????????
Regards
I figured that a richmond 5 with 2.73 rear will act as an overdrive, does it???????????????
Regards
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From: Forked River NJ
Re: 2.73 Rear Gears????????? (Pacha)
Looking through the spec guide that I have a 2.73 was listed as an option in 68 and 69 as an economy gear. It could be had with a turbo 400 with the lower performance big blocks. Don't know how many were made but it is listed.
Looking a little further in a parts manual it lists for 69-71 2.73 ratio posi is manditory with this. it had 41 teeth on the gear and 15 on the pinion. That is a large pinion gear. It was done so somewhere there is a GM gear with this. The 80 -82 rear is a totally different rear.
[Modified by Gordonm, 8:30 AM 11/1/2001]
Looking a little further in a parts manual it lists for 69-71 2.73 ratio posi is manditory with this. it had 41 teeth on the gear and 15 on the pinion. That is a large pinion gear. It was done so somewhere there is a GM gear with this. The 80 -82 rear is a totally different rear.
[Modified by Gordonm, 8:30 AM 11/1/2001]
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: 2.73 Rear Gears????????? (Pacha)
http://www.tomsdifferentials.com/cat15.htm
I buy from toms. 2.73 would be a very good choice with 1-1 5th gear. I'm 2.86 gearing in Od and I would like just a little more. It shows a US gear 2.73. I have richmond 4.11 and they still look nice after 12-14 years.
I buy from toms. 2.73 would be a very good choice with 1-1 5th gear. I'm 2.86 gearing in Od and I would like just a little more. It shows a US gear 2.73. I have richmond 4.11 and they still look nice after 12-14 years.
Burning Brakes
Joined: Aug 2000
Posts: 925
Likes: 1
From: LT1 and LS5 Coupes... New Orleans, LA
Re: 2.73 Rear Gears?????????
First of all, I want to say it's good to be back on the board and thanks for the kind words :D
Gordonm is totally correct on the factory use of the 2.73 gear as an optional ratio on the 68-69 big block Automatics. This ratio possibly could have been 'written in' on the 71-74 big block order form, although it was technically not an option. It was again offered in 1975 as an Economy ratio on the L-48 Automatic. It was never available with a Manual tranny due to the poor first gear torque multiplication that would have probably caused clutch warranty headaches for Chevrolet.
I'm running the 2.73 in the LT-1 now along with the Richmond 5-speed, and I like it a lot. The 3.28 1st gear of the Richmond makes for great launches, the 4th gear ratio of 1.23 gives you about a 3.36 ratio for great highway acceleration (about 3000rpm @ 70), and then you still have 5th for relaxed cruising of about 2300 @ 70 mph. Along with swapping in an overdrive tranny, this is another option for dropping highway rpms while still maintaining good overall acceleration. You can find the gears occasionally, but they are quite rare. I picked up a ring and pinion from Ikerd's last year for $125.
Gordonm is totally correct on the factory use of the 2.73 gear as an optional ratio on the 68-69 big block Automatics. This ratio possibly could have been 'written in' on the 71-74 big block order form, although it was technically not an option. It was again offered in 1975 as an Economy ratio on the L-48 Automatic. It was never available with a Manual tranny due to the poor first gear torque multiplication that would have probably caused clutch warranty headaches for Chevrolet.
I'm running the 2.73 in the LT-1 now along with the Richmond 5-speed, and I like it a lot. The 3.28 1st gear of the Richmond makes for great launches, the 4th gear ratio of 1.23 gives you about a 3.36 ratio for great highway acceleration (about 3000rpm @ 70), and then you still have 5th for relaxed cruising of about 2300 @ 70 mph. Along with swapping in an overdrive tranny, this is another option for dropping highway rpms while still maintaining good overall acceleration. You can find the gears occasionally, but they are quite rare. I picked up a ring and pinion from Ikerd's last year for $125.
Melting Slicks
Joined: Aug 2001
Posts: 2,043
Likes: 1
From: Elkhorn WI
Re: 2.73 Rear Gears????????? (Allan71)
Allan71.......referring to the post of his MIA status !
:yesnod: http://forums.corvetteforum.com/zerothread?id=175797 :yesnod:
[Modified by ylose, 2:40 PM 11/1/2001]
:yesnod: http://forums.corvetteforum.com/zerothread?id=175797 :yesnod:
[Modified by ylose, 2:40 PM 11/1/2001]
Race Director
Joined: Dec 1999
Posts: 11,096
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From: Sierra Foothills CA
Re: 2.73 Rear Gears????????? (Gordonm)
Looking through the spec guide that I have a 2.73 was listed as an option in 68 and 69 as an economy gear. It could be had with a turbo 400 with the lower performance big blocks. Don't know how many were made but it is listed.
Looking a little further in a parts manual it lists for 69-71 2.73 ratio posi is manditory with this. it had 41 teeth on the gear and 15 on the pinion. That is a large pinion gear. It was done so somewhere there is a GM gear with this. The 80 -82 rear is a totally different rear.
[Modified by Gordonm, 8:30 AM 11/1/2001]
Looking a little further in a parts manual it lists for 69-71 2.73 ratio posi is manditory with this. it had 41 teeth on the gear and 15 on the pinion. That is a large pinion gear. It was done so somewhere there is a GM gear with this. The 80 -82 rear is a totally different rear.
[Modified by Gordonm, 8:30 AM 11/1/2001]
