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9/5/09 11:18am - Original Message: '3.70 or 3.73 gearing'
sulm68
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Jacksonville, FL - USA

Vette(s):
1968 convertable 327 300hp All numbers matching, rally red with black interior. A/C, power windows, power brakes. Tremic 5speed

Joined: 8/28/2007
Posts: 44
I want to change the rear differential gear from a stock 3.08 to 3.73 in preparation for adding a tremic TKO 600 5 speed with a .64 5th gear.  A local shop is telling me the correct gear would be 3.70 and not 3.73.  I know this is not much of a difference but isn't there only one correct answer to this question. If so which is correct.  Thanks for the help.
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9/5/09 12:27pm - Reply: '3.70 or 3.73 gearing'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
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The factory gear ratio would be 3.73...aftermarket gear sets may be a slightly different ratio. Either will be pretty much the same, and either will fit the housing. SO...if all that is available for your year/housing is the 3.70, then that's what you can use with no problems.

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9/5/09 2:36pm - Reply: '3.70 or 3.73 gearing'
Phill's Vette Lifetime Member
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Apache Junction, AZ - USA

Vette(s):
1982,150K,Renegade CFI,Hooker Side Pipes,85 fuel pump,Bilsteins,HD suspension, Aluminum radiator, SharkBar/w 5-Point Restraints. 3:73 gears coming soon.

Joined: 10/15/2006
Posts: 285
I'm going to install a 3.73 differential this winter - most everyone I talk to says 3.73 is too much...... Let us know how you like it.
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Phill's Vette2009-09-05 12:36:44

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9/5/09 4:12pm - Reply: '3.70 or 3.73 gearing'
lukesvette Lifetime Member
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HOWELL, NJ - USA

Vette(s):
1979, Targa Blue (72 Color), Pace Car rear spoiler, L88 hood, Dark blue factory interior, 525HP 406, HD 700R4, 370 gears,Steeroids, composite rear spring, TT IIs wrapped in T/A Radials.

Joined: 5/18/2004
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My differential recieved a factory replacement set of 3.70s. I think that ratio was standard for a while.
 
LukesVette2009-09-05 14:13:34

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9/5/09 4:17pm - Reply: '3.70 or 3.73 gearing'
anips
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sonoma, CA - USA

Vette(s):
72 LT-1 AC coupe,69 l-36 coupe

Joined: 8/9/2002
Posts: 783
Joels right 3.70's are 3.700I812 and 3.73's are 3.7300u812, rounded off,so whats the diff?

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9/5/09 9:36pm - Reply: '3.70 or 3.73 gearing'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

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Paul(LukesVette) caught my typo...the 3.70 was factory...Embarrassed
Still, there will be no discernible difference in the two gear sets, except possibly on a loong road trip. The 3.70 might give ya a wee bit better mileage, but prolly not enough to make a big deal. You also won't be able to feel any difference in take-off  grunt between the two ratios.


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9/5/09 9:54pm - Reply: '3.70 or 3.73 gearing'
lukesvette Lifetime Member
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HOWELL, NJ - USA

Vette(s):
1979, Targa Blue (72 Color), Pace Car rear spoiler, L88 hood, Dark blue factory interior, 525HP 406, HD 700R4, 370 gears,Steeroids, composite rear spring, TT IIs wrapped in T/A Radials.

Joined: 5/18/2004
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9/5/09 10:08pm - Reply: '3.70 or 3.73 gearing'
DaveM Lifetime Member
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Flanders, NJ - USA

Vette(s):
1982 Black, ZZ4, Hooker Side Pipes, 3.55 Rear, Rebuilt & upgraded 700R4, All new suspension, brakes, & new Charcoal interior.

Joined: 1/27/2004
Posts: 2530
[QUOTE=Phill's Vette] I'm going to install a 3.73 differential this winter - most everyone I talk to says 3.73 is too much...... Let us know how you like it.
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[/QUOTE]
On an '82 the 3.73 may be too much. The 700R4 trans has a 3.08:1 first gear (very low) and with a 3.73:1 rear you will be thru 1st gear in about a 1/2 second. I have 3.55:1 rear gears and they are fine, still goes thru 1st in a heartbeat. This only applies to the '82.
Dave


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9/5/09 10:44pm - Reply: '3.70 or 3.73 gearing'
Phill's Vette Lifetime Member
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Apache Junction, AZ - USA

Vette(s):
1982,150K,Renegade CFI,Hooker Side Pipes,85 fuel pump,Bilsteins,HD suspension, Aluminum radiator, SharkBar/w 5-Point Restraints. 3:73 gears coming soon.

Joined: 10/15/2006
Posts: 285
yeah, that's what I'm hearing. If I don't like it, I will rebuild the original differential with 3:55 and sell the 3:73.
Thanks Dave!
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Number 28 of 200 Made on July 28th, 1982
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9/6/09 6:05am - Reply: '3.70 or 3.73 gearing'
sulm68
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Jacksonville, FL - USA

Vette(s):
1968 convertable 327 300hp All numbers matching, rally red with black interior. A/C, power windows, power brakes. Tremic 5speed

Joined: 8/28/2007
Posts: 44
[QUOTE=Phill's Vette] I'm going to install a 3.73 differential this winter - most everyone I talk to says 3.73 is too much...... Let us know how you like it.
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[/QUOTE]

With the overdrive in the 5 speed I am planning at 70MPH the RPM's will be 2078 which should be OK with my mostly stock 300HP motor.  If anyone has any opinions about RPM ranges at highway speed I'd love to hear them.  The reason I'm changing the rear end is raise the highway RPM at 70 MPH from 1824 to something a little higher.  


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9/6/09 5:24pm - Reply: '3.70 or 3.73 gearing'
ossw1
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Rocklin, CA - USA

Vette(s):
1970 T-Top350/350hp numbers matching 4 speed. It's a mess and 1970 Convertible 4 speed.

Joined: 4/2/2005
Posts: 484
I have 3.08 375 hp 4 speed car would a 3.70 be better then a 3.08? 
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9/6/09 7:55pm - Reply: '3.70 or 3.73 gearing'
anips
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sonoma, CA - USA

Vette(s):
72 LT-1 AC coupe,69 l-36 coupe

Joined: 8/9/2002
Posts: 783
most definatelly, it would be alot quicker, of coarse your gas milage would go down the drain and the motor would work a little more at cruise and top end world drop a little, a happy medium would be 355's which I have in the LT-1 and I get about 10-12 MPG average. anips2009-09-06 18:02:20

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1/1/10 9:38pm - Reply: '3.70 or 3.73 gearing'
fifty7belair Lifetime Member
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Rainier, WA - USA

Vette(s):
1978 Pace Car

Joined: 4/16/2005
Posts: 25
Just to clear up. 3:70 is the correct ratio for the fatory corvette rearend housing. 3:73 gears fit in the 10 bolt and 12 bolt chevy rearends but will not fit in the factory corvette rearend housing. I think you'll like the 3:55 better as well.
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