Rear gears - recommendations/cost
Thread Starter
Pro
Joined: Sep 2004
Posts: 690
Likes: 0
From: Madison WI
Rear gears - recommendations/cost
OK, so I really want to replace the rear end gears in my 72 L-48. I'm still not 100% sure what I have in there but using a rear-end gear calculator, it seems I have 3.08's or taller (read: worse), assuming my tach is reasonably accurate. My brother took the jack to St. Louis so I don't have a way to check for sure 
Once school starts in September I'm hardly going to be doing any highway driving (not going to get to do much driving during the school year at all, actually ), so highway RPM won't be much of a concern at all. That being said, what would you guys recommend as far as what to swap out the gears for? I was thinking 3.43's seem pretty reasonable, or should I even go as short as 3.73's?
Also, how much can I expect to pay for a job like this INCLUDING the gears themselves?
Thanks in advance guys
Once school starts in September I'm hardly going to be doing any highway driving (not going to get to do much driving during the school year at all, actually ), so highway RPM won't be much of a concern at all. That being said, what would you guys recommend as far as what to swap out the gears for? I was thinking 3.43's seem pretty reasonable, or should I even go as short as 3.73's?Also, how much can I expect to pay for a job like this INCLUDING the gears themselves?
Thanks in advance guys
Tech Contributor
Joined: Aug 1999
Posts: 15,177
Likes: 3,995
From: Connecticut, USA
If you have an original automatic car you should have 308's, a WR 4 spd and you'll have 336's. Ratios available are 273,308,336,355,370,373,390,411 Of these not all are available from the same sources.
I only use Tom's US Gears and they run about $275-300 depending where you buy them. Add in about $600 for a standard rebuild and another $50 UPS one way.
I charge about $1,200 depending on the required work, (less UPS), for a full custom blueprinted rebuild with new gears. If you want to build one yourself I have a complete setup less gears ready to build.
You should think about how you're gong to drive the car, with gas going over $3,00 gallon those 308's might not be all that bad.
Let me know if I can help.
Gary
I only use Tom's US Gears and they run about $275-300 depending where you buy them. Add in about $600 for a standard rebuild and another $50 UPS one way.
I charge about $1,200 depending on the required work, (less UPS), for a full custom blueprinted rebuild with new gears. If you want to build one yourself I have a complete setup less gears ready to build.
You should think about how you're gong to drive the car, with gas going over $3,00 gallon those 308's might not be all that bad.
Let me know if I can help.
Gary
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Originally Posted by gtr1999
If you have an original automatic car you should have 308's, a WR 4 spd and you'll have 336's. Ratios available are 273,308,336,355,370,373,390,411 Of these not all are available from the same sources.
I only use Tom's US Gears and they run about $275-300 depending where you buy them. Add in about $600 for a standard rebuild and another $50 UPS one way.
I charge about $1,200 depending on the required work, (less UPS), for a full custom blueprinted rebuild with new gears. If you want to build one yourself I have a complete setup less gears ready to build.
You should think about how you're gong to drive the car, with gas going over $3,00 gallon those 308's might not be all that bad.
Let me know if I can help.
Gary
I only use Tom's US Gears and they run about $275-300 depending where you buy them. Add in about $600 for a standard rebuild and another $50 UPS one way.
I charge about $1,200 depending on the required work, (less UPS), for a full custom blueprinted rebuild with new gears. If you want to build one yourself I have a complete setup less gears ready to build.
You should think about how you're gong to drive the car, with gas going over $3,00 gallon those 308's might not be all that bad.
Let me know if I can help.
Gary
I have the 3.73s in mine but I have a Tremec with a .68 OD.
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
rebuilt from Ecklers: less than $900....
http://www.ecklers.com/product.asp?p...BSCS4A422WBWA9
or Summit, $599:
http://store.summitracing.com/defaul...=egnsearch.asp
http://www.ecklers.com/product.asp?p...BSCS4A422WBWA9
or Summit, $599:
http://store.summitracing.com/defaul...=egnsearch.asp
Le Mans Master
Joined: Apr 2000
Posts: 5,981
Likes: 0
From: Houston,Tx. USA
I'd seriously consider the 3.08; the guy who owned my car changed the gears and I'm running 3200 - 3500 at 65-70 mph (est since my speedo does not work...I know I'm running around that becuase the limit here is 65 and a I get passed a lot).
Thread Starter
Pro
Joined: Sep 2004
Posts: 690
Likes: 0
From: Madison WI
Originally Posted by Chopper Larry
I'd seriously consider the 3.08; the guy who owned my car changed the gears and I'm running 3200 - 3500 at 65-70 mph (est since my speedo does not work...I know I'm running around that becuase the limit here is 65 and a I get passed a lot).
Advanced
Joined: Jul 2005
Posts: 54
Likes: 0
From: Southampton PA
I just purchased the complete set up of 3:70's from corvette central. I'm replacing the 3:08's in my big block. I purchased them from corvette central for $1,192 including shipping. I will get a $400 core charge back when I send the old one's back. I should have them in the car in a week or so and will let you know how it goes.
Just an fyi they were shipped direct from a company called Ikerd.
I have the phone number if your interested but they may not sell direct.
I know I have to change the gear in the trans but i'm not sure what color or tooth count I need but I'll start my own thread.
Just an fyi they were shipped direct from a company called Ikerd.
I have the phone number if your interested but they may not sell direct.
I know I have to change the gear in the trans but i'm not sure what color or tooth count I need but I'll start my own thread.
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Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
The 3.08 is probably your best choice. I have 3.55 and at 65mph it's running at >3000rpm...
MidAmerica sells a rebuilt 3.08 unit for 1099 INCLUDING a $300 core charge......
http://www.madvet.com/shop?frame=4.1443
MidAmerica sells a rebuilt 3.08 unit for 1099 INCLUDING a $300 core charge......
http://www.madvet.com/shop?frame=4.1443
Drifting
Joined: Jun 2004
Posts: 1,881
Likes: 9
From: staten island ny
I've been contemplating either rear end gears or a 4 sp auto tranny swap. I thought the tranny was the more expensive way to go but after reviewing gear prices plus labor it's just as expensive as the trans. I believe my 79 with auto is running 3.73 revving about 3200 at 65 mph, I was thinking about 3.08. Any idea what kind of drop in rpm's I could expect?
ESU
ESU
Tech Contributor
Joined: Aug 1999
Posts: 15,177
Likes: 3,995
From: Connecticut, USA
Depending on your tire size about 500 rpm. My 308's run about 2700-2800 rpm on the highway.
Remember guys you get what you pay for. Ask the questions on how things are put together just as you would if you built an engine.
Gary
Remember guys you get what you pay for. Ask the questions on how things are put together just as you would if you built an engine.
Gary
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Originally Posted by ESU
I've been contemplating either rear end gears or a 4 sp auto tranny swap. I thought the tranny was the more expensive way to go but after reviewing gear prices plus labor it's just as expensive as the trans. I believe my 79 with auto is running 3.73 revving about 3200 at 65 mph, I was thinking about 3.08. Any idea what kind of drop in rpm's I could expect?
ESU
ESU
.65/3.73=.17
.17*3200=544
A typical 4 speed auto will drop it by almost twice as much, for a 7000r4 it is a .36 drop (.64 overdrive) plus throw in another 200 rpm drop if you have a locking torq convertor.
Drifting
Joined: Jun 2004
Posts: 1,881
Likes: 9
From: staten island ny
gtr1999 and fevre, thx for the info. Lot of money for just a 500 rpm drop. Droppin the 1000 rpm with a new tranny seems more like it coupled with the lower first gear. I've got a 1990 blazer thats on its last lega body wise but runs great, wonder what tranny is in it? Could be a swap lol.
ESU
ESU
Drifting
Joined: Nov 2001
Posts: 1,469
Likes: 6
From: 68 427 4.11s Roadster
Why not 4.11s?
You could kind of guestimate what you want by taking an arbitrary torque value. A guess of what you already have and doing the math of the rear end ratio on it.
150 ft. lbs with your 3.08s= 462 ft lbs is where you are now at some rpm that equals 150 ft lbs engine torque. Some assumed driving speed/engine rpm.
150 ft lbs x 4.11s = 616 ft lbs.
616-462 = 152 ft lb increase.
3.08/4.11=75% of your 3.08s milage assumed.
18 mpg=13.5 mpg
Or $20 of gas now costs $26.
You could kind of guestimate what you want by taking an arbitrary torque value. A guess of what you already have and doing the math of the rear end ratio on it.
150 ft. lbs with your 3.08s= 462 ft lbs is where you are now at some rpm that equals 150 ft lbs engine torque. Some assumed driving speed/engine rpm.
150 ft lbs x 4.11s = 616 ft lbs.
616-462 = 152 ft lb increase.
3.08/4.11=75% of your 3.08s milage assumed.
18 mpg=13.5 mpg
Or $20 of gas now costs $26.
Melting Slicks
Joined: Jul 2005
Posts: 2,545
Likes: 3
From: 406ci SB, AFR 180 Heads - 490 HP @5,600 RPM 529 lb-ft @ 4,100 RPM
Originally Posted by gtr1999
If you have an original automatic car you should have 308's, a WR 4 spd and you'll have 336's. Ratios available are 273,308,336,355,370,373,390,411
You should think about how you're gong to drive the car, with gas going over $3,00 gallon those 308's might not be all that bad.
You should think about how you're gong to drive the car, with gas going over $3,00 gallon those 308's might not be all that bad.
) With the 456's it's an animal from a standing start. 
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
What are gears really going to get you?? In the quarter you would be lucky to cut 2 or 3 tenths off your quarter mile ET. Somewhere I have a good test of different gears and it wasn't as much as you think.
With the price of gas I would stick with the 308's. Why drive a high revving gas hog on the highway just to pick up a few tenths if you raced.
Save your money and enjoy the car.
With the price of gas I would stick with the 308's. Why drive a high revving gas hog on the highway just to pick up a few tenths if you raced.
Save your money and enjoy the car.
Drifting
Joined: Nov 2001
Posts: 1,469
Likes: 6
From: 68 427 4.11s Roadster
If gas milage was an issue no one would be driving any of these ancient gas guzzlers. These are "impractical 2 seaters" and meant to be fun toys. Not 4 cylinder fuel sippers.
If you want to know what the difference is figure out what it would take to get 150 ft lbs out of your engine. How much would it cost yada yada yada.
That same 150 can be much much larger. Think of it in terms of an engine rebuild.
If you want to know what the difference is figure out what it would take to get 150 ft lbs out of your engine. How much would it cost yada yada yada.
That same 150 can be much much larger. Think of it in terms of an engine rebuild.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Originally Posted by Techno
If gas milage was an issue no one would be driving any of these ancient gas guzzlers. These are "impractical 2 seaters" and meant to be fun toys. Not 4 cylinder fuel sippers.
If you want to know what the difference is figure out what it would take to get 150 ft lbs out of your engine. How much would it cost yada yada yada.
That same 150 can be much much larger. Think of it in terms of an engine rebuild.
If you want to know what the difference is figure out what it would take to get 150 ft lbs out of your engine. How much would it cost yada yada yada.
That same 150 can be much much larger. Think of it in terms of an engine rebuild.
High horsepower doesn't necessarily mean gas guzzling. I put out more horse then 99% of the cars on this forum and still pull down a solid 15 mpg and I don't drive the speed limit.
My friend is running 355 gears with a 350 and he has to buzz above 4 grand all the time just to run with us and we are in the low 2000 range. Who is getting the more comfortable ride, a cooler running motor and better gas mileage.
Gas mileage does count regardless of your income
