What rear gears to go with - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Dean23 · 08-19-2002, 09:27 PM

What rear gears to use

Dean23 · 08-19-2002, 09:28 PM

Oh yeah I have a 350hp 350, 700r4 17 inch wheels, L79 cam9.5 comp.

gabet40 · 08-19-2002, 09:42 PM

for racing? for cruising? for all around? ill put in my vote for 3.73 out of these choices but all around im going with a 3.42 i do a lot of cruising and a little hot rodding. but for racing, the lower the better of course

Dean23 · 08-19-2002, 09:46 PM

strictly street, cruisin, maybe the odd run at the track

Church · 08-20-2002, 07:11 AM

What size tire are you running? If it is around 28" tall, I'd say stick with the 3.73, at 65 mph you would be pushing a little over 2900 rpm @ 1:1 then overdrive would put you at a little under 2100 rpm.

colohusker · 08-20-2002, 09:01 AM

not listed, but right now i'd go with 3.07, but want to go to 3.73 or 4.10 when it's no longer a work truck....

For street and cruising, i'd go with the 4.10. If you're going to be taking the occasional road trip, I think I'd go with the 3.73.

68 Suburban · 08-20-2002, 09:20 AM

I like my 3.07 and the 15+ mpg that comes with it at 75-80 mph.

Bamm · 08-20-2002, 12:49 PM

17" tires and 700R4= 4.10gears. Trucks like this, gas mpg is going to hover anywhere around 10-17 tops with your 700R4. All this depends of course on your engine buildup? When I had my 700R4 built, the guy said that in lockup it would knock 70 points off of my final drive ratio- 4.10 gears with a 700R4 = same as a turbo 350 transmisson with a 3.40 rear gear. Can anyone back up this info?.........JB

gabet40 · 08-20-2002, 01:13 PM

as of right now i have 3.08s but my 18" wheels on 40 series tires are only 25 1/2" tall. so even with my torque converter locked up on the freeway im still at about 2300 @ 75 mph. cruisin in my stocks are great though. ill stay at 80mpg @ about 2100.
but i dont like waiting til im at about 3000rpm to really feel the power when im pullin off the line. i think 3.42s will help me off the line a lot but not loose too much cruisin mileage. plus the pinion in the 3.42s is the strongest out of them all, according to my rear end guy

Dean23 · 08-20-2002, 08:28 PM

With 4.10's and a .75 overdrive youyr rear ratio should then be 3.08 not 3.40.

Project1970 · 08-20-2002, 09:43 PM

Quote:

Originally posted by Bamm 24
17" tires and 700R4= 4.10gears. Trucks like this, gas mpg is going to hover anywhere around 10-17 tops with your 700R4. All this depends of course on your engine buildup? When I had my 700R4 built, the guy said that in lockup it would knock 70 points off of my final drive ratio- 4.10 gears with a 700R4 = same as a turbo 350 transmisson with a 3.40 rear gear. Can anyone back up this info?.........JB

Your tranny man was conservative, heh.

If you want to see what your effective final drive ratio is with a 700R4 vs a non-OD transmission, multiply your rear end ratio by 0.75 (the ratio of 4th gear in a 700R4).

Some examples...700R4 on a:
2.73 rear: 2.04 final drive ratio!
3.07 rear: 2.30
3.42 rear: 2.56
3.73 rear: 2.79
4.11 rear: 3.08
4.56 rear: 3.42

So, on the freeways, a 700R4/3.73 should behave like a TH350C/2.73, or very close to it...and a 700R4 on a 4.56 rear still gets you a nice 3.42 final drive ratio for the freeways.

I voted for 3.73, because IMO it's just the perfect rear for a 700R4/4L60/4L60E. I've been in two trucks with that combo and it just works really really well.

Oh, he also forgot to factor in the lockup in the torque converter. It's good for another couple hundred RPM drop.

Bamm · 08-20-2002, 11:17 PM

Man I am glad I know now to multiply and not just subtract .75 like I thought he said. I was getting worried that I might have to try my gozinta's. You know 1 gozinta 1 = 1 time, 1 gozinta 2 = 2 times...............Therapy, I know Iknow get therapy, you guys keep reminding me..............................JB

NSANE68!!! · 08-20-2002, 11:28 PM

I've got the 4:10's and a WHOPPING 4 miles to the gallon.

and the only thing I can run is premium or better

that hurts a little, but hey this is what I look like with my foot in it

Chevyman69 · 08-21-2002, 12:43 AM

A lot of you guys are obviosuly not reading his post, he has a 700R4 so choices are a lot more flexible. Personally I would run 373's, have em in my 69( no its not being driven on the account it has no body) but my driver 92 is 350/700R4/373's and I love it. 307's in a truck with overdrive is a waste of time. Your rpm at cruise would be so low that you would be bogging the engine and I can almost guarantee the mileage would improve if it spun faster like what a 373 gear will give. You need to have at optimal vaccuum for mileage so a little rpm won't hurt it. Depends on tire height too but like the 92( its a 4X4 though) has 245/75/16's and cruises at 2100 rpm at 65 mph so a lower tire may net a higher speed say 2300 but thats a lot better than 3100 without overdrive. Plus with the 700r's first gear you get very nice out of the hole acceleration and a good cruise rpm. Oh yeah did i say I liked 373's

.

Huck · 08-21-2002, 08:46 AM

A 700R4 and my 5speed final drives are about equal. Running a crate 350 with headers, duals, edelbrock1406, HEI and a 308 rear gives me 20+ MPG consistantly. Recent trip back and forth thru West Virginia Mountains still gave me 19MPG with a topper on my truck. As previously stated 308s are tall for most applications. I sometimes pull a flat bed or a Bass boat with no problems till I hit hills but I believe I would have that down shift issue with 340 or 373 gears as well. If I did it again, I would go with 340 gears as they would probably allow the 350 to run at a little higher RPM without much sacrafice in MPG. BUT, the 5speed has it all over a 700R4 except when in heavy traffic. Want to slow down with a load--you have 5 gear choices----. Worried about TV cable adjustment--No Worries. No cooling problems, No leaking problems. Can pull all day in 5th if I want---and less expensive conversion in the long run. I do have a 700R4 that I will put in my next project as that one Moma will drive --getting things like---MULCH, FLowers, and other useless cxxp!! MY .02---Huck

Longhorn Man · 08-21-2002, 07:45 PM

I drove huck's blue baby, and I must say, it is truely an awsome job he did there.

HvyChevy454 · 08-21-2002, 07:48 PM

id have to go w/ the 3.73 to try to salvage soem gas mileage. Im running a 3.08 right now gettin 9.3 MPG highway. thats w/a TH350 and 29 tall MT's running 75 at 2800 RPM.

Tracy Focht · 08-22-2002, 11:10 AM

I guess I'm just more aggressive. I chose the 4.10's...with a 28" tall tire and a 700r4, just fine IMHO.

View Poll Results: What rea gears to use
3.73	28	84.85%
4.10	5	15.15%
4.56	0	0%
5.13	0	0%
Voters: 33. You may not vote on this poll

08-19-2002, 09:27 PM	#1
Dean23 68cst_ss490 Join Date: May 2001 Location: edmonton,canada Posts: 1,363	What rear gears to go with What rear gears to use __________________ Dean edmonton,canada a winter wonderland 2005 Chevrolet Avalanche LT cold air intake, performance exhaust, Comp cams cam, jba shorty ceramic headers. http://www.cardomain.com/ride/3090973

08-19-2002, 09:28 PM	#2
Dean23 68cst_ss490 Join Date: May 2001 Location: edmonton,canada Posts: 1,363	Oh yeah I have a 350hp 350, 700r4 17 inch wheels, L79 cam9.5 comp. __________________ Dean edmonton,canada a winter wonderland 2005 Chevrolet Avalanche LT cold air intake, performance exhaust, Comp cams cam, jba shorty ceramic headers. http://www.cardomain.com/ride/3090973

08-19-2002, 09:42 PM	#3
gabet40 Registered User Join Date: Dec 1999 Location: Modesto, CA Posts: 565	for racing? for cruising? for all around? ill put in my vote for 3.73 out of these choices but all around im going with a 3.42 i do a lot of cruising and a little hot rodding. but for racing, the lower the better of course __________________ Current owner of 2016 2500 Silverado Midnight Edition. Former owner of: 69 1/2 ton, change from long/fleet to short/fleet, shaved door handles, shaved tailgate, 4/6 drop, power windows, 700r4 72 blazer, 350 with Holley Commander 950 DFI, crane energizer cam, 350 tranny, dual sanderson blockhuggers/magnaflow exhaust

08-19-2002, 09:46 PM	#4
Dean23 68cst_ss490 Join Date: May 2001 Location: edmonton,canada Posts: 1,363	strictly street, cruisin, maybe the odd run at the track __________________ Dean edmonton,canada a winter wonderland 2005 Chevrolet Avalanche LT cold air intake, performance exhaust, Comp cams cam, jba shorty ceramic headers. http://www.cardomain.com/ride/3090973

08-20-2002, 07:11 AM	#5
Church Carolina Classic Trucks Join Date: Jan 2000 Location: The South Posts: 792	What size tire are you running? If it is around 28" tall, I'd say stick with the 3.73, at 65 mph you would be pushing a little over 2900 rpm @ 1:1 then overdrive would put you at a little under 2100 rpm. __________________

08-20-2002, 09:01 AM	#6
colohusker Registered User Join Date: Apr 2002 Location: Longmont, CO Posts: 436	not listed, but right now i'd go with 3.07, but want to go to 3.73 or 4.10 when it's no longer a work truck.... For street and cruising, i'd go with the 4.10. If you're going to be taking the occasional road trip, I think I'd go with the 3.73. __________________ ------------------------------------------------ I say it's only money, my wife says it's only a truck.... '71 C10 Deluxe, factory ac, ps, pb, should be done by 2102 Longmont, CO husker95@hotmail.com Last edited by colohusker; 08-20-2002 at 10:30 AM.

08-20-2002, 09:20 AM	#7
68 Suburban Registered User Join Date: Oct 2000 Location: From Chicago, Live in Phoenix, AZ Posts: 6,802	I like my 3.07 and the 15+ mpg that comes with it at 75-80 mph. __________________ Just sitting here contemplating contemplation.

08-20-2002, 12:49 PM	#8
Bamm Cowboy Fan for Life!!!!!! Join Date: Apr 2002 Location: Amelia, Virginia Posts: 2,921	17" tires and 700R4= 4.10gears. Trucks like this, gas mpg is going to hover anywhere around 10-17 tops with your 700R4. All this depends of course on your engine buildup? When I had my 700R4 built, the guy said that in lockup it would knock 70 points off of my final drive ratio- 4.10 gears with a 700R4 = same as a turbo 350 transmisson with a 3.40 rear gear. Can anyone back up this info?.........JB __________________ 1967 ShortBed Fleetside 3/4 Drop 350/700R4 Tilt wheel 18 x 8 Torque Thrust II's Future mods: All new gauges & wood bed My Zip is 23002 I ship UPS, USPS

08-20-2002, 01:13 PM	#9
gabet40 Registered User Join Date: Dec 1999 Location: Modesto, CA Posts: 565	as of right now i have 3.08s but my 18" wheels on 40 series tires are only 25 1/2" tall. so even with my torque converter locked up on the freeway im still at about 2300 @ 75 mph. cruisin in my stocks are great though. ill stay at 80mpg @ about 2100. but i dont like waiting til im at about 3000rpm to really feel the power when im pullin off the line. i think 3.42s will help me off the line a lot but not loose too much cruisin mileage. plus the pinion in the 3.42s is the strongest out of them all, according to my rear end guy __________________ Current owner of 2016 2500 Silverado Midnight Edition. Former owner of: 69 1/2 ton, change from long/fleet to short/fleet, shaved door handles, shaved tailgate, 4/6 drop, power windows, 700r4 72 blazer, 350 with Holley Commander 950 DFI, crane energizer cam, 350 tranny, dual sanderson blockhuggers/magnaflow exhaust

08-20-2002, 08:28 PM	#10
Dean23 68cst_ss490 Join Date: May 2001 Location: edmonton,canada Posts: 1,363	With 4.10's and a .75 overdrive youyr rear ratio should then be 3.08 not 3.40. __________________ Dean edmonton,canada a winter wonderland 2005 Chevrolet Avalanche LT cold air intake, performance exhaust, Comp cams cam, jba shorty ceramic headers. http://www.cardomain.com/ride/3090973

08-20-2002, 11:17 PM	#12
Bamm Cowboy Fan for Life!!!!!! Join Date: Apr 2002 Location: Amelia, Virginia Posts: 2,921	Man I am glad I know now to multiply and not just subtract .75 like I thought he said. I was getting worried that I might have to try my gozinta's. You know 1 gozinta 1 = 1 time, 1 gozinta 2 = 2 times...............Therapy, I know Iknow get therapy, you guys keep reminding me..............................JB __________________ 1967 ShortBed Fleetside 3/4 Drop 350/700R4 Tilt wheel 18 x 8 Torque Thrust II's Future mods: All new gauges & wood bed My Zip is 23002 I ship UPS, USPS

08-20-2002, 11:28 PM	#13
NSANE68!!! SLICER AND DICIER Join Date: May 2001 Location: Quuen Creek Posts: 1,383	I've got the 4:10's and a WHOPPING 4 miles to the gallon. and the only thing I can run is premium or better that hurts a little, but hey this is what I look like with my foot in it Attached Images __________________ 01 Tahoe 22's 2/4 drop and tv's 68 chevy money pit 51 chevy belair 95 Honda 900RR 05 GMC Siearra (company truck)

08-21-2002, 12:43 AM	#14
Chevyman69 Vortec 350's Suck Join Date: Nov 2000 Location: Pickardville Alberta Canada Posts: 544	A lot of you guys are obviosuly not reading his post, he has a 700R4 so choices are a lot more flexible. Personally I would run 373's, have em in my 69( no its not being driven on the account it has no body) but my driver 92 is 350/700R4/373's and I love it. 307's in a truck with overdrive is a waste of time. Your rpm at cruise would be so low that you would be bogging the engine and I can almost guarantee the mileage would improve if it spun faster like what a 373 gear will give. You need to have at optimal vaccuum for mileage so a little rpm won't hurt it. Depends on tire height too but like the 92( its a 4X4 though) has 245/75/16's and cruises at 2100 rpm at 65 mph so a lower tire may net a higher speed say 2300 but thats a lot better than 3100 without overdrive. Plus with the 700r's first gear you get very nice out of the hole acceleration and a good cruise rpm. Oh yeah did i say I liked 373's . __________________ 69 Chev CST 10 reg cab lwb Daily Driver: 92 Chev Reg Cab LWB Silverado 4x4, K.I.A 7:51 AM 04/22/03 Will be resurrected

08-21-2002, 08:46 AM	#15
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,261	A 700R4 and my 5speed final drives are about equal. Running a crate 350 with headers, duals, edelbrock1406, HEI and a 308 rear gives me 20+ MPG consistantly. Recent trip back and forth thru West Virginia Mountains still gave me 19MPG with a topper on my truck. As previously stated 308s are tall for most applications. I sometimes pull a flat bed or a Bass boat with no problems till I hit hills but I believe I would have that down shift issue with 340 or 373 gears as well. If I did it again, I would go with 340 gears as they would probably allow the 350 to run at a little higher RPM without much sacrafice in MPG. BUT, the 5speed has it all over a 700R4 except when in heavy traffic. Want to slow down with a load--you have 5 gear choices----. Worried about TV cable adjustment--No Worries. No cooling problems, No leaking problems. Can pull all day in 5th if I want---and less expensive conversion in the long run. I do have a 700R4 that I will put in my next project as that one Moma will drive --getting things like---MULCH, FLowers, and other useless cxxp!! MY .02---Huck



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08-21-2002, 07:45 PM	#16
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	I drove huck's blue baby, and I must say, it is truely an awsome job he did there.

08-21-2002, 07:48 PM	#17
HvyChevy454 Slowly getting CRSS... Join Date: Jul 2001 Location: Lutz, Florida Posts: 656	id have to go w/ the 3.73 to try to salvage soem gas mileage. Im running a 3.08 right now gettin 9.3 MPG highway. thats w/a TH350 and 29 tall MT's running 75 at 2800 RPM. __________________ -Nic Lutz, Fl My Team Website The Heavy Chevy Website ------------------ 72 Cheyenne 10 LWB GM 12-bolt 3.08 w/ Auburn Posi 91 454 Edel Performer RPM Intake 750 cfm carb Comp Cam 268/.495 Hedman Headers Dual 3'' Exhaust 71 Cheyenne 20 4x4 Fact. A/C PS PB Tilt Currently in the works... Speak Softly and Carry A Big Block... There is No replacement for Displacement... "If everything seems under control, you're just not going fast enough." - Mario Andretti Last edited by HvyChevy454; 08-21-2002 at 07:50 PM.

08-22-2002, 11:10 AM	#18
Tracy Focht Registered User Join Date: Dec 1999 Location: Stillwater, OK 74075 Posts: 2,936	I guess I'm just more aggressive. I chose the 4.10's...with a 28" tall tire and a 700r4, just fine IMHO.

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