What gear to use with the 402/th400?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

gregbr · 06-26-2009, 02:54 AM

Hi All! On my restored 70 GMC (see pictures in signature) it came from the factory with the 402/th400 & 3.07 gears. Engine rebuilt, 30 over, Crane 270-2H (WG1104) cam, timing set at 10BTDC, factory intake & exhaust manifolds & Rochester, th400 stock rebuild with 350 torque converter, Eaton series 3 posi. While it drives great on the open road 55-60 (I always baby it), it seems sorta sluggish on take off. I'm thinking about a regear to a 3.42 to keep the same Eaton Posi.

Only driven to local shows and occasional trips around town. Would never drive it long distance or above 65, stays garaged, can't leave it out. What would you do & why?? Could I still be off on the timing and make a difference??

Just checked those pictures and I never loaded the ones showing it completed. Will fix that this weekend.

JimKshortstep4x4 · 06-26-2009, 04:44 AM

My son's 72 has the 3:07 gear with a 402 in it and it has good power on acceleration. The cam is a mild one with the power curve in the 1,000-4,000 rpm range. What is the power band for your cam?

I would try bumping the timing up to 12-14 degrees tdc. Also, has the distributor been curved for the engine?

While a 3:42 gear will help the acceleration you may not need to go that route. If you do take the truck on a long trip the 3:42 gearing might turn into an irritation!

Jim

**special-K** · 06-26-2009, 05:05 AM

I`d try Jim`s suggestion,first.But,if still not happy,I think 3.42s will fill the bill.I`ve always been a grunt gears kinda guy,until more recently.I think 3.42s are a great compromise between 3.07s and 3.73s.My shortbed project has them because I hope to some day run a Gear Vendors o/d unit and it`s as tall a gear I`d run with o/d.In the mean time,or if the o/d never happens,the gears will be as hiway friendly as I need.Cruising 65 max. is fine with me and I`m not afraid of running the 3,000 rpm range.I prefer 2-lane hiways anyway.There was a time before o/d with a national speed limit of 70 mph.

prostreetC-10 · 06-26-2009, 09:19 AM

One thing for sure is that a torque bulding BBC doesn't need the gears them little small blocks benefit from. My truck to the left has 3.73's and my old '68 BBC custom camper had a 3.54 setup. I wish I had the 3.54's. Still good for a trip on the highway but also deep enough for a nice hole shot on one of them there rice burners. I think you would be really please with a 3.42 set and I'd throw those 3.07's out in the field.

Shyguy · 06-26-2009, 09:50 AM

My son is running 3.42 gears behind a mild built 454 with a 3 speed and really likes the setup.

He won the burn-out contest in the local car show earlier this month.

The truck the setup is in is a '67 body on a probably 69 frame and suspension.

I wouldn't toss the 3.07s, may come in handy some day. Of course we seem to gather a lot of stuff that will come in handy some day.

Danny

LUV2XCLR8 · 06-26-2009, 09:56 AM

My Blazer Build has a 342 and Factory Posi, but I'm running a 700R4.

71 super · 06-26-2009, 10:31 AM

Greg i replaced the 3.07 rear in my bb with 3.42 and it is still a little sluggish imo but everything i have had previously has been 3.73 or numerically higher- all the way to 4.56 so i have a little bias, but in retrospect I wish would have gone to 3.73.

69sixpackbee · 06-26-2009, 11:09 AM

I have 3.54's in my Dana 60 rear. Good compromise. Albeit, it is a 4-speed though.

69GMCLonghorn · 06-26-2009, 12:17 PM

I loathe people with HIGHWAY GEARS!!

prostreetC-10 · 06-26-2009, 12:49 PM

Quote:

Originally Posted by 69GMCLonghorn

I loathe people with HIGHWAY GEARS!!

What?

It's not like they are at the plant installing them. We tend to get what comes in our trucks. I had an 80 Sliverado that I'm sure had 8.53's in it. I had about a top speed of 43!!

gregbr · 06-26-2009, 10:35 PM

Thanks for the input! I rebuilt the original dizzy, did not change anything on the springs & weights. I have not had it curved to the engine. My 67 4WD has a th350 & 3.73 and runs pretty good on 33" tires, That's why I thought the 3.42 would be better on the 402 2WD. I will adjust the timing this weekend and see what happens.

Daves72'GMC · 06-27-2009, 12:58 AM

I have a 402BB 30 over with turbo 400 and 3.54 dana 60 and an edelbrock cam a little bigger than stock and good on the highway and quick from the start and good milage.

tim21391 · 06-27-2009, 01:51 AM

i got the 3.07 i think and its got plenty balls

prostreetC-10 · 06-27-2009, 01:55 AM

Hey Tim....got any pics of your Mustang? I have a Fastback in my signature link below. Mine has a little 289 lawn motor engine.

gregbr · 06-27-2009, 11:26 PM

Tim, What cam & timing are you running? Engine stock or modiffied? Maybe I can adjust mine Sunday evening.

tim21391 · 06-28-2009, 01:12 AM

i have an rv cam in mine.. not sure.. but i actually dont know what timing im at because im having trouble settin it i converted over to hei these past few days.. but when i had stock points in it had plenty of balls.. but it has a holley double pumper carb and an edelbrock performer intake

69GMCLonghorn · 06-28-2009, 01:49 AM

RE: the comment about highway gears, just having a little fun.

**special-K** · 06-28-2009, 06:09 AM

Quote:

Originally Posted by 69GMCLonghorn

RE: the comment about highway gears, just having a little fun.

And,it sure was obvious to me coming from a Longhorn ma....I mean feller who must have the grunt gears.I love grunt gears,screaming on the hiway,or just goin`slower than the rest.

prostreetC-10 · 06-28-2009, 09:26 AM

I missed one part of your posting. You say it seems sorta sluggish. You need more initial timing than 10 degrees. Most big blocks like the 16 to 18 degree mark. It will raise your idle so you will need to drop that down but you will probably pick up more low end drivablility......especially in these heavier rigs with those gears.

gregbr · 06-30-2009, 10:24 PM

Set timimg today at 14. Unable to road test due to yard work blocking the shed. Maybe Thurs....

prostreetC-10 · 06-30-2009, 11:50 PM

Don't be afraid to throw a little more in it. If you run into detonation (pinging) then you have to back it off but I bet you could get away with 18.

BossHogg69 · 07-01-2009, 12:16 AM

my '69 has 3.73's and when I was rolling the 454/TH400 combo it ran good at 60-65 on the highway. 70 got a little annoying. 3.42's would probably be a good compromise, but I like the way 3.73's come outta the hole!

prostreetC-10 · 07-01-2009, 12:37 AM

I just finally looked at your pics and didn't realize that we were talking a 4wd. What size tires are on it? Tire diameter does come into play. I'm running 29's with a 3.73 setup. If you have 31/10.5 or taller, you can run deeper gear and get away with it. All the more reason to S-can those 3.07's

gregbr · 07-09-2009, 08:09 PM

Not sure what you saw, but the restored Big Block truck, the Gold colored one, is 2wd with 275-60-15 or 29" tires. The White truck is a 67 4wd with a 350/th350, 3.73 posi and 33" tires. The 4wd seems to have better take off then the BB.

'72customdeluxe · 07-09-2009, 08:14 PM

you might try a 2000-2400 rpm stall converter first. It would help a good bit, yourcamshould need it, and it will help you still if you decide to get the 3.42's eventually

06-26-2009, 02:54 AM	#1
gregbr Senoir Member Join Date: Mar 2002 Location: Rock Hill, SC USA Posts: 1,214	What gear to use with the 402/th400?? Hi All! On my restored 70 GMC (see pictures in signature) it came from the factory with the 402/th400 & 3.07 gears. Engine rebuilt, 30 over, Crane 270-2H (WG1104) cam, timing set at 10BTDC, factory intake & exhaust manifolds & Rochester, th400 stock rebuild with 350 torque converter, Eaton series 3 posi. While it drives great on the open road 55-60 (I always baby it), it seems sorta sluggish on take off. I'm thinking about a regear to a 3.42 to keep the same Eaton Posi. Only driven to local shows and occasional trips around town. Would never drive it long distance or above 65, stays garaged, can't leave it out. What would you do & why?? Could I still be off on the timing and make a difference?? Just checked those pictures and I never loaded the ones showing it completed. Will fix that this weekend. __________________ 67 Chevy, Small back glass, Factory 4WD, Factory Shortbed, Factory V8, Lifted 4" 70 GMC Sierra Grande, Factory Shortbed, Factory 402/400 turbo, Super Custom Interior. Numbers matching with SPID & Build Sheet. 68K Original Miles. Restored 2010 70 GMC Restoration Pictures http://67-72chevytrucks.com/gallery/...00&ppuser=4424 Last edited by gregbr; 06-26-2009 at 02:57 AM.

06-26-2009, 04:44 AM	#2
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: What gear to use with the 402/th400?? My son's 72 has the 3:07 gear with a 402 in it and it has good power on acceleration. The cam is a mild one with the power curve in the 1,000-4,000 rpm range. What is the power band for your cam? I would try bumping the timing up to 12-14 degrees tdc. Also, has the distributor been curved for the engine? While a 3:42 gear will help the acceleration you may not need to go that route. If you do take the truck on a long trip the 3:42 gearing might turn into an irritation! Jim __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC

06-26-2009, 05:05 AM	#3
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: What gear to use with the 402/th400?? I`d try Jim`s suggestion,first.But,if still not happy,I think 3.42s will fill the bill.I`ve always been a grunt gears kinda guy,until more recently.I think 3.42s are a great compromise between 3.07s and 3.73s.My shortbed project has them because I hope to some day run a Gear Vendors o/d unit and it`s as tall a gear I`d run with o/d.In the mean time,or if the o/d never happens,the gears will be as hiway friendly as I need.Cruising 65 max. is fine with me and I`m not afraid of running the 3,000 rpm range.I prefer 2-lane hiways anyway.There was a time before o/d with a national speed limit of 70 mph. __________________ "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 ~

06-26-2009, 09:19 AM	#4
prostreetC-10 My Carbon Footprint Join Date: Oct 2008 Location: Orygun Posts: 5,527	Re: What gear to use with the 402/th400?? One thing for sure is that a torque bulding BBC doesn't need the gears them little small blocks benefit from. My truck to the left has 3.73's and my old '68 BBC custom camper had a 3.54 setup. I wish I had the 3.54's. Still good for a trip on the highway but also deep enough for a nice hole shot on one of them there rice burners. I think you would be really please with a 3.42 set and I'd throw those 3.07's out in the field. __________________ A quick "pedalfest" *Still getting loose (carb test)* 496 Initial fire up video!

06-26-2009, 09:50 AM	#5
Shyguy Junior Member Join Date: Dec 2006 Location: Southeast Missouri Posts: 2,436	Re: What gear to use with the 402/th400?? My son is running 3.42 gears behind a mild built 454 with a 3 speed and really likes the setup. He won the burn-out contest in the local car show earlier this month. The truck the setup is in is a '67 body on a probably 69 frame and suspension. I wouldn't toss the 3.07s, may come in handy some day. Of course we seem to gather a lot of stuff that will come in handy some day. Danny __________________ '67 Chevy C-20 short stepper - build complete, 454/SM-465. '75 C-30 Single Cab DRW-350 small block/NP-435. '77 GMC-6500 Dump Truck, 427 Tall Deck. '92 GMC K-3500 Duallie, 454/4L80E.

06-26-2009, 09:56 AM	#6
LUV2XCLR8 The LuvShack Garage Join Date: Jan 2004 Location: Maple Grove, TN (West Side) Posts: 30,468	Re: What gear to use with the 402/th400?? My Blazer Build has a 342 and Factory Posi, but I'm running a 700R4.

06-26-2009, 10:31 AM	#7
71 super Registered User Join Date: Sep 2005 Location: Canton North carolina Posts: 3,080	Re: What gear to use with the 402/th400?? Greg i replaced the 3.07 rear in my bb with 3.42 and it is still a little sluggish imo but everything i have had previously has been 3.73 or numerically higher- all the way to 4.56 so i have a little bias, but in retrospect I wish would have gone to 3.73. __________________ 67 blue step side- bb 68 gold and white swb cst anniversary 68 custom swb hot rod Ls swap 69 swb cst 6 cylinder/ overdrive 69 black/black cst bb swb 70 orange and white cst Canada built truck swb bb 71 black and white super swb bb 71 red and white super swb 72 green and white super swb 4x4 62 nova wagon 400 series Ls swapped 68 Camaro 327/4 speed- 1 owner, original paint 66 Volkswagen bettle 69 auto stick Volkswagen Beetle

06-26-2009, 11:09 AM	#8
69sixpackbee Registered User Join Date: Jan 2001 Location: Sabinal, Texas Posts: 1,706	Re: What gear to use with the 402/th400?? I have 3.54's in my Dana 60 rear. Good compromise. Albeit, it is a 4-speed though.

06-26-2009, 12:17 PM	#9
69GMCLonghorn Registered User Join Date: Dec 2006 Location: Porter Ranch, CA Posts: 978	Re: What gear to use with the 402/th400?? I loathe people with HIGHWAY GEARS!!

06-26-2009, 10:35 PM	#11
gregbr Senoir Member Join Date: Mar 2002 Location: Rock Hill, SC USA Posts: 1,214	Re: What gear to use with the 402/th400?? Thanks for the input! I rebuilt the original dizzy, did not change anything on the springs & weights. I have not had it curved to the engine. My 67 4WD has a th350 & 3.73 and runs pretty good on 33" tires, That's why I thought the 3.42 would be better on the 402 2WD. I will adjust the timing this weekend and see what happens. __________________ 67 Chevy, Small back glass, Factory 4WD, Factory Shortbed, Factory V8, Lifted 4" 70 GMC Sierra Grande, Factory Shortbed, Factory 402/400 turbo, Super Custom Interior. Numbers matching with SPID & Build Sheet. 68K Original Miles. Restored 2010 70 GMC Restoration Pictures http://67-72chevytrucks.com/gallery/...00&ppuser=4424

06-27-2009, 12:58 AM	#12
Daves72'GMC Registered User Join Date: Mar 2003 Location: Asheville, N.C Posts: 952	Re: What gear to use with the 402/th400?? I have a 402BB 30 over with turbo 400 and 3.54 dana 60 and an edelbrock cam a little bigger than stock and good on the highway and quick from the start and good milage.

06-27-2009, 01:51 AM	#13
tim21391 Registered User Join Date: Jul 2007 Location: Salina, Kansas Posts: 1,998	Re: What gear to use with the 402/th400?? i got the 3.07 i think and its got plenty balls __________________ 1972 C-10...402/400..flowmaster 40 series 1967 Mustang 347 stroker/C-4 1966 Mustang 289/3-speed 2013 Mustang V6/6speed w/300 ponies I may be 23, but i sure do knows 67-72s are sexy! Its not MPG its smiles per gallon! build started 11/25/08 build thread: http://67-72chevytrucks.com/vboard/s....php?p=2993796

06-27-2009, 01:55 AM	#14
prostreetC-10 My Carbon Footprint Join Date: Oct 2008 Location: Orygun Posts: 5,527	Re: What gear to use with the 402/th400?? Hey Tim....got any pics of your Mustang? I have a Fastback in my signature link below. Mine has a little 289 lawn motor engine. __________________ A quick "pedalfest" *Still getting loose (carb test)* 496 Initial fire up video!

06-27-2009, 11:26 PM	#15
gregbr Senoir Member Join Date: Mar 2002 Location: Rock Hill, SC USA Posts: 1,214	Re: What gear to use with the 402/th400?? Tim, What cam & timing are you running? Engine stock or modiffied? Maybe I can adjust mine Sunday evening. __________________ 67 Chevy, Small back glass, Factory 4WD, Factory Shortbed, Factory V8, Lifted 4" 70 GMC Sierra Grande, Factory Shortbed, Factory 402/400 turbo, Super Custom Interior. Numbers matching with SPID & Build Sheet. 68K Original Miles. Restored 2010 70 GMC Restoration Pictures http://67-72chevytrucks.com/gallery/...00&ppuser=4424 Last edited by gregbr; 06-27-2009 at 11:27 PM.

06-28-2009, 01:12 AM	#16
tim21391 Registered User Join Date: Jul 2007 Location: Salina, Kansas Posts: 1,998	Re: What gear to use with the 402/th400?? i have an rv cam in mine.. not sure.. but i actually dont know what timing im at because im having trouble settin it i converted over to hei these past few days.. but when i had stock points in it had plenty of balls.. but it has a holley double pumper carb and an edelbrock performer intake __________________ 1972 C-10...402/400..flowmaster 40 series 1967 Mustang 347 stroker/C-4 1966 Mustang 289/3-speed 2013 Mustang V6/6speed w/300 ponies I may be 23, but i sure do knows 67-72s are sexy! Its not MPG its smiles per gallon! build started 11/25/08 build thread: http://67-72chevytrucks.com/vboard/s....php?p=2993796



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06-28-2009, 01:49 AM	#17
69GMCLonghorn Registered User Join Date: Dec 2006 Location: Porter Ranch, CA Posts: 978	Re: What gear to use with the 402/th400?? RE: the comment about highway gears, just having a little fun.

06-28-2009, 09:26 AM	#19
prostreetC-10 My Carbon Footprint Join Date: Oct 2008 Location: Orygun Posts: 5,527	Re: What gear to use with the 402/th400?? I missed one part of your posting. You say it seems sorta sluggish. You need more initial timing than 10 degrees. Most big blocks like the 16 to 18 degree mark. It will raise your idle so you will need to drop that down but you will probably pick up more low end drivablility......especially in these heavier rigs with those gears. __________________ A quick "pedalfest" *Still getting loose (carb test)* 496 Initial fire up video!

06-30-2009, 10:24 PM	#20
gregbr Senoir Member Join Date: Mar 2002 Location: Rock Hill, SC USA Posts: 1,214	Re: What gear to use with the 402/th400?? Set timimg today at 14. Unable to road test due to yard work blocking the shed. Maybe Thurs.... __________________ 67 Chevy, Small back glass, Factory 4WD, Factory Shortbed, Factory V8, Lifted 4" 70 GMC Sierra Grande, Factory Shortbed, Factory 402/400 turbo, Super Custom Interior. Numbers matching with SPID & Build Sheet. 68K Original Miles. Restored 2010 70 GMC Restoration Pictures http://67-72chevytrucks.com/gallery/...00&ppuser=4424

06-30-2009, 11:50 PM	#21
prostreetC-10 My Carbon Footprint Join Date: Oct 2008 Location: Orygun Posts: 5,527	Re: What gear to use with the 402/th400?? Don't be afraid to throw a little more in it. If you run into detonation (pinging) then you have to back it off but I bet you could get away with 18. __________________ A quick "pedalfest" *Still getting loose (carb test)* 496 Initial fire up video!

07-01-2009, 12:16 AM	#22
BossHogg69 motor exploder Join Date: Mar 2009 Location: Pittsburgh, PA Posts: 2,346	Re: What gear to use with the 402/th400?? my '69 has 3.73's and when I was rolling the 454/TH400 combo it ran good at 60-65 on the highway. 70 got a little annoying. 3.42's would probably be a good compromise, but I like the way 3.73's come outta the hole! __________________ Adam 1969 Chevy CST/10 stepside, DART Big M/TREMEC Magnum Extreme/3.73's w/Detroit Truetrac 1965 Chevy Bel Air Wagon (daily driver), 327/TH350,10 bolt w/3.08's 1961 Chevy Bel Air Sport Coupe, ZZ454/M21/9" rear w/3.50's & Detroit Truetrac 2005 GMC 1500 ccsb 2wd, 6.0L/4L65e/3.73 G80 2006 GMC 2500HD ccsb 4x4, DMax LBZ/Allison 6spd/4.56's w/Detroit TrueTrac Use the SEARCH function on this forum - it is your friend!!

07-01-2009, 12:37 AM	#23
prostreetC-10 My Carbon Footprint Join Date: Oct 2008 Location: Orygun Posts: 5,527	Re: What gear to use with the 402/th400?? I just finally looked at your pics and didn't realize that we were talking a 4wd. What size tires are on it? Tire diameter does come into play. I'm running 29's with a 3.73 setup. If you have 31/10.5 or taller, you can run deeper gear and get away with it. All the more reason to S-can those 3.07's __________________ A quick "pedalfest" *Still getting loose (carb test)* 496 Initial fire up video!

07-09-2009, 08:09 PM	#24
gregbr Senoir Member Join Date: Mar 2002 Location: Rock Hill, SC USA Posts: 1,214	Re: What gear to use with the 402/th400?? Not sure what you saw, but the restored Big Block truck, the Gold colored one, is 2wd with 275-60-15 or 29" tires. The White truck is a 67 4wd with a 350/th350, 3.73 posi and 33" tires. The 4wd seems to have better take off then the BB. __________________ 67 Chevy, Small back glass, Factory 4WD, Factory Shortbed, Factory V8, Lifted 4" 70 GMC Sierra Grande, Factory Shortbed, Factory 402/400 turbo, Super Custom Interior. Numbers matching with SPID & Build Sheet. 68K Original Miles. Restored 2010 70 GMC Restoration Pictures http://67-72chevytrucks.com/gallery/...00&ppuser=4424 Last edited by gregbr; 07-09-2009 at 08:11 PM.

07-09-2009, 08:14 PM	#25
'72customdeluxe Registered User Join Date: Jan 2008 Location: Tejas Posts: 691	Re: What gear to use with the 402/th400?? you might try a 2000-2400 rpm stall converter first. It would help a good bit, yourcamshould need it, and it will help you still if you decide to get the 3.42's eventually __________________ '72 cheyenne super step, '05 long bed gmc

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