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#1 |
Registered User
Join Date: Jul 2013
Location: Chandler, Arizona
Posts: 58
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Hey Big Block guys, what diff gears are you running?
Hey Big Block guys, what diff gears are you running? I currently have a 68 swb with a 454/TH400 setup and I have 3.73 diff gears...can you see where this is headed yet?
![]() I'm not too sure how I will feel about "losing" some bottom end, so I'm curious what others running a 3 speed trans have "remedied" for this. Thanks! ![]() |
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#2 |
Registered User
Join Date: Sep 2014
Location: Mansfield TX
Posts: 71
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Re: Hey Big Block guys, what diff gears are you running?
I drove my '67 for years with a 468/th400 with 3:73.
I would have loved having a 4th gear, but I wouldn't sacrifice the low end for the lower RPM on the high end. I'd definitely recommend a 4spd tranny.
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1967 C10 custom |
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#3 |
Senior Member
![]() Join Date: Oct 2009
Location: Godley, TX
Posts: 17,963
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Re: Hey Big Block guys, what diff gears are you running?
don't mess with the rear gearing - 3.73 is perfect for your setup and the addition of an o/d trans. 200R4 or 700R4 will give you highway cruising in o/d AND increase your low end torque multiplication. 700R4 and 2004R have deeper 1st gears than the TH400. If you are eventually going to put in a 4 spd auto - don't waste $ on the 3.08 as an interim measure now, because it won't work well with the eventual o/d trans, unless you're gonna cruise at 110 mph.
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#4 | |
Account Suspended
Join Date: Jan 2007
Location: Tucson
Posts: 2,183
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Re: Hey Big Block guys, what diff gears are you running?
Quote:
My 'remedy'? A Gear Vendors 0.7:1 overdrive. ![]() 6 speeds forward, I don't lose any bottom end and at 70 on the freeway it turns 2300 RPM! ![]() |
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#5 |
2WD Jimmy
![]() Join Date: Mar 2005
Location: Davis County, Utah
Posts: 2,564
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Re: Hey Big Block guys, what diff gears are you running?
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#6 |
Registered User
Join Date: May 2014
Location: San Diego, CA
Posts: 547
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Re: Hey Big Block guys, what diff gears are you running?
I picked up a previous project that he used to run a SBC with the 3.73 gears.
Well I dropped a big block with a th400 in it. While trying to get a driveshaft made, I got a lecture from the guy about the 3.73 being too much gear. He recommended something down in the low 3's. I haven't driven the truck yet, but I'm sticking with the 3.73 for now (and I'm shopping for a new driveshaft shop) I don't foresee myself cruising the highway at 70 for long long periods of time that I would worry about the RPM issue. |
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#7 | |
Registered User
Join Date: Jul 2013
Location: Chandler, Arizona
Posts: 58
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Re: Hey Big Block guys, what diff gears are you running?
Quote:
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#8 |
Registered User
Join Date: Jul 2013
Location: Chandler, Arizona
Posts: 58
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Re: Hey Big Block guys, what diff gears are you running?
x2 I would have to agree that solution would work best, however I would have to save up my pennies for that! lol I think I saw them for about $2600?
I wonder if the cost of building a 700r4 would be worth the trouble or possibly using a 4l80E which I believe would require the use of a controller. |
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#9 |
Senior Member
![]() Join Date: Jan 2002
Location: Williston, ND
Posts: 2,999
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Re: Hey Big Block guys, what diff gears are you running?
I have 3.08, 3.42, and 3.54 gears in all of my big block trucks. 3.08 is really not a low end take off gear but for cruising its perfect. Big blocks make low end torque so a higher rear gea won't be terrible.
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68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi |
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#10 |
Registered User
![]() Join Date: Nov 2013
Location: Winnipeg, Mb
Posts: 1,115
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Re: Hey Big Block guys, what diff gears are you running?
I have 3.08's. Still chirp the tires and good for treks to the lake
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#11 |
Senior Member
![]() Join Date: Aug 2009
Location: Wheeling, Illinois
Posts: 703
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Re: Hey Big Block guys, what diff gears are you running?
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#12 |
I built it
Join Date: Sep 2008
Location: Bakersfield ca
Posts: 744
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Re: Hey Big Block guys, what diff gears are you running?
4.56's are awful with a 454. even with 35's i dont like going over 60. i get better mpg in town than i do on the freeway. for my setup im thinking 4.10's would be the money gear
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'72 k10 lwb 454, th400, 205, d44ft, 12b rear, 4in skyjacker, 35x12.5-15 superswampers, 4.56, blazer tank. painless wiring harness '98 dodge 3500 12v 5sp 4x4. the truck that actually runs |
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#13 |
Registered User
Join Date: Jan 2012
Location: Redondo Beach California
Posts: 146
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Re: Hey Big Block guys, what diff gears are you running?
I'm running 3.73s with 402/400 turbo trans. Fine around town, but screams going 70 at 3,000 rpms on the freeway. I'm thinking about adding a gear vendor overdrive.
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343 NEVER FORGET 9-11 FIGHT ON!!! GO USC!!! PROUD OWNER OF A 1970 ![]() |
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#14 |
Registered User
Join Date: Oct 2012
Location: Arlington Washington
Posts: 1,808
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Re: Hey Big Block guys, what diff gears are you running?
I also have a 402/400 with 3.73 gears. Never driven the truck so can't speak on drive ability. I know the truck will be a weekend cruiser and rarely see the freeway so stop light to stoplight torque is what I'm looking for
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Scott 67 c10 sold 89 c1500 90 k2500 91 s10 #chevyonly ![]() |
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#15 |
Registered User
![]() Join Date: May 2013
Location: WEST PALM FLORIDA
Posts: 1,174
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Re: Hey Big Block guys, what diff gears are you running?
A built 2004r is a great option for your 373 gears , a posi is a good idea also , 342 gears are another option
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68 Long Fleet , ly6 , turbo 350 , 3-5 drop , original paint , front discs 67 Small window , 7 foot bed , tweaked 6.0 LSX 2004R Medium Olive 58 Apache fleet , 235 , offy intake , dual exhaust , 4 on the floor , red/white 69 Long Fleet , Custom , 6.0, 4l60 , AC , Medium Olive |
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#16 |
Who Changed This?
![]() Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,450
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Re: Hey Big Block guys, what diff gears are you running?
3.55s in mine. It's a bit steep for freeway cruising, but it is a Custom Camper, so that's a good gear when I'm towing. I've thought about an O/D, but that would just be a needless expense at this time. I'd never recover the monetary savings, given how little I drive it.
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~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA |
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#17 |
Registered User
Join Date: Jul 2018
Location: Corona, CA
Posts: 13
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Re: Hey Big Block guys, what diff gears are you running?
Hi Steeveedee,
I have the exact year and model truck you have. My truck has the 402 with the TH400 and 3.54 gears in the diff. When on the freeway hitting 65, my RPM's are close to 4K. Does your truck also run that high? Is there anything I can do, keeping the original tranny and diff, to improve the RPM's so they are not running so high? I would like to use it as a daily driver and hit the freeways from time to time. Any advice or input would be greatly appreciated. God bless, Tbone
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70 CST C20 |
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#18 |
Registered User
Join Date: Jul 2009
Location: Space Coast, Fl.
Posts: 1,050
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Re: Hey Big Block guys, what diff gears are you running?
TBone, old thread, but I wonder if your tach. is in error. To turn 4000 RPM at 65 mph you'd have little short 20" diameter rear tires according to this previously posted calculator :http://www.csgnetwork.com/multirpmcalc.html
What size are your rear tires ?
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Dad always said, "Son, WISH IN ONE HAND, and ......." -------------------------------------- -------------------------------------- Current toy trucks: '71 GMC 1500 SUPER CUSTOM short/step, orig. dk. blue, 350/700r, ps,pb, A/C '72 Blazer 2wd, ochre & white, 454, tremecTKO 500 5spd. ps, pb, A/C, tilt Last 10yrs of hobby vehicles, had a FEW more in the 50yrs. before these: '66 Plymouth Belvedere City of Miami cop car clone. '70 Nova 406"sb, 13.5-1, solid roller, Brodix, p.glide/t.brake, back halved, 9" Ford, spool 4.88, cage,ladder bar/coilover, 10.5 tire....... SOLD!! '67 C10 short/step side mount spare -- SOLD!! '72 Jimmy 2wd, 350/350, ps, pb, fun driver, lots of bondo & a shiny red paint job..... SOLD!! '69 Nova 350, 4spd, A/C, ps, p.b, ...SOLD!! |
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#19 | |
Registered User
Join Date: Jul 2018
Location: Corona, CA
Posts: 13
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Re: Hey Big Block guys, what diff gears are you running?
Quote:
Awesome! Thanks for the calculator! The motor that came in the truck when I bought it was a SBC 350. I am returning the original size BBC 402 that belongs in it. I am a novice with rebulding an engine. Wish I knew someone local that could assist me so I don't blow this thing up upon initial startup. I am also trying to figure out the correct pulleys that belong on this. I am running Power Steering, & AC. I think I am supposed to have 3 grove crank pulley and 2 groove water pump pulley. BUT, don't know the diameters of the pulleys that I need to purchase. I am even thinking of rebuilding the TH400 since it is the original on the truck. Thanks for the calculator! God Bless! Tbone
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70 CST C20 |
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#20 | |
Who Changed This?
![]() Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,450
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Re: Hey Big Block guys, what diff gears are you running?
Quote:
According to the calculator posted above, my truck runs about 3 grand. If your tach is set for a 6-cyl, it will show about 4 grand. 3 grand is still pretty wound up. I drive 55 all the time on the freeway for that reason, and the tall camper shell really kicked my mileage in the butt. That's about 2500 RPM, which is tolerable. I'm retired, so I'm in no hurry to get anywhere if I'm driving the truck. ![]()
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~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA Last edited by Steeveedee; 08-03-2018 at 10:59 PM. Reason: Thar's --> That's typo |
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#21 |
Registered User
Join Date: Apr 2018
Location: Waynesville, MO
Posts: 48
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Re: Hey Big Block guys, what diff gears are you running?
My 72 SWB, 454/TH350 trans and 3.73 gears is hitting about 4000-4200 at 65 MPH, I am just going to go with a 700R4, I'm not racing it just a cruiser so it should be fine.
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#22 |
Registered User
Join Date: Sep 2013
Location: Gonzales, La
Posts: 1,441
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Re: Hey Big Block guys, what diff gears are you running?
3.08 in my truck with a 462 ci/turbo 350 combo. The gearing doesn't hurt the low end too much as traction in the truck is the issue here. I can smoke the tires a good 50-70 feet and still cruise at 70 mph with 2500 RPM's. If I was racing it and no pleasure cruising it I would change to 3.73's.
My 6 cylinder 68 has 3.73's. Can't go over 60-65 mph without rolling over 3000 RPM's. No good for hey cruising.
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MyToys: Goldilocks the "Ol School Survivor" 1968 C10, SWB Stepside, 08/15 TOTM, 250 CI 6 cylinder, 3 on the tree, 3.73 rear, 3/5 static drop, 23,500 original miles. Samson the 1970 CST10, LWB, 462Ci, Turbo 350 tranny, 3.08 rear gear, PB, PS, A/C, AM/FM, 2/4 Drop. Brutus the 1998 Camaro Z28, 33,500 original miles, LS1, 519 RWHP/497 RWTQ. Member of the Louisiana Classic Truck Club, LCTC Member of the Louisiana C10 Club Member of the Baton Rouge Drifters Car Club |
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#23 |
Senior Member
![]() ![]() Join Date: Sep 2008
Location: Harrison, Arkansas
Posts: 9,816
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Re: Hey Big Block guys, what diff gears are you running?
I'm running 3.73's' but I'm having an overdrive trans built as we post.
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other Larry Build thread, Arkansas K10 https://67-72chevytrucks.com/vboard/...=755797&page=5 The ability to speak several languages is an asset, but the ability to keep your mouth shut in any language is priceless. |
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#24 |
Senior Member
![]() Join Date: Aug 2009
Location: Wheeling, Illinois
Posts: 703
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Re: Hey Big Block guys, what diff gears are you running?
468 th400 with 355 gears not pleasant sounding @70 mph on the highway lol, having a 200 4r installed in the next couple weeks. Read an article on the interweb that my 355 will turn into a 273 with the overdrive, we'll see.
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#25 | |
Registered User
Join Date: Jul 2013
Location: Chandler, Arizona
Posts: 58
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Re: Hey Big Block guys, what diff gears are you running?
Quote:
![]() From this point I'm thinking I will stay with the 3.73 gears and look for an old used 200r4 or 700r4, build it up and change out my yoke on the driveline. If I have to get a new driveline, then so be it. It would be worth it to me to upgrade the trans for an additional gear on the highway, best of both worlds in my opinion. I appreciate everyone's input! oh and for anyone wondering, here is a diagram of the different transmissions and lengths... ![]() Last edited by FstCarsNGuitars; 11-20-2014 at 10:47 AM. Reason: added diagram |
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