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#1 |
Registered User
Join Date: May 2012
Location: Pennsylvania
Posts: 132
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ReGearing Questions - Noobie
Hey I have a 1985 GMC 305/700r/208np and currently is geared to 3.08 , I have GM 10 bolts, but ive been told thats pretty much the same axle as the Danna 44? idk. Anyways I have a 4 inch lift and 33s right now, and the power is pretty good, tops out at 90 or so but this truck is my daily driver so keep that in mind. I'd like to put 35s on it and was curious on what i should regear it to, 1. for power spinning those tires, 2. MPG if any of yall could point me in the right direction... Thank you!
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#2 |
Registered User
Join Date: Jul 2011
Location: back 40, bc
Posts: 3,848
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Re: ReGearing Questions - Noobie
if you go with 35's, i would put some 3:73's in there. your 305 will thank you, & your 700 should keep hiway rpm's decent.
i had 3:73's in my k5 with 35's, could chirp the tires, 400 sb though. with a t350, revs weren't the best my stepper also has 3:73's with 33's, 350/5-speed, easily spin the tires, gets about 15 mpg with the overdrive |
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#3 | |
Registered User
Join Date: May 2012
Location: Pennsylvania
Posts: 132
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Re: ReGearing Questions - Noobie
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#4 |
Registered User
Join Date: Sep 2008
Location: San Carlos, Ca.
Posts: 3,048
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Re: ReGearing Questions - Noobie
I'm running 35's on the '63 with an overdrive manual (.73 Od) , 396 and 4.10 gears. Freeway speeds ( no speedometer yet but around 75-78) is around 2100-2200. Still barks 3 real hard and gets 4th easily. Tows real well and gets decent ( for a big block) mileage. 3.73's wouldn't be bad either. I think the 700r4 has a pretty deep 1st gear IIRC.
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Chris '63 k15 long step Vortec 7.4 - L29 Blackbear tune, Five 0 Motorsports injectors, Chris Straub Cam, NV4500, divorced 205 ![]() 52" front and 63" rear spring swap D44 / 14bff - disc axles Milemarker 9K and 10.5K hydraulic winches 63" & B52 Spring Install http://67-72chevytrucks.com/vboard/s...ng+swap+thread NV4500 Reverse Build Thread http://67-72chevytrucks.com/vboard/s...=reverse+build L29 - 7.4 Vortec Build http://67-72chevytrucks.com/vboard/s...&highlight=L29 |
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#5 |
Another Day, Another Dollar
Join Date: Nov 2008
Location: North Vancouver, BC
Posts: 1,316
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Re: ReGearing Questions - Noobie
I have 3:73's and 35's behind my th400 (no OD) and at 3 grand I'm doing about 60mph
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-78 K20 Cheyenne 454 long box, 4" lift, 35" MT's, '84 cab, '80 box "its hip to be square" ![]() |
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#6 | |
Registered User
Join Date: May 2012
Location: Pennsylvania
Posts: 132
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Re: ReGearing Questions - Noobie
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#7 | |
Registered User
Join Date: May 2012
Location: Pennsylvania
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Re: ReGearing Questions - Noobie
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#8 |
Registered User
Join Date: Jul 2011
Location: back 40, bc
Posts: 3,848
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Re: ReGearing Questions - Noobie
well, i live north of the border, so that's probably not much help.
my stepper came with factory 3:73's, my k5 i bought Yukon ring & pinions from Lordco (our version of autozone, o'reilly's, whatever) http://www.yukongear.com/ProductDeta...px?ProdID=5309 http://www.yukongear.com/ProductDetails.aspx?ProdID=541 there one of the pricier ones out there, but NEVER had a fail. Motive gear, & Richmond have better prices on theirs. could prob. pick up a set off ebay or something for $2-$300 |
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#9 |
Senior Member
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Location: Long Beach, CA
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Re: ReGearing Questions - Noobie
With a 305, I'd run 4.11s for sure. You'll probably get better gas mileage because you'll be running in a better part of the powerband.
'63GENIII and I both have 100 cubes on you so that's probably why 3.73s sound feasible to us. In your case the auto trans and torque converter end up picking up a lot of the slack for bad gearing. I stand by my recommendation for 4.11s
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Jason M. @argonaut62 1972 K5 Blazer CST, Turquoise 1966 K20 Short Fleet Pickup, Big Ugly 1964 C10 Short Fleet, Gertrude 2001 Porsche 911 Carrera 1996 Ford Bronco XLT 1980 Jeep Wagoneer 2008 Honda CBR1000RR 2005 Honda RC51 1981 Honda CB750C No dis-assemble Johnny Five! No dis-assemble! Last edited by argonaut; 10-09-2013 at 02:22 AM. |
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#10 | |
Registered User
Join Date: May 2012
Location: Pennsylvania
Posts: 132
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Re: ReGearing Questions - Noobie
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#11 |
Registered User
Join Date: Dec 2009
Location: Fairbanks, AK
Posts: 1,830
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Re: ReGearing Questions - Noobie
I agree with Jason at 4.11 minimum. I'd even go 4.56 if you are never going much over 55. My 91 has 4.56's, 33" tall tires and an overdrive. It feels great with the lower gears and isn't too wound out at 55 with the OD. Again, your 305 will thank you.
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-Marcus 1991 V3500 L29 454 4L80E NP205 D60/14 Bolt 4.56's 1984 K30 292 TH400 NP205 D60/14 Bolt 4.56's flat bed 7'6" Meyer Plow 2022 Silverado 3500 L8T Project Daily Driver Project Heavy Hauler Project Plow Truck |
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#12 |
Registered User
Join Date: May 2012
Location: Pennsylvania
Posts: 132
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Re: ReGearing Questions - Noobie
I drive it daily and drive it at 50-65mph, seems like what your saying 4.56s might be my best bet, I'm just now understanding the purpose of regearing, but would 4.56s get better mpg than the 4.11s?
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#13 |
Senior Member
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Location: Long Beach, CA
Posts: 1,813
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Re: ReGearing Questions - Noobie
Snow,
Logic would tell you that a numerically lower gear, and larger diameter tires would result in lower engine rpms at a given vehicle speed, and thus better fuel mileage. However if you gear it so that the engine is spinning an an rpm that is too low on the horsepower curve it will actually consume more fuel, because it is making power far less efficiently than at a higher rpm. Each motor has a sweet spot that is optimum for power and economy at sustained operation. This is what the engineers determined when they designed out trucks. In general, smaller displacement motors make power at higher rpms, than large displacement motors. so the gearing is usually numerically higher to put the motor in the sweet spot. So sometimes, when you've mixed and matched engines, transmissions, rear axles, and have a big heavy vehicle, it can be beneficial to numerically increase the gear ratio to get better power and better fuel efficiency. An example would be my F0rd Bronco. I had 33" tires on it with 3.55:1 diff gears and overdrive with a small block. I recent put 31" tires (close to stock size) back on it, and my fuel mileage has gone up by at over 1mpg. When you're getting 13mpg, that translates into an 8% increase. If I want to run 33" tires again, I really should install 3.73:1 gears in the diffs. Make sense?
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Jason M. @argonaut62 1972 K5 Blazer CST, Turquoise 1966 K20 Short Fleet Pickup, Big Ugly 1964 C10 Short Fleet, Gertrude 2001 Porsche 911 Carrera 1996 Ford Bronco XLT 1980 Jeep Wagoneer 2008 Honda CBR1000RR 2005 Honda RC51 1981 Honda CB750C No dis-assemble Johnny Five! No dis-assemble! Last edited by argonaut; 10-09-2013 at 07:07 PM. |
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#14 |
Senior Member
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Location: Long Beach, CA
Posts: 1,813
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Re: ReGearing Questions - Noobie
Did your pickup come stock with 305/700r4/np208 and the 3.08:1 gears?
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Jason M. @argonaut62 1972 K5 Blazer CST, Turquoise 1966 K20 Short Fleet Pickup, Big Ugly 1964 C10 Short Fleet, Gertrude 2001 Porsche 911 Carrera 1996 Ford Bronco XLT 1980 Jeep Wagoneer 2008 Honda CBR1000RR 2005 Honda RC51 1981 Honda CB750C No dis-assemble Johnny Five! No dis-assemble! |
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#15 | |
Registered User
Join Date: May 2012
Location: Pennsylvania
Posts: 132
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Re: ReGearing Questions - Noobie
Quote:
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#16 |
Senior Member
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Location: Long Beach, CA
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Re: ReGearing Questions - Noobie
I believe stock tire size that would have come on the pickup is a 235/75R15, which is about 29" in diameter. Now you want to step up to a 35" tire
So 3.08 original gear size / 29" original tire diam * 35" new tire diam = 3.72 theoretical new gear size Then take into account those 35" tires are much wider, and heavier, and are probably a less efficient tread pattern. This takes more power to spin and overcome friction. So we'd bump up from the 3.73 we calculated, to a 4.11. This will probably get you back to similar performance as what you originally had. So now consider how you will use your pickup. Will you be hauling much payload, or towing much? If so you might consider MTCK's recommendation and go up more to a 4.56 gear ratio to put the motor into a stronger part of the powerband at cruising speeds.
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Jason M. @argonaut62 1972 K5 Blazer CST, Turquoise 1966 K20 Short Fleet Pickup, Big Ugly 1964 C10 Short Fleet, Gertrude 2001 Porsche 911 Carrera 1996 Ford Bronco XLT 1980 Jeep Wagoneer 2008 Honda CBR1000RR 2005 Honda RC51 1981 Honda CB750C No dis-assemble Johnny Five! No dis-assemble! |
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#17 |
Newbee
Join Date: Jan 2010
Location: Phoenix, Arizona
Posts: 1,406
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Re: ReGearing Questions - Noobie
Excellent gears, at a reasonable price. USA made too. Just put the front and rear in my 69.
http://www.usgear.com/aftermarket.php |
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#18 | |
Registered User
Join Date: May 2012
Location: Pennsylvania
Posts: 132
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Re: ReGearing Questions - Noobie
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#19 | |
Registered User
Join Date: May 2012
Location: Pennsylvania
Posts: 132
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Re: ReGearing Questions - Noobie
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#20 |
Registered User
Join Date: Dec 2009
Location: Fairbanks, AK
Posts: 1,830
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Re: ReGearing Questions - Noobie
Just a thought, but if you are going to regear both axles and buy new tires, you might look into swapping in some 3/4 ton or 1 ton axles. Add up the costs. I've done both. You're just going to be into your 10 bolts for some pretty decent coin. With 4.11 @ 55 mph and 35" tires you'll be at just over 1500 rpm in overdrive. 4.56 would put you at just under 1700. That 700r4 has a nice low first and second gear and I think you'd be happy with either. Remember you need installation kits too!
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-Marcus 1991 V3500 L29 454 4L80E NP205 D60/14 Bolt 4.56's 1984 K30 292 TH400 NP205 D60/14 Bolt 4.56's flat bed 7'6" Meyer Plow 2022 Silverado 3500 L8T Project Daily Driver Project Heavy Hauler Project Plow Truck |
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#21 | |
Registered User
Join Date: May 2012
Location: Pennsylvania
Posts: 132
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Re: ReGearing Questions - Noobie
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#22 |
Senior Member
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Location: Long Beach, CA
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Re: ReGearing Questions - Noobie
Are you sure you have 3.08s?
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Jason M. @argonaut62 1972 K5 Blazer CST, Turquoise 1966 K20 Short Fleet Pickup, Big Ugly 1964 C10 Short Fleet, Gertrude 2001 Porsche 911 Carrera 1996 Ford Bronco XLT 1980 Jeep Wagoneer 2008 Honda CBR1000RR 2005 Honda RC51 1981 Honda CB750C No dis-assemble Johnny Five! No dis-assemble! |
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#23 |
Registered User
Join Date: May 2012
Location: Pennsylvania
Posts: 132
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Re: ReGearing Questions - Noobie
I mean 100% ? No. That's just what's in my dash, the dactory options sheet. I know for a fact the truck can hit 95 with 33s at 3k rpms I knows this because of the speeding ticket I got last year hah. Idk if this helps but if I'm at dead stop on flat ground, I can put the pedal to the floor (no brake) and spin my 33s no problem. The engine and trans have 365k on them too. It's crazy. I'm getting 10mpg or so too. But that's due to the carb, one it's a 350 carb and two I haven't had a chance to rebuild it yet.
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#24 |
Newbee
Join Date: Jan 2010
Location: Phoenix, Arizona
Posts: 1,406
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Re: ReGearing Questions - Noobie
Sounds like you have 3.73 gears. I have 3.08, and Im at 2000@55 with no overdrive! On 33's. There are thick gears ( like the ones in your link), and thin ones, depending on original ratio. Different spline axles too. Make sure of what you have before buying.
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#25 |
Newbee
Join Date: Jan 2010
Location: Phoenix, Arizona
Posts: 1,406
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Re: ReGearing Questions - Noobie
The axle shop that I buy my parts from, installs gears for $200- $250, plus parts. Cheap insurance of everything being right. If you have never done them before, you may want to consider having them done.
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