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#1 |
Registered User
Join Date: Feb 2008
Location: sacramento california
Posts: 204
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what gears do i need on differential?
Hi.can anybody tellme what gears do i have im not good at mat, on my truck i have a 454 engine 400 tranny 60/35/15 wheels and can only run on freeway about 45 to 50 miles p/h max. I dont want to put an other tranny just go 70 on the freeway does any body knows what numbers do i need to change in the differential and where is a good place to get them........... Thanks
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#2 |
Registered User
Join Date: Aug 2009
Location: Newberry,FL
Posts: 277
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Re: what gears do i need on differential?
You can either do two things, you can take the ring and pinion gears out or measure the overall diameter of your tire, then drive at any speed if your speedo is correct, but most times you need a gps to do this, and record the corresponding rpm of that speed. If you can give me that I can figure it out for you. 3.07s are a great highway gear (I got a Turbo 400 also), but if you want more of a street strip truck probably go with some 4.11 or 3.73s. You'll probably be turnin around 3600rpms with the 4.11s at 70mph compared to 2900 rpm with the 3.07s. This all depends on your tires though. Mine does2700 rpm at 60 with 3.07s but all of this also depends on tire size.
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#3 |
Registered User
Join Date: Feb 2008
Location: sacramento california
Posts: 204
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Re: what gears do i need on differential?
where can i get the parts?
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#4 |
Between Trucks...
Join Date: Mar 2002
Location: Los Angeles, CA.
Posts: 3,830
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Re: what gears do i need on differential?
What rearend are you working with?
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Beat it to fit, Paint it to match... ![]() |
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#5 |
Registered User
Join Date: Nov 2009
Location: stoddard nh
Posts: 693
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Re: what gears do i need on differential?
how accurate is that speedo? is the truck shifting into third? my buddy had a th350 the linkage was so crappy and bent that when going down from neutral it actually went past the D selection into 2. never got past 50 in that truck till we figured it out.
Last edited by 292farmer; 07-07-2010 at 09:05 PM. |
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#6 |
Registered User
Join Date: Feb 2008
Location: sacramento california
Posts: 204
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Re: what gears do i need on differential?
its a12 bolt and it shifts to 3rd gear on tranny fine
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#7 |
Registered User
Join Date: Nov 2009
Location: stoddard nh
Posts: 693
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Re: what gears do i need on differential?
ok just thought i'd ask on the tranny, and summit and jegs will carry your gears heres one a 3.73 http://www.summitracing.com/parts/RMG-4902801/ this is for a 4 series if i remember lower gears are the 4 series and 3 series are higher gears in stock axles (divided at 3.73? someone please verify/correct me) please double check though as u need to match the series between your new gears and your diff. good luck
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#8 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: what gears do i need on differential?
something is desperatly wrong. Even with a 4.10 gear, ytou should be able to go over 100 MPH. If you can't hit the speed limit, then something is way messed up on your truck.
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#9 |
Registered User
Join Date: Mar 2003
Location: San Francisco, CA USA
Posts: 2,454
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Re: what gears do i need on differential?
Don't guess at your axle ratio. Take a few minutes to count it directly and then you will know for sure.
Put matching marks on the pinion yoke and differential housing. Jack one rear wheel off the ground, put the transmission in neutral, and the parking brake off. Turn the wheel exactly TWO revolutions and count how many times the driveshaft turns, estimating any fractional turn as closely as possible. That number is your axle ratio. If the wheel is difficult or impossible to turn, you may have posi. In that case, jack both rear wheels off the ground and turn either of them only ONE revolution. Count the driveshaft turns the same way as for an open rear. Ray |
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#10 |
Its a Truck Thing......
Join Date: Dec 2004
Location: Sierra Vista, Arizona
Posts: 3,159
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Re: what gears do i need on differential?
Google Randy's Ring and Pinion, good folks to work with.
Smitty
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71 C10 283/3SPD Full Resto 71 GMC 1500 Sierra Grande http://67-72chevytrucks.com/vboard/s...d.php?t=518599 70 C10 Suburban Former military GSA truck. 72 Chevy Blazer 4X4, Sloppy Jo, Mountain Climber. Wife says no more trucks. http://67-72chevytrucks.com/vboard/s...d.php?t=707378 72 GMC 1 Ton Motor Home, wife said no more trucks until she saw this one. Gen 3 6.0/4L80E 4.10 http://67-72chevytrucks.com/vboard/s...d.php?t=761110 68 GMC Suburban was 3/4 ton, now 1/2.Wife shook her head 71 C30 Wrecker 71 C20 Scott-Bilt As weird as it gets..BB Cheyenne AC Truck 68 GMC Long Stepside. They keep following me home 71 C20 Longhorn/Ole Yellor 69 C30 Former Motor Home, Flat Bed time |
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#11 |
Registered User
Join Date: Nov 2009
Location: stoddard nh
Posts: 693
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Re: what gears do i need on differential?
i doubt it but he could have 5.13s like me!
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#12 |
Registered User
Join Date: Mar 2010
Location: fairfield IL
Posts: 78
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Re: what gears do i need on differential?
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#13 |
Registered User
Join Date: May 2009
Location: Eliot, Maine
Posts: 1,314
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Re: what gears do i need on differential?
yeah....the 4.57 in the back of my 72 burb 3/4 ton is terrible. i shift into third gear at like 25mph so highway driving makes that 307 small block spin fast. from my figuring it is turning about 3200rpm at 60 and i usually keep it at around 50 or so because of that. hope to have a 4.10 third member installed real soon. it won't have much impact off the line (thankfully) but that 10% reduction means the faster i go the more rpms i am saving. looking to be around 2900 rpm at 60 after the swap. the 3 on the tree with the clutch is like a t350 with a lockup converter, but it still won't be good for long highway drives until i can get a borg warner OD unit installed on that saginaw. then 60 will be around 2000rpm. nice enough behind a small engine, but when i get my 406sbc it will be awesome. don't want to be sucking gas and spinning rev's unless i put my foot into it!
personally, i think anything between a 3.42 and a 4.11 combined with an overdrive trans is the best bang for the buck. the t400 is nice if you tow a lot more than you drive solo but with gas prices and environmental concerns, some modern concessions are worth their weight in gold. a big block or a diesel could get away with a 3.08 though (a diesel could still use an overdrive ratio). a 3.07 is too soft behind a 350 that is used for towing. i want to keep the column shifter stick trans in my 72 burb, but if it had been a floor shift model, i would have kept the 4.57 and dropped in a 6 speed with 2 overdrive ratios (.8, .62 or .7, .52). you want your overall cruising ratio to be between 2.0 and 3.0 depending on configuration and primary use). |
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#14 |
Registered User
Join Date: Feb 2006
Location: nashville
Posts: 217
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Re: what gears do i need on differential?
Easy to just pop off rear cover and look, gasket and oil is not expensive
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1997 pontiac grand prix gt (daily driver) for now; 2004 dodge ram quad cab (wife's truck) 4.7; 2000 pontiac booneville (wife daily driver) 1972 chevy cheyenne 350 bored 40 over 700r trans 373 gears ( posi) soon to be daily driver; 2002 gsxr750 sold ![]() |
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#15 |
Registered User
Join Date: Nov 2009
Location: stoddard nh
Posts: 693
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Re: what gears do i need on differential?
i believe i saw on this board somewhere 12 bolts never went lower then 4.57. which if he doesnt have a tach depending on his exhaust he may sound like hes redlining, so hes keeping speed low thinking hes about to blow
![]() btullis99 yeah their low sounds like im racing nascar every morning on my way to work ![]() |
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#16 |
Registered User
Join Date: May 2009
Location: Eliot, Maine
Posts: 1,314
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Re: what gears do i need on differential?
a modern 6 speed behind a 292 would be awesome. i'd like to build an early 50's 1 ton panel truck with that setup. it would be so sleeper!
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#17 |
Registered User
Join Date: Nov 2009
Location: stoddard nh
Posts: 693
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Re: what gears do i need on differential?
i plan on trying to fit me and my dads c60 6 speed into my c25 behind it as it has a OD. heres my build thread if u guys wanna talk more, http://67-72chevytrucks.com/vboard/s...d.php?t=376520 i dont want to hijack/clutter this thread anymore, sorry cameney
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#18 |
Registered User
Join Date: Feb 2008
Location: sacramento california
Posts: 204
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Re: what gears do i need on differential?
No problem keep it coming I'm geting your ideas and sounds good
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#19 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: what gears do i need on differential?
stock, the 4.10 (maybe it was 4.11) was the deepest gear offered in the 12 bolt. The 4.56 and 4.57 were in the corperate (eaton) and dana rear ends in the 3/4 tons and one tons.
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#20 |
Registered User
Join Date: Jun 2010
Location: Wyandotte, OK
Posts: 15
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Re: what gears do i need on differential?
I have a similar problem. I am running 3.55 raito ring and pinion, The engine is a 305 and I think the tranny is a TH 400, The truck shifts fine thru all 3 gears but it turns 55 mph @ 2500 rpm (according to my tach and GPS)
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Greg A. Thurman I took this photo at a rest area near Washington DC I wish I had my 67 gas guzzler to park there. Gulf War Vet (USN) Retired Firefighter 67 C-10 72 C-10 |
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#21 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: what gears do i need on differential?
whats the problem? You're good for well over 100MPH there. 110 MPH at 5000 RPM, and it redlines at 5500.
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#22 |
Registered User
Join Date: Jun 2010
Location: Wyandotte, OK
Posts: 15
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Re: what gears do i need on differential?
I guess the problem is mostly me. I would like to cruise down the road 70mph @ no more than 3000 RPM, I may get that with a 3.07 raito but will it have enough power to get itself going from a dead stop.
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Greg A. Thurman I took this photo at a rest area near Washington DC I wish I had my 67 gas guzzler to park there. Gulf War Vet (USN) Retired Firefighter 67 C-10 72 C-10 |
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#23 |
Registered User
Join Date: Jun 2010
Location: Wyandotte, OK
Posts: 15
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Re: what gears do i need on differential?
To add ... I would like to keep the RPM down below 3 on the hiway because she will drink more gas than a drunk sailor in the last 15 minutes of Happy Hour. 2500 RPM seems to be the sweet spot on this motor.
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Greg A. Thurman I took this photo at a rest area near Washington DC I wish I had my 67 gas guzzler to park there. Gulf War Vet (USN) Retired Firefighter 67 C-10 72 C-10 |
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#24 |
Registered User
Join Date: Nov 2009
Location: stoddard nh
Posts: 693
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Re: what gears do i need on differential?
just thought of this if u don't have a lock up converter being an automatic they will slip, more then say one with a lock up converter, or a manual, especially im sure on an older untouched tranny, have u changed fluid or filters? so u may have decent gears that just seem a little lower then u realize.
longhorn man thanks on clarifying info on the 12 bolt gear ranges, like i said thought i saw it somewhere but wasnt sure. |
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#25 |
Registered User
Join Date: Nov 2000
Location: Huntsville Ontario Canada
Posts: 4,052
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Re: what gears do i need on differential?
I jUst got my 68 burbn on the road and I kinda like the 400 and 3:73's a little high but it keeps me under the speed limit all the time 3:55 would be great.
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1968 Suburban numbers matching all original truck now equipped with 6.0/4L80 on Accuair http://67-72chevytrucks.com/vboard/s...d.php?t=625017 1967 C/20 6.0/4L80 Roofing Truck 1990 V2500 Suburban "Plow Truck" 2005 TAHOE DD |
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