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FREEDGUY 
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 Topic: Differential Gear Ratio ??
Posted: 10 Nov 2020 at 7:04pm |
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How does a person know the gear ratio in a P/U truck ? I've looked on the door tag thinking it might be there but it wasn't. Ford 250 super duty is the truck I'm curious about. It's a 4x4 gasser if it matters. Thanks
Edited by FREEDGUY - 10 Nov 2020 at 7:05pm
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Boss Man
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Joined: 03 Mar 2018
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Posted: 10 Nov 2020 at 7:07pm |
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If I remember right there's a sticker or tag on the diff. You need to decipher the code on it. They used to stamp the ratio on the tag but that went away late 90's early 2000's
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steve(ill)
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Posted: 10 Nov 2020 at 7:07pm |
there is a CODE for AXLE on the door sticker... then you interpret it.....there is also a Tin TAG on one of the bolts on the pumpkin.
AXLE CODES:
37- 3.73
3L- 3.73 LS
41- 4.10
4N- 4.10 LS
43- 4.30
4L- 4.30 LS
48- 4.88
8L- 4.88 LS
53- 5.38
5L- 5.38 LS
Edited by steve(ill) - 10 Nov 2020 at 7:17pm
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Like them all, but love the "B"s.
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Tbone95
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Posted: 11 Nov 2020 at 7:42am |
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What is LS? Locking?
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Tbone95
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Posted: 11 Nov 2020 at 7:45am |
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I suppose a guy could, if you really wanted to, on a hoist preferably or jack the rear end up, you could turn the drive shaft and note the rotation of a tire. Might be hard to tell between 4.1 and 4.3, but I bet you could figure most of them out and even that one if you were careful.
*edit* figuring out when given KNOWN possibilities. Trying to figure out from scratch would be tough and only get you close is what I'm getting at.
Edited by Tbone95 - 11 Nov 2020 at 7:59am
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Strokendiesel002
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Posted: 11 Nov 2020 at 7:53am |
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LS should be Limited Slip.
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Tbone95
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Posted: 11 Nov 2020 at 7:58am |
 Strokendiesel002 wrote:
LS should be Limited Slip. |
AHA!  Yes, don't know why that didn't "click". Need another coffee.... 
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steve(ill)
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Posted: 11 Nov 2020 at 8:20am |
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Limited Slip is a clutch in the rear axle that keeps both wheels turning with some difference in speed between them............ FORD also has a LOCKER rear end that is an electric solenoid that drops a pin in the differential and LOCKS both tires together. 100% same speed, no slip.............. The axle code would include a "L" after the ratio.
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Like them all, but love the "B"s.
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Tbone95
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Posted: 11 Nov 2020 at 8:45am |
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Yep....for some reason that synapse just didn't fire this morning.
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farmboy520
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Posted: 11 Nov 2020 at 9:02am |
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Sometimes the VIN code will tell you also. Your operator manual could possibly tell what each position of the VIN code tells.
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On the farm: Agco Allis 9695, 7060, 7010, R66, Farmall H, and Farmall F20 (Great Grandpa's)
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DMiller
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Posted: 11 Nov 2020 at 12:55pm |
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If an Automatic trans will most likely be 3.73, not many 4.10s out there where SD trucks were engineered for work not speed.
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Bill_MN
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Posted: 11 Nov 2020 at 8:39pm |
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There are VIN decoders online you can type it in and will tell you all the factory build specs, I think Ford has one on their owner website.
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1951 WD #78283, 1918 Case 28x50 Thresher #76738, Case Centennial B 2x16 Plow
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jaybmiller
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Posted: 12 Nov 2020 at 5:34am |
best to raise it up and spin. that way you can CONFIRM what's on the diff tag.
do NOT trust the door sticker or vin # info... unless you've owned the ruck since new and NOBODY has done 'diff' work.... like changing the gears !!!
I KNOW of one truck that supposedly had 4.88s in it, reality was 5.38s !!! GREAT stump puller, lousy on the highway.....
chalk a tire,spin the driveshaft, counts revs......then you'll KNOW.
BTW, if a shop scans the door tag for a 'smog test', you can be surprised, when you find out the door came from another vehicle !!!
Jay
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3 D-14s,A-C forklift, B-112
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Never burn your bridges, unless you can walk on water
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farmboy520
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Posted: 12 Nov 2020 at 6:42am |
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I've heard also that the manufactures also make some of the gear ratio up in the transmission.
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On the farm: Agco Allis 9695, 7060, 7010, R66, Farmall H, and Farmall F20 (Great Grandpa's)
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Tbone95
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Posted: 12 Nov 2020 at 7:52am |
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I'm not sure what you mean farmboy?
The question was how do you know differential gear ratio.....so again, not sure what you're getting at. . . .
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steve(ill)
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Posted: 12 Nov 2020 at 9:36am |
I think what he means is the OLDER 3 speed auto trannies were always 1 :1 gear ratio in HIGH gear... Then they started making 4-5-6 and even 10 speed trans and the top couple gears can be OVERDRIVE.... maybe .7 or .75 :1 ............ that gives you the advantage of using lets say a 4.10 rear end for take off and pulling, then when you get into OVERDRIVE it would be like having a 3.25 rear axle with a standard old 1:1 transmission.... But that does not change the actual rear axle ratio, just gives you more OPTIONS.
trans ratio x axle ratio = final drive ratio
1 x 3.25 = 3.25 .75 x 4.30 = 3.22
Edited by steve(ill) - 12 Nov 2020 at 9:44am
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Like them all, but love the "B"s.
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Tbone95
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Posted: 12 Nov 2020 at 11:07am |
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Well......didn't want to insult anyone's intelligence before commenting, wanted to be sure we started from the same song sheet.
Sheesh....how long ago would you have had to buy a pickup w/out OD without special ordering it?
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steve(ill)
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Posted: 12 Nov 2020 at 1:03pm |
Overdrives have been around for a while, but keep getting MORE RATIOS.
My 2002 F150 had a 4 speed and OD was about .78 i think..
I have a 2013 now and it has a 6 speed... probably 2 OD.
The last couple years FORD has used a 10 speed and 3 are OD ...below is the new 10 speed FORD F150... note low gear is 4.69 , which is WAY LOW compared to old days.. and 8-9-10 gear are OD.. with highest at .63 .......... thats some SPREAD of RATIOS !
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Like them all, but love the "B"s.
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FREEDGUY
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Posted: 12 Nov 2020 at 5:26pm |
Under the "axle" heading on the door tag was a 37, is this a decent ratio to run on the highways ?? Seems like at 60 +, it drinks a lot of gas .
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jaybmiller
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Posted: 12 Nov 2020 at 5:29pm |
37 should be a 3.73 ratio, same as my old '73 CJ-5 was.. resonable compromise, Ok for pulling, 1/2 decent mileage ( better if OD in tranny)
Jay
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3 D-14s,A-C forklift, B-112
Kubota BX23S lil' TOOT( The Other Orange Tractor)
Never burn your bridges, unless you can walk on water
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steve(ill)
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Posted: 12 Nov 2020 at 5:50pm |
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I had a 2002 F150 with the 5.4 motor and 3.55 axle.....got about 16 MPG in mixed driving........ the 3/4 ton is heavier and 3.73 is 10% more engine speed so your not going to get anywhere near 16.
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Like them all, but love the "B"s.
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Tbone95
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Posted: 12 Nov 2020 at 5:57pm |
steve(ill) wrote:
Overdrives have been around for a while, but keep getting MORE RATIOS.
My 2002 F150 had a 4 speed and OD was about .78 i think..
I have a 2013 now and it has a 6 speed... probably 2 OD.
The last couple years FORD has used a 10 speed and 3 are OD ...below is the new 10 speed FORD F150... note low gear is 4.69 , which is WAY LOW compared to old days.. and 8-9-10 gear are OD.. with highest at .63 .......... thats some SPREAD of RATIOS !
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Hahaha, trust me, in my job, I’m well aware of how much transmissions have been redesigned over the last several years! It’s been great ( for business) 
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Michael V (NM)
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Posted: 12 Nov 2020 at 6:23pm |
well,,, yea,, its gonna like gas,, its a 3/4 ton, you didn't say what engine or trans, that will make some difference, but prolly not much I have a '96 F-250 4x4 with the 460 cid/7.5L 4 speed auto, 3.54 rear gears,(I'd prefer 3.73 or 4.11 for what I do, but it will fly if ya mash on it) if it gets 11 mpg,, I figure that's bout as good as it gets, lots les draggin a trailer...its my farm/work PU, so it is what it is..
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Dakota Dave
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Posted: 12 Nov 2020 at 7:55pm |
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You could get a three on the tree up till the End of the square body Chevy trucks. My 1984 had a three speed 250 straight six and 3.42 gears with pizza cutter tires. My cousin still drives it no overdrive was needed the national speed limit was 55mph.
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Coke-in-MN
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Posted: 16 Nov 2020 at 2:11pm |
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You can also take serial # to a dealer and they can look up the build sheet to give you full info on the vehicle .
Inside the glove box there is also a sticker that lists all the codes for the build but not what the code might actually mean .
You can take these codes and look them up online to find the actual numbers on ratios and if limited slip , locking, or other info.
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Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something.
"Challenges are what make life interesting; overcoming them is what makes life meaningful."
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