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Discussion Starter · #1 ·
Last summer I installed a fresh 318 with eddy 1406 carb, hooker long tube headers, and cherry bomb turbo mufflers. Starts runs, and drives like a 83 RC should. Got another rear axle 9.25 open end 3:21 and put it in, now, guess what? the 4X4 engages but binds up, that tells me the back end ratio is the wrong unit. Prior to this I had a limited slip 9.25 with 33X12.5X15 tires the truck was @ 2900 RPM at 70 MPH. So with this info can you tell what was in it before, and if not, how do I check the front axle ratio.

Big Red in Oshkosh, WI
 

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To get anywhere near 4k RPM at 70 MPH, you would have to have 5.13 or deeper gears, which I don't think are even available for the 9 1/4".  I would double check your numbers.  That said, if you still have the old rear, pop the cover off it and look at the gears, and/or count the teeth and divide.  Same can go for the front axle if it's missing it's tag.
 

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Discussion Starter · #3 ·
The old rear end is long gone, runs just peachy in 2WD, so with that, now we come to the front axle. I'm told there is a square nut on the front near the differential where you don't have to take the cover off.

I'm thinking it had a 3:55 before

Thanks.
 

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There is the fill plug, but I doubt you will be able to see enough through it to see any markings on the ring gear or count all the teeth.  Pull the cover, if it hasn't been done recently, you are probably due for a fluid change anyway.
 

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Discussion Starter · #5 ·
Gonna do that, thanks for the tip, someone said use a flashlight and look in there. I'll just pull the cover and be done with it

Now that I think about it @ 70 MPH I was running about 2900 RPM

Stephen
 

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2,900 RPM is more reasonable.  With 33s and 3.91 gears you would be around 2,944 RPM.  With an automatic with no lockup, a loose converter and a little room for error in the speedometer 3.55s are also possible.  If the speedometer gear was never swapped for the tire change, it throws everything off.  3.55s were an optional gear from the factory and much more likely, but the only way to know for sure is to look at the front.  If you get really lucky, you might have a small metal tag on one of the front cover bolts that will have a 3.2 or 3.5 on it that would signify 3.23 or 3.54 respectively.
 

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Discussion Starter · #7 ·
With the 4-inch lift I couldn't spin the tires, a little bit on dry pavement,. the motor was tired when I got it and it had 33 mud tires, speedo was calibrated but never changed to reflect difference in bigger treads. I'm a gonna look Monday to see what we have.

Pic below is what tires came with "Big Red"
 

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Worst case scenario to find out is you pull the differential covers and check the ring gear number or count teeth.  You should have a gear tag on both but counting or retrieving the number is your best and most accurate method.
 

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Discussion Starter · #11 ·
The rear axle is a 9.25 3:21 open end, and when 4WD is engaged it don't drive so well. so front is a Dana 44, now to see what that entails we shall find out soon and I'll let you know what we come up with.

I'm thinking the old rear end was a 3:55

But for now it stays in 2WD.
 

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Discussion Starter · #12 ·
The mystery has been solved. Here is what we have, in front is a Dana 44 3:91 and in back we have a open end 9.25 3:21. so there's about 7/Tenths difference in front and back ratio's which accounts for dogging and binding. I should have probably checked this way back when (last summer)

So now in the spring I'm swapping the front axle to a Dana 44 3:23 or 21 which ever it is.
 

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Yeah, that won’t work so good! :(

Glad you got it figured out. 
 

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heliosteve said:
The mystery has been solved. Here is what we have, in front is a Dana 44 3:91 and in back we have a open end 9.25 3:21. so there's about 7/Tenths difference in front and back ratio's which accounts for dogging and binding. I should have probably checked this way back when (last summer)

So now in the spring I'm swapping the front axle to a Dana 44 3:23 or 21 which ever it is.
l,d go with the 3.91,s MUCH better gearing
 

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I would rebuild the axle with a 3.91 gear set.  A used 9 1/4" is akin to buying a bomb with instructions in a foreign language.  Put in a new gear set, master install kit, solid pinion spacer and over-torque the side adjusters by about 50 ft lbs.
 

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Agreed on the re-gear.

Make sure you get pinion shims... the last diff bearing kit I bought for an mopar (8.25") did not.  :mad:

Also outer axle bearings/seals (cheap!) ...can't get to the adjusters otherwise.
 

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Steve, that is a good start but that crush spacer, warm your arm up so you don’t hurt yourself and throw it as far as you can! 

Buy the crush spacer elimination shim set.  You will be so much better off.
 

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agreed  Ratech 513-742-2111 
 
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