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Discussion Starter · #1 ·
I have a 91 5 speed cummins.What rear gears were available in this truck..I think mine are too high
 

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Discussion Starter · #2 ·
I had a 93 5 speed cummins that comparing it to. The 93 was the strongest truck I have ever pulled with but had 4.10 rear end and would only run 82 WOT. The 91 doesnt even like 5 gear til around 60mph...The 91 was a compant truck and had too fast engraved on the ignition key..
 

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I love my 410's with 37's I can burry the speedo at over 100 mph. But what was available was 354's or 410's
 

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Discussion Starter · #4 ·
I must have 3.54 forgot to say that it is a 1 ton cab and chassis dual rear wheel
 

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I have 3.54 in a 1990 W350 cab and chasis. They are a bit of a stretch from 3 to 4 on the Getrag but other than that 3.54s and the 5 speed tow along pretty well with stockish tires.
 

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Just pull the cover off and on the edge of the ring gear it will have the teeth count, example a 4.10 is 41-10.

Then you can put clean oil in it and know it's good to go.
 
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You'll either have 3.54 or 4.10, those were all that was available I believe.
 

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Easier than pulling cover is to jack the rear up and put it in neutral. Put a mark on the driveshaft and on another on the tire and spin the tire one full turn while counting shaft revolutions. Shaft spins 3.5ish times, it's 3.54, shaft spins just over 4 times, it's 4.10. Of course you still have the same gear oil in there, as opposed to the pull-cover procedure.
 

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Discussion Starter · #9 ·
Im almost positive i have 3.54 if so that will change. I havent had this truck long enough to do the complete running gear check that I do before driving one much...It will have 4.10 or lower soon. I am too old for speeding just want to pull the fifth wheel across Monteagle mountain on I24 at a decent clip.
 

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What size tires are you running? Pety sure my truck is a 3.54 and 60mph in 4th is really reving the engine with stock-ish tires. I usually shift at 50mph no problem unless I'm towing.
 

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Discussion Starter · #11 ·
235x75 r 16........seriously, this truck will fly but it is weak with a load....The key has 2 fast engraved on it....I wondering if they changed the rear gears in it before for mileage ?
 

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Look at the rear diff housing and see if it says "70" or "71". The early 727 trans trucks had D71 axles with 3.07's. Maybe someone swapped one in :confused013:

Just have to pull the diff cover and have a look inside to know for sure.:thumbsup:
 

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Discussion Starter · #13 ·
I will check the gears when I get time to get in the shop....Thanks for all the replies.
 

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They were in all non intercooled auto's, 89 to 91.
 

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Here is how you tell if you have the 3.07 ratio axle informally called the 'Dana 71'. The housing is cast differently to fit those tall gears. The pronounced corners circled in green are even more evident when the diff cover is still on.
 

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3.07 gears were still an option up to 93. There are a few people on the forum with factory 3.07's in the intercooled trucks with the getrag or 518. I know Phillip has factory 3.07 and his is a 93 I believe. He will probably chime in

Sent from AutoGuide.com Free App
 

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I imagine 3.07's would make backing up a heavy trailer a royal pain in tight spots.
Otherwise it would be sweet with a 5 speed.
Could be worse....
Getrag G360 reverse is 5.61:1
N4500 reverse is 5.04:1
Ford ZF reverse is 3.79:1 :shock:
 
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