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Discussion Starter #1
I am wondering about what rpm i should be at at 65 mph with 285's. I aqm running at just over 2k. Is this right or is my tranny poopie.
 

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auto or manual may be a huge factor here... I'm assuming it's auto by your tone though, and I have no clue on that one.

sounds a couple hundred high to me with 3.55's but it may be a lower gear ratio...
any clunk sounds or slippage in tow, uphill or any other time? why do you think it's going out? and have you checked your fluid lately and changed trans filter... just a suggestion.
 

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Discussion Starter #4
its an auto with 3.55's. I know its going into OD becuase when i press the button the rpsm will jump to 3k.
 

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Well not accounting for tq converter slippage.. .with 3.55's, and 285's you should be about 1690 rpms at 65mph in OD, and 2450 in D. 2K rpms in OD should be 77mph and 3K in D should be 80.

Have you accounted for your speedo error?
 

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Mopar1973Man.Com
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I've got stock tire size (265/75 R16) and 3.55:1 gears...





 

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Go for Broke
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the speedo will read a little low with the over size tires...(about3-4%)

i run 285's with an auto and 3:54

i can run 70-72mph at 2000rpm
 

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Discussion Starter #8
i used my gps. At 67mph with the stock tires i would run 2100.
 

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stock tires on a 2000 are 245 75 16 right? that's 30.46" tall, versus a 285 75 16 which is 32.83" tall. that's a 7.78% difference on your speedo. at an actual 60 mph, your speedo will show 55.6. if your speedo is indicating 65, you're actually doing 70.05 mph.
being an auto,you're probably ok. my manual with 3.55s at 2k rpm indicates about 68 mph which is 73.29 mph.
 

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the speedo will read a little low with the over size tires...(about3-4%)

i run 285's with an auto and 3:54

i can run 70-72mph at 2000rpm
Wording is always tricky, as it does not matter what size tire is on the truck the tac and the speedo will always read the same ie 2000rpm @ 65mph (as an example) the speedo will NOT read higher or lower just by changing tires.

but with a larger tire the veh will be traveling faster than the speedo shows, so you can drive 60mph (as per speedo) but actually travelling at 65mph
 

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hmm i run at about 2100rpm at 65mph and i got 245's(baby tires) with 4.10's and an auto does that sound correct?
 

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hmm i run at about 2100rpm at 65mph and i got 245's(baby tires) with 4.10's and an auto does that sound correct?
That sounds dead on.. Makes me think the OP has 4.10's not 3.55's
 

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I think the OP should check his gears cause I have the exact same set up 285/75/16s and 4.10 and at 65mph I run about 2050 RPMs with a corrected speedometer. easiest way to check your gears (if you dont know, you may know) jack up the rear of the truck put a mark of some sort on the driveshaft, and spin your tires and count the revolutions of the drive shaft if you turn a little over 4 times then you obviously have 4.10s not 3.55s.
 

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the speedo will read a little low with the over size tires...(about3-4%)

i run 285's with an auto and 3:54

i can run 70-72mph at 2000rpm
Sounds just right, same setup as me. :thumbsup
 

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I think the OP should check his gears cause I have the exact same set up 285/75/16s and 4.10 and at 65mph I run about 2050 RPMs with a corrected speedometer. easiest way to check your gears (if you dont know, you may know) jack up the rear of the truck put a mark of some sort on the driveshaft, and spin your tires and count the revolutions of the drive shaft if you turn a little over 4 times then you obviously have 4.10s not 3.55s.
If you only lift one tire the drive shaft will spin twice as fast... and if you lift both tires one will go the opposite direction and the ds wont spin at all... so lift one tire, 8.2:1 is 4.10's and 7.1:1 is 3.55's...
 

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If you only lift one tire the drive shaft will spin twice as fast... and if you lift both tires one will go the opposite direction and the ds wont spin at all... so lift one tire, 8.2:1 is 4.10's and 7.1:1 is 3.55's...
the wonders of open diffs...junk!
 

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Discussion Starter #17
hmm, i;m going to do a vin check.
 

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haha, yeah, to me an LSD is just about as worthless as open. i'm actually big into off roading, which is one of the reasons i bought my ram, so i can tow my off road rig around. i'm just between rigs right now!
 

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Yeah I have wheeled yotas for years, and up until the AAM LSD I wouldn't touch a LSD, actually prefered oped due to the predictability.. But the new helical gear, similar to a TT, is a pretty good unit, and best of all it doesn't get squirly on ice like a standard LSD... I would still prefer ARB's front and rear, but will probably keep the OEM LSD rear and put the OEM elocker up front.
 
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