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3.55 swap to 2.76 gears? #3070598
08/22/22 07:35 PM
08/22/22 07:35 PM
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HotRodDave Offline OP
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I have a 93 dakota I want to swap in a 2.76 gear in place of the 3.55 gear, is there any year difference or anything else I need to be on the look out for while looking for gears? I have a sure grip from a 2002 durango R/T, will it work in the older dak diff? Are used gears OK to use as long as they look good? If used is a bad idea where does a guy find new ones? What about the 2.45s? they need a different carrier correct? Can I use a limited slip carrier from an earlier car in the 8.25 with the axles in the truck if I find a deal on a 2.45 with the LSD?


I am not causing global warming, I am just trying to hold off a impending Ice Age!



Re: 3.55 swap to 2.76 gears? [Re: HotRodDave] #3070625
08/22/22 08:38 PM
08/22/22 08:38 PM
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MoonshineMattK Offline
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I've used plenty of old gears. If they don't have excessive wear you are fine. Takes a lot to wear gears out in a passenger car setting.

Re: 3.55 swap to 2.76 gears? [Re: HotRodDave] #3070630
08/22/22 09:23 PM
08/22/22 09:23 PM
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Depending on your reason for doing so, be aware that the change may move the engine out of its most efficient range resulting in a loss of mileage as well as placing and additional load on the engine and transmission.
Where you do the majority of your driving as well the terrain may also be a factor to consider beer

Re: 3.55 swap to 2.76 gears? [Re: TJP] #3070738
08/23/22 11:03 AM
08/23/22 11:03 AM
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HotRodDave Offline OP
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With this truck most of my driving is on mostly flat highway doing 75 MPH, often times 600 miles a week. It is well past where it feels like it would like another shift plus I am going to do some stuff to give it more very low RPM TQ. It has short 15 inch tires, the rams with the same engine had the same gears and much taller 16" tires, more weight and worse aeromatics and still went down the highway just fine so I am sure it can easily pull the higher gear. This is why the dakota never got much better MPG than a ram, the engine was turning much more RPM than nessacary.


I am not causing global warming, I am just trying to hold off a impending Ice Age!



Re: 3.55 swap to 2.76 gears? [Re: TJP] #3070767
08/23/22 12:26 PM
08/23/22 12:26 PM
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moparx Offline
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Originally Posted by TJP
Depending on your reason for doing so, be aware that the change may move the engine out of its most efficient range resulting in a loss of mileage as well as placing and additional load on the engine and transmission.
Where you do the majority of your driving as well the terrain may also be a factor to consider beer




this ^^^^^ iagree
if this were me, [you really DON'T want to be me biggrin] i would try to borrow a much larger [taller] set of rear tires to see how this would affect your mileage. you can mathematically get close to figuring out what gear ratio the taller tires would simulate, then go from there.
this would be easier, quicker, and cheaper than buying a gear set and having it installed [if you can't do it yourself].
if you find something you don't like, drive-ability wise, you could try a different height tire and test again.
as above, i have seen a loss of mpg going to a shorter gear set many times, even though a well figured out equation suggests otherwise.
just my opinion and experience. your "mileage" will vary.
beer

Re: 3.55 swap to 2.76 gears? [Re: moparx] #3070812
08/23/22 01:59 PM
08/23/22 01:59 PM
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HotRodDave Offline OP
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Originally Posted by moparx
Originally Posted by TJP
Depending on your reason for doing so, be aware that the change may move the engine out of its most efficient range resulting in a loss of mileage as well as placing and additional load on the engine and transmission.
Where you do the majority of your driving as well the terrain may also be a factor to consider beer




this ^^^^^ iagree
if this were me, [you really DON'T want to be me biggrin] i would try to borrow a much larger [taller] set of rear tires to see how this would affect your mileage. you can mathematically get close to figuring out what gear ratio the taller tires would simulate, then go from there.
this would be easier, quicker, and cheaper than buying a gear set and having it installed [if you can't do it yourself].
if you find something you don't like, drive-ability wise, you could try a different height tire and test again.
as above, i have seen a loss of mpg going to a shorter gear set many times, even though a well figured out equation suggests otherwise.
just my opinion and experience. your "mileage" will vary.
beer



I had good results with a 275-65-20 on my full size ex cab long bed 318 magnum (same exact engine) with 3.55s. With my very short 15" tires the math comes out around 3.1 gear ratio to match the top gear RPM, 2.76 is not much of a stretch especially considering how much smaller this truck is both in weight and aero.


I am not causing global warming, I am just trying to hold off a impending Ice Age!



Re: 3.55 swap to 2.76 gears? [Re: HotRodDave] #3071037
08/24/22 10:19 AM
08/24/22 10:19 AM
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HRD my 92 dakota has 8.25 with 3.55. Don't know what axle is under yours. That 2002 RT though will have 9.25 rear though and likely 3.92 gears.

If it were me I would start out by running a taller tire to see where you like the rpms then possibly do a gear swap later. Lots easier to swap a couple used tires on than make a mistake on the gear choice.

I ran a 31/10.5/15 tire on my 92 dak 2wd fit fine in the rear, slight scrub at full lock on front. The tall tire made it great as an interstate cruiser.

Last edited by mgoblue9798; 08/24/22 10:22 AM.
Re: 3.55 swap to 2.76 gears? [Re: mgoblue9798] #3071088
08/24/22 01:07 PM
08/24/22 01:07 PM
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HotRodDave Offline OP
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Originally Posted by mgoblue9798
HRD my 92 dakota has 8.25 with 3.55. Don't know what axle is under yours. That 2002 RT though will have 9.25 rear though and likely 3.92 gears.

If it were me I would start out by running a taller tire to see where you like the rpms then possibly do a gear swap later. Lots easier to swap a couple used tires on than make a mistake on the gear choice.

I ran a 31/10.5/15 tire on my 92 dak 2wd fit fine in the rear, slight scrub at full lock on front. The tall tire made it great as an interstate cruiser.


I have run much taller tires with a much larger truck and the same engine and was fine with the results, now I want to gear to get the same or very slightly more RPM reduction than the taller tires gave. A taller tire is less effective than a gear swap as it puts the truck higher up in the wind and most any tires are gonna be wider as they get taller witch will also reduce the effect I am after. I have thought this thru and experimented and am convinced it is the right thing for me to do, my only question now is how to do it not "if" I should do it. As for the R/T diff... yes it is a 3.92, they all were, I am just planning to use the limited slip carrier if it will fit and not the gears themselves.


I am not causing global warming, I am just trying to hold off a impending Ice Age!



Re: 3.55 swap to 2.76 gears? [Re: HotRodDave] #3071094
08/24/22 01:23 PM
08/24/22 01:23 PM
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What is the rear tire height? Hoe about 3.2 or 2.9 gears. 2.76 is to too far the other way. Does it have and OD trans?

I’ve never liked 2.76 axle in anything, kills the torque. Even with 25” tall rear tires.

Jump on a 10 speed bike and take off on 8th gear, that’s what a 2.76 does, takes it out of the power band.

Re: 3.55 swap to 2.76 gears? [Re: NANKET] #3071099
08/24/22 01:54 PM
08/24/22 01:54 PM
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Dave,

looks like Cass has what your after.


https://www.doctordiff.com/8-1-4-ring-and-pinion.html


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Re: 3.55 swap to 2.76 gears? [Re: NANKET] #3071122
08/24/22 03:14 PM
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HotRodDave Offline OP
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Originally Posted by NANKET
What is the rear tire height? Hoe about 3.2 or 2.9 gears. 2.76 is to too far the other way. Does it have and OD trans?

I’ve never liked 2.76 axle in anything, kills the torque. Even with 25” tall rear tires.

Jump on a 10 speed bike and take off on 8th gear, that’s what a 2.76 does, takes it out of the power band.




Again, I am not concerned about the ratio and TQ. I had a 2.76 gear in my 318 cuda with a smiilar tire height, it still had more power than the tires could handle and this 318 has more TQ.


I am not causing global warming, I am just trying to hold off a impending Ice Age!



Re: 3.55 swap to 2.76 gears? [Re: mdwyer] #3071123
08/24/22 03:15 PM
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Originally Posted by mdwyer
Dave,

looks like Cass has what your after.


https://www.doctordiff.com/8-1-4-ring-and-pinion.html


I have tried calling and e-mailing him and can't get ahold of him, I just might swing by his shop as I drive within about 10 miles of him on my trip.


I am not causing global warming, I am just trying to hold off a impending Ice Age!



Re: 3.55 swap to 2.76 gears? [Re: HotRodDave] #3071150
08/24/22 05:12 PM
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97 and newer used a 29 spline axle. 27 on the older 70`s 80`s and up to 96.

Re: 3.55 swap to 2.76 gears? [Re: mopars4ever] #3071172
08/24/22 07:00 PM
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HotRodDave Offline OP
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Originally Posted by mopars4ever
97 and newer used a 29 spline axle. 27 on the older 70`s 80`s and up to 96.


I suppose that means I can't use this limited slip carrier I already have. I guess I will be looking fur one of those also. That is why I asked, thanks!


I am not causing global warming, I am just trying to hold off a impending Ice Age!



Re: 3.55 swap to 2.76 gears? [Re: moparx] #3071635
08/26/22 01:36 PM
08/26/22 01:36 PM
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MoonshineMattK Offline
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Originally Posted by moparx
Originally Posted by TJP
Depending on your reason for doing so, be aware that the change may move the engine out of its most efficient range resulting in a loss of mileage as well as placing and additional load on the engine and transmission.
Where you do the majority of your driving as well the terrain may also be a factor to consider beer




this ^^^^^ iagree
if this were me, [you really DON'T want to be me biggrin] i would try to borrow a much larger [taller] set of rear tires to see how this would affect your mileage. you can mathematically get close to figuring out what gear ratio the taller tires would simulate, then go from there.
this would be easier, quicker, and cheaper than buying a gear set and having it installed [if you can't do it yourself].
if you find something you don't like, drive-ability wise, you could try a different height tire and test again.
as above, i have seen a loss of mpg going to a shorter gear set many times, even though a well figured out equation suggests otherwise.
just my opinion and experience. your "mileage" will vary.
beer


Was worried about this when I bought the 5spd for my charger. Was 3.23w/OD, Now I have a 2.76 and overdrive

Oversize tire is a great idea to try







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