what gears should I run in my 3/4 ton lifted gmc?

[BDadsV2500]

Kimber,

With the exception of the xmsn, I have an almost identical set up. I have a 700r4 and 37's on Ol' Red. I changed my gears out to 4.10 and went to a 22 tooth silver speedometer gear to keep my speedometer accurate.

From the factory, unless special ordered, all 1976-1987 3/4 ton GMC or Chevy trucks with the Dana 44 front and 14 bolt 10.5 rear came with 3.73 gears. You have several options open to you, however the cost does vary. If you want to attack a long term solution, maybe a gear swap first and then a xmsn upgrade later on. If you just want a gear swap, then 4.10s should do you fine, but like mentioned before, your truck will scream. If the engine actually makes what you were told at the flywheel, I agree that you should not have any problems moving the truck with the gears in it now.

Upgrading to a 700r4 is always an option too. The gearing is quite different and you'll have an overdrive for non-towing situations. Of course all of this is just my opinion on what I have done and experienced with all the trucks I do work on.

B

 

[ruedger455]

I appreciate all the advice. And my truck is in 4 wheel drive all the time lol. Its got the np203 transfercase. Im starting to think that maybe the 4.10s would be my best bet. I just like the idea of having the 4.56s just incase I go bigger and heavier with my tires.

 

[marks86]

bottom line here is 4.56 gears/three speed auto even with a 37" tall tire is not practial for street/daily driving

-4.56/OD
-4.10/three speed
-4.56/44"
-never going over 50

these are all ways to get around it

 

[rich weyand]

This is handy. RPMs at 60mph.

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[marks86]

This is handy. RPMs at 60mph.

You must be registered for see images attach

what motor and trans does this chart apply to

 

[MadOgre]

This is handy. RPMs at 60mph.

You must be registered for see images attach

Thanks Rich.

Green @ 35" @ 4.56 gears.

 

[Chaz]

The chart is slightly misleading,,,,, I wouldn't look at it,,,its probably accurate but its assuming you have a full lock up transmission,,,,if a T350 is like my T400 your gonna be several hundred rmps over the chart just because your tranny dosent lock up. Plus 35 inch tires rarely exactly measure 35 inches diameter, mine are 34 inch mounted on the truck.

If your never gonna drive on the highway or exceed 50 mph then I'd run 4.56,s,,,bitchen gear ratio.

If its your DD and your gonna take trips anywhere I wouldn't go any deeper than a 4.10 ratio,,,,3.73 is actually not a bad gear for highway,,,its only 1 tooth difference on the ring gear from a 4.10,,,

Or you can do a trans swap to an overdrive transmission or add an overdrive gear like gear vendor (expensive).

 

[ruedger455]

Lol yea my top speed is usually 55. That seems like alot of money to throw down for 4.10s just to have it only be 1 tooth difference.

 

[marks86]

Lol yea my top speed is usually 55. That seems like alot of money to throw down for 4.10s just to have it only be 1 tooth difference.

its one tooth different on the ring hes saying, still different on the pinion

 

[ruedger455]

Aah, so how much of a change would I see going from 3.73s to 4.10s and 3.73s to 4.56s?

 

[MadOgre]

If you are having a hard time getting it rolling with 3.73s I don't think 4.10s are gonna be the answer. That being said you should verify that you do indeed have 3.73s. 4.10s are still on the low side for 35s and if your gonna go bigger ? Its all fine and dandy to get low rpms on the highway but if your burning your clutch packs everytime you need to get going is it worth it ? My experience with big tires is that if you have them your gonna use them. Its just to hard to resist ! When you use them you want to be able to spin them with out burning up your transmission.

You should definitely verify that you have 3.73s though before deciding.

 

[marks86]

based off that chart, but once again idk what engine and trans that chart is based off of

lets pretend we know that chart is for a 350/3speed auto with a 35" tire

3.73-4.10 you will see 2323-2565 rpm increase
3.73-4.56 you will see 2323-2845 rpm increase

 

[marks86]

If you are having a hard time getting it rolling with 3.73s I don't think 4.10s are gonna be the answer. That being said you should verify that you do indeed have 3.73s. 4.10s are still on the low side for 35s and if your gonna go bigger ? Its all fine and dandy to get low rpms on the highway but if your burning your clutch packs everytime you need to get going is it worth it ? My experience with big tires is that if you have them your gonna use them. Its just to hard to resist ! When you use them you want to be able to spin them with out burning up your transmission.

You should definitely verify that you have 3.73s though before deciding.

i agree start by making 100%sure you have 3.73

maybe find a buddy with 4.10s
come to NY and ill take you for a ride with 4.56

 

[ruedger455]

Lol how do I determine that I have 3.73 gears without opening everything up? Im pretty sure that the year and axles I have came with 3.73s.

 

[MadOgre]

You have to open it up.