need advice on gear ratios for towing with 89 GMC 2500

[Tyler]

Hi everyone,

I'm new to this forum and have a towing question, so forgive me if it is a repeat.

I have a 1989 GMC 2500 4x4 with a 5 speed manual transmission and the lighter duty 6 bolt hubs. I got the truck as a gift from my dad and would like to get it to tow better without spending a ton of money. The truck has a freshly rebuilt TBI 350 motor and currently has 285/75/16 tires and 3.73 gears. I use the truck for wood hauling in the winter and would also like to use it to pull a trailer weighing between 5000 and 7000 lbs in the summer. I pulled 5000lbs last weekend and I had a hard time getting the truck up to highway speeds and it really struggled up hills.

right now the effective gear ratio with the 3.73 gears and 285's is about 3.46:1. In order to get it to pull better (i'm not expecting miracles) I would like to upgrade to either 4.10 or 4.56 gears. I don't expect diesel results, but it is clear that an upgrade is needed. Would 4.10 gears with the 285's be enough gear? Or would the 4.56's be a better choice? Any advice would be greatly appreciated.

 

[am92]

With 285s and 4.10 ratio gears you'll bring your effective ratio back to more or less stock. 4.56 gears will give you a little better pulling power, but will cause you to run at higher RPMs at highway speeds which isn't good. I'd go with 4.10s, but the swap from 3.73 to 4.10 won't make a big engouh difference to be worth the cost unless you plan on doing it yourself IMO. Gear swaps cost around $1K for just the rear end, and if you want to be able to use your 4WD you'll need to have the front done too. To you, if may be worth it for the amount of towing you do though...hope that helps and good luck!

 

[94_C/1500]

Do the usual TBI mods, complete tune up, and 4.56 gears. If you weren't towing or hauling much, I'd say 4.10s.
FYI, the best mod I've don't to my engine was just advancing timing 4 degrees. So I recommend doing that first, then all the TBI stuff.

 

[ksalling]

My 91 2500 ran a ton better with advanced timing as well. I have heard quite a bit about the TBI mods but haven't been able to try those out. After doing the mods my truck broke down so I decided to shut the whole operation down.

 

[gunz]

The gearing would really depend on often you actually tow. if its occasionally, then stay with what you have and do the tune up mentioned above. If you pull this load every week, then 4:56 would be my humble recommendation.

 

[TUCSONDUDE]

sorry have to check, but you are towing in 4th and not 5th?
considered going to 265s? it would be close to equivalent to 4:10s(after added weight, and overall ratio, and assuming same amount of wear)

FYI i have never pulled a trailer.

 

[LiftedGmc355]

if it were my truck i would go with a 4:10 ratio mainly because the 4:56 is a little low when u hit highway speeds. a 4:10 ratio will give you a little more low end pull, and shell take the hills better. Check out the ultimate TBI mods. My girlfriends dad used to haul a 7500lb camper behind his 94 1/2 ton 350 lol