Can't decide what gears to run...need opinions

[ivorton74]

I've searched here on the forums and read threads but still can't make up my mind about my rear gears. I'm swapping a 5.3/4l60e in my truck with 3.08 gears. On one hand I know it might be good for fuel economy which is what I want but on the other hand I want that low end and passing power along with the fun factor. So its between the 3.08, 3.42 or 3.73...which do I run? Truck is going to be a daily driver and around where I live there is a lot of 55, 65 and 75 mph highways. I'm running 235/75/15s but may run 275 or 255/60s down the road too.

[chuckmc8]

3:07 is too tall with OD in my opinion. I run 3:73 with 29.3" rear tire. I've heard that 3:42 would be nice, but AFAIK that gear set wasn't an option in the 71/71 diffs

[ls1nova71]

I have 3:08's in my '71 swb with a 5.3/4l60e and I get around 17-18 mpg regardless of how or where I drive. I thought on the highway it would do better, but I think they're just a bit too tall and take the engine out of its optimum performance range trying to keep the truck moving. My last twoo trucks had 3:73's and I like that fear better. If my truck didn't have the factory posi in it, I would have already changed it.

[Gumby]

hotrod mag gave 3:55s the best of both worlds votes, like the 3:42s in my Bird.

[Clyde65]

I put in 3.73's and I like them just fine, like others have said, 3.08's are too tall ( that is what I had), so I think you will be happier with the 3.73's but 3.42's are a nice happy medium.

[68Stepbed]

I vote 3.42 or 3.73 for daily driver duties. Remember, you have OD with a lockup converter, so the 3.73's aren't going to hurt at higher speeds. I'm running 4.11 in my truck and it still does fine at 80.

[Keith Seymore]

Originally Posted by chuckmc8

3:07 is too tall with OD in my opinion. I run 3:73 with 29.3" rear tire. I've heard that 3:42 would be nice, but AFAIK that gear set wasn't an option in the 71/71 diffs

x6 (or whatever number we are on).

3.42 is my "go to" gear and then I move up or down depending on the specific need. With an overdrive I would recommend 3.73 (which is what I have in my truck).

K

[JNJchev77]

I am switching to 3.73 this weekend! 3.08's don't do justice to the 5.3/4l60e, no need for the tall gears with that overdrive. Can't wait to get the outta there... then it's on to the tuner!

[littlevictories]

i have 3.73's and a 700r4 currently. with 255/60-17s its about 2000 rpm at 65mph

Had I a choice I'd put 3.42s for the long trips I plan on taking in this thing.

[ivorton74]

well 3.73 it is then. im gonna run my 3.08s for the time being until I can save some cash and get a 3.73 with a posi unit.

[mooseknuckles]

I'm running 3:42's for daily highway driving, still has tons of bottom end....I had 3:08's in it, crazy top end, still pulled pretty hard....

[68GMCCustom]

changed my trucks 3.08's to 3.73's years ago. Seems like the best 12 bolt performance/economy compromise. Like 3.55 as an option too. otherwise go....
4.10-4.56 for performance
3.55-3.73 for performance w/economy
3.23-3.42 for economy w/performance
2.56-3.08 for straight economy

[ivorton74]

Originally Posted by 68GMCCustom

changed my trucks 3.08's to 3.73's years ago. Seems like the best 12 bolt performance/economy compromise. Like 3.55 as an option too. otherwise go....
4.10-4.56 for performance
3.55-3.73 for performance w/economy
3.23-3.42 for economy w/performance
2.56-3.08 for straight economy

the third one is actually what I want...economy with performance...maybe I should just go with a 3.42

[Houston Ben]

I have a 2011 5.3 w/6L80 and 3.42 gears no posi. I can peel on will... I am putting in a True Trac this week to hopefully help with my tire spinning problem!!!! I run around 2000 rpm @ 70 mph

[crazy longhorn]

On a 29" tire, with OD....3.73 will be the best "all around gear'. If you are more into performance, I would go 4.10? I have 3.42 gears in my truck...1 st is deep, & OD is .76. The old truck will cruise @ 100-105 mph, @ 3100 on the tach in OD? 4.10,s were a little deep with that combo & a 383....unless you like to run 90 mph in an 1/8 mile (not the best way, on a street ride)! The 3.42's, will be a freeway flyer , with the OD Just think about where you use the truck the most, & set up for your useage....Longhorn

[ivorton74]

Its pretty much all highway where i live so highway mileage is important right now but i would like a bit of performance at the same time

[crazy longhorn]

What do plan to run for tire size(diameter)?

[ivorton74]

Im currently running 235/75/15s but will change to either 275/60 or 255/60 15 tires eventually

[69sinker]

I'm running 275 60 15's, 3:73's,5.7 w/ 4l60e. I've been on a 4000 mile trip the last few weeks and I've been getting 18-20mpg. I had thought about going to 3:55's before the trip, but 18-20 makes me happy. Running about 2100-2200 rpm at 75mph. With that being said I would go with 3:73's. Dave

[Super73]

I will put it out there again. With an auto trans, gears have less of an impact on performance than the torque converter does. With a lock up OF trans, unless you are towing, I would put a fairly big converter in the truck and keep a very tame gear.

I have run 1.67 60's with a heads cam 5.7 with 3.73 gears and a 30" tire. I am quite sure I could have gone in the high 1.5's if I had a 5,500rpm converter vs the 4,500 I had in the truck.

My point, even a 3,200rpm verter coupled with a 3.73 gear will out run a stock converter with 4.56's.

I will be changing again from a 4.56 to a 3.90 in the coming months and will be happy to share the info again.

[Billett]

Does the higher stall change the highway manners any? Or does it just affect the "launch" performance. Converters still mystify me...

[Jmiller022]

So your saying a 3k converter and 3.23s would be good?

would the converter not hurt mileage though while cruising?

[Super73]

With a lock up converter mileage on the freeway is not sacrificed at all. What I like doing for customers with big stalled 60e or 80e transmissions is:

Under minimal throttle, short shift the 1-2 and lock the verter early. This keep heat way down in the trans. I progressivly increase shift mph based on throttle postition as well as lock up.

I have people running 4000-4400 rpm converters and still getting mid 20mpg on the freeway with 3.23 gears and cutting high 1.5 - low 1.6 60's in f-bodies.

[Jmiller022]

Originally Posted by Super73

With a lock up converter mileage on the freeway is not sacrificed at all. What I like doing for customers with big stalled 60e or 80e transmissions is:

Under minimal throttle, short shift the 1-2 and lock the verter early. This keep heat way down in the trans. I progressivly increase shift mph based on throttle postition as well as lock up.

I have people running 4000-4400 rpm converters and still getting mid 20mpg on the freeway with 3.23 gears and cutting high 1.5 - low 1.6 60's in f-bodies.

So you do tuning? if so, any mail order stuff?

[Billett]

haha I was thinking the same thing. I'd prefer a chassis and street tune, but I might get a better tune from you without you even setting eyes on it