Will 3.08 Gears work for me???

[mx jim]

I wanted to put 3.08 gears in my truck so that i could do 75mph on the free way and get i little bit better gas milage. Right now i have 3.73 gears and i can only do 65mph and i am geting 10 miles per gallon. So what i wanted to know is if i am going to notice i big big diffrence in how the truck takes off from a dead start having 3.08 gears then it did before with the 3.73 gears? I have a 350 motor with about 350 hp and a 350 trans and my tires are 28" tall. Well thanks for the help James

[Longhorn Man]

My 69 had the dreaded 3.07 gears and a pretty healthey motor. It is a pig out of the hole. Sometimes it feels like I am trying to launch a friggin buick...and not the turbo one either.

[da-burb]

I've got 3.07 gears and get 10mpg. I have 4.10's in a 3/4 ton 4x4 and get 10. I have had only 1 truck that did better. It had 3.07's with a 327/th350 and 2 barrel rochester that did 17mpg.

[70c10]

You will feel less performance for sure out of the hole. I believe you will also need a 3 series carrier when going down to those gears. You have a 4 series now.

[mikep]

Ive got 4.57 gears and I get 10 mpg and I can zip right up to 110 mph.

If you can only do 65 mph you have other problems that have nothing to do with your gearing. 3.73's are pretty mild gears for a truck . You might want to look at tuning or general motor health before you invest in a new set of gears and setup that wont fix your problem. 3.08's are pretty miserable to drive with in a heavy truck with tall tires unless you are running a big block with LOTS of low end torque.

[70c10]

That's why I'm thinking of going to 4:11's.

[crazy longhorn]

3.08 gears leave a lot to be desired for performance, but the 3.73-4.10s turn the rpms up a bit on the hyway. I think the answer.....altho more costly is overdrive(best of both worlds). my longhorn has needed another gear since i put the 4.10s in. I run a 28" tall tire, & have looked at many options on the OD trannies, or add on units. It was a big ouch, but I spent the bucks for a 6 spd richmond. With the 4.10 gears, & a 3.28 1 st ratio it should dance out of the hole like a rabbit, & will cruise on the road in OD like it has 3.11 gears. ......crazyL

[Longhorn Man]

You can probably go over 65 no problam...and hold it there all day long. Do you have a tach? I only ask becouse i find many people with no tach are afraid of scattering there motor and get a little nervouse when they hear the engine sounds at 3000 RPM so they back off.
I actually heard from a Longhorn owner (4.56 gearing) that his truck was only designed to drive 45 MPH, and it had only been faster going down a hill. He would not believe me that the 402 was good for 100+ MPH in his truck.

[Wasted Income]

Make sure your secondaries are correctly adjusted so that they are not opening while cruising. This will kill your milage.

I had 3.07s with a lockup 700-r4 and 235-75-15 tires....HATED THEM!! I think my fuel milage got better when I did the 3.73 swap. Probably because the motor was lugging down big time on the highway (1800rpm or so at 70 mph.......)

[mtdave2]

keep your gears and get a gearvender. next to putting in a 5 or 6 speed, its the best way to get the best of both worlds

[Gene]

I have 3:07 gears and out of the hole is ok I spin the tires for about 20 feet. But I want 3:73's, so I can go to an OD trans. I get around 15 mpg with a mild 350 and 350 turbo trans.

I would say that the 3:07's get a little better MPG but do you really wanna give up the acceleration to save a few gallons? These trucks were meant to suck gas:p

[71MoneyPit]

I guess it depends on the motor setup, the MoneyPit has 3.07's but because of the brute torque of the 500 Caddy it jumps out of the hole like it has 4.11's,4.11's and up don't work well with caddy motors because they like to tug not rev.

[bpmcgee]

I just did this swap -- 3.73s to 3.08s. I've only had it back a couple of days, but it DOES appear to get better gas mileage.

I've got a 350 with a 4 speed. I'd have to say that the acceleration, while not neck-wrenching, is certainly decent.

Brian

[O'l Buck]

My K-10's got 3.07's and I hate them. I can't figure for the life of me why anyone would order a 4x4 with 3.07's......It makes 12 mpg, but it's a total turd with a trailer and it's not much good in the mud..........runs like a scalded dog on the highway though.....hehe

[Slammed67]

I've got 3:07 gears with my 700R4 and I love it. It has no problem off the line and will easily chirp the tires when I hit 2nd gear. The whole point of an overdrive trans is to be idleing along down the highway at 70mph. 3:08's with a THM350 might make it a dog though.

[Dean]

700R4 has a much lower first gear if I remember correctly.

[70c10]

yes it does

[Palf70Step]

I know someone who did that to their 70. It's a 350 with a mild cam & 3 speed manual. Runs real strong here. Pulls a tralor well too, BUT we are FLAT down here. Don't know how great it would feel in hilly territory. Depends on what you do with it or want to do with it. It'll pull and run OK, just may seem like a very old man ride in some cases.

If you got the money, go with an OD of some sort and keep the gears.

[jays68yak]

I have the 3.07's in my suburban. Wanna trade your rear end for mine?

Screw the gas mileage. Im not going to get anthing decent anyways. It would get better if i ditched the 650 double pumper holley and got a vac second version.

[MandarinSixSeven]

I went from 3.73's to 3.08 and did notice a bit better gas mileage, and it still pulls pretty good off the line, I find that with the little traction my truck made its almost faster off the line because before I would just sit there and spin the tires. But when I need to I can still lay some good rubber, so day though if I can ever afford some 18-20' rims with sticky rubber, then I will prolly go back to 3.73 or higher. For now with 15's it 3.08's work really well I actually like it better.

[Ed ke6bnl]

Originally posted by MandarinSixSeven
I went from 3.73's to 3.08 and did notice a bit better gas mileage, and it still pulls pretty good off the line, I find that with the little traction my truck made its almost faster off the line because before I would just sit there and spin the tires. But when I need to I can still lay some good rubber, so day though if I can ever afford some 18-20' rims with sticky rubber, then I will prolly go back to 3.73 or higher. For now with 15's it 3.08's work really well I actually like it better.

My boy started this thread because he is just 17 and short on funds and trying to make do for the time being. Let me make it clear that this truck has no problem what so ever going pass the 60 mph mark it probably was built to redline at 6500 his concern is the long freeway runs with the engine tacking about 3000 for a long period. He got ticketed for chirping the tires at a stop and has added 3 five gallon jugs of water secured to the back of the bed for traction, this truck wants to brake the tires free in all the gears. He is mainly concerned about the poor gas mileage and any excess wear from constant high rev on the freeway. We did check the secondarys as mentioned to see if they are sticking and they are working fine. We pulled a plug and it does seem that it is running rich on fuel and will check the edelbrock manual and maybe see about the jetting. We may see what the best vehicles are for a rear end transplant since his has been making a whine since its purchase last year. Thanks and any suggestion will be taken seriously. Ed ke6bnl

[mikep]

Man, I remember my first wreckless endangerment citation. Or was it the exhibition of speed ticket ..hmmmm . Got my license suspended on both of them . Judge Roy Bacon in the Hamilton county Ohio courthouse saw me on both. What a guy . Those were good days.

Anyway. 3000 rpm wont saw a motor in half. Youre really not going to see excessive wear from running at a higher RPM . In fact you might even see less wear in an engine run with lower gears as there is less stress put on the motor to go a given MPH than with higher gearing. Lugging a motor is bad for bearings pure and simple .Running a lower gear will even allow you to use a lower octane gas in many situations. I know thats the case with mine. When I had 3.54's I HAD to use 92 octane. Now with the 4.57's I get by with 89 octane no problem. Its probably a wash on the gas cost/fuel mileage in my case . You'll probably see better gas mileage with the higher gearing but in a truck that sees any "truck" duty the higher gearing will cause more long term problems than it solves unless you have an excess of low end torque. Towing, hauling and acceleration will suffer and you really do have more of a chance of lower end wear with the higher gearing.

[Dreaminator]

A couple of thoughts. First, consider running a 29 or 30 inch tire. Assuming he is running a 25 or 26 now that will change his ratio to something like this:
26/30 x3.73 = about 3.23. Tighten the tranny with shift kits and you should come off the line smoking while running about 500-600rpms less at 65 mph. If you are really serious about mileage go overdrive. You can go Gear Vendor but that is at least $2800 after installation (need to mod drive shaft) or add a GM 700. Remember, later model 700s (sometimes 460) are electronic and cost probably $700 to 1000 installed. Finally, GM rears do not coast very well. There is lot of drag when you back off the throttle and that seriously indluences gas mileage.

[Longhorn Man]

And some engines will get better MPG spinning faster. I know for a fact mine does. It wants to spin 3000 RPM.

[540 Stroker]

Our trucks really weren't made/designed for high gas mileage numbers. 10mpg isn't that bad-all things considered. Anyone that's getting mid teens to 20MPG on the highway in a heavy, non aerodynamic old truck has a OD trans and/or EFI. Anyways, the revs he's seeing on the highway won't hurt the engine. If he was holding 4000+ rpm for any length of time, that might warrant the gear change you are thinking about. Modern overdrive transmissions and EFI engines have spoiled us somewhat.