who swapped to a 3.08 gear and how do you like it ?

[19673ontree]

OK , I am wanting to take my truck down to the shade's run in tn this september but I have to travel down I 81 for 2 hour's and with my truck geared like it is I just don't see it happening !

I bought a complete 12 bolt ring gear and pinion and center chunk 3.08 last fall and have it out in the garage in a 5 gallon bucket of oil I guess maybe next weekend I will put it in , should be able to run the 80 mph OK with the 3.08 , I'd really enjoy taking my truck that weekend ,

anyway post up if you have done this and with a 250 six banger too !!!

my truck is a 250 3spd on the column !

[70k52wd]

I have a 350 and went from 3.73 to 3.08. It lost all low end take off power. Sure it will cruise 80, but it could do that before. The gas saving was almost not worth mention. Keep what you have. Two hours, make it two hours and fifteen minutes and go the speed limit. Your six cyl and three spd will thank you for not changing.

[bigguy69]

i have done this. the truck has a 350,th350. it was geared 3.73. i put the 3.08 gear in the truck and it does alot better going down the interstate. it is a little slower out of the hole, but the truck is just a cruiser. i like it better with 3.08 myself.

[19673ontree]

you know now that I think about this my truck must be a 4.11 because I got up on the interstate with it on one trip just to see how it felt and I tell you it is about maxed out at 60 ! I don't have a tach so I am not sure what the rpm's were , I want to be able to stay in front of those big truck's , they get mad as hell if you slow them down !

[69halfton]

if you wanted to commute to work everyday on the interstate, id say change them.

but if in all reality, you only going to be making 1 or 2 trips, the fuel & time saved won't be worth the time spend in my opinion.

that 250 wouldn't do back on the highway with the 3.08s since they typically have lots of torque, but I really think you'd hate it in the city.

a buddy of mine went from 3.08s to 3.73s and says he would never go back. belive it or not, his in-town fuel milage actually got better, less luggin it or something i geuss..

[19673ontree]

YEA now I forgot to mention that , I take the truck to elizabethon (2 HR's) drive but it's posted 45mph and 55mph the whole way there and it use's more gas on a trip like that than it use's around town and up hill's at say 35mph ,
I just did not want to wind the six banger that hard for that long , but I guess it can take it I have never seen a 250 six banger broke

[LockDoc]

-
I switched from a 3.73 to a 3.07 (that would be the actual ratio) in the White Truck and I love it. Cruises better, raised my mileage, and still does really good on the low end. Of course I'm running a 454 and th400 so that might make a difference..

LockDoc

[chev-obsession]

Originally Posted by 19673ontree

you know now that I think about this my truck must be a 4.11 because I got up on the interstate with it on one trip just to see how it felt and I tell you it is about maxed out at 60 ! I don't have a tach so I am not sure what the rpm's were , I want to be able to stay in front of those big truck's , they get mad as hell if you slow them down !

dude, i had a 250 six and a sm456 4 speed, and i maxed out at 70 doing 4,000 rpm's, so im guessing that you have 3.73's most likely

[special-K]

Take Rt11 or the Blur Ridge.
I had the same combo in a`72 shortbed.I don`t know if it was 3.73 or 4.11.I thought it was 4.11,but no option listed,so it was prolly 3.73.It sang down the highway @65,but I`d do that all day long.We are just so used to o/d we`ve forgotten how this was an everyday thing.Let it sing,but no 70-80.

[19673ontree]

special K I thought about getting on route 11 in bristol and following it to I think Rutledge tn ? then I would only have to stay on I 40 a few mile's ,
I have not gone down route 11 myself I always use 81 but they say it's 45mph and 55mph ,

[68Stepbed]

Well, I can tell you this. My dad has a 350/M20 combo in his 56 with a 3.00:1 gear ratio. His car struggles to get going, but does real god on the open road. He's got a 3.55 chunk for it, so he'll end up changing. You won't be happy with the 3.08's. These old banger trucks were built for work use. Theywere never meant for long highway use, which I'm sure you already knew that.

I never pushed my old 250/3spd combo past 70mph, but my wife had it to 90 a few times. So it will handle the interstate at 70.

My suggestion would be to take 11E from Bristol into Morristown, then get on 25E into Newport. At Newport, get on 25/70 till you get to Hwy 411. Follow 411 north into Sevierville. Take a left on Veterans Blvd. all the way into Pigeon Forge!

As you come up 411 on your way into Sevierville, you pass by my workplace. If you come by during the week, I'll be there. I usually drive my truck to work on Thursdays and Fridays of big show weekends, so you wouldn't miss it.

[prostreetC-10]

A couple of other things to think about that I didn't see posted or I missed is.....

A) Do you EVER plan on doing an engine change? If you plan on beefing up the power, maybe getting a little cam in a small block or something like that, you will not want the 3.08's. My truck you see to the left was a 250 as well with 3.73's. Although it spun up pretty high, I was so excited because I knew I would only have to do a posi carrier swap when I switched to my BBC. I was lucky and got the EXACT same backlash when I switched to an Eaton, making it a super easy swap.

B) This is probably the most important. 3.08's are going to be super hard on your clutch setup. You will have to put a ton of RPM's into your motor to get that rolling. It's going to put excessive heat into your flywheel and pressure plate. It might even eventually start to make your clutch "chatter" from heat spots. I would never consider 3.08's with a manual trans....for any reason!!!

[Ackattack]

In my 72 GMC I had 3.08s for a long time, and really with a hopped up 327 it did pretty good.

When I switched to a TPI 350 and 700R4, it was a major dog out on the highway so I switched to 3.73s and that was perfect (with OD).

[67chevemall]

I bought a set of 3:07 a few years ago for the same reason. I like the highway travel.
I took the truck on a 20 hour crusie and wished it didn't rev so high.

But I can't decide if I want to make the change. If you go the speed limit I think it is all good with the 3:73's


I wonder how much lower the rpm's would be with 3:07 instead of 3:73 with 383/ M21

[prostreetC-10]

In just trying to guess the difference, you have to understand "ratios". There is a much bigger difference from 3.00 to 3.5 than from 3.5 to 4.0. If you have a 4.11 rear end and you go to 4.88's....that's not nearly as dramatic as going from 3.08's to 3.55's. The same is true for going down in ratios. It's a huge change.

[Kas68c10]

the previous owner put 3.07's in the jimmy, it runs down the road great, but I haven't towed with it, or really tested it on hills and such. I ran the 68 short box with the original 250 and 3 in the tree as a daily driver for 6 years. That little trip wont hurt her at all! In canada, the speed limit is 60 mph and I ran it at 65 or so for 5 hours straight (well, had to stop for gas) I wouldnt change the gearing just for that trip, I'd need another reason. I put the o/d in mine as i was highway running alot...

[hgs_notes]

With a 28" tire and 3.73 gears, the RPM at 70 mph is about 3136. With 3.07 gears the rpm at 70 is 2581.

Running 3000 isn't an engine killer, though sometimes it sounds like it is.

Drivability concerns more how you use it. If you are not pulling stumps on the farm or drag racing, or hauling heavy loads, or any number of reasons for needed the extra low end torque, the swap should not be big problem. Take off power will have more to do with what first gear ratio is in the transmission than than the rear end. So it depends on the 3 speed you have. If you want to cruise the highways like me, you'll like the lower rpm.

If it's not a daily driver, the gas mileage won't be a big factor.

[Dark Knight]

I swapped to a 3.08 and I love it! I had 4.56 gears in my old 3/4 ton axle. My little 6 sounded really pissed off when you were cruising @ 70 down the freeway. 10 mpg just wasn't cutting it. Not with gas prices the way they are now... Go for it! You can even drop in an aftermarket HD clutch if you're worried about it. I don't think you'll need to though.

[Longhorn Man]

My old 69 GMC short fleet had the 3.07 gears and a cammed out small block, would pull away from a stop like a freight train. The only thing that sucked is with a 2500 RPM cruise speed, I couldn't put the 2800 - 3200 stall converter the cam needed, so i had to pop it in neutral at every stop.
My big block burb has a 3.07 gear in it now (up from 3.54) and I like it a lot. It is a little slower off the line, but it isn't a race truck, nor a pulling truck. (I doubt the OP is doing either of those with his)
I say grab a rear end, swap the whole assembly in it, if you like it, sell your original axle to one of the guys complaining about there 3.07 gear.
If you don't like it, swap it back and sell the 3.07 gear.

I can't stand putting my longhorn on the freeway. 4.10 gears suck if you aren't pulling or racing. And if you build an engine for massive low end torque, then you still don't need the low gears, even for racing and towing.

[WorkinLonghorn]

I would be more concerned about safety in one of these trucks going 70-80 MPH in traffic than gas mileage.Even with your brakes in perfect condition these things will not stop as fast as modern cars and so if there is an incident in front of you, you better have a nice big cushion at 80 MPH!
Not to mention that there is almost zilch chance of making any kind of evasive manuver at that speed.
I've always felt "the need for speed" as much as the next guy, but I never felt like it was a good idea to cruise over 60-65 in one of these.
If it was me, I'd keep what you have,especially with that 250,and just drive at or below the limit and to the right if necessary.

[Lated]

I have a 305 with a three on the tree. I swapped my 3.73s for 3.08s about a year ago. At the time I was in Maryland and it did ok off the line. Now that I'm in Colorado and much higher than sea level, it's not making as much power and the truck is a pain to get moving. Never paid much attention to mpg before the swap but with the 3.08 I only get 9mpg, couldn't have been much worse before. On the highway I know the RPMs are a lot lower because the truck is much quieter (not sure what the difference in RPMs is, tach quit working) but around town and on even the littlest bit of a hill my truck doesn't want to move. I'd much rather have the 3.73s back.

[prostreetC-10]

Gee....it seems like a matter of opinion!

One this is for sure...you can't have both. Just weigh the time and $$$ to the gain (if any).

[hgs_notes]

Originally Posted by WorkinLonghorn

I would be more concerned about safety in one of these trucks going 70-80 MPH in traffic than gas mileage.Even with your brakes in perfect condition these things will not stop as fast as modern cars and so if there is an incident in front of you, you better have a nice big cushion at 80 MPH!
Not to mention that there is almost zilch chance of making any kind of evasive manuver at that speed.
I've always felt "the need for speed" as much as the next guy, but I never felt like it was a good idea to cruise over 60-65 in one of these.
If it was me, I'd keep what you have,especially with that 250,and just drive at or below the limit and to the right if necessary.

I have to disagree with you on a couple things.

First, compared to a newer truck, these weigh about a ton less than a large SUV, and probably 1000 lbs or more, less than a new pick up. That makes a huge difference in braking. My truck stops a LOT better than my wifes yukon XL. You might as well compare it to a motorcycle as a car, it's not a fair comparison.

Second, these trucks have a lower center of gravity than newer trucks. They just don't sit as high, 2wd or 4x4's. The handling on these is really quite good. Try and turn hard in a new truck at 80 mph and you will find yourself waking up in a hospital asking what happened.

The old truck is likely more stable given the size, based on weight, center of gravity and using the same style modern radials.

[19673ontree]

HEY THANK's GUY's !

I may just buzz down 81 like it is !!!

[WorkinLonghorn]

I have to disagree with you on a couple things.

First, compared to a newer truck, these weigh about a ton less than a large SUV, and probably 1000 lbs or more, less than a new pick up. That makes a huge difference in braking. My truck stops a LOT better than my wifes yukon XL. You might as well compare it to a motorcycle as a car, it's not a fair comparison.

Second, these trucks have a lower center of gravity than newer trucks. They just don't sit as high, 2wd or 4x4's. The handling on these is really quite good. Try and turn hard in a new truck at 80 mph and you will find yourself waking up in a hospital asking what happened.

The old truck is likely more stable given the size, based on weight, center of gravity and using the same style modern radials.

Wow,you have a lot of confidence in your truck.

In my 5200 lb.(with tools) GMC the brakes work great when there's a 1400Lb camper on the back. But since there was no weight-sensitive propotioning system, the rears skid way before they should when the truck is empty.
Maybe you have your prop. valve set correctly for the way you always drive. I seem to need an adjustable one.
Even so I just don't think 80 MPH is wise or necessary in any pick-up.