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Mileage, gearing

Discussion in 'Chevy Trucks' started by mstyles0927, Jan 31, 2001.

  1. mstyles0927

    mstyles0927 Junior Member
    Messages: 20

    I had a 1976 1/2 ton 2WD LB AT truck with a factory 350 in it. When I wrecked it, I bought a 1980 1/2 ton 4WD SB MT truck with a used-up inline 6.

    When the inline 6 finally gave up the ghost, I pulled the 350 from the 76 and dropped it into the 4x4. I have rebuilt the carburetor myself with a kit from AutoZone(2 barrel), replaced the plugs and wires, checked the timing, etc (you know, a basic tune-up). I left the 4 spd manual tranny in the 4WD. Also, I know the 76 LB had a bigger gas tank (I think 18 or 20 gallon) than the 80 (16 gallon).
    But it seems like the 4x4 really drinks the gas much harder than the 2WD--I hit the station to refuel a lot. Is this common--I haven't made the time to pull the rear differential to look at the gear ratio, but this thing is really hitting the old wallet now?
    Last check on the highway trip to the lake I got just under 13mpg. In the city (with all the traffic and lights) it drops to around 11-12mpg.
    Any ideas out there?
  2. John DiMartino

    John DiMartino PlowSite.com Veteran
    Messages: 2,154

    4x4's do use quite a bit more fuel than 2wds especially in older rigs.you might have like a 3.73 in the 4x4 and had 3.08 in the 2wd,which will make it even worse than it should be.
  3. mike reeh

    mike reeh Senior Member
    Messages: 114

    man you get 13mpg!! i envy you :)

    a quadrajet or other 4bbl will wake up the motor at full throttle but say bye bye to gas mileage...

    like john said, its probably in the gearing, plus its a heavier truck. i definately know what you mean when you say its really hittin the old wallet.. :)

    good luck

    mike reeh
  4. 85w/350

    85w/350 Senior Member
    Messages: 190


    I also envy you I drive a 2wd sb GMC w/350 and it gets 10-1/2mpg in the city and 12mpg on the highway...i just mounted some 31 inch tires in hopes of helping my highway mileage by slowing down the RPM's a bit...city probably got worst I'll be filling up soon so i'll post another within the next few days
  5. Joseph Meidling

    Joseph Meidling Junior Member
    Messages: 19

    I will be looking for a 4wd, 1500 series to commute back and forth to work in. I was thinking about the 4.3L?? Any input would be appreciated. The commute is 30 miles each way.
  6. mstyles0927

    mstyles0927 Junior Member
    Messages: 20

    Thanks for all the input. It seems like maybe I don't have it too bad, compared to some of you guys! I guess you have to give up the gas mileage for the privilege of driving one of the best trucks in the world!

    Thanks for all the input.
  7. Mowman

    Mowman Junior Member
    Messages: 12

    25 MPG + !!!!!!!!

    Yes, 25 MPG pulling my trailer and equipment. I bought this truck new (ordered) it in 1998. I wasn't mowing much then and wanted the best MPG. S-10 w/ 2.2 Vortec 4 w/5 speed trans. I'm now pulling a 5x10 open trailer w/ Walker mower and misc. equipment, about 1900lbs. It handles it fine. Next truck will have a 4.3 V-6 and auto w/ 4X4 for snow removal. But hey for now it's getting the job done.
    And I'm whining at 25, don't know how you guys do it, 8-12 MPG?
  8. 85w/350

    85w/350 Senior Member
    Messages: 190

    give it up

    If you are complainig about 25mpg somethig is wrong...I see you also have a 4cylinder compared to our 8's...the 4.3 is a good little engine and I have seen up to 30mpg out of one in an s-10, but it was highway mileage, not a 4x4 and definately not pulling a 19,000lb trailer...now a days if you can even find a chevy truck much less any truck (I'm talking real trucks 1/2tons and bigger) that can get 25mpg you found yourself a deal....

    In my opinion sometimes you have to give up the mileage for power and for driving a dependable truck that will run practically twice as long as any other vehicle...my mileage is bad and i wish it were better and i am going to change the gearing soon hopefully to 3.08's from 3.73's...
  9. roland26

    roland26 Junior Member
    Messages: 8

    mileage and gearing

    my 84 gmc has a 350/300 gm crate engine with hedders,edelbrock manifold and quad jet. it has a 700 with 28" tires. with the 308 gear it runs about 2000 rpm at 65.
    and it get 13mpg. but according to the vac gage I am in the
    carb alot.I think my final gear is 2.10 (in od) and that is toooo high. I am going to 3.42 (mabe a 3.73) and mabe I want be in the carb so deep. with the 3.42 I think the final drive will be about 2.60 and the 3.73 about 2.80. do these figures look correct. I dont expect 17 to 18 mpg but 14 to 15 would be nice. roland
  10. 85w/350

    85w/350 Senior Member
    Messages: 190

    I heard that the 3.42 with the 700 tranny is a nice setup as far as gearing and gas mileage...as far as the numbers i'm really not sure
  11. MTCK

    MTCK Senior Member
    Messages: 346

    The 700r4 transmission has a 70% overdrive, which would give you a 2.61 final drive ratio with 3.73 gears or a 2.40 final drive with 3.42. Hope this helps.
  12. 75

    75 PlowSite.com Addict
    Messages: 1,382

    Mileage and gearing

    Considering that you're running a 4x4, and with all the other information you have posted, I don't think you're doing that bad. That transmission sounds like the same one in my welding rig, (1979 Chev C-30 dually, 350 gas) around here we call them "farmer four gears". Good transmission, that grunt low 1'st gear is nice for launching and pulling but there isn't much top end! That will really make a difference in the mileage. Hey, 85w/350, couldn't have said it better myself. Sure my truck (1975 GMC C-35, 350 gas, T400, 2wd dually) uses more fuel (I'm lucky if I hit the 10 mpg mark!) but it doesn't cost me a lot in other ways. It's paid for and I do pretty much all my own repair work. I guess my employer feels the same way too, that's why he's running the '79 I drive and just put a bunch of $$$ into a body job and mural on the hood.

    1975 GMC C-35
  13. John DiMartino

    John DiMartino PlowSite.com Veteran
    Messages: 2,154

    Joe M,the 4.3 V6 will be fine in a 1500 4wd for commuting,just dont put big tires on it,it'll bog it down.I know a couple of guys with them,and they test drove the 4.8 270hpV8 first,there isnt a very big difference in power,the 4.3 has more torque at lower RPM's and has 200hp on the top end.If you plan to tow anything over 3000 lbs,on a regular basis,go fop the 5.3/V8.
  14. steveair

    steveair Senior Member
    Messages: 176


    Not to say it can't be possible, but I find it hard to believe a s10 is getting 25 mpg, especially pulling a trailer.

    Just got rid of my 99 gmc sonoma, 2wd.5 spd manual/2.2 liter, and the best mpg I got was 23 on the highway with no load. Avg, commuting 30 miles each way to work was around 20-22. No way can I imagine getting 25 mpg out of the 4 cyl pulling a 2k trailer.

    I once had a 2.6 liter isuzu pickup, and that never did any better than 23 or so on the highway also. If you are seriously getting 25 mpg pulling a trailer, then I would keep that truck forever and sell it on ebay as a 'rare vehicle' because it doesn't sound possible. Maybe, and I mean maybe, 16-17 with a trailer, but that I doubt. I use to put a yard of mulch in the back of the truck and I couldn't leave 4 th gear. Just no way.

  15. Chopper Lover

    Chopper Lover Junior Member
    Messages: 21

    I know it has been a while since the original post but I was wondering if you have manual or automatic hubs on your front end.

    Automatic hubs, depending on the transfer case, will sometimes activate themselves when any slip is noticed. They are also creating drag in your sytem while you are driving causing a need for more fuel to be used.

    For less than $80 you can easily install manual hubs and you will see a slight increase in your fuel economy. I had switched mine in my old 1982 because I could never tell if they had disengauged when I shifted back to 2WD. I picked up about 1 MPG.

    Just an idea.
  16. RTallday

    RTallday Member
    Messages: 79

    I get 10 miles to the gallon in my 79 K-20. Thats with 33 inch tires!! The 4X4 will generally get worse gas mileage than the 2 wd, cause there is more weight in a 4X4. Also, u have the transfer case, and the tranny is cast iron, so theres a lot more weight there. I also have 4:10s. I would guess you have 3:23s or 3:73s. Good luck.

  17. mike reeh

    mike reeh Senior Member
    Messages: 114

    what kind of tranny are you talking about? a manual gearbox i take it..

    but god you said it all when you said the xfer case is heavy! what a freakin monster a 203 and 205 are.. not as heavy as a 3/4ton rear axle! 14 bolt axles are unholy beasts.

    all that added weight PLUS a front axle, its hard to beleive they dont get MUCH worse mileage vs. a 2WD..

  18. mstyles0927

    mstyles0927 Junior Member
    Messages: 20

    Yes, Manual Hubs

    Chopper Lover, I have the manual locking hubs. I thought about looking for automatic hubs to switch, but figured the time and expense were not worth it. The 4 spd manual and probably lower geared rear-end probably make the mileage as bad as it is.

    I do 'lock' the hubs every 2 or 3 months and run them locked but in 2WD for a day or two when I haven't used the 4WD in a while. I had a friend tell me this was a good idea to keep the manual hubs in good working order. Anybody ever heard of this? Good or bad?
  19. Chopper Lover

    Chopper Lover Junior Member
    Messages: 21

    Yes, it is a good idea to lock the hubs from time to time to keep them lubed up and working freely. When I switched mine to manuals the hub manufacturer (Warner, I think)recommended once a month for 2-3 miles. I would guess what you are doing will work just as well.

    As for switching to automatic hubs I would say no. Normally you will know when you are going to need them and can lock them in advance. If you wake up and have a foot of snow on the ground you can always lock them as you clean off your truck.

    I got rid of the automatic hubs on my 1982 because that model truck required you to back up for 20 feet or so to unlock them. I would always hear one unlock right away, but never the other. Rather than taking the chance of burning one up, I switched to the manuals. On any truck I order from here on out you can be sure I will go with manual hubs if it is available.

  20. mstyles0927

    mstyles0927 Junior Member
    Messages: 20


    Thanks for the info.

    As I mentioned, I have the 3 spd + 'granny gear' manual tranny. Is it a good idea to mess with the rear gears to move to something like a 3.08 or the like in a 4WD? I can get the rear-end from my old 2WD truck if needed, but I am afraid of 'messing up' the 4WD or something.