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82 K3500 tranny ID and replacement

Discussion in 'Chevy Trucks' started by Gator-aide, Jun 6, 2009.

  1. Gator-aide

    Gator-aide Junior Member
    Messages: 11

    Hello All,

    I got this great old 4x4 Chevy firetruck from an auction recently. I'm using it specifically for my landscape business, hauling a dump trailer etc. So the stock automatic is just a three speed, I gauged my fuel economy towing the trailer (with a ton or so in it) at 7mpg last week!

    I know towing economy is naturally low.......but this seems downright horrible. I have yet to clock the MPG without the trailer. So I am looking for some modification to get better mileage. I noticed by 25 mph, I'm in 3rd gear all the way up to highway cruising speed.

    So I'm open to any suggestions, but I'm thinking of swapping in a 4-speed? I looked at overdrive units from Gear vendors and there $3000.00, so a new tranny seemed like the better deal. A neighbor of mine is a good mechanic and said he could do the install.

    So the main question is a new 4 speed's compatibility with my existing 7.4 liter engine, drivetrain etc? I'm not sure what tranny and transfer case are on it currently. I'm definitely no mechanic, but I climbed under this morning and counted 13 bolts on the hydramatic tranny pan. The transfer case had a couple part numbers on it as well, but I wasn't sure which to write down. Any help on the ID or suggestion for mating a new tranny to this old hog would be appreciated. I love this truck, and want to keep it as my main work truck but the gas is killing me! I included a few pics of the gateraide....Thanks

    IMG_8556.jpg

    IMG_8557.jpg

    IMG_8558.jpg
     
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    For identification purposes the trans would be the vulnerable Turbo 400 and the transfer case is the unbeatable NP 205 which is one of the toughest combos GM ever had. Axle gear ratios will be 4.56, which is why your in high gear at 25 mph.

    MPG's with that truck of course wouldn't be its strong point but you don't purchase a 1 ton with a 454 for fuel mileage. The biggest thing that affects MPG's on these trucks is the 4.56's in combination with the 454 as they work better and pull just as good with a 4.10 ratio and will deliver better MPG's in the process. Although even with a gear swap your numbers won't rise to more than about 9-10 MPG. Thats all they ever got even on their best day.

    A trans swap is possible but a gear swap would be less expensive since your only real option for a trans swap would be a 4L80E, which is electronically controlled. You'd first need the trans and then have to purchase the stand alone controller and wiring harness ($$) to operate it. It's a great swap but unfortunately due to the cost involved that places it in about the same price category as the Gear Vendor overdrive unit you already looked into. But you could do a gear swap (to the 4.10) for around a grand. wesport
     
  3. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    That's a sharp looking truck, though I'm not sure if I'm too fond of the color. I like the service body also.
     
  4. Gator-aide

    Gator-aide Junior Member
    Messages: 11

    Thanks B&B,

    The gear swap does sound like a good idea for a smaller investment. Yep, I knew I was getting into the lower end of the mileage scale when I got this thing! I'm surprised that my only option on the trans swap is to the newer 4L80E? And I'm not sure I want to throw 3-4k in quite yet.anyway, so any idea where I could get the new gears?
     
  5. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    The 4L80E is your only choice because its really the only overdrive trans you'd use in a 1 ton truck. Sure you could do an old 700-4R but don't expect it to live long in that type of application. So that would be more or less a waste of money. Swapping to a manual overdrive trans would be cost prohibitive as well if you wanted to row your own gears..so that only leaves the 4L80E auto.



    Search around on the web, there's plenty of choices. Drive train Specialists, Randy's ring & Pinion, and Drive Train Warehouse are just a few off the top of my head. You can source a pair of gear sets and all the components to install them for around $600-700 if you dig around enough...leaving the rest for labor. Don't be afraid to check ebay or Craigslist even for a used set if you're on a really tight budget.
     
  6. Gator-aide

    Gator-aide Junior Member
    Messages: 11

    Alright that makes sense. Thanks for leads on the vendors....I'll check around.
     
  7. Gator-aide

    Gator-aide Junior Member
    Messages: 11

    Anyway that an Allison would be compatible with the old big block?
     
  8. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    So I ran some numbers. I assumed that fuel is $3 per gallon, the job will cost $1,000, and your 7MPG test is not fair given you were pulling a trailer. Much to my surprise, this project would pay for itself pretty quickly, depending of course on how many miles you drive per year. On the very conservative side, lets say your mileage increases from 9MPG with your current gears to 10MPG with new gears. That's an 11% improvement in economy. At $3 per gallon, you would have to drive 30,000 miles to break even. I do almost that much per year. On the more aggressive side, let's say you go from 8 to 11, is just under 10,000 miles. If the cost of fuel goes up, faster payback. I would imagine your real numbers would be somewhere in the middle, but you get the idea.

    Also, this analysis assumes you don't recover any of your investment when you sell the truck, or sell your old ring and pinion gears. It's probably reasonable to assume you could get a few bucks (if not more) for your old gears. I have no idea about the resale impact. I don't think it would hurt it, that's for sure.

    Hey B&B, would that truck have come with a lockup converter? My 81 half ton had it. I'm thinking maybe his isn't working anymore. That of course would be a big help.
     
    Last edited: Jun 7, 2009
  9. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    It's certainly do-able but unfortunately not on a budget. Even by closely watching your numbers and buying used components it's tough to swap one in for under 3 grand. The stand alone harness, controller, and software needed to tune it once its installed is $1600 by itself.

    I like your thoughts though as engine/trans swaps are one of my specialties. :nod:
     
  10. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    No lock up converters on the T-400's. In fact there were no lock up converters on the heavier duty trans applications until the 4L80E's were first used beginning in the mid-late '91 model year.

    They really don't add much MPG to speak about on a heavy truck unless your running highway speeds anyway, so a lockup capable trans wouldn't be of much help in Gators case unless he is in fact running the majority of the miles above 50-55 MPH. Especially so with 4.56's since engine RPM's would be rather high anyway which reduces converter slippage thus raising efficiency.
     
  11. Gator-aide

    Gator-aide Junior Member
    Messages: 11

    Thanks for running some numbers 2COR, looks like the gear swap will definitely pay off in the short term. I do drive at least 20-30 miles a day that are at 55-66mph, so would like to replace the tranny in time for the overdrive, but I'm definitely into investing in a better gear ratio now. Are all I need the ring and pinion gears and the install kit? From drivetrain warehouse the gears and the install kit would be under $300.00 average cost, anything else I'm leaving out......this seems too cheap?

    Mechanic buddy of mine also suggested just getting a whole new rear end if I could find one at the junkyard. But what are the chances I'll find one with the 4.10 ratio I'm after? I can hunt around and see what I come up with. Thanks for the direction B&B
     
  12. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    You've overlooked the fact that you need TWO gear sets and TWO install kits if you intend on ever engaging the 4WD in the future. Can't have two different ratios between the front and rear axles. Bad things happen when you do that. :D

    Finding a rear 14 bolt complete axle assembly with 4.10's already installed is do-able but won't save you much (of any) money in the long run vs swapping the gear set only. And finding a 4.10 equipped Dana 60 axle to swap into the front for under a grand will be ultra tough...as they're worth their weight in gold. payup
     
  13. Gator-aide

    Gator-aide Junior Member
    Messages: 11

    Aaaah, but of coarse I need two! You can tell I'm more gardener than mechanic.

    I'm starting to think I should leave this old hogs engine setup close to what it is. I can modify the heck out of it, and its still going to be a tanker on gas. Maybe I should leave it as is, put a flat bed or dump bed on it, and leave it for heavy days where I haul big loads in the truck and trailer.

    Then I can get a small block truck for the daily driver, maybe a 2500 series with a utility bed (or even use the utility bed off the one ton if compatible) and run a more efficient fleet......whaddya think?
     
  14. BigLou80

    BigLou80 Senior Member
    Messages: 558

    Another fairly low cost fuel saving sawp would be to TBI or MPI( but then your spending some $$)
    I have a friend who has done several and says he gains 1 or 2 MPG and a lot better drivability by doing it. around here you could get all the parts out of a junk yard for $200-$300 and if swap takes an afternoon.

    B&B will correct me if I am wrong but look for an 88 and up truck with a 454 and an automatic.
     
  15. Gator-aide

    Gator-aide Junior Member
    Messages: 11

    Big Lou,

    I'm unfamiliar with TBI and MPI.........can you explain?
     
  16. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    TBI is Throttle Body Injection. The fuel injection system GM used from 1987 up through 95. MPI is multiport injection. It's a more sophisticated system, therefore more expensive. TBI would be a good upgrade, and greatly improve driveability. A couple real simple things you can do is make sure your tires are properly inflated, and keep your speed down. If you could afford another smaller truck to do most of your driving, that would probably be wise.
     
  17. Gator-aide

    Gator-aide Junior Member
    Messages: 11

    Alright so I'm getting the bigger picture here. There are definitely some upgrades I could do with gear swaps, and the tbi install. B & B.....you were saying it would be cost prohibitive and a real pain to swap it with a manual trans? I'd ultimately love to have a stick that could a little better mileage.......and a lot more fun to drive!

    And maybe around 4k isn't too bad for a new tranny setup either manual or automatic.......it would be an investment in my business....correct me if I'm dreaming at this price. So it appears I could put 2-8k in this truck with some nice modifications, or just get a used small block truck for even more, and have the versatility. Thanks for all the help......I'll start diggin...
     
  18. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    It's just like anything else, its all in what you want to spend. If your on a tight budget it would be cost prohibitive for the advantages (long term payback) but if your willing to put the 3K into while gaining the enjoyment of rowing your own gears then its certainly do-able. You could do an NV4500 5-speed overdrive swap for approx 3K...and even swap to the 4.10's too if you find a good enough deal on a good used trans.

    Judging by the pics it looks like the truck would be worth it and provide years of service for your investment.
     
  19. 70monte

    70monte Senior Member
    Messages: 468

    Thats a very nice looking truck! Just for reference, I have a 98 K3500 4x4 reg cab long bed with the 454/4L80E auto tranny and I only get about 8-9 mpg towing. I also have the 4.10 gears. The best mileage I've gotten is about 12.9 not towing. This is with all new plugs, newer plug wires, new dist cap&rotor, and new pre-cat O2 sensors. My truck has 99,200 miles on it. With your engine, tranny, and gear ratio combo, you are never going to get very good mileage towing or other wise.

    I personally would leave the truck as it is and either sell it or keep it and get another truck with a small block and two wheel drive as a towing rig.

    I wish I could have found a truck like that when I was looking for a towing truck. I like that body style.

    Wayne
     
  20. Gator-aide

    Gator-aide Junior Member
    Messages: 11

    Hey Wayne,

    Is is a nice body style right? Happen to luck out and pick it up at an auction at the pismo beach yard.....nices line,city maintained........its in beautiful shape...... Think I'll keep it:drinkup:

    Ya I have learned a ton more about engine/tranny performance just since joining this forum about 8 days ago.....kudos to this site and to everyone whos replied

    I knew the first time I heard this think fire up.......that it was definitely no joke.....and that the gas economy was one of the things that would always suffer. And since reading around here I now understand why, and that it will be very good. I'm a landscaper, always had an interest in tweaking things, so I was more curious what I could do and how much effect these different mods would have on performance/economy. Thats interesting your 4L80E still only gets 8-9 towing, that was what combo I was thinking of getting ideally, but I see the differnce is small. I'm gonna change the gears, and probably rest at that for a bit..