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Whats behind your "happy 4th" gear?

Discussion in 'The Hokey Ass Message Board' started by NEWFISHER, Jul 4, 2012.

  1. NEWFISHER
    Joined: Dec 16, 2011
    Posts: 591

    NEWFISHER
    Member
    from Oregon

    I'm running a 250 6 / SM 465 granny low 4speed open drive and a 10 bolt with 3:08s in our 50 Suburban. Low gear is useless unless the trailer is hooked up, starts off well in 2nd. Freeway speed tops at 65 and is plenty fast for a 60+ yr old rig.

    We pull a 2500 lb 20' Avion a lot in the summer behind the burb and its a hill hating 35 mph struggle in 3rd, sometimes 2nd on the big ones and on flat land, 4th is very tired feeling at 50 - 55 mph. My plan is to swap rear end gears and toss in a 700r4 ( I drive it everyday 70 miles to work and back also running errands etc after work). Getting the best mpg I can with a 250 / 700r4 combo is high on the list, but being able to more comfortably pull the hills towing in 3rd would also be a plus.

    My question is: What rear end gears are you truck guys running with a 700r4 and occasionaly pulling a load at freeway speeds for a few hours through some hills?? I have seen 3:73s and 4:10s used and am wondering what you all would suggest with this set up.

    Here's our hound hauler/get out of town set up.
    [​IMG]
     
  2. smiffy6four
    Joined: Apr 12, 2010
    Posts: 333

    smiffy6four
    Member

    Stick in a chev 6.2 diesel and a 700r4. I drove a motorhome to Florida and back to Ontario with this combo, and got 29mpg at a constant 70mph! Don't know what rear axle ratio is, but could find out. Talk about having your cake and eating it! This rig flattened most hills and was easy driving.

    This is going into my 63 Step Van, so I can afford to drive it anywhere, just 'cause I wanna. :D
     
  3. Salty
    Joined: Jul 24, 2006
    Posts: 2,259

    Salty
    Member
    from Florida

    If I'm not mistaken the OP didn't ask about a diesel conversion he asked about rear gears for a 700R4.

    While I don't have the silver bullet answer for you If you dont have a 700R4 yet I would call up Gearstar trans (amazing service) they will ask you a bunch of questions, be able to give you advice on the rear gear choice and likely sell you a job rated awesome transmission as well......

    I don't work for them, have no association with them whatsoever HOWEVER, got treated outstandingly well, they were very through and ensured I would be happy with my purchase. They ain't cheap but they will custom build you whatever it is you want and then back it up.
     
  4. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 8,128

    junkyardjeff
    Member

    3.50 or 3.55s would be a nice gear with o/d but you might need a slightly bigger motor to make it happy pulling the trailer with whatever gear you decide to put in it.
     

  5. samurai mike
    Joined: Feb 24, 2009
    Posts: 515

    samurai mike
    Member

    You might try 3.73 or 4.10s with the four speed you have now. You may just need to spin the 250 up a little more!
     
  6. modeleh
    Joined: Oct 29, 2009
    Posts: 380

    modeleh
    Member

    Great looking rig you have there. 4.10s and the overdrive would be my choice, or leave the manual trans and run 3.50s.
     
  7. R Pope
    Joined: Jan 23, 2006
    Posts: 3,309

    R Pope
    Member

    I would find a 292 and leave the 4 speed where it is!
     
  8. bonesy
    Joined: Aug 14, 2005
    Posts: 3,000

    bonesy
    Member

    I ran 3.73 with a 700r4 with 29" tall tires. The truck had a 250HP 327 and ran like a champ. Honest 24 mpg at 75 mph and could still pull the occasional car trailer.

    I would run 3.73/700r4 combo again in a heartbeat.

    (Beautiful setup too by the way.)
     
  9. NEWFISHER
    Joined: Dec 16, 2011
    Posts: 591

    NEWFISHER
    Member
    from Oregon

    Thanks for the comments. I forgot about the tire height in the mix, I remember it making a big difference on one of Dad's trucks. I'll measure them and edit.

    A 292 would cool, but this 250 runs really nice. I have a 700r4 , lokar shifter, round boot etc, but mabey starting with 3:73 and keeping the 4sp? A truck is supposed to have 3 pedals, but I'm getting lazier the older I get and tossing it into D every day through 20 stop lights and 70 miles of highway sounds kinda nice. The 4:11s would make better sense for pulling the trailer and 3:73s for better economy seems to be the ticket, but cam , carb and tire size also play a huge roll in mpg from what I'm learning. Bumping it up to see if anyone else has input on what they have experienced.
    Thanks
     
  10. squirrel
    Joined: Sep 23, 2004
    Posts: 50,203

    squirrel
    Member

    my wife has a late model Silverado, with the six (262 ci), overdrive trans, and 3.42 gears. That truck kicks down all the time pulling a trailer. The engine is just too small. It gets great mileage when not towing, and lousy mileage towing.

    My 57 one ton pickup with a 454, SM420, and 3.73 gears (and tall tires) does a lot better, although it will go slow if I'm pulling a very heavy trailer through the mountains.

    Overdrive will help a bigger (350 ci) engine get better mileage when you're not towing.

    Good luck, sounds like you might have some more trials in your future...
     
  11. greaseyknight
    Joined: Sep 27, 2010
    Posts: 225

    greaseyknight
    Member
    from Burley WA

    I read somewhere that for the best fuel economy, top gear @ 60 should put the rpm's somewhere at the beginning of the torque curve. In you situation, I would think that OD should be at the lower end of the torque curve, and 3rd gear towards the top.

    Plug in the numbers, and play around with different ratio's here http://vexer.com/automotive-tools/speed-rpm-calculator
     
  12. NEWFISHER
    Joined: Dec 16, 2011
    Posts: 591

    NEWFISHER
    Member
    from Oregon

  13. Needs More Cubic Inches !!!!....Try a beefed up 292 GMC six with more compression and a stump-puller camshaft...390 CFM four barrel and headers....leave the SM 465 alone !!!...change to 3:55s out back.
     
  14. Fat Hack
    Joined: Nov 30, 2002
    Posts: 7,709

    Fat Hack
    Member
    from Detroit

    If you can find a 3.90 gear, that might be the best all-around set-up with the 250 six in a rig like that. If not, you have two compromises...go for a 3.73 or a 4.10 ratio. The 700r4 will get you going easier, but be sure you have the TV (throttle valve) cable hooked up and adjusted properly before you drive it an inch!!
     
  15. Hey NewFisher,

    You may contemplate a steeper gear, and then adding something like a Ranger overdrive unit. I have a 64 C10 with a 292, and an SM420, and will be adding the Ranger here shortly. It allows you to split any gear with a 27% overdrive.

    http://www.high-impact.net/transmission_and_gear/rangeroverdrive.htm

    I know the sm420 and 465 often suffer a bit in that three/four area. A bit more rear gear, and the option to split gears may improve your situation. Just another option!
     
  16. squirrel
    Joined: Sep 23, 2004
    Posts: 50,203

    squirrel
    Member

    The ranger is neat, how much are they?
     
  17. Depending on the vendor, I've seen them range from just under $1000, up to around $1500. Crazy that they vary that much, so, watch out when you go to buy one. I'm excited to get mine installed. With a 3.73 rear, and 30" tires, it should put me at 2150rpm at 70mph in my C10! Can't wait to see what it will do to my mileage.
     
  18. NEWFISHER
    Joined: Dec 16, 2011
    Posts: 591

    NEWFISHER
    Member
    from Oregon

    Thanks guys. The pumped 292 would be cool, but last on the list. I'm digging the simple single carb and getting decent milage( keeping it simple for awhile). The ranger is cool, similar to a gear vendors unit theat I could get my hands on, but I'm kinda leaning ttowards ditching the manual for a more "6:00am, no coffee, 20 stop lights , then 30 plus mile drive to work" automatic. I know don't hate me, trucks need 3 pedals....I get it. It just seems easier right now. So back to the 700r4 swap behind a semi lethargic 250. The 3:90 gear set does seem to split the difference and may be my answer with this combo. Ill start looking for a set and see what's out there. 10 bolt car 7 3/4 is what I remember it having ( notes are at work). Thanks for all the input!
     
  19. Dyce
    Joined: Sep 12, 2006
    Posts: 1,926

    Dyce
    Member

    Quote ( I drive it everyday 70 miles to work and back also running errands etc after work).
    I always tune the drive train for what I plan on using it for the most. If you pull the camper you are more than likly on vacation so what's the hurry? You say you drive it 70 miles a day. I'd tune it to be happy going down the road every day..... I think your biggest problem is the 250. You have a truck, and the 250 just wasn't made to pull. It was more of a car or light truck engine. If your stuck on an inline I like the 292 suggestion. For economy? The best all around truck engine I have ever had was a 334 stroker. It's a 305 block and a 400 crank. It kicks a 350's ass on the low end, and is easy on gas. Not HAMB freindly, but I had to mention it because I think it fits your needs.
     
  20. squirrel
    Joined: Sep 23, 2004
    Posts: 50,203

    squirrel
    Member

    http://www.summitracing.com/parts/MGR-G875390/

    Interesting....factory gearing in the old Chevy trucks from the 50s was, get this-- 3.90
     
  21. Deuces
    Joined: Nov 3, 2009
    Posts: 21,582

    Deuces
    Member
    from Michigan

    I have 3:55's in all 3 of my rides... :D:rolleyes:
     
  22. sdluck
    Joined: Sep 19, 2006
    Posts: 2,808

    sdluck
    Member

    The 2004r is smaller ,has closer gears,and a slightly taller 4th gear .67 vs 70.
     
  23. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 8,128

    junkyardjeff
    Member

    I found out on my 66 F250 that a bigger motor with more torque helps out alot,I first went from 4.10 gears to 3.54s and the gas mileage stayed the same but dropped in a fresh 460 and if I keep my foot out of it I get better gas mileage then with the original 352 and plenty of power to tow what I want.
     
  24. 48 Chubby
    Joined: Apr 29, 2008
    Posts: 1,014

    48 Chubby
    Member Emeritus

    I really don't think that a drive line change is going to improve your fuel mileage.
    I really don't think that your towing performance will be helped by any thing other than the substantial boost in torque that would come with a bigger engine.
    Suburban+camper+every thing needed for a camping trip= like 7,000 plus pounds.
    6 cylinder Chevy= 135 horses on a good day.
    You can have any thing you want, but you can't have every thing you want.
     
  25. young'n'poor
    Joined: Jan 26, 2006
    Posts: 1,280

    young'n'poor
    Member
    from Anoka. MN

    What are your rear gears now? I've never had a six cylinder truck but with overdrive and a stock six I would imagine you need 4 something gear to tow relatively comfortably.

    How often do you go on vacation with the trailer? If its not very often I would just set th truck up to be comfortable everyday and tow slow on vacation.
     
  26. Cymro
    Joined: Jul 1, 2008
    Posts: 742

    Cymro
    Member

    How about a 5 speed manual box with closer ratios than the current wide ratio four speed? Fifth is usually overdriven so it may improve your fuel consumption in the process.
     
  27. SteadyT
    Joined: Sep 11, 2007
    Posts: 482

    SteadyT
    Member

    The 2004R is the superior trans, no doubt... but the 700R4 is the better fit considering the weight of the vehicle and the dinky c.i.

    I imagine the 3.06:1 first gear will be welcome in his ride.
     
  28. NEWFISHER
    Joined: Dec 16, 2011
    Posts: 591

    NEWFISHER
    Member
    from Oregon

    3:08s now and we camp nearly every other weekend in the nicer months with once a month in the spring and fall.
     
  29. Packattack
    Joined: Jul 20, 2012
    Posts: 2

    Packattack
    Member

    I'm doing the exact same maths on a tranny swap for my Packard, minus the towing capacity. The factory Ultramatic is getting tired and slippy, and after going through just about everything that you have so far, I've determined that the 200-4R is the right one for me. I'm running a stock 130hp Thunderbolt L8, a stock 3.90 pinion set and Coker 760x15s that measure 28.7" tall. Doubling the amount of ratios behind this engine will far better utilize the brutish torque it develops, and the .67:1 OD will lower cruising RPM @ 70 mph by nearly 1000. In my studies, I've found that many people consider the 200-4R a "weak" transmission because they are confusing it with the TH200 3 speed, which was infamously bad. In your application, I'd suggest hunting down the beefy version of the 200-4R that came with a Monte Carlo SS or Buick T Type/Grand National. It has lower ratios than the 700R4 and a taller OD, and a smaller case size which will make it much easier to fit in a car that's designed around a breadbox sized manual. The only rub to using either of the GM overdrives is the electric lock-up solenoid. If you're already running a 12v system, no worries. Install a relay on your brake switch circuit to unlock it on decel and you're golden. As was previously mentioned, a TV cable is also a good idea since it makes the valve body... behave better. My car is 6v and I really really do NOT want to make the change, since I like playing my optional Del-phi radio while I chase two little yellow globs around at night. I'm going to pick up a 200-4R this weekend that came out of an 85 Regal and inspect the lock-up solenoid to see if I can't figure out how to actuate it with 6v. The circuit is actually fairly simple. There's a mechanical pressure switch on the 4th gear hydraulic circuit that energizes the solenoid. It only needs battery feed to operate. Mechanical components don't care what voltage you run through them, as long as the amperage isn't too high. I think it will work. The big question mark is whether the solenoid will energize with enough force. I'll cross that bridge after I swim around it a few times, and I hope my rambling contains one or two pieces of info you can use.
     
  30. NEWFISHER
    Joined: Dec 16, 2011
    Posts: 591

    NEWFISHER
    Member
    from Oregon

    I ended up with a 3:73 rr from a 68 C10 ( only 1/2 wider wms and same 1310 joint) and a 700r4 using the TCI lock up kit with the vacuum switch and added manual trigger for 3rd lock up when towing. Couldn't be happier. Soft 4th lock up smooth and great milage so far with the 390 Holley and the mild built 250 stovebolt
     

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