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Technical automatic overdrive?

Discussion in 'The Hokey Ass Message Board' started by fastcar1953, Mar 16, 2020.

  1. yes

    22 vote(s)
  2. no

    18 vote(s)
  1. fastcar1953
    Joined: Oct 23, 2009
    Posts: 2,624


    Do you have a automatic overdrive in your car or truck and why? Is it for gas mileage? Less wear on engine? Both ? My truck has it , only because it was there when i bought it. I do travel a lot so it helps some on gas. If i would have built it i probably would do a 3 speed auto or lower gears. I have thoughts on changing rear gears. Currently running 3.42 would like 4.10 or 4.11. When i was younger i drove a lot of 60's chevy's. Most had 3.73 gears with 2 speed powerglide. Cars seem to run as good as new cars. Gas mileage was lower but so was gas prices. I even drove a stock 1953 chevy 210 about 15000 miles in a year and a half. It had the babbit rod 235 with stock speed and 4.11 gears. All my friends said i would blow it up, but i drove the crap out of it. Went to Americruise in 96 , drove 580 miles round trip. Average speed 75mph. no a/c and hot as hell. The fastest speed i saw was 95 mph downhill. I did have tall 235 /75/15 tires on back. Funnest car i ever drove. Would pass anything without a hesitation. Overdrive is nice but not needed in my opinion. Do you remember those days? P.S. When i type it's not all together, but when i post it is. What am i doing wrong?
  2. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,015

    jimmy six

    I didn't install one when changing my trans and rear end. Everything is fine. Typical 3 speed automatic and 2.74 gears
    Elcohaulic likes this.
  3. gimpyshotrods
    Joined: May 20, 2009
    Posts: 18,777


    Not an automatic, but my car has two overdrive gears, both 5th, and 6th.

    The range makes it like having 2.56:1 and 5.13:1 gears, in the same car, at the same time.
  4. Garpo
    Joined: Jul 16, 2016
    Posts: 240


    I used a Toyota auto behind my flatmotor. Kit from Flatattack in Australia. 4 gears with 4th about 0.66 to 1.
    Used with a 3.9 rear this gives 2000rpm at 100k (62mph) which is our speed limit. Runs real happy at that.
    There is a noticeable drop in engine noise compared with 3rd gear (direct)
    Never measured fuel economy. Does not seem the thing to do when you are having fun.
    Last edited: Mar 18, 2020
    vtx1800, Bandit Billy and fastcar1953 like this.

  5. plym_46
    Joined: Sep 8, 2005
    Posts: 4,018

    from central NY

    I have 4.11 rear gears. 3380 rpm at 63 mph. Stroke is 4 5/8 inch. Kinda busy for highway running. Added .070 OD, 2280 rpm now at indicated 65. Much happier, quieter, fuel mileage in OD 21 without 17. 40 more miles per tank.
    j-jock and Hnstray like this.
  6. I sometimes hear people say that spending money on an overdrive trans is a waste as in it'll take you forever to make your money back in gas savings. I've never seen that as the main reason. Years ago I had an older but off topic 4-speed Z/28 and I can tell you, 3000 RPM on the highway gets real old, real quick. Overdrive just makes the car so much more useable. Any increase in gas mileage is just icing on the cake.
  7. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 8,944


    OD in my DD and great fuel economy given the price of gas down here, you guys are lucky over there. Live down here and other countries and you'll see why we all complain about the price of gas. I've OD in my 35 Chebby and get 28mpg; adding an OD to my 46 Olds and hope to get comparable gas mileage. I'd love a Tremec in my FE powered 64 Ford, it's NOT real economical at all but that's not what I bought it for. :D
    Bandit Billy and Hnstray like this.
  8. Hnstray
    Joined: Aug 23, 2009
    Posts: 12,179

    from Quincy, IL

    @fastcar1953 .....depending on your key board, hit ‘enter’ or ‘return’ twice to double space between sentences when you want to start a new paragraph.
    Joined: Aug 1, 2009
    Posts: 674

    from 94577

    You forgot, 'better acceleration'.
    More gears, that have a decent gear drop between them(not the 700), will allow the engine to stay within the useful power band allowing for quicker acceleration.
    That 1.76 first gear on a PG loses out to a 2.52 in a Th350 and that again loses out to the 2.74 in a Th2004R.
    If you are a total acceleration nut, you can regear the final drive so when in OD you are at the same RPMs in cruise as you would be with a PG or TH350 in 1:1.
    If those have a final drive of 3.42:1, with a .67 OD to get the same top gear rpm you could stick 5.13:1 final drive in the rear.
    If you could get it to actually hook and shift right, that would make for some quick off the line acceleration. Albeit, overgeared.
  10. This is how hot Rodders should view the benefits of OD.

    joel and gimpyshotrods like this.
    Joined: Jul 20, 2006
    Posts: 2,422


    My convertible just has a 3 speed automatic (400 TH). When I built it the rear end I used had a 2:56 rear gear in it. I thought for fuel mileage that would be ok. I felt the 455 would be ok with that gear but made the car a gutless wonder. Several years after I started driving it I swapped in a 3:08 gear set. That woke up the car and I really didn’t see much change in fuel milage
  12. FrozenMerc
    Joined: Sep 4, 2009
    Posts: 2,762


    I put a Ford AOD behind the FE in my '62 Mercury Monterey Wagon. The rear has a 3.6:1 gear in it with rather tall 30" tires. I did it for all the reasons that make a overdrive great. Good acceleration, minimize RPM drop between gears, good highway mileage, and minimize wear and tear on the engine and my ear drums. The car is much more enjoyable to drive (especially on the wide open interstates of the great plains) than it was with the factory Cruis-O trans and 3.0:1 rear end.
  13. Gman0046
    Joined: Jul 24, 2005
    Posts: 6,260


    My 60 Pontiac has a 2004R out of an 87 Grand National. With the torque converter locked up its under 2000 RPM's at 80 MPH. On interstate highways it can run all day long without breaking a sweat.
  14. buffaloracer
    Joined: Aug 22, 2004
    Posts: 806

    from kansas

    My first car was a '51 Mercury with 4.10 gears and OD. Loved it then and haven't changed my mind.
  15. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 2,111

    from Brooks Ky

    Most 4 speed (overdrive) trannys have a lower first gear than 3 speed auto trans do. Changing to a 3 speed auto would hurt both low end performance and top end speed/economy. Best to stick with overdrive.

    You are probably hitting enter at what you think is the end of where you want the line to be. Try typing until the computer starts the next line and I think you will see a difference.;)
  16. fastcar1953
    Joined: Oct 23, 2009
    Posts: 2,624


    Overdrive is better, i get that. I just don't think it's needed. Power windows and cruise control are nice with a/c but not needed.
    Most people i know want better gas mileage and will spend a lot of money on overdrives. They just don't drive their cars 1500 miles a year or less. They go to local shows and cruise ins otherwise car sits in garage. Seems like a waste to me.
    Overdrive would benefit me. I drive about 6000 miles a year or more. That's just the hot rod .
    Thanks for the opinions.
  17. My ‘40 Chevy has a 700r4 with 3.55 rear gears, the ‘40 Ford coupe has a super T 10 with 4.11’s and my ‘28 rpu on ‘32 rails has TKO500 - gear ration undecided yet.
  18. I have been running a TH400 with a stage II Transgo kit and a Hone-O-Drive since 1974, and I love it. I was running 4.57 gears, and it kept the rpms reasonable at 70 mph.
    I used to haul a heavy slide in camper as well as pulling a 20 ft boat, and the flexibility in terms of the gearing available, yielded all the power I needed as well as good economy.
    I know it saved gas, but I think the biggest saving was that I wasn't wearing out the moving parts. I have since changed to a 3.73 gearset, and am getting even better economy, but more importantly, lower cabin noise.
    I love my OD.
  19. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 2,111

    from Brooks Ky

    Necessary.......NO Desirable.......Yes Put your Hot Rod in drive and and prevent it from going into overdrive and then take a long drive on any expressway. You don't HAVE to use overdrive, but watching your engine roar at todays highway speeds isn't the best way to go.:D
  20. Torque Torque and more TORQUE

    There’s a balance of RPM and torque that you want to be in most of the time. That greatly depends on your goals.

    The gear ratios in transmission and rear end are direct multiplying factor in a torque equation.
    (Engine torque) X ((trans gear ratio) X (rear gear ratio)) = torque at axle flange / tire radius.

    The OD trans has a natural consequence of needing AND favorable use of a numerically higher rear gear ratio. That numerically higher gear ratio X the trans numerically higher low gear ratio increases the engine’s torque and accelerates the car like a swift kick right in the ass.
    On the high end, the trans OD gear ratio actually divides the rear gear ratio down providing lower RPM for any given road speed.

    Algoma56 likes this.
    Joined: Jun 3, 2005
    Posts: 8,287


    Well I voted no because the cars in my life right now don't have it. Would I? Sure I would. The 47 Cadillac I'm currently caring for has a 3.70 rear axle and a stick shift (as ordered). In local traffic it's perfect. You're never that "old car in the way" among the current crop of drivers we're surrounded by. That's rather nice really but up around 60-65, well let's just say you know it. It's not straining but just feels like 1 more gear would be sweet. The 41 packard we're playing with has the uber-awesome-best-ever Packard 356 straight 8. Yeah, the badass with 9 mains and rated at a conservative 160 HP. Even though I haven't driven it yet I know I already wish it had the factory O/D. My time with the 47 Clipper that did have it? You had to keep an eye on things because you're over 70 before you know it. That's not a bad thing out there on your own but those old things don't inspire freeway gymnastics when that twit in the other lane is texting and might invade your space. My Ford, also yet to hit the road, has tall tires and 3.78s. Doing the math says about 2600 at 65 MPH. Now I never have had a flathead Ford 'under foot' in my 45 years of the life but even though it's fresh I gotta wonder how hard that is on only 221 cubes pulling a 2800lb car. Some say no worries, others just raise a right eyebrow. We'll see I guess.
  22. s55mercury66
    Joined: Jul 6, 2009
    Posts: 3,980

    from SW Wyoming

    I have a 428/C6 combo in a land yacht. Do I wish it overdrive? Yes, I do, but, I'm not willing to spend the cash required to do the job. I have found it much cheaper to swap the 9 inch center section if I want to go on a long trip, or if I want to go to the 1/8th mile down in Evanston. I will bring up one thing though, and that is the fact that a lot of folks like to see overdrive when they are looking to buy.
  23. Last summer we finished a 54 Chevy truck.
    It’s got a zz34 crate engine, 350th and a 3:55 rear gear. It goes pretty good and fun to drive off the light. Once in the 55-60 Cruisin speed it seems like there should be another gear not to enjoyable. So much so everyone fiddles with that locar thinking it might be in second gear.

    I suggested two options/
    1: OD trans and a 3:73
    Even more fun off the light and way more enjoyable
    2: de tune the engine a little, move the power band lower and 3.08 ish rear gear.

    Option 1 :eek:too much money.:eek:
    Option 2 :eek:too much money for castration :eek::mad:

    That th350 and 3.55 gear is called a perfect compromise. Gets it but Leaves some on the table off the light and goes highway speed fine it’s just not enjoyable. Nobody is really happy but they got what the needed walking away thinking they should have did better/ that’s the perfect compromise right?
    ekimneirbo likes this.
  24. Installing one now. Partly for mileage, but mostly for better around town performance. The first gear will now be 3.06 to 1, and I'm replacing the 3:00 in the rear with 3.55.
    Engine RPM will drop by 500 at 75 mph, plus I'll have better acceleration. If I didn't already have the transmission, I might have just swapped the rear gears, when necessary, for my long trips.
    31Vicky with a hemi likes this.
  25. 392
    Joined: Feb 27, 2007
    Posts: 1,206


    I put a 46rh behind my hemi and I’d have to say it’s one of the best choices I made, 3.50 gears and tall rear tire. Total blast around town and a pleasure going down the highway. I couldn’t see not having it because sacrificing one hurts the other.
  26. buick bill
    Joined: Dec 18, 2008
    Posts: 731

    buick bill
    from yreka;ca

    I went to a lot of trouble to put a 200 in my f1 . with 2.56 rear I wish I had a do over .cant tell a difference of the line .millage not much different . but, it idles at 75 ! lower rear would probably fix everything . but for 1000 mi a year none of it makes sence . hindsite really SUCKS !!!
  27. gimpyshotrods
    Joined: May 20, 2009
    Posts: 18,777


    So, you have a 200-4R and 2.56:1 rear gears?

    That is like having 1.72:1 gears, with a TH350, if you can even get to 4th. If you have tires that are proportionally correct for an F1, you would only find these useful with over 1000hp, on a dry lake bed, pulling away from a push truck.

    What's stopping you from putting 3.55:1, or 3.73:1 gears in the rear axle (or others, depending on all the pertinent variables)?
    Truckdoctor Andy and Just Gary like this.
  28. choppedtudor
    Joined: Nov 28, 2009
    Posts: 684


    I'm running a 700r4 behind my flathead in the 31 far so good
  29. Dave Mc
    Joined: Mar 8, 2011
    Posts: 2,227

    Dave Mc

    A.O.D. & 302 Ford in my 33. 255/70/15 Rear tires , Ouija board said I needed 411 gear to accommodate . all is good @ Highway speeds & over 20 MPG. IMG_0207.JPG
    gimpyshotrods likes this.
  30. brokedownbiker
    Joined: Jun 7, 2016
    Posts: 620


    302, AOD, 3.55 gears in my '51 Ford. Wanted to be able to cruise on the freeways without the engine screaming. My OT '66 Mustang has 302, 4 speed, 3.25 gears and turns 3100 RPM at 70. No bueno., didn't want to end up like that again.

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