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Overdrive: Is It Worth It?

Discussion in 'Early CJ5 and CJ6 Tech' started by Cj5dale, Dec 10, 2022.

  1. Dec 10, 2022
    Cj5dale

    Cj5dale Member 2023 Sponsor 2022 Sponsor

    Knoxville, Tn
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    Thinking about getting an overdrive for my ‘70 cj5. It has a dauntless v6, T14a, and Dana 18 Tcase.

    Just curious if it’s worth the money/time?
     
  2. Dec 10, 2022
    Boyink

    Boyink Super Moderator Staff Member

    Tulsa, OK
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    What gearing do you have, and how do you use your Jeep?
     
    dnb71R2 likes this.
  3. Dec 10, 2022
    Cj5dale

    Cj5dale Member 2023 Sponsor 2022 Sponsor

    Knoxville, Tn
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    I think it is all stock. I don’t do any major off roading. Either my Jeep or I would probably break in half at our ages :)

    I can confirm the gearing but it sure could use a “4th” gear.
     
    CraigE likes this.
  4. Dec 10, 2022
    timsresort

    timsresort Active Member 2023 Sponsor 2022 Sponsor

    South Lake Tahoe CA
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    I think the best attribute of an overdrive is not so much for a 4th gear, but is splitting gears to get it just right, especially in mountain terrain. I love mine.
     
    Danefraz and Fireball like this.
  5. Dec 10, 2022
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member

    Bozeman, MT
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    Axle Gearing is important....I have v6 with T14 and with 4.88 gears, the OD is 100% worth it. If it had 3.73 gears, maybe not as beneficial. Tire size also matters.... running 3.73 gears with smaller tires makes it more worthwhile. 3.73s with like 33 inch tires and not sure there is any real need.
     
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  6. Dec 10, 2022
    Cj5dale

    Cj5dale Member 2023 Sponsor 2022 Sponsor

    Knoxville, Tn
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    I’m running 31x10.50x15 tires currently

    I’ll check out the gears to see what I have.
     
    Ol Fogie and FinoCJ like this.
  7. Dec 10, 2022
    3b a runnin

    3b a runnin Active Member 2023 Sponsor 2022 Sponsor

    virginia
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    This
     
  8. Dec 10, 2022
    colojeepguy

    colojeepguy Colorado Springs

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    Overdrive is THE BEST single mod you can make to a CJ (assuming you have low gears like 4.88 or 5.38).
    V6, 4.88s and OD makes for a really nice setup.
     
  9. Dec 10, 2022
    timsresort

    timsresort Active Member 2023 Sponsor 2022 Sponsor

    South Lake Tahoe CA
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    In the mountains, this is the best.
     
  10. Dec 11, 2022
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Pullman, WA
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    I've got a mix of Jeeps here with and without overdrive.
    • 1969 V6 with a T-14, 3.73 gears and no overdrive. I like this Jeep as it is it's simple and geared well for most things. The lowest gear is too high for serious rock crawling at 28:1 but it's fine general offroading and geared about right for cruising down the highway.
    • 1968 V6 with a T-90, 4.88 gears and an overdrive. This one also works pretty well. The T-90 has a higher first gear, so the crawl ratio isn't all that much better than the '69 at 34:1 but it is better. 3rd gear with the overdrive on is 3.7 so it's almost identical to a Jeep with 3.73s and no overdrive. Being able to split gears is nice with 6 speeds to choose from in either range. In practice this Jeep is a little better all around than the '69, but not enough to justify $1500+ for an overdrive and gear change. Having a T-14 would change the calculus a little and give you a 37:1 crawl gear with 4.88s.
    • 1971 with a Buick 350 V8, T-18 4 speed with granny gear, 3.73 gears and an overdrive. This is a nice combo. The crawl gear is 58:1 and the top highway gear is 2.8:1. I was planning on switching to 4.56 or 4.88 gears but the big Buick is happy lugging down the highway at 1800rpm and idles down to 400rpm or lower for trail use so I've just left the 3.73s in it. Having the OD is really nice for splitting gears on the trail. Particularly with the granny 1st gear being such a big jump to 2nd gear. It's really nice to have an extra gear in between them.
    If you've got 3.73s and don't llive in hilly country I'd say it's not worth it. If you have 4.88s now I'd do it. If you have 3.73s and live in hilly country or do more serious offroading then I'd regear the axles and do it. It you're really serious about offroading, a truck 4speed will give you the biggest bang for your buck in getting a low crawl gear while keeping the current high gear.
     
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  11. Dec 11, 2022
    Jeepsterjim

    Jeepsterjim Member

    Lincoln, CA
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    OD would be ideal if the rear diff ratio is 4.27 or lower.
     
    Rick Whitson likes this.
  12. Dec 11, 2022
    colojeepguy

    colojeepguy Colorado Springs

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    This. It's really nice to have the extra gear combos on the trail.
     
  13. Dec 11, 2022
    oldtime

    oldtime oldtime

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    Kaiser Motors certified the Warn OD as a “Jeep Approved Special Equipment and Accessory” in 1964.
    It was only certified for use with 4.88 and 5.38 final drive ratios.
    I fully agree with that and I think it would also be good with non Jeep IH 4.56 gearing.
     
  14. Dec 11, 2022
    47v6

    47v6 junk wrecker! 2023 Sponsor 2022 Sponsor

    USA
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    I have an OD with the 4.3/sm420/5.38 and 35" tires. I have not wheeled this on rocky trails, so take that for what it is... If I didn't get my OD for under 400 bucks I would say its not worth it for the OD aspect.

    I LOVE the Rube Goldberg aspect of this whole setup, but I don't really need more gears and I dont need the OD because 55-60 is already scary enough in my flat fender with the stock 2a windshield and all the rattles and what not of driving around in a tractor go-cart.

    Obviously other people have applications that really work for them with the OD as a gear splitter. I just don't need it yet. When I go out to Colorado this summer, I may have a change of mind.
     
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  15. Dec 11, 2022
    Jw60

    Jw60 Sitting up n buckled down. 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Doesn't that transmission need the 10 spline bowl gear?

    I run an overdrive but I've got a 4.3 with 5.38's the overdrive makes it equal to 4.10s.
    I have an sm465 on the bench and 4.27's that will make it effectively the same as my current 1st and 3rd o/d
    I do drive on I70 with it. It's the sound of hearing loss.
     
  16. Dec 11, 2022
    Cj5dale

    Cj5dale Member 2023 Sponsor 2022 Sponsor

    Knoxville, Tn
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    So I checked for a tag on rear diff to see if that would give an indication of the ratio but it only had that tag with the instruction to use the correct lube.

    so I read online that you can get a rough idea of the ratio by determing how many turns of the rear driveshaft it takes to make the wheel turn once.

    so I marked the driveshaft and the tire and did the test.

    it took a little more than 4.75 turns of the driveshaft to make the tire turn once.

    is that a valid way to get an idea of the gear ratio?
     
  17. Dec 11, 2022
    hooliganrick

    hooliganrick Sponsor

    San Diego, CA
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    It is worth it. I have the same setup as you with the 4.88 gearing, and 31x10.5 tires. I can easily cruise at freeway speeds now 65-70mph without the fear of being run down or blowing up my engine. 65 mph at 2800+/- rpm....right in the power zone, and running 70 mph is easy too. Before the OD, it would hit rpms up to 3200+. I was getting alot of oil blowing out from the breather, pcv grommet, and even the rear seal. It makes driving much more enjoyable. For daily driving, I just leave it in OD. No more head jerking off the line from a stop. I kick myself for not doing it sooner. Turns your jeep into an all around vehicle. mpg also went up...which is always a plus
     
    Last edited: Dec 11, 2022
  18. Dec 11, 2022
    Stakebed

    Stakebed Member

    Lake Co....
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    Yes it is roughly valid. Computes to 4.88 ratio.

    I have OD in my M38a1 (5.38's and short tires) and my '57 Willys stakebed (4.88's & ~32" tires). Both vehicles have stock drivetrains. Both benefit greatly from the OD on the highway. Neither would be fast enough to drive safely on the highway without Warn overdrive.
    Additionally, with only 3 spd transmissions, the OD helps with choosing an ideal gear ratio while off road.
     
  19. Dec 11, 2022
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Pullman, WA
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    If you've got 4.88s, definitely do an overdrive.
     
  20. Dec 11, 2022
    duffer

    duffer Rodent Power

    Bozeman, MT
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    Another who believes 4.88's and an OD are near perfect with the 225. That works pretty well both on and off road, even with a relatively crappy first gear ratio. Definitely worth the install in this case.
     
    colojeepguy likes this.
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