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Warn Overdrive

Discussion in 'Early CJ5 and CJ6 Tech' started by Jeepman31, Jan 30, 2017.

  1. Jan 30, 2017
    Jeepman31

    Jeepman31 New Member

    Colorado, USA
    Joined:
    Jan 19, 2017
    Messages:
    47
    Hello,

    Could you guys please give me a quick run-down on the Warn overdrive? My 1970 CJ5 has this unit installed on my T-case (D18 I'm assuming).

    Does the overdrive have oil of its own, or is it using the oil from the T-case?

    How do you shift the overdrive? While moving, stopped, etc?

    Can you use the overdrive low range in combo with 4wd Hi and LO?

    Sorry if these questions have been answered before - just a newb here looking for some instruction!

    Thanks!
     
  2. Jan 30, 2017
    jwmckenzie

    jwmckenzie Sponsor Sponsor

    Boston, MA
    Joined:
    Mar 16, 2012
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    516
    I have a Warn behind a D18.

    Oil is shared with the t-case and transmission
    I shift it as it were another gear, on the move or stopped (mostly moving). Actually seldom shift out of OD. My axles are 4.88.
    It should work regardless of how you have the 4WD engaged. I don't off-road so maybe someone else can advise as to the wisdom of using the overdrive in 4WD.

    Also check out Herm's website.

    Herm The Overdrive Guy | Shift into High Gear!

    Here is a bit more information on the D18 and PTO

    The Novak Guide to the Dana Spicer Model 18 Transfer Case
     
    Last edited: Jan 30, 2017
  3. Jan 30, 2017
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member Sponsor

    Denver, CO
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    Jul 18, 2013
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    2,404
    Push the clutch in and shift it when moving or stationary - just like any other gear. It has a brass synchro to help mesh. Can be used with any main transmission gear, high or low range on the t-case etc. Everyone probably has their favorite way of using it - and depends on what your typcial driving conditions are and what engine and gearing you have as well tire size. I typically use it in the standard (not engaged) position when driving around town, and mostly engage it when cruising in 3rd gear at higher speeds (v6 t14 and 33inch tires). In the mountains, I may use it with 2nd gear to help find the right power band on steep hills if I can't hold speed with normal 3rd gear (which is rare with 4.88s). When I had 31 inch tires and the denver city traffic didn't like me shifting from 1st to second at minimum speed from a stoplight (run up my backside), I would leave the OD engage most of the time. Those with 4cyl probably have a tendency to use it between shifting transmission gears. I really like the OD off road - helps find the exact right power (rpm band) to wheel speed for any given situation.
     
  4. Jan 30, 2017
    Jeepman31

    Jeepman31 New Member

    Colorado, USA
    Joined:
    Jan 19, 2017
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    Thank you guys, that makes sense and really helps. Much appreciated!
     
  5. Jan 30, 2017
    aekdbbop

    aekdbbop Member

    TN
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    Jul 31, 2014
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    374
    so ,my top speed is 57 or so with the f134 and t90.. what kind of gain would you get with the OD?
     
  6. Jan 30, 2017
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

    Tantallon, Nova...
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    None :(

    Unfortunately due to the engines torque curve & the nature of wind resistance you won't get any speed gain from the overdrive- 60-65 is about tops.

    But you'll cruise a lot easier in the 45-55 range of speeds, you'll notice a lot less engine noise with the OD & the gear splitting it allows sure does help going up hills.

    And most importantly it's another shift lever on the floor to impress your friends & confuse the thieves :)

    H/
     
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  7. Jan 30, 2017
    Mark Wahlster

    Mark Wahlster Member

    Silverton, OR
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    Dec 17, 2015
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    386
    The OD is between the tranny and transfercase which is what allows the OD to work in all gears in both ranges. I have been told using it like a splitter each time you run through the gears can be hard on the units.
     
  8. Jan 30, 2017
    jpflat2a

    jpflat2a what's that noise?

    Riverside CA
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    What units ?
    Do you even have an overdrive ?
    Not true at all. The unit is designed to be used.
     
  9. Jan 30, 2017
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

    Medford Mass USA
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    "Between" is correct in a sense, but it actually is on the back side of the transfer case. The Warn overdrive is an auxiliary planetary transmission that replaces the output gear of the transmission. It has two ratios, 1:1 and 1:0.75 (IIRC). It also is synchromesh, having a brass blocking ring just like your transmission gears. This means that you can split all your gears between the two ratios as you wish - though I don't know about whether routinely splitting all the gears is good for it or not. I imagine the blocking ring would wear out faster if you do a lot of shifting, but whether that's significant or not I don't know.
     
  10. Jan 30, 2017
    1967 CJ5A

    1967 CJ5A Mike

    Raleigh, NC
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    When I shift from overdrive to direct, I always put the trans in neutral first. This makes less spinning mass for the synchronizer to have to change speeds. This way, the OD shifts easier and there is less wear.
     
  11. Jan 30, 2017
    Daryl

    Daryl Sponsor Sponsor

    Bonney Lake, WA
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    Very important to keep the oil in the transfer case topped off. Most problems with them start with low oil. Some of the later Warn units had very poor surface hardening and can be problematic. Warn's quality control was not very good at times throughout the almost 30 years that they produced the units. Advanced Adapters bought the rights to the unit and have been building them for many years now. As with just about anything on an old Jeep if you take care of it it they really help. If you beat on it, it won't last long. And yes I have had a couple dozen Jeeps with an overdrive so I am not just repeating Internet lore.
     
  12. Jan 30, 2017
    Mark Wahlster

    Mark Wahlster Member

    Silverton, OR
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    Yes I do have a 30% OD from Herm the OD guy who is the onecthat told me most the ODs he has to rebuild is due to people super trucking them splitting every gear as they go.
     
  13. Jan 30, 2017
    colojeepguy

    colojeepguy Colorado Springs Sponsor 2019 Sponsor

    At the foot of...
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    This mirrors my experience. The Warn unit in my Jeep was worn (warn was worn haha) where the bearings ride on the planetary hub. A friend of my dad's gave me a box with three disassembled overdrive units in it, and they all three had wear in the same location. One had obviously been running low on oil, but the other two were just plain worn out. Then, I bought a used one and guess what? It was the same way! I ended up buying a new planetary hub from advance adapters to get my Jeep put back together.
     
  14. Jan 30, 2017
    1967 CJ5A

    1967 CJ5A Mike

    Raleigh, NC
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    One tip that I read online (I think it was here) was to raise the passenger side of the Jeep slightly when filling the transfercase. This allows you to get a little extra oil in there.
     
  15. Jan 30, 2017
    Daryl

    Daryl Sponsor Sponsor

    Bonney Lake, WA
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    Just drive the right side up on a 2x4. Works great.
     
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  16. Mar 8, 2017
    dieseljeeper

    dieseljeeper New Member

    spanaway, wa
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    Howdy, noob here, but my m38a1 has been one of my pet projects since the 80s. When I got it it had been hacked up bad so I did a resto mod. T He latest version is a Kubota turbo diesel, a SM465 trans, d18 tc with a warn overdrive. The shift pattern is start off 2nd direct, 2nd overdrive and leave it in overdrive through the rest of the gears. The axle gears are 4.11 incedently. This works best for this set up because it closes the gap from 2nd and 3rd.
     
  17. Mar 8, 2017
    jzeber

    jzeber Well-Known Member Sponsor 2019 Sponsor

    Morgan Hill, Ca
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    I have found that when shifting the OD to let the engine "rev down" before shifting. I will occasionally get grinding if the engine RPM's are too high when shifting.
    On the Rubicon trip last year we were heading off the trail and the others that had OD's said they are fine to use in 4wd. I hadn't until this past weekend and it worked fine.
     
  18. Mar 9, 2017
    termin8ed

    termin8ed I didn't do it Staff Member Sponsor

    Mason, MI
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    The powerflow goes thru the overdrive planetary at all times regardless if you have it in drive or overdrive range. It doesnt care what transmission gear or transfercase range you are in.
     
  19. Mar 10, 2017
    Alan Rogers

    Alan Rogers New Member

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    Dec 6, 2015
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    I went down to the hardware store. Bought a 90 degree elbow. Screwed into t case and used plug on as cap. Now t case oil level is approx 1/2 in higher. Works great for me.
     
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  20. Mar 11, 2017
    dieseljeeper

    dieseljeeper New Member

    spanaway, wa
    Joined:
    Mar 7, 2017
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    re:termin8ed
    The unit is always turning but when it is in direct the planet carrier is locked to the shell by the synchro so the carrier turns with the shell without turning the planets. Kinda makes the whole mess into one long gear. A good plan to have if one of your planet pins break
     

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