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Author Topic: overdive or not  (Read 1838 times)

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Offline CraigM

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Re: overdive or not
« Reply #15 on: December 12, 2018, 05:16:54 PM »
I agree 100% with what old time is saying. My initial post asked if anyone hade tried the 4.27 ratio but I have not had any replies to that but from the feed that I have received on how the OD pulls I feel if I use a 4.27 without OD it will pull better than OD with 5.38 I have had a lot of experience with gearing and ratios. From my experience over the years the more direct you can go the less power it takes to pull the same load. Just for fun go to you tube and check out maasdam sorghum mills and you will see some of the old equipment that I have been working with over the last 45 years we use open gears with belts and chains also some old transmissions and rear ends from the 40's are incorporated into the mill. I will be doing a little engine work and I should be around 70 HP when done.   
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Offline oldtime

Re: overdive or not
« Reply #16 on: December 12, 2018, 07:00:11 PM »
Well its certainly true that the omission of O.D. unit� reduces a small percentage of frictional drag.
Please realize that any change of 5% or less is getting very near to� "imperceivable status"" without test equipment.
Yes a 10% change should certainly be noticable by "seat of the pants" feeling.

What really matters here is that the O.D. unit (additional split gearing ratios's) allows you to much better keep the engine in it's prime RPM operating range.
The engine operating range is fully as important as the gear ranging ability.
Especially true with meager power output.
« Last Edit: December 12, 2018, 07:01:16 PM by oldtime »

Offline JeepFever

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Re: overdive or not
« Reply #17 on: July 15, 2019, 02:37:32 PM »
I used to have an overdrive on my '2A,  but could not use it in a driveline swap  (went to centered diff in rear)

I miss having that "in-between" gear.

To compare,  at say 55mph,  and hit a hill the engine will not pull
  OD & 5.38: 2500 rpm,  then downshift to 3300 rpm
          4.27 : 2650 rpm,  then downshift to over 4000

True that the 4.27 will go a little farther up the hill before downshifting,  but it is a big gap to the next lower gear.

Then if you consider off-roading,   with 4.27 axles  lo-lo would  29:1   . . .  painfully tall in certain conditions

Offline johnrb3b

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Re: overdive or not
« Reply #18 on: July 19, 2019, 09:20:00 AM »
The above post is one of the main reasons to go the overdrive route. You don't sacrifice your low ratio gearing for off-roading, or simply doing a parade at 2 mph.

Yes, an overdrive will cost you about $1,000 for a new one. Perhaps half or 3/4 of that for a used one. If your time is worth anything your labor cost with make the two pretty close to equal.

Both my 3Bs have 5.38 gears and overdrive and I wouldn't re-gear to 4.27 for any reason. Of course bolting on the overdrive is about 1/100 of the work compared to re-gearing both axles.

My 57 Station Wagon has 4.27 gears but those are behind the L6-226 flat head. Parades require a lot of clutch in-and-out. I wish it had 4.88s or better 5.38s then adding an overdrive would give me the best of both worlds.

I'll repeat what another poster said. Drive it for a while with the 5.38s, then decide how much faster speed or lower RPM you want. Overdrive will give you a bit of both. If you re-gear to 4.27 you'll probably miss the low gearing when you start up in 1st gear. Voice of experience. Even with the higher horsepower, I wish my Wagon had lower gearing.
« Last Edit: July 19, 2019, 09:23:41 AM by johnrb3b »
1946 2A - - - 1949 me - older than most of my Jeeps
1954 3B - - - 1957 Wagon - - - 2010 4-door JK
past Jeeps ---> '54 3B - no tub --- '59 3B - no engine
past addiction - VW ---> '69 bus --- '70 camper

Offline athawk11

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Re: overdive or not
« Reply #19 on: July 19, 2019, 01:21:11 PM »
I finally added an OD this spring.  The value to me is the flexibility it gives you, whether on the road or off. 

Craig seemed pretty set on his approach...even after a dozen folks tried to sway him toward and easy and effective option.  I wonder what he ended up doing.
2-1949 CJ3As
1-1946 CJ2A