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Topic Summary

Posted by: athawk11
« 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.
Posted by: johnrb3b
« 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.
Posted by: JeepFever
« 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
Posted by: oldtime
« 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.
Posted by: CraigM
« 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.   
Posted by: RICKG
« on: December 12, 2018, 04:24:57 PM »

Quote
Quote
The

The absolute best gearing for hilly high speed on road use and off-road applications is the� 5.38 differential ratio compounded by 25% Warn O.D. unit. PERIOD.


I believe this is what the entire group of participants is suggesting in this thread.� Personally, I concede 100% to oldtime's knowledge on this type of stuff.� He is incapable of steering you in the wrong direction.
Yup.. with my strong L134, 5:38's and OD I'm happy but still prepared to do much downshifting as the load increases. I can't imagine this combination w/4:27's.. not enough motor..
Posted by: athawk11
« on: December 12, 2018, 03:42:43 PM »

Quote
The

The absolute best gearing for hilly high speed on road use and off-road applications is the� 5.38 differential ratio compounded by 25% Warn O.D. unit. PERIOD.


I believe this is what the entire group of participants is suggesting in this thread.  Personally, I concede 100% to oldtime's knowledge on this type of stuff.  He is incapable of steering you in the wrong direction.
Posted by: oldtime
« on: December 12, 2018, 10:38:41 AM »

The 5.38 with OD will "pull" very much better than a 4.27 geared L-134.

The 4.27 differential gears only became standard at a much later date.
That gear ratio change was due to need for increased speed occurring through out the 1960's.
The increased output of the Hurricane made that ratio change feasable.

The optimum RPM output of a Go Devil is 2000 RPM.
2000 RPM yield maximum torque output.
The Hurricane operates most efficiently  at 2200 RPM.

So the Hurricane is basically 10% better for high speed applications.
I've run both engines for hundreds of thousands of miles as full time daily drivers.
I've run them up to 4000 RPM during tests and at all day long sustained speeds of 62 MPH.

The friction resistance of the O.D. planetary unit is a negligible consideration at best.

The absolute best gearing for hilly high speed on road use and off-road applications is the  5.38 differential ratio compounded by 25% Warn O.D. unit. PERIOD.


Posted by: CraigM
« on: December 11, 2018, 10:15:48 PM »

 I was trying to find out how well OD pulled verses 4.27 ratio I do want lower RPM's. The  51 CJ3a I have has a dana 44 and so 4.27 gears are available for it so based on the input and discussion it looks like that is the option I will try. My reasoning is it should have less rolling resistance than 5.38 ratio with OD. Here is the calculation for running 2750 rpms with standard 28" tires is 55 MPH. It will not have my CJ done for a while but when I do I will update this post.
Posted by: 1955CJ-5
« on: December 11, 2018, 09:03:25 PM »

The idea of an overdrive is to give you fewer engine rpm's for a given road speed, or, a greater road speed for a given engine rpm.
 
It does nothing for power.

You still have 60 hp, or less.

I have overdrives in both the 3A and the CJ-5.

The Cj-5 does a little better but the 3A really doesn't have the power to effectively use an OD.

Basically, the OD allows me to drive 45-50 mph with lower, more comfortable engine RPM...

The slightest uphill and you need to shift into direct.

The 3a does much better with the windshield down....lots of frontal area on a CJ and nothing in the way of aerodynamic design....

Unless you are trying to create maximum drag!

Overdrives can be added at any time.

I suggest you drive the jeep awhile with direct drive and see how you like it.

Remember, you may not go any faster with an OD, but you will go at a more comfortable engine rpm....
Posted by: athawk11
« on: December 11, 2018, 09:02:44 PM »

I don't have an overdrive, but based on your hilly local terrain and your desire for top end speeds of 50-55 mph, an overdrive with standard 5.38 gears seems like a good choice for you.
Posted by: aboyandhisdog
« on: December 11, 2018, 08:32:24 PM »

An OD won't help on hills at all unless you are going DOWNhill.  So maybe I don't really understand what you are asking.  If you want the best performance going up hills, wouldn't the 5.38 be the obvious choice?
Posted by: CraigM
« on: December 11, 2018, 08:12:32 PM »

Its not about speed 50 to 55 is ok I am more concerned about running at a lower rpm while traveling also it is hilly around here and I would like it to pull the hills without downshifting 
Posted by: aboyandhisdog
« on: December 11, 2018, 04:38:20 PM »

Craig,   Is sticking with the 5:38 rear end and installing a 25% overdrive an option for you?  That is the set up I have and I could not be happier.  I'll leave the top speed question to others who know more than I do, but I can tell you it is MUCH easier for me to run 50-55 on the highway now with the overdrive.  I could not hit those speeds without the OD.  Maybe I could if pressed, but I would be really revving too high for my old L134.   I'm pretty sure that Jpet's OD tests were done before he did a complete rebuild on his engine.  I have no idea if driving his L134 60mph+ at near or over 4000rpm had anything to do with it, but I would never drive mine that fast.   And don't forget, at speed like that you have very real concerns about handling and braking in my opinion.
Posted by: mtnman37879
« on: December 11, 2018, 03:06:59 PM »

Watch the video. https://www.youtube.com/watch?v=3NHyqV4IiMM It shows why you won't get more speed. It all boils down to Horsepower and torque and the 134 hasn't enough of either. The 134 that ran 100 hours at 4400rpm did it on a test stand not under real world use.