Page Index Toggle Pages: [1] 2  Print
Hot Topic (More than 10 Replies) overdive or not (Read 1068 times)
 
CraigM
Project Jeep
*
Offline


First Car 1975 CJ5

Posts: 26
Location: Jasper County IOWA
Joined: 11/17/18
Gender: Male
overdive or not
12/10/18 at 21:02:50
Print Post  
Has anyone replaced the rear end gears to a 4.27 ratio and if so how does it pull I have been considering an overdrive which is 125% speed gain and 4.27 would be 120% speed gain over 5.38 ratio. My thoughts are the 4.27 would pull easer because it has a little lower ratio. The overdrive systems use planetary gears and planetary gears pull harder than a direct gear drive would, so adding overdrive would have the extra drag of a planetary system along with the 125% gain in speed.
  

67BSA 441Victor 1978 KX125 
Back to top
 
IP Logged
 
Mark W.
3A Lover
**
Offline


Chug A Lug

Posts: 60
Location: Silverton OR
Joined: 12/23/14
Gender: Male
Re: overdive or not
Reply #1 - 12/10/18 at 23:54:24
Print Post  
What rear end do you have? As changing a D41 is not really an option.If you have a D44 then you will find that while the hwy speed and power will be close to the same between your two options. But your bottom end trail performance will suffer with the 4.27's.
  

Chug A Lug

1948 CJ2A Tub and Title
1949 CJ3A Windshield
1957 CJ5   Frame and Springs
134L T90 9.25" D18 D25 and D44 30 spline
11" Brakes, Saginaw Steering, 12V electrical
currently in a zillion pieces.
Back to top
 
IP Logged
 
mtnman37879
Flatfender Enthusiast
***
Offline


Plays With Jeeps

Posts: 163
Location: East Tennessee
Joined: 03/20/17
Gender: Male
Re: overdive or not
Reply #2 - 12/10/18 at 23:56:19
Print Post  
If you want to go faster you need more engine. The little 134 only makes 60hp and it won't make it for very long at the required 4000rpm.

https://www.youtube.com/watch?v=3NHyqV4IiMM
« Last Edit: 12/11/18 at 00:02:33 by mtnman37879 »  

People think I go out of my way to piss them off.
Trust me, It's not out of my way at all.
Back to top
IP Logged
 
Mark W.
3A Lover
**
Offline


Chug A Lug

Posts: 60
Location: Silverton OR
Joined: 12/23/14
Gender: Male
Re: overdive or not
Reply #3 - 12/11/18 at 02:37:20
Print Post  
5.38 gears 30" tall tire = 3300 rpm at 55mph
5.38 gears 30" tall tire 25% OD = 2500 mph at 55mph

At 4000 rpm in direct drive you would be doing 66.4mph with the OD you would be doing 88.5 mph

Not sure what your talking about going 4000 rpm And Roos took a box stock 134L and ran it at 4400 rpm for 100+ hours. Granted your engine has to be in proper condition to run at its peak.
  

Chug A Lug

1948 CJ2A Tub and Title
1949 CJ3A Windshield
1957 CJ5   Frame and Springs
134L T90 9.25" D18 D25 and D44 30 spline
11" Brakes, Saginaw Steering, 12V electrical
currently in a zillion pieces.
Back to top
 
IP Logged
 
oldtime
Flatfender Enthusiast
***
Offline


Still Plays With Jeeps

Posts: 164
Location: Greater St Louis
Joined: 10/16/14
Re: overdive or not
Reply #4 - 12/11/18 at 10:32:09
Print Post  
5.38 FDR was standard ratio for all CJ's prior to 1963.
In 1963 the 4.27 ratio became standard behind all F-134's.
If your stricktly concerned about increasing road speed then 4.27 ratio will work very well with these little engines.
However 4.27 FDR will decrease the off-road ability.

In 1964 Kaiser Jeep Corportaion designated the Warn 25% O.D. units as "Jeep Approved Special Equipment"
These unit are only approve for Jeeps having 5.38 and 4.88 Differential Ratio's.
5.38 with 25% O.D. provides a compound FDR of 4.03.
That gearing is the absolute optimum for use behind the 134 Willys engines.
I tried 4.88 DR with 25% O.D. behind a strong running F-134 in order to try gain a little more top speed.
Sufficient  acceleration was lacking and so I went back 5.38 ratio plus 25% O.D. unit within 1 week on my full time daily driver CJ-3B.
  
Back to top
 
IP Logged
 
mtnman37879
Flatfender Enthusiast
***
Offline


Plays With Jeeps

Posts: 163
Location: East Tennessee
Joined: 03/20/17
Gender: Male
Re: overdive or not
Reply #5 - 12/11/18 at 15:06:59
Print Post  
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.
  

People think I go out of my way to piss them off.
Trust me, It's not out of my way at all.
Back to top
IP Logged
 
aboyandhisdog
Flatfender Master
Owner Member 2012
2016 Sponsor Member
2015 Sponsor Member
*****
Offline



Posts: 719
Location: Fort Collins, Colorado
Joined: 12/14/10
Re: overdive or not
Reply #6 - 12/11/18 at 16:38:20
Print Post  
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.
  

Tom

Back to top
 
IP Logged
 
CraigM
Project Jeep
*
Offline


First Car 1975 CJ5

Posts: 26
Location: Jasper County IOWA
Joined: 11/17/18
Gender: Male
Re: overdive or not
Reply #7 - 12/11/18 at 20:12:32
Print Post  
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
  

67BSA 441Victor 1978 KX125 
Back to top
 
IP Logged
 
aboyandhisdog
Flatfender Master
Owner Member 2012
2016 Sponsor Member
2015 Sponsor Member
*****
Offline



Posts: 719
Location: Fort Collins, Colorado
Joined: 12/14/10
Re: overdive or not
Reply #8 - 12/11/18 at 20:32:24
Print Post  
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?
  

Tom

Back to top
 
IP Logged
 
athawk11
YaBB Administrator
Owner Member 2012
2016 Sponsor Member
2015 Sponsor Member
*****
Offline


1949 CJ3A

Posts: 2742
Location: Arvada, Colorado
Joined: 01/26/11
Gender: Male
Re: overdive or not
Reply #9 - 12/11/18 at 21:02:44
Print Post  
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.
  

2-1949 CJ3A 
1-1946 CJ2A
Back to top
 
IP Logged
 
1955CJ-5
Flatfender Master
2013 Sponsor Member
2016 Sponsor Member
2015 Sponsor Member
*****
Offline


It wasn't always green....

Posts: 2294
Location: Boise, idaho
Joined: 12/18/12
Gender: Male
Re: overdive or not
Reply #10 - 12/11/18 at 21:03:25
Print Post  
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....
  

1955 CJ-5, A friend for 55 years....1951 CJ-3A, a new addition. 1929 Model A Ford Closed Cab Pickup...
Back to top
 
IP Logged
 
CraigM
Project Jeep
*
Offline


First Car 1975 CJ5

Posts: 26
Location: Jasper County IOWA
Joined: 11/17/18
Gender: Male
Re: overdive or not
Reply #11 - 12/11/18 at 22:15:48
Print Post  
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.
  

67BSA 441Victor 1978 KX125 
Back to top
 
IP Logged
 
oldtime
Flatfender Enthusiast
***
Offline


Still Plays With Jeeps

Posts: 164
Location: Greater St Louis
Joined: 10/16/14
Re: overdive or not
Reply #12 - 12/12/18 at 10:38:41
Print Post  
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.


  
Back to top
 
IP Logged
 
athawk11
YaBB Administrator
Owner Member 2012
2016 Sponsor Member
2015 Sponsor Member
*****
Offline


1949 CJ3A

Posts: 2742
Location: Arvada, Colorado
Joined: 01/26/11
Gender: Male
Re: overdive or not
Reply #13 - 12/12/18 at 15:42:43
Print Post  
oldtime wrote on 12/12/18 at 10:38:41:
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.
  

2-1949 CJ3A 
1-1946 CJ2A
Back to top
 
IP Logged
 
RICKG
3A Guru
****
Offline


I never met a mule i didn't
like.

Posts: 262
Location: idaho
Joined: 10/16/12
Gender: Male
Re: overdive or not
Reply #14 - 12/12/18 at 16:24:57
Print Post  
athawk11 wrote on 12/12/18 at 15:42:43:
oldtime wrote on 12/12/18 at 10:38:41:
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..
« Last Edit: 12/12/18 at 16:25:58 by RICKG »  

OD MULE MC51986
Back to top
 
IP Logged
 
Page Index Toggle Pages: [1] 2 
Print
Bookmarks: Facebook Google Google+ Linked in Twitter Yahoo