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Beacher425 Member
Joined: May 16, 2010 Posts: 59
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Posted: Fri Aug 23, 2013 10:52 am Post subject: 5.38 to 4.88 or overdrive |
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looks like i will have to replace the ring and pinion in the rear diff of a 1955 M38a1. Also wanting to get overdrive to decrease engine RPM at 45mph. Not looking to go any faster. Opinions requested on these options:
1. replacing with 5.38 in rear (about $400) and add overdrive (about $1000)
2. Replace with 4.88 in rear (about $400) and front (about $400)
3. Replace with 4.27 in rear (about $300) and Front (about $300)
Is changing the gear ratio only changing the ring and pinion or are there other parts I'm not yet factoring in?
Thanks. |
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chuck Member
Joined: Jan 09, 2010 Posts: 143 Location: Nashua NH
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Posted: Fri Aug 23, 2013 4:02 pm Post subject: |
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Go with the stock 5.38 gears plus overdrive. The best combo for an underpowered vehicle to begin with. I added overdrive to my M38 and love it.
Chuck |
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wesk Site Administrator
Joined: Apr 04, 2005 Posts: 16365 Location: Wisconsin
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Powermwt Member
Joined: Apr 13, 2005 Posts: 53 Location: Fort Worth Texas
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Posted: Sat Aug 24, 2013 12:30 am Post subject: |
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The MB/GPW got around well enough using 4.88 with only 54 HP.
I have installed and used a Warn overdrive before and they are great, but if the intent is not to go faster I do not see the point in installing aftermarket parts to solve an issue that does not exist.
That 1955 M38A1 got around great the way it was for a lot of years and you have overlooked a 4th option.
4. replacing with 5.38 in rear (about $400). This is the most economical solution.
Hey, just saying. _________________ 1944 MB-NAVY-
MZ-1 |
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Beacher425 Member
Joined: May 16, 2010 Posts: 59
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Posted: Sat Aug 24, 2013 5:02 am Post subject: |
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thanks all
I have decided to replace with 5.38 and but off the overdrive maybe around Christmas. maybe i'll get lucky and I can find a used one. |
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wesk Site Administrator
Joined: Apr 04, 2005 Posts: 16365 Location: Wisconsin
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skyjeep50 Member
Joined: Feb 20, 2007 Posts: 606 Location: Illinois
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Posted: Sat Aug 24, 2013 7:30 am Post subject: |
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Your jeep will be quite happy with the revs at around 45 mph. Not much need to change gears if that is all the faster you will be traveling. One other option is to use 7.50X16 tires on the A1. That is what I have and it adds about 6 mph road speed at an indicated 50 mph on the speedo. _________________ 1951 M38 |
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Powermwt Member
Joined: Apr 13, 2005 Posts: 53 Location: Fort Worth Texas
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Posted: Sun Aug 25, 2013 1:48 am Post subject: |
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Yes Wes, but the A1 has 1/3 more HP... 72 vs. 54.
And the low range in the transfer case is lower, 2.43 vs. 1.97.
I did say I thought is would be more economical to go with the 5.38. _________________ 1944 MB-NAVY-
MZ-1 |
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wesk Site Administrator
Joined: Apr 04, 2005 Posts: 16365 Location: Wisconsin
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Posted: Sun Aug 25, 2013 7:59 am Post subject: |
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The transfer low range is of no consequence here. We are discussing highway driving. Both transfer are 1:1.
Quote: | but the A1 has 1/3 more HP... 72 vs. 54 |
You must compare apples to apples. 54 is Net HP for the WWII Jeep The WWII Jeep Brake HP was 62.5. The M38A1 Brake HP is 72. The net difference is 11.5.
The M38A1 in stock form cruises the highway easily at 55 MPH. I drove mine at that cruising speed every day to work in SD in the 80's. The time proven method to increased highway speeds with the stock engine and at the same time have no adverse impact on the other operating parameters is to add an overdrive.
Adding 4.88 gears and keeping the stock 7.00-16 tires will have an adverse impact on acceleration rates in both high and lo ranges and in both 2 and 4 wd. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php |
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