Model 18/20 - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 04-17-2002, 12:18 AM Thread Starter
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Model 18/20

While helping a friend put a new clutch in his 1970 CJ 5, we decided to try to figure out where all his oil leaks were coming from. When we separated the tranny and transfer case, we found MULTIPLE cracks and other misc. ugly things. Consequently he is in need of a new case. I have 2 of them kicking around the shop, but of course his is the large hole version and mine were both small hole. I have been led to believe that a model 20 case can be used by swapping the guts from a model 18, and when he went shopping for a new one he was told the same thing. Does anyone know for sure if this is correct before he spends good money on something that won't work ? It seems that the large hole 18's are pretty far and few between these days.
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post #2 of (permalink) Old 04-17-2002, 10:18 AM
Nickmil
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Re: Model 18/20

Yup,
The guts from an 18 will fit in the 20 case with no mods. Use the gears and other castings (front and rear output housings, shafts, etc.) from the 18. Done it tons of times. The 20 case is a little bit stronger than the 18 case anyway and more readily available. You can even build a 2-1 18 case if you wanted to! Don't know why anyone would want to but rebuilt one recently that this had been done to. I think it may have been out of a race Jeep and he didn't need the lower low range. Nickmil.
post #3 of (permalink) Old 04-17-2002, 10:23 AM
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Re: Model 18/20

What modifications are needed to swap the guts from a small hole dana 18 to a dana 20? I have a 1955 M38A1 that I assume has a small hole 18 and a dana 20 from a 1969/70 wagoneer. Thanks.
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post #4 of (permalink) Old 04-17-2002, 05:53 PM
Nickmil
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Re: Model 18/20

As I posted earlier you do not need to make any mods to the case itself. It is a bolt-together affair. You probably have a 26 tooth 18 transfer case (stock in the m38a1). The 20 case is a good upgrade as you probably also have a case with a 1 1/8" intermediate shaft with caged bearings and the 20 case uses a 1 1/4" intermediate shaft with loose needle bearings. This is a good thing because there are more needle bearings on the larger shaft which distributes the load better. You can use the loose needle bearings and larger intermediate shaft on your 26 tooth intermediate gear no problem. The ID is the same as the 20 intermediate. To mate the 20 housing to your existing T-90 (if you are still running it) you will need to change the rear bearing retainer from your current stepped unit. The current bearing supports the rear output shaft and goes between the transmission and transfer case. That's what indexes or centers the transfercase and keeps it in line with the output shaft of the transmission. You will need to remove that bearing, the little spacer behind the bearing, and the flat stepped plate (it's lightly pressed in unless rusted in place[img]images/icons/crazy.gif[/img]). Be careful not to let the output shaft slide out of the input or the pocket bearings will fall down inside the tranny (Then you get to disassemble the whole tranny[img]images/icons/frown.gif[/img]). In place of the flat, stepped plate, you will need to install a rear bearing retainer from a T-86. It replaces the old one with a slight press fit. This a larger unit with a bearing inside it and will index the large hole case as well as support the tranny output shaft.
If this is as clear as mud or you have any questions feel free to e-mail me. Nickmil.
post #5 of (permalink) Old 04-17-2002, 06:22 PM
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Re: Model 18/20

That's exactly what I was wanting to know. I will be saving this reply for when I get around to the M38A1 rebuild. Thank you very much, that was a wealth of information.
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