Dana 18 Dilemma

Hi everyone I am trying to figure out how I can piece together a functioning drivetrain for my '52 MD out of what parts I currently have. I could use your collective help with a couple of questions. But first, this is what I am working with.

In the Jeep:
-Jeep t18 with 3-5/32" index ring on rear mounting plate (I believe the trans is from a late '70s CJ, not sure about the rear mounting plate)
-Dana 18 with 1-1/8" intermediate shaft and 3-5/32" input bore (original to Jeep)

On the bench:
-Dana 18 with 1-1/4" intermediate shaft and 4" input bore (I believe from a '69 CJ)
-Warn Overdrive w/6 spline planetary

The original Dana 18 in the Jeep is completely roached and needs to be rebuilt with lots of new parts. My big hole Dana 18 is in really good condition, plus it has the overdrive.

My questions are:

How critical is it that the indexing ring on the transmission matches the input bore of the t-case? I know I can physically bolt the large hole case up, but I worry about the bull gear (or OD) not meshing properly with the intermediate gear without the indexing ring/case bore interface.

Can I throw the all the guts of a 1-1/4" dana 18 into the older 1-1/8" case? I seem to recall reading the gearing is interchangeable, and that it will just require the new IS and associated bearings.

Thanks in advance for your help.

 

Very.
Can you change the back of the trans to the larger size? My T18 takes the large bore tcase.

 

The plate definitely unbolts. I just can't find any information, let alone pictures or part numbers of the plate that works with the large hole 18 or 20.

 

The locating bore is critical especially with an overdrive. You may be able to find an indexing ring or bearing combination that works but do not run it with just the mounting bolts.

 

Thanks for validating my concerns. Just bolting it up is off the table. Now I either need to find the different plate, fab up a ring, or swap internals.

 

Your rear transmission adapter plate with 3-5/32”was originally mated to a Jeep T98.
One option is to locate a Jeep T18 rear adapter plate with a 4” index bore.
Otherwise you can put all your big hole D18 guts (excepting the intermediate shaft and bearing) into the early case and call it good.
The T18 requires a 6 internal spline overdrive with a 29 tooth bowl gear.

 

See post #206 in my T18 thread, it shows the back of the trans clearly.
http://www.earlycj5.com/xf_cj5/index.php?threads/152977/

 

To me the path to least resistance and do what you want is to use the large hole gears (29 tooth input gears) in the small hole case. It’s a non issue, all bolts in. As long as your overdrive is 6 spline it will work as well as Oldtime noted. As said above, that index size is critical. They have to match to keep everything in alignment. Another option would be to find a factory adapter from a Jeep T-18 for the large index and use that. I don’t know if he still does but Richard of R&P had a bunch of the adapters. Worth a check. 503-557-8911.

 

You can use it with a 6 spline shaft and 26 tooth bowl gear also.

 

It’s definitely a T18. After scraping the crud away the adapter is stamped T98. Looks like whoever did the swap did some mix and match from the parts bin.

 

Thanks for the lead.

 

The large index case is a bit stronger than the small index and if you decide to go with TeraLows (or whatever Herm is calling them these days), there is less grinding or no grinding involved. I would be looking for the factory adapter as Nick suggested, and use the later case.

 

If I can't track down a T18 adapter plate economically, what are your thoughts on turning an adapter ring that would step up the size of the small indexing ring I have on the current T98 adapter plate to 4"?

 

Yes you could bore the smaller adapter out to 4”.
In fact the early Jeep T18’s used the T98 adapter casting blanks.

 

?
I’m not following you on this one Ken. The adapter uses an external step to index the transfer case. I don’t see how you could bore the adapter to increase the size of the indexing step.

 

Didn't T86's use an adapter ring between small and big bore? Would that work for this?

 

Interesting idea. I still have the blown up T-14 that came with the big hole t-case. There appears to be a 4" indexing ring of some sort on it. Not sure about the ID. After work tonight I'll pull it and see if it could be used as an adapter to the adapter.

I can't say how much I appreciate the insight that this forum brings. Compared to the JT forum, the technical knowledge here is astonishing.

 

Thanks Nick, a quick non thinking reply was my mistake,
It’s a 4” ring that needs to index into the 4” bore of the transfer case.
Machining an extra ring might work but the ring then must cover the bolt hole relieved areas.

 

The T-86 used a rear bearing adapter. It wasn’t a ring but a housing that had the transmission output bearing in it and indexed to the 4” bore transfer case. The T-90 and T-86 units can interchange to use either the small or large case but only on T-90’s, T-86’s, or many aftermarket adapters for various custom transmission applications. Will not work with a factory T-18 adapter.