3.15 Low D-18 Transfer Case

Is there a way to determine if a D-18 transfer case has the 3-15 low gear installed?
Can I tell by opening the output cover or the bottom cover?
I have a FrankenJeep that has the low range speed I want for my CJ5.

 

You'll know quickly with either cover removed.
I don't think they are cast but milled from round stock.

Spin the gears and note any numbers. Or count teeth. The Tera low set also has a much larger intermediate gear on the helical side.

 

Introductions | ECJ5 (earlycj5.com)

 

Just pull the PTO cover-no need to drain case. A TeraLow gear will be marked "TL20A". It will be 26 tooth, but way different than the Dana/Spicer 2.43:1 gear set 26 tooth gear. Top is the Dana gear, bottom TeraLow.

 

I'd pull the inspection cover like John said, but if it's an unknown t-case, might be a good idea to change the oil anyway

 

I am thinking your "FrankenJeep" probably has lower ratio axles.

You didn't mention what your "FrankenJeep" is, just that you want that low speed for your CJ5, nor did you provide any details for your CJ5.

It is a large jump of imagination to assume your "FrankenJeep" has a lower geared transfer case, and just wishful thinking that it has Tera Low gears. I think that is unlikely.

Most early Jeeps had 5:38 axles standard, as did early CJ5 Jeeps up through early 60s, then things started to change.

 

You get a gold star. Uncovered the diff. Tag that had 5.38 stamped on it.
The frankenjeep has no jeep bodywork at all. The frame is cut off just behind where the front of the rear springs attached. The rear axle is now solidly mounted. Much like a tractor. It has a F134 engine and a T90 transmission. I use it to move firewood.

 

My older Jeeps with the 5:38 axles are like driving a tractor in many ways.