Progress and Review D18 Terra Low Gear Kit

Progress update. Installed the D18 Terra Low kit into a D20 case with large hole and the needed 1 1/4 shaft. Did not have to grind case at all, but did grind end of 4x4 shift rail just a bit to clear low range gear. Clearance is also close at low range shift fork boss, where shift rail goes through it, to low range gear, (1/16 to 3/32) I left it at that. I also question as to whether you really need a large hole or even a 1 1/4 shaft hole. The gears fit in through the oil pan, but I suppose a small hole may not have room for the low range gear. I actually set shafts and gears in to my old small hole case and it seemed to me they would fit. As for the 1 1/4 shaft hole, I am thinking you could use a 1 1/8 shaft with the caged bearings inside the Terra Low Intermediate gear instead of the loose needle bearings. I measured inside diameter of a stock intermediate gear from a 1 1/8 shaft case and it was the same as the Terra Low Gear. Although I would think better wear with the 1 1/4 shaft since larger bearing surface, any thoughts? Also I have heard of D18 cases cracking at intermediate shaft hole. I am concerned about this, do not want to wreck $700 gears, and actually ordered a D18 case Girdle made by Tri County Gear that is suppose to strengthen it. $125 with out overdrive and $85 with overdrive. Have not recieved it yet, and now just remembered that I really do not have a D18 case, I used a D20 case. So the girdle may not even fit - anyone know? Also anyone know if a D20 case is stronger or heard of any D20 cases cracking? Also I am no longer going to run my overdrive, but instead use a Dana PTO and eventually set up a rear PTO Winch. Any thoughts if bolting in a overdrive or pto to the rear inspection hole strenghtens case?

Plan on being able to road test in a few days. Will update again.

Sorry to those of you that already read this on my original post for help installing. I tried to change the title and thought It worked till it actually came up.

 

Are they? I have never actually seen a D18 large hole case. I ask beause one thing I had to modify after installing the new case, whatever it may be, into the vehicle was to shorten the oem clutch linkage cross tube. The threaded boss on drivers side of case for the ball stud is about 1/2 inch closer to frame rail. Also a note to those doing what I did is to make sure your new case has the threaded boss for clutch ball stud if have a manual trans. The first case I got did not have it.

 

The bore in the intermediate gear is the same for 1.125" with caged bearings and 1.25" with loose needles. I measured. I used the original gear from the 1.125" shaft small hole case when I rebuilt it into the D20 case to go with the T18. The 1.125" shaft itself should not be a problem, but I don't know about the fit of the gears inside the case. Years ago when I was talking to Mark Faulkner (sp?) at Tera about this he said the small hole case didn't have the clearance needed for the gear, but I never checked myself...

I spoke with Jack O'brien on the phone one time a few years ago and one of the things he mentioned to me was that there were different castings for D20 cases and the cases found in FSJs were normally the heaviest and strongest. That guy was incredible. He knew casting numbers off the top of his head. He is the worlds foremost authority on the Dana 20.

One thing I've learned the hard way is that different D20 cases have the fill plugs in different places. The one I used when I did my Dauntless/T18 swap was from an FSJ and the fill plug ended up under the speedo gear fitting. I had to put a flush fill plug in the hole and fill it from the overdrive hole. Good thing I don't have an overdrive

One othe thing I've learned is that some D20 cases require more grinding than others. Another is that more grinding is required when putting D18 gears in a D20 with the Early bronco upper gear to make a 2.46:1 Dana 20 versus Tera Dana 20 gears in the same case. I don't recall any grinding for the lower gears on either install. Seems like I only had to grind for that upper rear output gear. I guess I could look at the articles and see...

 

Finally got the heep back on road and off. Definately a noticeable difference in low range. It crawls with the t18 in first even with the 3.73 axles. I immediately tested it on a nearby steep hill 50 foot tall of packed mine tailings that I have been up and over a few times and I could not make it in first gear with engine idling. Seems too slow of crawling and it lost traction, no traction aids in axles - soon to fix with 5.38 and power locks front and rear and then 3 inch wider D44 axles with 4.27 ARBs. Made it fine in second gear. I do not think I will be using first too much, which will be nice since it is not synchro'd. I did hear from a reputable drivetrain shop that the Low Gear kit can break the t case main output shaft. They were suprised I installed it with a t18 having such a low first gear. They said the common install is in jeeps with 3 speeds. Oh well, just have to be a bit careful with the right foot, if that is possible. I also am concerned about breaking the case, so I made a spacer of 3/8 inch mild steel that matches oil pan rail and sandwiched it between case and oil pan. I may beef up the oil pan itself and weld it soild to the new spacer in future. I also bolted in my rear PTO to the case thinking it may help stiffen case and have plans for rear winch. Another issue is reverse is very slow, so if need a bit of momentum, I will probably shift to hi range. I do think I am hearing more gear noise in hi range on road driving under load. Quiet when coasting. I say think because I took out my winter carpet so I cannot remember it being that loud before but it may have been. I set end paly to .005 and am using Amzoil 75-90 Synthetic. I cannot imagine the crawl ability with 5.38s. Going to find out though, just because I have all the stuff so I may as well try it.

happy wheeling