Converted 9 sp to 13 sp into an 18sp?

No you can not change a 13 speed road ranger to an 18 speed. It has nothing to do with torque raitings. Both the 13 and 18s have torque ratings of 1650, 1850, and 2050, Ft Lbs. Their is a 2250 18 speed but it still has nothing to do with the torque ratings.The gear ratios are different on the low side. The ratios are closer on the 13 speed. Instead of a 200 rpm split it would only be about a 125 rpm split and thats just a pointless shift. Low gear in a 13 speed is 12.31 to 1. An 18 speed is 14.40 to 1. Thats more than 2 full turns slower for the 18 speed. The 13 still has 5 gears to get to high range but not nearly as much over all ratio to get their. Thats why splitting the low side of a 13 is just not practical. Now if you were talking Mack trannys you definetly can change a 13 to an 18. The trans itself id exactly the same. All you need to do is change the shift knob but not with the road ranger.

 

Go take another look at the ratio charts, except for the lower low gear, the ratios of the two transmissions are functionally identical. The low split ratios of 1-4 in the 18 are within a couple points of the 1-4 ratios in the 13. They lowered the lowest gear a half step because the 18 was replacing the 15 as the heavy haul choice. But in doing so, the jump from L high to 1 low became a full step of 44%. If we put the same shifter in two trucks, one 18 and the other a 13, you would not be able to tell the difference if you were told not to use low gear. The 13 would actually feel more 'right' if you did split all 5 bottom ratios because the 1H-2L gap would more closely match the rest of the transmissions spacing! If they weren't labeled, you wouldn't be able tell which was which by looking at their blueprints!

As an aside, back in the day, you could drive a 13 like an 18 because there was no interlock on the shifter or in the air mechanism. The old 13's actually used the old style separate range shift clamped to the shifter shaft, with the splitter in the knob. Kind of like the old 15's had deep reduction up on the dash.

 

Mr. Hammer not sure about torque specs but your right about counter shafts in back half interchanging because my 18913 has one counter shaft from 18918 in it. could not find one for 13 and part number is different on 18 but look alike on table. been running it for 6 mo now

 

Yep! Dimensionally, all the guts are identical; it's simply a matter of stronger parts (and better oiling/cooling) to get the higher torque rating (an edit to add that while these apply to the tranny as a whole, it mainly applies to the splitter section in our discussion here, as 13's are available in all but the highest rating of the 18's. Sorry Melpromud for not being clearer.) Whether via surface hardening, heat treating, or different alloys, or some combo of these. Up until the point the case webs aren't strong enough to hold the shafts in place, anyways!

 

The 18 uses the underdrive/direct as well. You'd just have to sit down with the parts list for the two and see what's different. My guess would be everything but the case, shift mechanism, and maybe bearings. Maybe I'll be bored and go see...

 

hmmm! Even the aux case is different on the 18, probably the different bearings. Some of the synchronizer parts are the same, but the splitter gear has an extra bearing in the 18. So you'd pretty much end up buying the entire auxiliary section to do it right. Not sure how spendy that'd get.

 

I got to thinking more about this... Are you sure the splitter is in under while in low range? Think about it a minute, if that were the case, the splitter would have to be the same in the 13 and 18, as all the torque is going through the splitter section. My guess is that the air relays put the splitter in direct when you range shift to low. I do know that the old trick of moving the range shift, then splitting 4th gear doesn't work anymore. I had just assumed it was an interlock but never really thought about it until now; back to Roadranger.com to see what I can find...

 

There are complete manuals available as pdf files! And you were right yooper, power does go through the underdrive in low range. Where the extra loading happens is on the splitter gear in splitter high/ range low. If you go look at the power flow diagrams you'll see it.

 

You were right on my earlier post that only low in the 13 is realy different than the 18. The percentages from 1st to 4th are almost identical.
As far as lifting the high low range selector to release the interlock and use the spliter in the low side. Im not sure now but the last 13 road ranger I drove was a 1994 model and it wouldn't work. It would grind like hell and the only way to stop the grinding was to come to a complete stop. Even going to neutral and putting the spliter back did nothing. It completly scrambled the tranny. At least Mack was smart enough to use the same tranny and just a different shift knob with the interlock. This type of shifting works great on the Mack trannys and let you use all 18 speeds. The mack 2130 and 2180 are exactly the same. (313 and 318 also). The Roadranger 13 and 18 seem to be different monsters.