13 to 18 conversion

That, and another bearing!

The short answer is yes, if you replace the red roadranger valve with a blue one you will be able to split low range. The difference between the 13 and the 18 is in the back end, the 18 has a much larger bearing on the overdrive gear, The 13 depending on the age actual has no bearing on the overdrive gear, just a retaining bar or disc. As the torque rating of transmission goes up the major changes in the transmission are an increase in the width of the gears and an increase in the size of the bearings. Since the 146 series the overdrive has been in the front box, the rear boxes are in fact "underdrives". Top Gear with the button pushed forward is direct drive from the front overdrive gear back. Switching a 13 to 18 would not likely cause an immediate problem, however if you were to apply max torque in the overdrive position in low range frequently you certainly damage the transmission.

 

fuller 13 can not be converted to a 18 the low side ratios are diffrent a Mack 13 can be by removing the lock on the splitter there ratio's are the same on the low side

 

This guy has it and has been inside of one.

Yes, the 13 and 18 do have different low gear ratios. But the simple question was, way back when it was asked, can you make a 13 into a 18. The simple answer is yes. Now as long as you are just looking to gain the splits in between the lower gears you will have accomplished your goal. Now you will not get the low gear that the 18B gear set has, you will have an 18A gear set. The splitter is always taking the torque of the engine, it is turning and driving even when not split. The transmission is made to handle the torque that it is rated for, in low or high range, split or not. No matter how you try to dance around it, the splitter gears are always in use whether "split" or not.

 

We covered this in another thread awhile back. The power path in low range/high split is unique. The engineers at Eaton put the extra bearing at the back of main box for a reason. Go to the roadrunner site, look at the troubleshooting manual, it shows power flows in various gears.

 

not bad for a first post huh

 

I rebuild fuller transmissions for a living and I have the end all discussion on this topic. Yes you can convert a 13 to an 18 by relocating the tee fitting on the slave valve from the top to the center air line which is the main supply rather than the high side supply the take the roadranger valve apart and grinding the interlock to allow the splitter to be used on the low side.. what will happen when you split the 13 on the low side is a different story. The 18 speed has a bearing p/n 4300902 in the hub of the splitter gear and a thick round washer and a 5/8" bolt that retain the gear and bearing to the output shaft of the transmission, the 13 has a thick oblong washer a 5/8" bolt (no bearing) that retain it to the output shaft. The reason for the bearing in the 18 speed is because when you split in low range the splitter gear is under the full torque driving the two countershafts and turning much faster than the output shaft (using the bearing). This in not the case when you split in high range.. in high range the splitter gear is splined directly to the output shaft so there is no diffrential speed between the gear and shaft. The short explanation is the diffrential speed between the splitter gear and the output shaft when split on the low side of a 13 will damage the gear and the oblong washer that retains it to the output shaft. For anyone with a question or an issue with your transmission message me and I will be glad to help. Thanks!

 

I have converted many RTLO18913A transmissions. You have to install an 18 speed output shaft 18 speed high range gear and a small list of other internal parts. For anyone wanting to just change your air setup to an 18 don't do it! You will 100% for sure burn out your retaining washer and high range gear... Then leading to a synchronizer failure in high range.

 

What I've been told by a mechanic that has done these conversions is: if you have a RTLOC transmission it can be converted by connecting an airline and changing the shifter button. If it's not an RTLOC, it doesn't have a necessary bearing and will wear extremely fast and fail

 

That's because the convertables are pretty much a 13 or 18 speed that have the splits locked out. That way noobs at mega fleets don't tear apart transmissions and the truck has better resale value being sold as a 13 or 18.