HOW TO INSTALL A SLIP YOLK ELIMINATOR
You have to be a special kind of nerdy to get giggly over part number deciphering and acronyms. I’m not talking about the “Wut R U Doing?” texts I get from my daughter, that’s a whole other language. No, I’m talking about the day-to-day codes and shortened wording in order to keep everything accurate and avoid confusion. The last cypher I had to break down was “NP241DLD SYE”.
If you’re following along and that jumble of letters and numbers made sense to you, great. However, if it looked like Elon Musk’s kids name, fear not. This will all get cleared up as we continue to cover New Process chain-driven transfer cases. On top of that, a recent installation of a Slip Yolk Eliminator (SYE) from Tom Wood’s Custom Driveshafts let us know what to look out for in one of these aluminum boxes.
“NP” stands for New Process. The company New Process Gear made transfer cases and transmissions found in many major manufacturer’s vehicles since the beginning of the automobile or at least as far back as 1913.
Since about 1990, the chain-driven variant discussed here is found primarily in Mopar, Ford and GM vehicles. The “NP” and the rest of the numbers can be found on a round metal tag screwed into the back of the transfer case and is easy to spot as they are typically red.
The three numbers that follow the manufacturer stamp depict three major components of the transfer case. In our case, the 2 of 241 tell us that we have a 2-speed transfer case.
The numeral 4 is the strength level. This number ranges from 0 to 9 and has no real basis on factual numbers other than 0 is made of playdoh and 9 is “strong like tractor.”
The final number, 1 in our case, depicts how the transfer case is shifted and what options it may have. For us, the 1 is what we wanted; a part-time, manually-shifted unit that fits perfectly in the 1999 project Dodge Dakota that’s getting ready for a complete drivetrain swap.
Some of the New Process variants have a final letter or two. These stipulate what manufacturer the transfer case was made for and possibly a sub-variant. To truck nerds, “D” is for “DODGE” and “LD” stands for the “Light Duty” version.
In simpler terms, this all means that we have a 2 speed, part time, manually-shifted, chain-driven transfer case with a 2.72 low range (also found on the ID tag). Other ID numbers will tell us that we have a unit from a 2000 or 2001 pickup truck.
In a vehicle with solid axles, as the suspension system cycles, the distance between the transfer case and the differential changes. Some vehicles have a slip-joint built into the center of the driveshaft, and others, like our NP241, have a slip joint (AKA slip yolk) built into the tail housing of the transfer case. For a factory vehicle with limited suspension travel, this is just fine. However, as travel increases, the slip yolk has a tendency to fall out of the back of the case, causing severe damage and leaking fluids all over the trail. It also limits the choice of joint styles for the driveshaft to a single joint attachment, which has limited travel and can hinder articulation. It’s a bit of a bummer, but it was done to keep costs low.
The Slip Yolk Eliminator kit from Tom Wood’s Custom Driveshafts is going to allow the use of a solidly mounted flange on the back side of the transfer case so we can use almost any size or type of U-joint configuration. We also have the advantage of using a longer driveshaft. This may not be that big of an issue on the Dakota, but for those of you in a short wheelbase vehicle, the added length can make a huge difference.
At the time this magazine was printed (July/2020), the SYE kit for the NP241DLD was in the $500 CAD range and comes complete with a new output shaft, bearing retainer, flange and the very important Torrington bearing and adapter sleeve that needs to be installed. The SYE installation is exactly the same as the Chevy and Dodge transfer cases with the exception of the bearing and the difficulty involved in getting the old one out.
Tom Wood includes an excellent set of instructions covering the installation. However, we wanted to give some insight with respect to this particular bearing and how to replace it.
While we had our transfer case apart, we decided to replace all the seals as well. A typical seal kit is around $60 CAD and we scooped ours from a local transmission rebuilder.
Once we had the case open, there were other problems we had to address. Luckily, parts for the NP series of transfer cases made in the last 30 years are easy to source and are relatively cheap. As we opened up our “unknown history” case, we checked and replaced parts as needed to get our Tom Wood SYE kit installed and ready for the truck.
For more information visit Tom Wood’s Custom Driveshafts at www.4Xshaft.com or Kelowna Transmission and Auto Repair at kelownatransmission.com