Introduction: How to Rebuild a Dana Spicer Transmission for a Lil' Gasser 7 1/2" Gauge 1 1/2" Scale Locomotive
This 'Ible" will take you through the steps to disassemble, repair if needed, pack and reassemble a small F-N-R transmission for a Cannonball scale ride-on locomotive powered by a small gasoline engine. The little yellow locomotive is the one we will be working on and discussing here. Please use caution and seek assistance if this is to involved tfor you. This is only how rebuilt my transmission. and is for your entertainment only. I am not responsible for your actions outcome or other that may happen in ride on scale railroading or other activities related to this 'Ible, any, or otherwise.
I had the fortunate opportunity to purchase my first 7 ½” gauge train this past summer of 2011 for my birthday with the help of my loving girlfriend, which is a 20 year old ‘Lil Gasser made by Cannonball Mfg. I got a great deal for the locomotive and riding car for less than two thousand dollars and couldn’t wait to get it home to ride. I did some research and found my switchers history through the Sacramento Valley Live Steamers and some old newsletters. I found out I have a version 2 with the larger 3 hp Briggs engine with a Dana/Spicer Transmission. I wanted a little more history on the locomotive in case I needed the info. in the future for maintenance, etc.
Well, right in the middle of January 2011 I went out on a cold day to ride my little train and the transmission was not shifting into forward or reverse from the neutral position. I let it warm up some more to be sure it wasn’t just cold transmission oil/grease inside the box. It finally shifted but, not so smoothly and I had a funny feeling in the pit of my stomach, you know that “something’s wrong” feeling? I made some phone calls and lots of searching on the internet for a replacement of this hard to find transmission. To my luck I found a gentleman who lives ½ mile from me who builds and sells gasoline powered switchers and industrial locomotives in gauges ranging from 7 ¼” to 15” gauge. I gave him a call and he had told me what suitable replacements I could find or, I could take a little time to re-build what I had with some improvements. I decided to re-build with his offer to help. Why re-build? Two reasons, he’s a machinist and is willing to help out (I could use the help and learn some new skills); and, I will be upgrading and improving its performance with minimal investment of money. I have built many structures for layouts in California and Oregon from N scale to 1” and up to 2” scales, that’s fine for wood working skills but my mechanic skills on small engines have something that is to be desired, so I might as well jump in with offered help and learn.The first thing I did after getting the locomotive home was to remove the battery and lead weights from the “nose” or hood of the locomotive to have a little more working room. Next, I disassembled the hood for even more open space. This was a simple operation of removing 8, small star head (torx) machine screws. Next, I unbolted the transmission from the cab wall and frame and removed the chain from the drive wheels and the second chain from the clutch, which was a little difficult due to the cramped space between the wall and clutch. A very small loop of chain made it more difficult but with a little patience and finesse I did not have to remove the link pin (Thank God). I slid a spare box end wrench under the traction chain so that I did not need to fish it back up to the top of the frame later and made reassembly much easier. Styrofoam cups with labels of each step of nuts and bolts with photos made everything easy since there were no instructions or drawings. This also kept the parts from being misplaced or lost.
Now the transmission was out and separated from the Lil Gasser and I could open it up and make any repairs and tune-ups if necessary. The Spicer transmission is held together by six ¾” by 20, 7/16” hex head nuts and bolts. This made for easy removal and went into another cup. I removed a “C” clip from the end of the output shaft and the next step was to separate the two halves of the transmission case. I did this by carefully and slowly inserting a 2” putty knife since it didn’t just open up with a light tap of a rubber mallet. (sealed with blue RTV). A light twist with the putty knife and I could pry the two halves apart with my hands. What I found inside was a black, greasy mess. Craig Adams assisted and coached me through the process, but as we took everything apart he was telling me that it looked like the gears were in excellent shape and the problem may have been over lubrication, more on that later. I wiped out as much of the grease as possible with some paper towels before spraying with carburetor cleaner. I used an old tooth brush and paint brush to brush some of the build up and get into the nooks and crannies found in the case. I then wiped down each part with a lint free towel and placed in on a sheet of paper that I numbered and sketched where the part came from. I was very surprised to find only 7 or 8 parts inside the whole thing to make my locomotive move forward, reverse or idle in neutral. There were 3 gears, a shifter key between the two large drive gears with a key way between the gears on the output shaft. This allowed the forward spinning gear to engage or the reverse gear to engage by moving the “lock” back and forth on the shaft to lock into a “key” in the center of each gear.
Please excuse me for not using correct names or terms here I know what it does but, don’t remember the proper name (s) for it. That’s what happens when someone like myself does not have the fortune of having mechanical knowledge or engineering experience. I also used a clean piece of paper for the photos so there are not any drawings or huge grease stains on the paper
Next, I removed the links on the end of the shifter bar and pushed the bar to the inside of the transmission case to remove it. When I did this, Craig asked me if I saw a ball bearing and spring pop out or, if I took it out of the little hole that was covered with aluminum tape. My answer was, “No, I did not”. So with a little searching in the bottom of the washout tub we found the bearing but not the spring, Craig used a small Allen wrench to pick out and remove the spring. He proceeded to tell me that it looked like there was so much lubrication in the transmission that it locked the bearing and spring in the “open” position which allowed the transmission to unlock itself from gear and looked like to be the whole problem. This little “lock” is called the detent. I cleaned the ball bearing and spring using carb. cleaner and a Q-Tip saturated with more cleaner to clean out the hole which holds the spring and bearing. The detent went into another cup as the cleaning and grease removal continued. The photo here shows the small hole to insert the detent into the case with the shifter inserted to the first “click” to lock the detent into the case.
The drive or input shaft and gear was removed and cleaned and the remaining large drive gear and output shaft was removed and also cleaned. With the remaining half of the transmission case to be cleaned, the bushings were looking nice and clean and tight fit with the shafts everything was now ready to be re assembled and slathered with some new grease.Craig recommends using a grease called Cleuber Lube but he could not remember which number he used. I called the local supplier where he gets it from and they did not have any individual tubes in stock and told me I needed to purchase a case as a minimum order. I was not going to spend over $250.00 for a case of grease when I needed only a few ounces so I went to the next best option; the local racing shop and got me a tube of Lucas Oil’s Red compound synthetic grease for $6.00. More than enough to repack this little “box” 4 to 6 times.
Now that all the cleaning has been done and the parts all laid out everything is ready to be reassembled, lubricated and sealed. The first thing you need to do is to repack the detent and push the shifter rod back into the case it was just removed from. To do this, an extra pair of hands does make this very quick and effortless. First lightly rub a very small amount of grease on the spring and slide the spring back into its hole, then the ball bearing on top of the spring. Next, apply a small amount of grease into the two notches on the shifter rod. Start the rod into the shifter hole from the inside of the case with the “fork” also inside the case. Now with the assistance of a second person, use your helper to depress the bearing into the hole against the spring through the weep hole across from the bearing, using a 3/32” Allen wrench. Push the shifter rod to the Allen wrench and keep pressure on the shifter rod while your assistant removes the wrench, pushing the rod through to “lock” the detent into place behind the shifter. You may need to lightly tap the end of the shifter rod where it is joined to the fork with a rubber mallet to drive it completely through the hole into its first locking position, just one click. Next, slide the output shaft lock sleeve onto the fork. It does not matter which side faces you since both sides are identical. Now slide the output shaft through the bushing, then the flat spacer washer, and through the first large gear inside the case and guide the lock sleeve over the shaft. Align the key hole on the lock ring with the key grove on the shaft, insert the removable key into the shaft and press the lock ring over the key and the shaft to the second position of the shifter.
Now the remaining steps are quick and easy and takes just a few minutes. Now is the time to grease the large drive gear installed in the case. Put enough grease to cover the teeth of the gear. Greasing in the case makes assembly a little cleaner. Place the short input shaft into its guide 90° to the output shaft. Don’t forget to lightly grease the transfer gear on the end and align the bushings to their keys in each bearing. The keys are very small and there are notches for the keys to fit in to keep the bushings from spinning. Grease the second large drive gear and slide it onto the output shaft. Before you place the second half of the transmission case over the assembled gears, put some grease over the outer edge of the empty case and place this onto a piece of binder paper to make a pattern for a 1/16” cork gasket.
Cut out the pattern, tracing the grease marks on the paper then transfer the paper pattern to the cork and carefully with a sharp razor knife, cut out the cork gasket from the cork. Use a single hole punch to cut out the holes for the bolts, then dry fit the gasket onto the case and trim, if needed, any areas that protrude into the inside of the case or touch either of the drive shafts. I apologize for not taking a photo of this process but you can get an idea from this alternate photo.
Place the C clip over the end of the output shaft opposite of the chain drive gear. Turn the input shaft to test the smoothness and ease of the transmission. You should also be able to observe the output shaft turning in both directions when shifted into forward or reverse and, no turning when in neutral. It should not take much effort to turn the input shaft. If it does, take apart the case and check the assembly and alignment of the gears, then reassemble and repeat the test to turn the gears.Finish the assembly by tightening the nuts and bolts and retest the alignment of gears as previously mentioned.
Now is the time to be patient, go slow and take a deep breath. Reinstalling the transmission back into the ‘Lil Gasser can be frustrating since the drive chain from the clutch to the input shaft is so short but it can be done. I loosened the front cab wall where the transmission is mounted for some extra “wiggle room” to provide a little more slack room on the chain to get it back on the gears. Set the chain on the smaller transmission input gear first then align the chain on the clutch gear and work the chain over the first sprocket on the clutch gear and turn the clutch gear by hand until the chain had threaded all the way around and is on the sprocket, the same way you would put the chain back onto a bicycle peddle. You won’t get it on the first attempt because of the very confined space but, don’t worry and keep trying. It took me nearly twelve attempts before I got it. Next slip the output drive chain over the output sprocket, this is very simple and easy since the chain is much longer and there is open room to do so. Now is the time to fasten the front cab wall back to the side walls with the little star screws. Since there is one bolt that can not be removed from the front cab wall and the transmission is hanging from this one bolt, slide the remaining bolts through the cab wall from the engine compartment, through the wall and the transmission mounting holes.
Finger tighten all the nuts after placing a flat washer then locking split washer over the bolt. Tighten all four nuts and bolts with a box end wrench and drive socket. Once tightened. Attach the shifter bar from the locomotive gear shifter, to the transmissions shifter rod using new cotter pins and the linkage joiners. Test shift the gear shifter and watch the transmission shifter bar and listen and feel for the clicks, You may need to make a small adjustment on the shifter at the rear of the cab like I did to get it to cleanly click into forward. If so, remove the rear cab wall and grind or file a flat spot on the round bar for the set screw to have a flat purchase to keep the bolt from slipping on the round stock rod. This makes for a more positive, and slip free adjustment. Slip the back wall back over the shifter and fasten into place. Go out to the track and give it a test run under a load. I started and tested my Gasser on blocks in the garage to be sure it shifted F-N-R before taking it out onto the club track.I am extremely happy with the outcome of my first rebuilt transmission and the improved performance of my Gasser. The best part is the cost was less than $20.00 for everything I needed from the carburetor cleaner to the grease, RTV and gasket. That sure beats trying to find a new transmission and, or changing the drive train and power from gasoline to electric.