Replacing i2 Elastomeric Couplers

[glen_d]

I haven't seen a lot of comments from people who have had problems with elastomeric couplers, so I thought I'd post my experience with replacing them on my i2.

My wife's i2 has been growling loudly on the right side for the last month, so I removed each transmission from the base to inspect the elastomeric couplers. On both couplers, the elastomer was sticky and disintegrating into little bits that were evident in the area that encloses the couplers. I cleaned the elastomers and both halves of the couplers with a wax and grease remover used for paint prep (safe for plastics) and re-assembled the i2. The couplers were initially quiet but quickly degraded to their former noisy operation within a few minutes.

The elastomer coupler consists of two assemblies:

1) A white hard plastic hub with eight lobes on the exterior. This is a light press fit onto the hex-shaped output shaft of the motor in the base. The eight exterior lobes are covered with a soft elastomer shell about 1/8" thick. The elastomer shell is a separate part that can be removed and replaced separately from the hard plastic (although these two parts are sold as an assembly by Segway).

2) A white hard plastic cup on the transmission input shaft. It has 8 interior lobes that match the shape of the elastomer-covered hub on the motor output shaft.

Here's a picture of the couplers I removed from the output shaft of the motors in the base:






The white flecks in the picture are a small portion of the debris that resulted from the elastomer disintegration. The elastomer slides onto the white plastic hub one way - there is a small web at the bottom of each of the elastomer's 8 interior corners that fit into notches in the base of the hub.

I ordered a pair of replacement elastomers from Segway of Annapolis for about $34 and received them in Alaska just three days later. To replace the couplers, I followed these steps:

1) Lay the i2 on its side (on a wheel) and work on the transmission that is now facing up.

2) Remove the hubcap and wheel. The wheel is retained with three 13 mm nuts.

3) Pull the center console trim loose by hand and remove it from the machine. This allows access to the rear trim.

4) Remove four screws (TORX T25) that secure the trim across the rear of the base. Two screws are in the center of the trim (normally hidden by the center console trim), the other two are at each end of the trim near the transmission. If you don't remove the screws at the ends, they will prevent you from removing the transmission when attached to the spacer. Leave the trim itself in place until you remove the fender - it's easier to remove then.

5) Remove a screw from each end of the trim across the front of the base (TORX T25). Leave the trim itself and the two center screws in place - they won't be in your way.

6) Remove four screws (TORX T20) that secure the fender. These screws are usually hidden by the wheel. Now remove the rear trim by pivoting it around the end near the installed transmission/fender until the trim can be easily pulled clear.

7) Remove three screws (TORX T25) that secure the trim piece on the inside surface of the transmission (next to where you stand). These screws are always visible.

8) Remove three large bolts securing the transmission and spacer to the base. These fasteners are TORX PLUS 40. Although a regular TORX bit will fit into a TORX PLUS fastener, the regular bit cannot achieve the necessary torque to loosen or fully tighten the fastener. You must obtain a TORX PLUS 40 bit to remove and replace these three bolts (about $7 from Craftsman).

9) The transmission is indexed on the spacer with two roll pins, and the spacer is indexed on the base with another two roll pins. When mated together, the base, spacer, and transmission form an enclosure for the elastomeric coupler. The spacer is sealed to the transmission on one side and the base on the other with a bead of silicone sealant. To remove the transmission, tap it from the inside with a rubber mallet to move it outwards and off the roll pins. Depending on which silicone seal breaks first, you may end up removing the transmission and spacer as a unit, or you may end up with the spacer left on the base. Either condition will allow you to proceed.

10) Now clean any debris from the coupler (the white hard plastic cup) mounted on the transmission input shaft, then set the transmission aside.

11) Remove the defective elastomer from the white plastic hub on the exposed output shaft of the motor in the base. At this point, you can proceed two ways. The simplest procedure is to clean the hub and transfer the new elastomer to the old hub - as long as the old hub is in good shape, this is what I recommend. You may also choose to replace the entire hub and elastomer assembly. To do this, remove the elastomer with your fingers, then grasp the plastic hub with a pair of large pliers and pull straight up. The hub will come off the output shaft with about 30 - 40 pounds of force. If it doesn't come off at first, try moving your pliers to several different locations along the perimeter of the hub. To install the new hub, press it onto the motor output shaft. If you don't know that you can press the new hub onto the shaft (50 - 100 pounds of force), I suggest replacing only the elastomer.

WARNING: The motor output shaft is supported by bearings which can be damaged by excessive force such as might be created by hammering the hub onto the shaft. The danger is that you will brinell the bearing races (dimple them) if you strike the new white plastic hub with a hammer to drive it onto the shaft. If you can't press (physically push with about 50 - 100 pounds of force) the hub onto the shaft, the best alternative I can offer is to lightly tap the hub in place using a 1" wooden dowel as a drift and a soft-faced mallet, all the while slowly rotating the shaft. Be aware that even this procedure might cause slight bearing damage. Some of you may think I'm being overly cautious here . . . I am . . . because it's your Segway, not mine.

12) With the new elastomer in place, it's time to put things back together. But first, here's some speculation about why my elastomers failed in the first place. My i2 was among the very first sold, so perhaps mine included a batch of chemically imperfect elastomers that broke down into sticky goo over time. Another explanation might be that the RTV silicone used to seal the transmission to the spacer and the spacer to the base gassed off acetic acid during cure. In the now-sealed chamber, the elastomer reacted with the acetic acid and broke down into the goo I found. One output shaft had a little bit of surface rust that would be consistent with this circumstance.

To account for these two possibilities, I replaced the elastomers and did *NOT* use silicone to re-seal the parts. When I broke the silicone seal, silicone was left on both parts in such a manner that was very likely to be water-tight after simply re-assembling the parts. Just to make sure, I added a very thin rope of plumber's putty (about 1/8" diameter) to the mating surfaces where the old silicone existed. I positioned the putty so it would squeeze out away from the coupler enclosure. The putty does not contain anything that will harm plastics.

Other alternatives for resealing I can think of are to add more silicone, remove the old silicone and add new, or add nothing.

13) Decide how you will reseal the parts together, then place the transmission/spacer onto the roll pins on the base and tap them into place with a soft-faced mallet. Add the three large bolts to snug the transmission down, then torque to 35 - 40 Nm (25 - 30 pounds feet).

14) If you are only replacing one coupler, replace the rear trim and secure with four screws. This is easily accomplished by inserting one end of the trim next to the installed fender, then swinging the other end into place. If you are replacing both couplers, leave the rear trim off for now.

15) Replace the fender and secure with four bolts. Replace the inner transmission cover and secure with three bolts. Replace the wheel and secure with three nuts, then replace the hubcap.

16) The procedure for the other side is the same. Remember to add the rear trim before you install the last fender. Although the rear trim can be installed very last, I found it easier to install in the manner I suggest in step 14.

That completes the steps I used to replace the elastomers on my i2. A few final notes . . .

- I've read several discussions about torque values and torque wrenches with some mirth. If you have experience with fasteners in a variety of materials, the Segway is no different with regards to torque than many other machines. For me, torque values involved in this project for all but the transmission bolts are meaningless. The little screws secure plastic parts: Over tighten them enough and you'll break the plastic. Just past snug is sufficient and a dab of Loctite 242 will keep them that way.

- For the transmission bolts, I just guessed at 25 - 30 lbs ft because past experience tells me I'll get pretty close . . . and I even have a torque wrench. The transmission bolts actually had enough residual Loctite on them after removal that they had to be screwed all the way back in using a ratchet. I didn't use any more Loctite, but a little more Loctite will give you some peace of mind if you're worried they'll loosen. Of course, the most accurate method would be to clean the bolts of all residual thread sealer, apply uncured thread sealer, then torque the bolts to the manufacturer's specifications using a properly maintained and calibrated torque wrench.

- I'll try to add some pictures to this post in the future to clarify the location of fasteners.

- Instead of using a mallet to loosen the transmission, some posters have suggested the use of a large bar clamp that can be expanded between the transmission sides. This is a neat way to achieve the same effect.

- If you've had a different experience or other suggestions about the procedure to replace the couplers, I and other readers will be interested to hear about your experience. Comments from a dealer authorized to perform this repair would be great.

Glen