It's about time to get caught up on this topic since it is cold and icy out today. I was able to rebuild the final drive(s) with all new parts and now with about 2500 miles on one of them I don't foresee any issues going forward. I'm just going to continue riding and enjoying our LT.
First off I'd like to say that riding on a rear drive that has over 180k might be a bit risky. Not safety wise necessarily, but risky in regards to reliability. In the future I will probably switch out the drive with less than 100k if I am getting indications of contaminated oil or large bits on the magnet. In regards to this observation I have to admit that I did see a darkening to the oil on the last two oil changes (which I do at every engine oil change of 6k) going back to last Fall (2013).
I am guilty of wanting to see, for myself, just how far a "good drive" will go. I'm really "guilty" since most of the miles traveled on this bike are two-up, and therefore I could have put not only myself at risk of some kind of injury (or at least the inconvenience) I was putting my wife at risk too. As it turned out the indicators of a failing drive were so pronounced that one would have to be a total idiot not to know that it was time to find a safe place to stop and call a tow truck.
Pauline and I were on our second day of a 5 day 5k mile rally starting from home near Portland Oregon and ending in Salt Lake Utah. We had left earlier in the day on July 2nd from Lewiston ID and traveled the wonderful Hwy 12 (Lolo Pass) to Missoula MT to catch I90. We were considering staying the night in Red Lodge if there was a place to stay, but when we got there at sunset we changed our minds. We decided to put on our heated gear and travel over the Beartooth Pass then spend the night in Cody. By HID light, and the stars, we climbed up and over the pass as midnight approached.
There were two cars that passed us going the opposite direction toward Red Lodge, and we only came upon one car going the same direction so it became clear that if something happened it might be awhile before help would arrive. At the very top there were still snow drifts on each side of the highway. We had a conversation about how ugly it would be to be stranded in the middle of the night in such a desolate, and cold, place. We came across an animal (very large and dark) after we turned onto the Chief Joseph hwy toward Cody. Pauline said, "did you see the bear?" I said I saw something but I was on the brakes and steering the other way and did not get the pleasure of seeing the beautiful beast. We came across the only car going our way and I dropped a gear to pass and shortly after that I had a "what was that" moment when I felt a strange feeling in the grips and foot pegs. It was the dreaded "rumble strip" feeling but we were on smooth pavement. Pauline felt it too and picked up on my slowing down and asked if the bike was all right. We traveled for about 2 miles while looking for a good place to turn off and found a slow truck turn-out with an extra wide shoulder.
The car we had passed came up and asked if we were okay. After some discussion and trying to put together some options our phones refreshed and we had cell service. I pushed the "HELP" button on our SPOT tracker and they called us right away, and in about an hour we were on a tow truck to CODY with a room reserved for the night. The tow truck driver - a young man from Virginia, was very experienced (saying he averages over a dozen tows out of Yellowstone a week) and friendly.
The next day I scoured the town of Cody and found a local V-twin shop willing to give us assistance. Everyone, without exception, in the town of Cody was helpful and friendly. We were able to strap our LT into a Uhaul, and head for home later that day.
What I found in my drive:
After getting home I immediately removed our old drive to see what went wrong. First off there was no oil leak until I removed the wheel and a drip of oil fell to the bench. I removed the plug and drained out some really foul black oil and shavings.
The drive removed shows the seal wet with drive oil and looking a little chewed up.
After removing the seal/bearing housing it is clear I have a classic crown gear bearing failure. But there is more! I have a ruined housing from the crown bearing spinning, and a ruined tapered bearing, and the hub for the crown gear has worn significantly because the tapered bearing spun on its pressed fit shaft. In other words I have a possible good outer housing and pinion shaft (maybe) out of all this mess.
Another look at the crown gear and bearings:
This picture shows the tapered bearing and the 2mm shim that was under it on the crown bearing hub. The wear was from the bearing spinning on the shaft and it was down under 1mm in a couple spots. Amazing really how much punishment this drive can take and still keep going!
This picture is the crown gear hub and the shaft that the tapered bearing would be pressed onto. The end of the shaft is now worn .005 undersized and not useable in its current shape. However I was able to strip out a used drive that was given to me. The drive was removed from a wreck and the outer housing was really beat up. It looks like scrap aluminum to me.
Next was building some special tools to hold the drive for dis-assembly and reassembly. I needed to hold down this awkwardly shaped part. I modified my cylinder head tool that I mount in my bench vice. This seemed adequate to the task, and I didn't have to take time to design a more elaborate device.
Next is to heat up the housing to get the pinion bearing retainer nut off. The heat gun proved it was not up to the task so I sourced an electric oven at the local thrift store and it did the trick.
Following the instructions of heating pinion retaining nut to 212 degrees with a heat gun and removed with a 36mm deep socket and breaker bar. Then heating the housing to 248 degrees (in the oven) I was able to remove the "threaded ring" with a "pin socket". Heating is very necessary since there is locktite (thread locker) on the retaining nut and sealant on the threaded ring. Heating will soften both to remove the parts.
The pin socket I use is a Performance Tool Spindle Nut socket # W1271. It is a 4 pin 2.375" and fits perfectly. I believe Dave (Saddleman) is using a GreatNeck 25072 of a same size. Well there is one exception to the "perfect"; the socket is designed to fit over the end of a spindle and help support the torque supplied to the pins. So I made a sleeve to help align the socket with the ring.
With the pinion gear and bearings removed I found minimal wear in comparison to the other parts.
The pinion needle bearing outer race is a pain to get out being deep into the housing. Using the puller that Curtis suggested in an earlier post from 3-Jaw Pilot Bearing Puller
By manipulating this puller and using a heat gun it comes out pretty easy. This picture isn't too clear but you can get the idea.
I cleaned all of the parts and started putting the drives back together with all new parts. The total costs for all new bearings and seals set me back about $350 each. Before assembly I thoroughly cleaned the threads in the housing as well as every nook and cranny.
I made my own tools for the most part. Seal and bearing drivers can be bought, but some are a bit specialized for size and depth reasons. Some bearings are an easy install; for instance the tapered bearing outer race fits into the housing easily with heat. I installed the pinion outer needle bearing and race into the housing first. I heated the housing to nearly 250 degrees and the bearing fit in with very little use of the driver. Before the housing cooled I then installed the tapered bearing outer race (it also fit in nicely and after the housing cooled both were a tight fit.
Removing the pinion bearings are fairly easy with a press and puller. Assembly, after cleaning the shaft, is simply the reverse process. Use of a light assembly lube is a good idea and then place the pinion into the housing. This is done by heating the housing again (248 degrees) and chill the pinion and bearings in the freezer. after the housing cools and with a new seal placed into the threaded ring a sealant (Locktite 577) is placed on the threads in the housing then torqued (118 Nm). Placing the shaft sealing ring onto the shaft is next taking care not to damage the seal itself. I used a light weight oil to help this part slip in. Then I assembled the crown gear assembly on the work bench by heating the bearings and chilling the crown gear. The bearings just fell on with no effort. A temporary install of the crown gear and the housing cover allows you to lock the drive in your mounting fixture so you can torque the pinion nut (locktite #271
) at 200 Nm.
I took the old housing cover and made a tool from it since the bearing seat was badly worn. This made measuring the distance from the housing cover to the crown bearing for proper preload. The old housing cover was worn from the damaged crown gear bearing spinning. It still wasn't a slip fit and was somewhat egg shaped. I chucked it up in my lathe's 4-jaw chuck and dialed it in on a surface that wasn't damaged. I cleaned up the bore and made is a slip fit so I could use a dial indicator to test distance between the housing cover and the crown gear bearing.
Since I had changed crown gear and used a different tapered bearing thrust washer I took my time with these measurements. The issue is the gears need to mesh properly and the adjustment for that is the depth that is set for the crown gear against the pinion gear. This is done with the pinion bearing thrust washer thickness. Having already assembled the pinion bearing - complete with sealant and licktite - I was concerned I got the cart ahead of the horse. But first I needed to measure the housing cover clearance and shim the crown gear bearing. I picked a zero clearance fit for this process since all I was going to do was inspect the gear mesh using Dykem high spot blue dye.
With a sigh of relief I determined that the gears were meshing properly (the BMW manual shows that the gears should mesh in the center) I then set about to fine tune the crown gear backlash.
I made a couple more tools to set up a dial indicator somewhat like the BMW manual says to do. But the readings were not consistent and I determined I needed to make something that would lock the pinion into position so I could just measure the crown gear movement. As luck would have it I had a couple old drivelines laying around and made another tool out of a driveline yoke.
After getting the backlash correct which was tricky since I didn't buy shims. I made my own shims on my lathe made out of some stainless steel bar stock. After some back-n-forth I settled for any measurement within the tolerance. I then re-measured the backlash with the housing cover that was not altered. I was then confident that I had the correct run-out on the crown gear and pinion, plus I was now confident that I could measure for pre-load of the crown gear. Using the cover that I converted to a tool got me into the ball park, but when I measured the two other covers I found a .0005 to .001 difference between the three.
I was lucky to have bought some assorted shim sizes for the crown gear because I needed them. I was able to dial in both drives and shim them with the least amount of pre-load allowed (.002 - .0039). Since conventional wisdom thinks too much pre-load is what causes the premature failure of the crown gear bearing why make it any tighter than necessary? We'll see when time and miles are clicked off.
My goal here is to not say I've done anything that most mechanically inclined individuals are not capable of doing. My goal is to pull down the curtain and show that it isn't that difficult if you can persevere and look for solutions. I asked a lot of questions and have nothing but praise for Curtis, John and Dave for blazing the trail by removing some of the mystery surrounding these rear drives. This post is lacking a lot of detail because I did not document every step, and I took a long time to do the job(s) and get them right. I also looked at all the manuals from BMW to Clymers and the data for set-up is all the same. I checked with BMW to see if there were any changes over the years, nada. Therefore using the manuals will get you the desired results.
Thanks for reading my post and hanging in there for this long post. The more we know, the less we fear.