Big Brown Christmas Sleigh showed up late last night with a package that will be another winter project. 🙂 For some reason the current final drive has a gear set of 31/11 (Should be 33/11 for a GS?). With the more technical off road elements, and a dry clutch my hope is the R850 R Final drive with 37/11 will satisfy the need for slow off road, without hampering faster freeway operations too much.
Found a 37/11 Final drive assembly on eBay. It had been disassembled some time ago, and found to have the large Crown Gear bearing failed. It was a good price at just under $220 delivered.
From a cursory inspection this morning it appears the gears are in good condition. Housing, End Plate, etc. look okay. Pinion does not feel "notchy" when turned. No signs of damage from the bearing cage disintegration and loss of bearing balls.
Besides needing the housing bored for ABS sensor use, and large Crown Gear bearing replaced, there are signs of slight weepage from the pinion seal, and light corrosion from sitting disassembled. The small Crown Gear bearing shows signs of wear, and there are indents on one of the Paralever mount bearing race. If this unit came into my shop, I would do my best to talk the sidecarist into a complete rebuild to meet the more severe demands. I'd want to figure out the cause of bearing failure, and set it up very carefully for the extreme duty of aggressive off road sidecar use, as well as the high load high speed road use.
I would love to do this rebuild myself. I'd like to know if the bearing failure was due to external influences, or if setup could have been optimized for better durability. I've done a lot of different differentials in my youth. Would need to buy the pinion socket, fabricate the mounting jig, and a bar for setting backlash. The housing would still need to go to a machine shop for the ABS sensor mod. So all in, I'm not sure doing this myself is the best return on investment. I'm going to contact Virginia Motorrad on Tuesday and get their thoughts. I watched a video set overview of disassemble/rebuild. Gentlemen doing the work in the video seems to be a conscientious tech who can be trusted. Will post up after we talk, text, email... or whatever it is we do these days to communicate. 😉
Pictures are: 31/11 gear stamp on drive unit currently installed. *Cover ready to be bored for ABS sensor. * Guts but no Glory yet. * Bearing failure (seems common). * 37/11 gear stamp on eBay bought FD
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Anton Largardier (Virginia Motorrad) is certainly the guy for BMW transmission and final drives and he stands by his work.
You could do a lot worse.
Sometimes it's worth it to do it yourself for the learning experience sometimes it's just easier to send it out to an expert. If you think you might be wanting to rebuild more of them in the future, I'd do it myself. Sounds like you have some experience.
I put new seals in my race rig's final drive but for anything more intense than that I would probably send it to Anton.
You guys were having way too much fun. 😉
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Just a minor bit of info. The stampings on the casings indicate which crown and pinion was originally installed in that particular casing at the factory. But the casings are all the same (except some are ABS and some are non-ABS). Any previous owner could have installed a different crown/pinion set. Though, outside of the sidecar community, this is rarely done. So the stamping will be right 99% of the time.
A better indicator is the stamping on the end of the pinion gear. Like this pic below shows a 2.82 so you know it's a 31:11 --
Gear ratios for the different BMW models:
37/11 (3.364) -- 850R; 850GS
34/11 (3.091) -- 1100RS before ‘93
33/11 (3.00) -- 1100GS; 1100R
32/11 (2.91) -- 1100RT; 1150RT
31/11 (2.818) -- 1150GS/A; 1150GS; 1150R; 1100RS after ‘94
33/12 (2.75) -- 1100S
Quote from DRONE on November 24, 2023, 8:14 pmGear ratios for the different BMW models:
37/11 (3.364) -- 850R; 850GS
34/11 (3.091) -- 1100RS before ‘93
33/11 (3.00) -- 1100GS; 1100R
32/11 (2.91) -- 1100RT; 1150RT
31/11 (2.818) -- 1150GS/A; 1150GS; 1150R; 1100RS after ‘94
33/12 (2.75) -- 1100S
Great info! Thanks for posting this. 🙂
I counted the teeth in the picture of the Crown gear before hitting the Buy It Now! button, because I was thinking the same thing. The original "thought" was to put this gear set into the current final drive. Which would have made yet another unit with incorrect stamping.
Picture of pinion shaft stamp on this FD after cleaning all the old grease so it is readable.
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I replaced my 07 R1200GSA final drive with a R900RT (part#33117705739) for a ratio of 3.0:1 and found that it was almost a waste of money for how little it helped.
Quote from StrongBad on November 25, 2023, 4:50 pmI replaced my 07 R1200GSA final drive with a R900RT (part#33117705739) for a ratio of 3.0:1 and found that it was almost a waste of money for how little it helped.
This was my concern as well, and part of why I went with the 3.36:1 ratio. If that doesn't fit the application it's time to think hard about the expectations.
Did you ever try the 3.36 ratio?
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I was looking at lowering the gearing for more technical terrain and avoiding flogging the clutch. With the OEM final drive the bike's speed at idle was just over 12mph. The new final drive dropped it down to 10mph at idle and the top speed is still over most interstate speed limits. I now think the best way to get a nice gear for would be to use the gearbox out of the HP2 enduro which uses a lower 1st gear.
The rig's gearing has fallen pretty far down on the budget priority. Currently retirement travels are at the top of the list.
Quote from StrongBad on November 26, 2023, 11:19 amI was looking at lowering the gearing for more technical terrain and avoiding flogging the clutch. With the OEM final drive the bike's speed at idle was just over 12mph. The new final drive dropped it down to 10mph at idle and the top speed is still over most interstate speed limits. I now think the best way to get a nice gear for would be to use the gearbox out of the HP2 enduro which uses a lower 1st gear.
The rig's gearing has fallen pretty far down on the budget priority. Currently retirement travels are at the top of the list.
a lower 1st gear for the transmission would be the perfect answer.
I'm with you. After these "winter projects", the next few years are getting out and traveling. I actually started that about 6 months before retirement. Then got a case of the "Severe Stupids" and bought an old broken down farm house to refurbish. About burned myself out over the past year. Completed less than a third of what needs doing. So I'm looking forward to the break. Maybe the place will fall in on itself, and it can just bulldozed for a new build. 😉
Living in the middle of the Rockies, and not getting out to enjoy them is against the law here in Utah. 🙂
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I believe final drive bearing failure was common on these models. Brought a trip to the John Day rally short when a riding buddie's failed half way there.. We made it back to the Dealer but he got a ride of shame on the back of my ST1300 to make it all the way home LOL. Another friend of mine went through his and stated that the shim and clearance has to be perfect for it to live any length of time. Most were not so many had repeat fails as the dealers would just slap a new bearing in with out proper checking of the clearance.. Which to my understanding is a real pain in the butt with the Two case halves. I tend to believe him as Ron is about as Anal about his maintenance as they come.. Any ways following along as I have one of my own to do.. As a spare. And Anal is not in my repertoire. LOL
Quote from MGV8 on November 26, 2023, 9:36 pmI believe final drive bearing failure was common on these models. Brought a trip to the John Day rally short when a riding buddie's failed half way there.. We made it back to the Dealer but he got a ride of shame on the back of my ST1300 to make it all the way home LOL. Another friend of mine went through his and stated that the shim and clearance has to be perfect for it to live any length of time. Most were not so many had repeat fails as the dealers would just slap a new bearing in with out proper checking of the clearance.. Which to my understanding is a real pain in the butt with the Two case halves. I tend to believe him as Ron is about as Anal about his maintenance as they come.. Any ways following along as I have one of my own to do.. As a spare. And Anal is not in my repertoire. LOL
Thanks for bringing this up! Your comment mirrors the insight from Anton in the assembly video. He makes an almost off-the-cuff comment regarding preload. Having setup the Ford 8.8 differential I caught that, because it has similar needs for high stress applications. Looking forward to discussing with Anton this week. Will post up his thoughts.
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Hey you kids get out of my yard !!!!
I second Drew's remark Anton is a Transmission FD wizard, I can hardly believe how well the 5spd in the Red K shifts after he OH it.
Germans like shims final drives also need shims BMW says you can charge up to 5 hrs to rebuild one it's not as easy as a automotive differential . I went to a BMW dealer that was having a winter sale to give their techs something to do I gave them a use able 31 /11 and said make it a 37/11 MISTAKE the bill was 1200 $ .
Hope you guys had a nice holiday !
Question to those of you running on and off road with your BMW R11xx rigs: How many miles are you getting without a Final Drive bearing failure?
Thinking about the extreme off axis loads the large bearing on the Crown Gear is subjected to. I get why BMW went with a standard roller bearing. It is much easier to build the differential, and less expensive. But for durability an Angular Contact Bearing would be a better choice. https://www.nbcbearings.com/understanding-of-angular-contact-ball-bearings/ A 7917 bearing is about twice the cost, and would be more work to set up.
I've used these before in applications similar to the load stresses the rear hub sees on this bike, and had excellent success. If you guys are getting 50K miles without failure (once properly setup) it probably isn't worth the amount of effort to install the AC bearing. But if your experience is much less, than it would be worth it to upgrade. Especially with the kind of off road loads SYZ will be subjected to.
Thanks for your thoughts. :cheers:
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Scott @sheath, you are opening one of the ugliest cans o' worms in the motorcycle world, when you start talking about BMW rear diff bearing failures.
For a long time, BMW refused to acknowledge they even had a rear diff bearing failure issue. Yet....1000's of BMW riders were experiencing rear diff bearing failures, to the point that (and this is serious) riders that were participating in THEE IronButt rally, the 11,000 miles in 11 days Rally would literally carry a secondary rear diff with them on their 2 wheeled motorcycles, so that WHEN...not if, but WHEN the rear diff bearing failed on their BMW's, they had a spare rear diff to install...during that 11 day rally. There were instances of riders having a rear diff fail on them five (5) miles short of the Start of the rally, and that knocked them out of the rally.
BMW lost a lot of customers over that issue, and only AFTER close to 10 years of customers screaming at BMW that it was a design error, a problem related to the BMW bikes, and not the fault of the riders, and AFTER BMW saw the evidence in sales numbers, with many riders going to Honda, because 99.99% of Honda shaft drive rear diffs do NOT fail, as in ever.....finally BMW acknowledged and admitted that they had a problem.
Uh............Good Luck. At least you have the Screaming Yellow Zonker thing going for ya'
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