Driveline backlash, acceptable rotational tolerance or impending failure?

[pwillikers]

Vehicle: '11 RT w/51K mi.

 

I've owned three shaft drive BMWs.  This one's drive line is perceptibly clunkier than the others.  I measured the rear wheel's free rotation when in first and sixth gears at the circumference of the rear tire (see the pics for the process).  I'm quite surprised how large the backlash is.  I'm also surprised at the variance between measurements in first and sixth gears:

 

2.5" (64mm) in first gear and

3.75" (95mm) in sixth gear.

 

Please measure yours in the same manner and report back.  

 

No other symptoms:

• The drive line is smooth and the clutch is near perfect under operation, save for the need to "drive around" the excessive drive line play.
• There is no discernible vibration at all and it is quiet with no audible indication of impending driveshaft failure.
• I peeled the rear rubber boot back and observed that the drive shaft rotates immediately with rear wheel rotation thus indicating that the rear drive and the rear driveshaft U-joint are in good shape.
• I listened with a stethoscope along the swingarm while rotating by hand and all is quiet (but this is inconclusive).
• I'm within a couple thousand miles of needing new tires.  At that time, I'll dig in and inspect the front driveshaft U-joint and whatever other suspects I'll be able to access with the body work off.  Any suggestions?

 

What is your counsel?

• Is this backlash excessive?
• The variance between first and sixth gear measurements of 1.25" (38mm) suggests a significant internal transmission variance.  Is this a potential issue?

 

What are the likely sources?

• front driveshaft U-joint,
• transmission input or output splines,
• clutch splines,
• transmission internal malfunction,
• engine primary drive,
• how to isolate/confirm the various suspects?
• OR, just relax, these measurements are typical.  Are they typical? 

  

Please measure yours and report back to determine if they are typical or if there's need for concern. 

 

Thanks for your efforts.

 

 

[Hati]

I don't remember the exact spec, but there is definitely an amount of backlash that is within limits. On my '13 R I have no backlash at all. On the previous gen (hexhead) RT I had, it was from (bad) memory under 50 mm. 

 

I think there is no point comparing backlash in different gears, as you compare one gear to the other effectively. With the final drive health check you just need to have it in gear so the drive shaft does not move and you get drive shaft to wheel backlash only.

 

Your 64 mm backlash seems a bit excessive to me, but I could be wrong with the amount.

[dirtrider]

On 10/23/2023 at 7:02 PM, pwillikers said:

Vehicle: '11 RT w/51K mi.

 

I've owned three shaft drive BMWs.  This one's drive line is perceptibly clunkier than the others.  I measured the rear wheel's free rotation when in first and sixth gears at the circumference of the rear tire (see the pics for the process).  I'm quite surprised how large the backlash is.  I'm also surprised at the variance between measurements in first and sixth gears:

 

2.5" (64mm) in first gear and

3.75" (95mm) in sixth gear.

 

Please measure yours in the same manner as I and report back.  

 

No other symptoms:

• The drive line is smooth and the clutch is near perfect under operation, save for the need to "drive around" the excessive drive line play.
• There is no discernible vibration at all and it is quiet with no audible indication of impending driveshaft failure.
• I peeled the rear rubber boot back and observed that the drive shaft rotates immediately with rear wheel rotation thus indicating that the rear drive and the rear driveshaft U-joint are in good shape.
• I listened with a stethoscope along the swingarm while rotating by hand and all is quiet (but this is inconclusive).
• I'm within a couple thousand miles of needing new tires.  At that time, I'll dig in and inspect the front driveshaft U-joint and whatever other suspects I'll be able to access with the body work off.  Any suggestions?

 

What is your counsel?

• Is this backlash excessive?
• The variance between first and sixth gear measurements of 1.25" (38mm) suggests a significant internal transmission variance.  Is this a potential issue?

 

What are the likely sources?

• front driveshaft U-joint,
• transmission input or output splines,
• clutch splines,
• transmission internal malfunction,
• engine primary drive,
• how to isolate/confirm the various suspects?
• OR, just relax, these measurements are typical.  Are they typical? 

  

Please measure yours and report back to determine if they are typical or if there's need for concern. 

 

Thanks for your efforts.

 

 

Morning  pwillikers

 

Figuring the drive line backlash at the rear wheel is about impossible to tell where it is coming from. Some BMW 1200 bikes have a lot & others not so much. 

 

The problem is, it is accumulative, as there are a number of places in the drive line that have some lash & depending on what gear the transmission is in effects the overall rear wheel backlash. Drive line temperate can also have some effect as thinner (hot) gear oil can allow more gear to spline, or shifting-slider to spline rotation than cold thick gear oil. 

 

If you look at JUST the transmission part then typically there is more lash in the shifting sliders to gear slots in the lower gears as the motorcycle isn't ridden far in those gears & more lash makes lower gear shifting easier. The higher gear shifting-parts lash is usually  less as the motorcycle is typically ridden in those gears once through the upshift sequence.   BUT, keep in mind that depending on WHERE the lash is in the transmission (or clutch splines) the rear wheel lash (rear wheel circumference movement) can move farther in high gear than in lower gears. 

 

If the transmission is locked up solid (not just in gear but the output shaft is prevented from moving) then any rear wheel lash would be in the ring gear to pinion lash & in the drive shaft/drive shaft U joints. It also couldn't/wouldn't change with trans gear selection. 

 

On the other hand (assuming no lash at all in the transmission, drive shaft, & final drive) but the clutch splines are worn then the lash measured at the rear wheel would increase as the transmission was upshifted from 1st to 6th, with 6th having the most rear wheel movement, & 1st having the least rotational movement. Because of more gear reduction in 1st gear the input shaft would have to rotate farther for the same rear wheel movement. Or put another way, for the same amount of play in the clutch splines the rear wheel would rotate farther in 6th gear than in 1st gear.  

 

I haven't ever seen a BMW spec on the driveline backlash in each gear at the rear wheel circumference (BMW would be foolish to offer that as there are so many variables in the drive line that effect that). 

 

About all you can do is try to see how much lash you have in the clutch splines (remove starter then take a look as you rotate the rear wheel with transmission in gear) then see if you have excess lash in the final-drive drive shaft area. If those look to be within reason then about all that is remaining is inside the transmission  itself. 

 

Your BMW uses a constant mesh transmission so ALL the gears are meshed & spinning any time the input shaft is spinning. This means that shifting into any gear just takes locking the appropriate gear to the shaft it is on.   This is done using sliders with dogs on it, those dogs fit into slots or holes. To allow easy shifting there needs to be clearance in the dogs to slots. This dog to slot clearance is where most of the transmission lash occurs but the sliders also need to slide easily & smoothly on the splined shafts so there also needs to be some clearance is those splines (so more internal lash here). Then you have the actual gear teeth lash as the gears need some tooth to tooth clearance to run quietly & lubricate. There also needs to be some clearance in the gearing of the input shaft to the intermediate shaft so add in a little lash from that area.   This all adds up to a significant combined lash inside the transmission. 

 

Then, depending on where in the transmission internal reduction the lash occurs the rear wheel can show more rotation in the higher gears then lower gears due to the gear reduction in lower gears & overdrive in the higher gears.  

 

    

 

 

[jdub53]

In the interest of science, I just replicated that measurement method on my 2013 RT w/48k miles and came up with 2.5" (63.5mm) backlash in first and 3.325" (84.5mm) in sixth. Difference between the two is .825" (21mm) compared to your 31mm backlash difference between the two gears. This was measured using a virtually new Bridgestone T32GT rear tire (< 100 miles on it), but any circumference difference between the two tires should be insignificant considering we're both using imprecise tape measures.

 

 

This is my ninth shaft drive BMW over several decades and ~525k miles (seven Boxers, two K-bikes), and I can't say the performance of this gearbox gives me any cause for concern. Just a few weeks ago I had the driveshaft out/Paralever housing removed while I replaced both front and rear accordion boots for cracking, and all of the exposed splines were perfect as were the driveshaft u-joints.  

 

 

[6speedTi]

I too was concerned only to find out this is normal. When I decided to pull back the final drive and inspect the splines,  boot and driveshaft end I decided to see where the backlash was. On my bike it's all in the gearbox. The final drive and driveshaft are tight. Curiosity now over. So for me it's turn on the ignition,  push the starter button and enjoy the ride. 

104,000 miles and still enjoying the ride.  

[pwillikers]

Thank you gentlemen(?) one and all. 

 

jdub, thank you for measuring yours.   I'm reassured yours turned out to be virtually identical to mine. And that you performed a recent, thorough inspection finding no anomalies.  This is very good anecdotal data.  (Also, a very nice new T32GT you're sporting there :-).

 

DR, as usual your knowledge and assessments are illuminating.  Thanks for the thorough causation discussion. 

 

As mentioned, when I soon change tires, I'll work forward from the rear drive through to the clutch splines in an attempt to isolate where the majority of the backlash lies.  I'll report back.  Given the reports here, I assume I'll find, as did 6speedTi, that most will reside within the transmission.  For now, I'll just "push the starter button and enjoy".

 

There are few communities as knowledgeable, insightful and willing to help as this.  You guys are tremendous.  Thanks.

[Hati]

No longer relevant.

[wbw6cos]

ChatGPT.  

 

Click the link and find that it has nothing to do with your post.  

 

 

(reported)

[Old School]

I've only had My 2012 R1200RT about a week, and have noticed that when I am riding at low speeds in first gear, such as in a parking lot, I hear/feel some clunking that seems to be coming from the clutch or transmission

as I feather the clutch and throttle. Again, this is only noticeable in first gear at low speeds.  I have seen other comments here and elsewhere regarding BMW transmissions being somewhat clunky.

If what I have described is normal, I have no problem accepting this as just part of the bike's character. I just don't want to ignore something that may be a symptom of a problem.

BTW, the bike just turned 40K miles.

[dirtrider]

10 hours ago, Old School said:

I've only had My 2012 R1200RT about a week, and have noticed that when I am riding at low speeds in first gear, such as in a parking lot, I hear/feel some clunking that seems to be coming from the clutch or transmission

as I feather the clutch and throttle. Again, this is only noticeable in first gear at low speeds.  I have seen other comments here and elsewhere regarding BMW transmissions being somewhat clunky.

If what I have described is normal, I have no problem accepting this as just part of the bike's character. I just don't want to ignore something that may be a symptom of a problem.

BTW, the bike just turned 40K miles.

Morning Old School

 

More than likely normal as the BMW 1200RTs do have a number of places in the driveline that can all add up to noticeable driveline lash. 

 

You can usually mitigate it with more precise clutch control & throttle/to/clutch timing. 

 

Due to the normal amount of lash in the BMW boxer bike drivelines, & the thin wall alloy transmission, swing arm, & final drive housing that easily transmit the internal noises to the riders ear they can be somewhat clunky until the rider figures out how to decrease it with clutch control & throttle control. 

 

The BMW is a solid clutch disk (no spring hub),  shaft drive, with a ring & pinion final drive (that is fairly direct without much cushioning). On the other hand  a (street) chain drive motorcycle usually has a rubber cushioned rear chain sprocket hub & the chain itself can damp a lot of the low speed clunkiness.   

 

If you are worried maybe join a local BMW club & have some of the long time BMW owners take a ride on it or have your local dealer take a look at it.

 

Without riding it myself I can't say for sure that your motorcycle is normal but I can say that it probably is normal.  

[Old School]

Thanks Dirtrider,

I will be scheduling an appointment at an independent BMW only shop in the Phoenix area to have the non working heated grips diagnosed. I'll have them check the driveline lash also. 

[pwillikers]

Old School, Measure your lash per the first post in this thread and report back please...  in the interest of science of course.

[Old School]

Ok, maybe this weekend. 

[9Mary7]

On 1/4/2024 at 10:56 AM, Old School said:

Thanks Dirtrider,

I will be scheduling an appointment at an independent BMW only shop in the Phoenix area to have the non working heated grips diagnosed. I'll have them check the driveline lash also. 

Which one is that? Asking for a friend...seriously I am.

[Old School]

On 1/5/2024 at 1:30 PM, 9Mary7 said:

Which one is that? Asking for a friend...seriously I am.

It's called Moto Ghost, in north Phoenix. Check their website. 

[Old School]

On 1/4/2024 at 12:53 PM, pwillikers said:

Old School, Measure your lash per the first post in this thread and report back please...  in the interest of science of course.

Here is what I measured. As you can see, 21/2" in first gear and an additional 1/2" in sixth gear.

[pwillikers]

Thanks, Old School.  Your findings are consistent with others.

[Old School]

Just a quick update. I took the bike to Moto Ghost last week. After diagnosing the grips, they looked the bike over and did a test ride. Jeremy, the owner, said everything appears normal.