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Transmission backlash on R1100RT Should I worry


Gothicman

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Ever since I bought my 1998 R1100Rt 10 months ago, it has clunked when I take up the bite on the clutch, naturally my fear is that I go away from home town, and something goes bang!

Plus apart from a bit of a crunch now and then between 2nd and 3rd shifting in either direction, the bike runs good.

I have just tried to be a little careful with the taking up of the drive train, so as to prevent this clunk as much as possible, having had 3 airheads in the past I am used to the clunky almost bomb proof gearboxes so am not too worried about that aspect although I would naturally prefer it were smother but with a 17 year old bike with 56k I suppose you have to expect something’s.

However this clunk as I take up the drive I am beginning to worry about, to the point I am only riding it close to home, which kind a defeats the object of having a touring bike if you cant tour with it!

Totally convinced that it had to be the driveshaft, I pulled the final drive off, and took a look at the first uj joint it was OK slid my hand in an felt the second uj joint that goes on the splines of the output shaft and that felt OK, so I am thinking that it must go the gearbox and up to the clutch, but just not sure anymore what it could be, if I measure the backlash at the wheel it is about 3” which would explain why the clunk, but what is it most likely to be? Or is it an accumulation of all the joints put to gether with small amounts that I can not feel as a singular fault?

Should I be worried?

Any thoughts would be appreciated.

Thanks

David

 

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Clive Liddell

Hi David,

Welcome to the Board!

 

I have not checked my RT's backlash for a long time (about 110k km) so went out to check it again today with the following results:

 

Bike in 1st gear 2.0" backlash

2nd 1.75"

3rd 2.0"

4th 1.75"

5th 2.75"

 

If I think back (not reliable) to when the RT was newer around 2001 I recall the backlash was more in the lower gear(s) and less in the higher gears - but not a large discrepancy. Looking at the current backlash at 120k km it has settled to more uniformity between the lower gears except 5th gear is slightly higher than I recall...

 

Affecting the figures could be the force applied to the tyre when measuring where a higher gear would transfer more torque back to the torsional damper on the gearbox input shaft.

 

The backlash is necessary to assist in gear changing on a sequential gearbox since our bikes do not have the inherent slack on a chain drive (sometimes assisted by a rubber cush drive in the rear drive).

 

I would say you have no problem but it would be of interest to check in all the gears :)

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I just checked my 98 RT and get the following:

 

First: 2.25"

Second: 1.75"

Third: 2.25"

Fourth: 2.15"

Fifth: 2.5"

 

I assume you are measuring the travel on the outside of the tyre Clive?

It isn't easy to get an accurate reading, I tried to get hard over readings.

 

Another thing that I learnt on this forum David is to preload the gear shifter when changing from 2nd to 3rd, this stops that crunch.

 

 

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Thanks to Clive and to Reecehk, I am away from home for a couple of days, but will be home tomorrow when I will check it is all gears, and yes I am checking from the outside of the tyre, along with the measurement of the backlash, is my apprehension or fear concerning the clunk as the backlash is taken up as I take up the bite of the clutch and the drive of the bike, is to whether it is LIKELY that something is going to go bang and I break down at the side of the road.

I have had 3 airheads and never experienced anything like this volume of backlash with them, but then the design of the drive train is completely different, well the shaft in fact, I can see that there are more wear points on the R1100 .

So what do you think is it a concern or just normal wear and tear that is unlikely to cause a breakdown?

Regards

David

 

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Can I suggest folk measure at the wheel rim. This is then constant and repeatable unlike the outside of the tyre which varies considerably.

Also note that the 1100 has a 18" wheel and the 1150 has 17".

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Clive Liddell

Hi Reece and Andy,

 

Yes Reece, I just sort of eyeballed past the ruler to the selected tread sipe :>) I think yours and my figures while different are in a similar ballpark also given the differing milages.

 

Andy, agreed about the diameter of the wheel and/or tyre but I think we are probably within a quarter inch anyway...

 

BTW I had to dig out my old inch tape measure for this little project. Sales of imperial measuring equipment has been banned in South Africa for the last 60 years :>)

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Banned!!! That seems extreme. :P

It's all metric here in SA but like you I still have some old imperial measures, The Americans are holding fast to old ways.

I must admit, I do miss mph, was always a challenge to 'crack the ton'. :grin:

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Morning Gothicman

 

3" of backlash at the rear tire is no big deal on an oilhead.

 

BUT it DEPENDS --on how much lash is where-- If ALL the backlash is in the drive shaft then you have big problems. On the other hand, if, you have a little lash in the clutch splines, a little lash in the transmission shaft gears, a little lash in the input shaft dampener, & a little lash in the drive shaft splines, & a little lash in the final drive gears -- that could easily add up to a normal 3" of lash with nothing being out of spec.

 

Your big worry here is probably clutch disk to input shaft spilne wear & drive shaft U joint wear. Fortunately the 1100 doesn't have a big issue in this area but there have been cases of spline failure & cases of U joint failures on a well used 1100RT.

 

If you want to get some idea of clutch/input spline wear you can remove the starter then use a pointed scribe or even a sharpened coat hanger wire & see how much clutch disk movement you have on the trans input splines (with clutch lever zip tied to the handlebars move the OD of the clutch disk without moving the trans input shaft)-- not exact as the clutch disk drops down on the splines but will give you an idea of spline wear.

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  • 2 months later...

So sorry for the long winded reply, but I had an accident 2 months ago (not on the bike, more a home decorations fall of a ladder kind of accident) which resulted in broken ribs and leg, which prevented me from getting up the stairs to the computer.

I am planning a return to the saddle next week and will try taking the starter out to have a look at the free play in the clutch splines.

concensus of opinion is that the backlash is nothing to worry overduely over, fingers crossed and hope I get some riding in before the bad weather turns bad for the winter here in England.

Thanks

All

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