Premature flexible coupling failure

Woe unto you that bought the first model year of a major remake, perhaps this section can help address any 2014 and later model Ural "imperfections". Here's a special section for folks with the latest rigs to discuss 2014 and later model-related topics such fuel injection, 3-wheel disc brakes, hydraulic steering dampers, spin-on oil filters and other anomalies that don't belong on true Russsian motorcycle ;-P We've gone from using big hammers and greasy wrenches to needing computers and Ouija boards in order to fix our rigs.
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Please keep this section specific to issues pertaining to 2014 and later models such as fuel injection, sidecar and rear disc brakes and so forth. Ask general or non-2014 and later specific questions in the main Hammerin' & Wrenchin' section.
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JayF
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Premature flexible coupling failure

Post by JayF » Sat Dec 02, 2023 2:31 pm

I'm doing the never ending 10,000 km (6500+ mi) service on my 2021 Gear-Up. After greasing all splines a reassembly, I had only just the rear brake pads left to install. The bike is on the center stand and I spun the rear tire by hand just to see if everything looked ok. I heard a "squeak, squeak" as the tire rotated. I scratched my head a minute and of course worked my way from the final drive to the gearbox. What I found was surprising (at least to me).

The rubber flex coupling was shot. The holes attached to the engine side seemed okay, the the ones that went to the driveshaft were oval and the rubber was tearing. I know that these are basically wear items, but I figured I'd get a lot more miles than that! I drive this thing like a baby. I'm not hard on the throttle and it is a commuter. I bought it with about 1,400 mi. (and 1 year old) so I basically had it since new.

Is this expected? Are these thing just a mixed bag and I got a junk one?

Lastly, the thing eats rear brake pads too. They wear out a set for each pusher (k37) tire change at about 3,000 miles. Should I be expecting to change the coupler every other tire change? It wasn't a difficult job, just not sure if that's normal.

Is there something else that could be causing this to fail prematurely? Thanks.
IMG_20231202_132505371.jpg
IMG_20231202_132433566.jpg
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Squeezed between OH and PA (northern panhandle of WV).
Current Rides: 2021 Gear-Up Sahara, 2006 Honda Goldwing audio/comfort w/ escapade trailer
Past Rides: 1996 Kawasaki (EN500) Vulcan, 1990 Yamaha Radian (YX600), 1980 Kawasaki 550 LTD.

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aduthie
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Re: Premature flexible coupling failure

Post by aduthie » Sat Dec 02, 2023 2:49 pm

Rear brake pads: replace with semi-metallic and they last much longer. (EBC FA473V)

Flexible coupler: I'm pretty sure they tear more often when they lack sufficient clearance between the two yokes. When you install the new coupler, make sure there is some clearance between the yokes and the rubber. Old spec was 0 to 4mm, but it's hard to confirm 0mm. New spec is 1-5mm. If there's no clearance, you adjust the position of that circlip on the driveshaft (item 8 ). Jon Heindl made a good video on the subject: https://www.youtube.com/watch?v=IGgP1xb2jQo

34326.jpg
Here's the factory process with mild edits to improve the translation:
Gap between cardan shaft and flexible joint is measured as follows:

1) Push cardan shaft and flexible joint in opposite directions by lifting bar. (Pry the coupler forward as far as possible using a tool such as a tire iron.)

2) Measure the gap with 1 mm and 5 mm feeler gauges

3) If gap is less than 1 mm (1 mm gauge doesn’t fit), stopper ring should be moved into next groove forward along the motorcycle drive. If gap is more than 5 mm (5 mm gauge fits with a gap), stopper ring should be moved into next groove backwards along the motorcycle drive.
Pretty sure almost no one has a 5mm feeler gauge, but it's easy enough to use a ruler or mark a piece of metal you've got lying around.
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Re: Premature flexible coupling failure

Post by AndyH » Sat Dec 02, 2023 3:06 pm

Or too much gap?
Thought mine was too tight, moved the circlip (stopper ring) one notch and my flexible coupling looked very similar to your photo in very little time.
Readjusted and a squirt of silicon lube every now and then has seen the coupling last 10,000 since service with no appreciable wear.
2015 Ural EU Tourist -

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Re: Premature flexible coupling failure

Post by Lokiboy » Sat Dec 02, 2023 3:31 pm

10,000 kms seems a bit premature. I can usually manage 30,000 kms between replacements.

Oh well, if nothing else you get to practice.

On replacing, grease the studs and use a channel lock wrench to pull the donut over them.

As for the gaps. I don’t bother measuring. After a few KMs they are going to do what they do. Sometimes there’s a slight gap and sometimes they’re pressed right up against the yoke. Just use silicone spray on the studs around every 5000 km to keep them from drying out.

Have fun.
2011 Gear Up - "Erika"
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Re: Premature flexible coupling failure

Post by aduthie » Sat Dec 02, 2023 6:05 pm

I definitely agree on silicone spray or silicone grease as a lubricant. I avoid non-silicone/regular grease.
Andrew Duthie / Nashville Motorcycle Repair / Ural and Vintage Sales & Repair

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Re: Premature flexible coupling failure

Post by Desantnik-VDV » Sat Dec 02, 2023 8:16 pm

JayF wrote:
Sat Dec 02, 2023 2:31 pm
The holes attached to the engine side seemed okay, the the ones that went to the driveshaft were oval and the rubber was tearing.

I believe oval holes can be indication of too much of back and forth free-play. Maybe the shaft was not synched, thus banging and stretching the rubber.
And if you look inside holes, you can see warn edge pattern where forks edges were sitting. You can measure the distance from the edge.

To my eyes your driveshaft side fork was probably sitting too far away, i.e. larger gap between two forks.
Alex
2007 GearUp - '007's БМД
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The rest is just history... 4 previous Urals with telescopic front ends, BMW airheads, bigger Hondas, bigger sidecars...

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Re: Premature flexible coupling failure

Post by treebone » Sat Dec 02, 2023 8:56 pm

I polished the forks to smooth some of the rough tooling marks. Seems to me they would act like a file on the rubber donut over time. Regular shots of spray silicone on the rubber and the donut looks very good at 13,000 miles.
If your rear brake pads are shot at 3000 miles, something is not right. Check to make sure your boot is not riding the brake pedal first, then check that the parking brake is not dragging.
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Re: Premature flexible coupling failure

Post by Draeger » Sat Dec 02, 2023 10:19 pm

So I have been told by a couple Ural folks that I should not downshift under power, because this stresses the donut. Instead, to just brake when slowing down and downshift after stopped or at very low speed. Is there anything to that? Thinking about my 2021 GU...
Nanaimo, Vancouver Island
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Re: Premature flexible coupling failure

Post by VWK75S » Sun Dec 03, 2023 6:56 am

aduthie wrote:
Sat Dec 02, 2023 6:05 pm
I definitely agree on silicone spray or silicone grease as a lubricant. I avoid non-silicone/regular grease.
Run my donut dry only on 3rd one on the GU.
John
The Ural's made Maine a much bigger state.

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2007 Retro 25,000kms
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Re: Premature flexible coupling failure

Post by stagewex » Sun Dec 03, 2023 12:57 pm

I've changed my donut once in close to 18 years. And that was only because I was changing the little u-joint so figured I'd perform some preventive maint.
It was not terrible so it sits as a spare in my trunk. It's not like you can pick one of these up at CycleGear. Get/keep a spare. The replacement apparently was from another IMZ supplier so it was ever-so-slightly smaller in size with a side-by-side comparison.

There had in fact been a bad batch or two of donuts that were eating themselves very quickly after owner installation. The OP has a reasonably new rig with not many miles so factory or dealer set-up perhaps not top-knotch? I can say at least for 2WD models as close to precise Phasing is really important and you might be surprised how bad yours may be if you check. The donut is taking the brunt of everything working perfectly or not perfectly together. I have never used any kind of lubricant of silicone spray at all but if it makes you feel good definitely do it. I suppose it ain't gonna hurt. But you also should not have to change the way you downshift under power or other way to give the donut a break. It is a service life item that is supposed to absorb a lot of pressure and vibration and torque. If it is not then something is not set-up correctly or you have a dud.
I did this swap from the OEM to the new donut in 2017 so my rig had 10 years on it at that point. Having only done this once I'm no expert of course. Just my opinion on service life or lack of from what I've read here based on other SS members.

IMG_0678.jpg
I'm going to say 12,000KM's. But sometimes those have been tough (off-road) KM's. You should not have to ride these machines daintily.

IMG_0679.jpg
That much of a difference between the OEM and new replacement left me either way too tight or kinda too loose restoring the cir-clip to it's original position.

jointPhasing.jpg
Figured I'd just throw this in as owners should check. Doesn't matter if you have an old dog like me or something new and pretty from the factory/dealership. I'm setting the "sag" (rear suspension) on a brand new Kawasaki KLX300 today. Embarrassingly off-kilter from the factory.
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Stagewex

2023 Kawasaki KLX300
1981 Suzuki GS850G
2008 Vespa 150S
2007 Ural Patrol
1991 Honda XR250L

2019 Honda CRF450L GONE
1995 BMW K75 GONE
1969 BMW r60/2US Model GONE
2006 Yamaha TW200 GONE
1986 Yamaha BW200ES GONE
2005 Honda Big Ruckus 250 GONE
1999 Harley Heritage Softail GONE
1996 BMW r1100rt GONE
2005 Kawasaki KLR650 GONE
1966 Honda CA95 Benly 150 GONE
1983 Honda 750 Intercepter GONE
1984 BMW r80 GONE
1974 Kawasaki Z1 900 GONE
1974 Honda CL450 GONE
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Re: Premature flexible coupling failure

Post by Desantnik-VDV » Sun Dec 03, 2023 4:55 pm

Better words from you, stagewex. :cheers:

I said synched in my post above, and I failed to use the correct term phased.
Alex
2007 GearUp - '007's БМД
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The rest is just history... 4 previous Urals with telescopic front ends, BMW airheads, bigger Hondas, bigger sidecars...

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Re: Premature flexible coupling failure

Post by phughes » Mon Dec 04, 2023 7:05 pm

I will just add that you may not be able to get the prongs on the gearbox end to line up exactly with the forks of the u-joints, but you can get them close.

I reached my donut at 19,000km on this speedometer, and it's still good 17,000km later at 36,000km. No noticeable wear. I used silicone grease on it when I installed it, and applied more when I had the gearbox out easier this year.
Phil

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2014 Gear Up
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Re: Premature flexible coupling failure

Post by Claus » Tue Dec 05, 2023 3:51 am

I experienced a much longer donut life with silicone grease as well. I personally use silicone oil that I spray into the coupling every now and then.
The donut on my 650 rig lasted around 60k km.But it´s also about the engine´s power (a 650 is far from what a newish 750 can supply) and about the donut´s quality. There have been poor batches through all years. Mounting with correct phasing and keeping a small gap between donut and forks is, too, prolonging the donut´s life.
But silicone grease in my opinion is no mistake at all. The donuts in my customership that were mounted and maintaines with silicone grease lasted longer than dry ones. Even if they were only cheap Dnepr knockoffs from China.(the worst quality)
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Re: Premature flexible coupling failure

Post by renovate7 » Tue Dec 05, 2023 7:56 am

Thanks for the picture of correct phasing. Printed and put in file.
2005 Ural Tourist

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Re: Premature flexible coupling failure

Post by stagewex » Tue Dec 05, 2023 9:43 am

Your welcome.
Here's a few pictures of one of the theatre lift systems I performed maintenance on every-other-year before my current desk job.
Pretty much the same exact formula for making sure all the drive u-joints were in "phase". After factory install by trained technicians we did find a few out of phase and corrected.

In the first picture the drives are identified by John Deere Yellow. The Red pipes are fire suppression. This is one of three (3) independent stage lifts in this particular theatre. Could only work on one stage lift at a time. This is the "Gala System" out of Canada.

Much more sophisticated than the old hydraulic systems in the older venues. Though the stage lift system at Radio City Music Hall is still working fine since the 1930's. Little known fact, the original elevators on Aircraft carriers were based on the theatrical RCMH lift system. The Navy studied it just before WW2 and then duplicated. With of course many more modifications:
IMG_0718.jpg

Chain driven:
IMG_0739.jpg

Miles (not really but a lot) of U-Joints. Pretty much the same science as our Urals or BMW's or any "shaftie" motorcycle:
IMG_0738.jpg
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Stagewex

2023 Kawasaki KLX300
1981 Suzuki GS850G
2008 Vespa 150S
2007 Ural Patrol
1991 Honda XR250L

2019 Honda CRF450L GONE
1995 BMW K75 GONE
1969 BMW r60/2US Model GONE
2006 Yamaha TW200 GONE
1986 Yamaha BW200ES GONE
2005 Honda Big Ruckus 250 GONE
1999 Harley Heritage Softail GONE
1996 BMW r1100rt GONE
2005 Kawasaki KLR650 GONE
1966 Honda CA95 Benly 150 GONE
1983 Honda 750 Intercepter GONE
1984 BMW r80 GONE
1974 Kawasaki Z1 900 GONE
1974 Honda CL450 GONE
1966 Riverside 125 (Benelli) GONE

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