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Sram i-Motion 3 coaster brake failure, any fix?

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Sram i-Motion 3 coaster brake failure, any fix?

Old 03-22-20, 04:30 PM
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Sram i-Motion 3 coaster brake failure, any fix?

I'm trying to service a Sram i-Motion 3 IGH with a coaster brake which doesn't work correctly. You basically have to spin the cranks backwards a few times until the brake engages. The only thing I've found on the matter is a recall of this hub fitted on some bikes made by Sram last year in certain markets due to brake failure*. The bike I'm dealing with is a different brand and is in Europe where there has been no recall as far as I can tell; it had been stored in a garage for a while during which time it was not used. Earlier this year it turned out that the coaster brake fails and poses real safety threat. It worked OK before the 'break' in the garage.


I also found this on the matter:
According to the company, some of the affected hubs may have been manufactured with grease that gets sticky over time, especially if the bike sits unused for a while or is stored in a hot area. When the grease becomes sticky, the brake pawls in the hub can fail to engage.
https://www.bicycling.com/news/a26521411/sram-recall-internal-gear-hubs/

I took the hub out of the shell, but the brake segments don't seem to be worn out. Here's a short video and some pictures showing the condition of the hub and brake:
https://streamable.com/jf1a0





Could this have something to do with the spring I marked.in the picture above or is this the grease as described in the quoted article?
How can I possibly fix the brake?


*more on that here:
https://www.cpsc.gov/Recalls/2019/sram-recalls-bicycle-gear-hubs-due-to-crash-and-injury-hazards

Last edited by Thomas1; 03-28-20 at 03:29 AM. Reason: video link fixed
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Old 03-23-20, 05:52 AM
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There are two possibilities I can think of. One is the internal pawls that rotate the brake actuation cam that pushes out on the rollers. You can test that by rotating the driver backwards and checking to see if the cam rotates and pushes the rollers out. The other is where the notches in the shoes engage the actuation arm plate.
See page 36 and 37 of this document for correct shoe installation.
https://cdn.sram.com/sites/default/f...glish-reva.pdf
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Old 03-27-20, 04:05 PM
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Thanks for your answer. In the meantime I tried and gave the hub an overnight dip in ATF. I put it all back together and tested it on the bike with the wheels upsidedown. The coaster brake engaged each time I tested it, so the original failure got fixed. It seems that the manufacturer's grease might have had something to do with it. However, new problems emerged: 1) I noticed that the thread on the drive-side axle nut was broken and spent half an hour loking for and checking various replacement nuts just to see that none of them fit. The Sram i-motion 3 axle nut is non-standard*, so I wasn't able to secure the wheel on both sides of the rear fork to test it (only tightened the drive side nut which I took from the othe side plus secured the coaster brake arm to the chain stay and connected the shifter). 2) two out of the three gears don't work, if I remember aright, the 1st and 2nd ones.The 3rd one works well. If I shift into 1st or 2nd gear the cranks and the sprocket on the rear wheel will spin, but the wheel won't move (it doesn't seem blocked either). Any idea why this happens and how can it be possibly fixed? Could anything of what I described above have influenced the hub operation?



*acccording to what I dug up on the Internet it's an M10.5 nut. I also noticed that Sram doesn't make it any easier for users of its i-motion 3 IGH: it's really difficult to find (some) spares for this hub. The chances you're going to find a nut in your home shop to be used as an improvised replacement are slim. I couldn't find this size even at the well-supplied hardware shops. Some LBSs have it, but it I need to wait for it. I also tried to find the non-drive side bearing retainer. First, Sram changed its design, which isn't provided for in the manual that shows a bearing retainer with, I think 3 or 4, recesses, while mine doesn't have them. Second, finding one borders on the miraculous. The guy at the LBS that runs spares for most of the IGHs available on the Polish market says their suppliers in the Netherlands and Germany ran out of their stock a while ago and the manufacturer stopped making them...

4 April 2020 update:
The problem of the gears solved. I inspected the assembly and compared it against the pictures I took before disassemblying the hub. While the hub was in ATF bath, one of the pawls in the planetray gear carrier fell off it on to the bottom of the container with ATF (at first I thought it was a spot of grime that had leaked out of the hub while it was dipped in ATF). I think it was probably caused by the spring securing the pawls, as it was partly below its normal position -- it can't have been securing the 'lost' pawl otherwise the pawl wouldn't have fallen off.
The question of the Sram i-motion 3 axlenut was a bit complex too, as there seems to be some confusion regarding its size. Even my LBS had the wrong size on its website. I took the wheel to the shop just to make sure the nut would fit, but when we tried threading the axlenut they listed as a replacement compatilbe with the Sram i-motion 3 axle it turned out the size was wrong. We tried on some other axlenuts they stock until one of them fitted (I can't remember its size, but it wasn't the M10.5).
Finally, I put the hub together, installed the wheel in the bike frame, and tested it in the backyard. The gears on the hub work correctly; the coaster brake is functional again. The only quibble I have now is that the brake squeaks when applied with some force. Other than that it seems OK.

Last edited by Thomas1; 04-04-20 at 05:06 AM. Reason: clarification
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Old 05-12-20, 09:40 PM
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Hi Thomas, I just acquired a BYK-450 3i for my daughter which uses the SRAM i-3 hub. It's displaying a similar problem, erratic action from the coaster brake, often requiring multiple pedal turns to engage, and can only click through 2 of the 3 gears. It was my niece's old bike and I think it too has been sitting idle in a basement for some time.
I'm planning to remove the hub and give it a clean and re-do the grease and oil. I've never worked on one of these internal hubs before - can you give any advice on disassembly and reassembly?
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Old 06-10-20, 08:40 AM
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Recalled!

SRAM I-Motion 3 hubs, with coaster brakes have been recalled by SRAM. They will pay you the "bluebook" value of the bike to take the bike to a shop, have the hub replaced with a different product, and send the hub back to them.

I just spoke to SRAM a couple of days ago and I'm going to start the process. I'm hoping to find another option for an internal geared hub to work on my Masi Soulville 3. Any ideas about a different internal geared hub that would work as a replacement for the SRAM i-Motion 3?
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Old 06-10-20, 07:15 PM
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Originally Posted by Really_bigair
SRAM I-Motion 3 hubs, with coaster brakes have been recalled by SRAM. They will pay you the "bluebook" value of the bike to take the bike to a shop, have the hub replaced with a different product, and send the hub back to them.

I just spoke to SRAM a couple of days ago and I'm going to start the process. I'm hoping to find another option for an internal geared hub to work on my Masi Soulville 3. Any ideas about a different internal geared hub that would work as a replacement for the SRAM i-Motion 3?
You have two choices, either of which would be fine. A Sturmey Archer S-RC3 or a Shimano Nexus 3 speed with coaster brake.
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Old 06-10-20, 07:20 PM
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Dan, Thanks for the response. Any idea if a Strumey Archer 3 speed IGH will work with my existing SRAM I-Motion Indexed 3-Speed Shifter? Would prefer to not replace the shifter due to the need to destroy a pair of expensive varnished Rivendell cork grips in order to change to a different shifter.
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Old 06-10-20, 08:37 PM
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Originally Posted by Really_bigair
Dan, Thanks for the response. Any idea if a Strumey Archer 3 speed IGH will work with my existing SRAM I-Motion Indexed 3-Speed Shifter? Would prefer to not replace the shifter due to the need to destroy a pair of expensive varnished Rivendell cork grips in order to change to a different shifter.
I don't know for certain if the shifters are compatible, but the most likely answer is that they are not.
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Old 04-30-23, 11:43 AM
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Some details

[QUOTE=Thomas1;21386823]Thanks for your answer. In the meantime I tried and gave the hub an overnight dip in ATF. I put it all back together and tested it on the bike with the wheels upsidedown. The coaster brake engaged each time I tested it, so the original failure got fixed. It seems that the manufacturer's grease might have had something to do with it. However, new problems emerged: 1) I noticed that the thread on the drive-side axle nut was broken and spent half an hour loking for and checking various replacement nuts just to see that none of them fit. The Sram i-motion 3 axle nut is non-standard*, so I wasn't able to secure the wheel on both sides of the rear fork to test it (only tightened the drive side nut which I took from the othe side plus secured the coaster brake arm to the chain stay and connected the shifter). 2) two out of the three gears don't work, if I remember aright, the 1st and 2nd ones.The 3rd one works well. If I shift into 1st or 2nd gear the cranks and the sprocket on the rear wheel will spin, but the wheel won't move (it doesn't seem blocked either). Any idea why this happens and how can it be possibly fixed? Could anything of what I described above have influenced the hub operation?

Thanks for your post as I have realised the same problem on a bik we have been give for our daughter. What exactly did you use for the bath? ATF? Did you afterwards use additional greases for bearings and gears. I noticed SRAM recommend only to use their own special grease.

BR
Henrik
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Old 04-30-23, 12:04 PM
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Originally Posted by henrikw
Thanks for your post as I have realised the same problem on a bik we have been give for our daughter. What exactly did you use for the bath? ATF? Did you afterwards use additional greases for bearings and gears. I noticed SRAM recommend only to use their own special grease.

BR
Henrik
Hey Henrik, this thread is about 3 years old so the OP may not be around or may not notice there is a new post. If you join the current active threads which there are plenty and get 10 posts you can private message them and they are more likely to see it, if still around, which looking at their low post count and join date is less likely.
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