Transmission Slip

Dogtrousers

Kilometre nibbler
Today, while riding up a steep (15% or more) hill, standing on the pedals. my transmission slipped resulting in a fall (no injuries, just bruising). When I remounted and continued up the hill it slipped again, but I was seated this time. I was in my bottom gear at the time and in neither incident did the chain come off. This wasn't the first time I've had slips in bottom gear, just the most dramatic.

Later in the ride, on a lesser hill, I put the bike into a moderately high hear and stood on the pedals. I managed to elicit a small slip.

Note also that this doesn't have anything to do with changing gear. I'd been in my bottom gear for a while when this happened, and the rear indexing seems fine. Just when there is a lot of stress on the system (like when I stand up on a steep hill).

This left me rather nervous in traffic: what if it happened when I accelerated onto a roundabout, for instance.

THe transmission is SRAM Apex 50/34 & 11-32. The kit is relatively new - the bike has done about 3,000 miles or maybe a bit more. The wheels are slightly older and have done maybe 800 miles more than that.

So what can it be?

Chain stretch? I measured the chain (while still on the bike, so not all that accurate) using a vernier caliper and got 6.107" for 6 link pairs, so less than 2% "stretch".

I'm not super fast or a racer so I doubt I'm putting all that much power through the system. On the other hand I'm a big lump (> 90kg) and do tend to ride up a lot of hills, which I guess will take its toll.

Stiff link? I've checked the chain and not found one. And anyway that would give me a "clonk" each time the sitff link went through the rear mech. Which doesn't happen.

I also fail to see how a chain could momentarily disengage then re-engage with a sprocket. If it had jumped off the gear altogether maybe. But it didn't. At least I don't think it did. I'm beginning to doubt my memory now.

Could it be the freehub perhaps? This is my favourite theory.

One other thing. It's always worth checking to see if it could be your own fault. I replaced the BB a while back. When I did this I think the chainrings ended up a smidge further out from the BB. I know this because the front mech can sometimes throw the chain off the inside when changing down if in a large sprocket at the back. I've been meaning to re-adjust it but as it's easy to get the chain back on without stopping I haven't bothered. I don't know why this could elicit these symptoms, but it's worth considering.

Any thoughts?

I'm thinking of asking my LBS to service the freehub (that's not a job I've ever done, as real bikes have freewheel blocks, not freehubs).

As I said in another thread I suspect that the underlying cause will turn out to be the fact that All Modern Bikes Are Rubbish, Not Like In My Day.
 
2% stretch is 1% more than I allow before swapping out the chain. Could be the chain and at a 2% stretch you may have to swap out the cassette too.

Check the cassette teeth for wear and 'sharking'.

Could also be the pawls, but usually when they fail, they fail for good and don't usually slip on and off.
 
OP
Dogtrousers

Dogtrousers

Kilometre nibbler
Thanks very much for the advice all.

Be aware that the chain measure was done by hand trying to line up a vernier with the chain rivets. I'll re do it to be sure.

Pictures are here, and don't look good. Esp the chainrings, which seem to be utterly buggered. To be honest I never scrutinised them before because, well, the bike is still pretty new.

(Sheesh. it's been carefully looked after, not used a huge amount, and already components are banjaxed. The BB died a short while ago)
 

Tom B

Über Member
Location
Lancashire
Worn cassette (and chain) cassettei have been using a bike with a 1% worn chain and a cassette that looked okayish. Same issues as you in 6-7-8 sprockets... Visual inspection of both was not too alarming.

New cassette and chain cured it in a trice.
 
OP
Dogtrousers

Dogtrousers

Kilometre nibbler
OK I've slept on this, and I've done a few more measurements and a bit more research in my records.

My initial measurement of chain stretch was not far off. I've taken several measurements and they all come in at between 1.3 and 1.9%
The bike has done a grand total of 3,914.8 km. That's about 2,400 miles. That's all.

I've come to the conclusion that I need to replace: The chain (deffo) the chainrings (very probably) the cassette (hell, why not while I'm about it).

I can't ride the bike in the meantime as I think it's dangerous in its present state (the bruise where my leg caught the end of the handlebar when I came off is coming up a treat; my right elbow is a bit bashed but working OK, and most importantly there is no hole in my treasured Aldi jersey).

So, further questions:
What do you think of my conclusions?
Any suggestions on a pair of 110mm bcd 34/50 compact chainrings? Obviously not from SRAM as theirs are clearly made of dairylea. I don't care about weight, they can be made of depleted uranium for all I care as long as they don't wear out so fast.

The pointy teeth on the chainrings are a total embarrassment. Mea culpa. I should have picked up on these earlier. In future it seems I need to check these weedy 10 speed chains for stretch about every mile or so. And carry a couple of spares.:cursing:

A more radical long term approach would be to use an 8 speed cassette, which would enable me to use an 8 speed chain. I would have to ditch the brifters obviously and rig some friction shifters on the downtube lugs where the barrel adjusters are. This would also give me a bike that's a bit more to my taste (I'm not sold on brifters). But first I need to replace those chainrings. I'm assuming that if I do choose to go 8 speed in the future then my new chainrings will be OK for this use.
 

raleighnut

Legendary Member
Location
On 3 Wheels
Thanks very much for the advice all.

Be aware that the chain measure was done by hand trying to line up a vernier with the chain rivets. I'll re do it to be sure.

Pictures are here, and don't look good. Esp the chainrings, which seem to be utterly buggered. To be honest I never scrutinised them before because, well, the bike is still pretty new.

(Sheesh. it's been carefully looked after, not used a huge amount, and already components are banjaxed. The BB died a short while ago)
That is well 'kippered'
 
By letting the chain get so worn, it has accelerated the wear on the other components, which is why they haven't lasted as long as they could do. If the chain is replaced once it gets to 0.5% stretched and no more than 0.75%, then you'll easily get a cassette lasting 3 chains worth, and even longer for the chain rings. Depending upon how well you clean the chain can also help prolong the life of the chain.

As chains are so cheap compared to the cassette and chainset, it makes sense to replace them sooner. I know some people have a complicated routine of rotating chains and alternating putting part worn chains back onto either part worn cassettes or new ones, but I can't be bothered to faff around like that, and just simply replace the chain once it gets too worn, and then at whatever point a new chain starts slipping at the back, then the cassette gets changed as well. I think my commuter bike, which is used in all conditions, had a new cassette fitted after at least 6,000 miles, and I've just replaced the chainset after 10,000 miles or so.

Although with reference to one of your other posts, if it was 8 speed, not 10, it would have lasted much longer!
 
OP
Dogtrousers

Dogtrousers

Kilometre nibbler
Cheers @Flying Dodo Checking and replacing the feeble 10sp chain more frequently is a big lesson learned.

I've just been down my LBS and agreed a batch of work on the bike. If I were to do it myself it would take me months (and I'd cock it up).

And I've put conversion to 8 speed on the bike's long term road map. It's not like I need all those gears. As long as I have the top one and the bottom one, and a few in between I'm happy.

I'm still gobsmacked that I've manged to completely fritz the transmission in a mere 2.5k miles. OK, so I ignored the accelerated chain wear, mea culpa, but I still gave the whole lot a good clean/relube after each ride.
 
Location
Loch side.
Chains should be replaced when elongated by 0.5%. If you let it "grow" to 1% you'll achieve one chain per cassette. Not an economical way to ride.
When you measure, don't mess around and guess. You have to have accuracy of better than what you're measuring and 0.5% doesn't give you much leeway. Don't use a vernier, the measuring distance is too small. Use a 13 inch ruler. Why 13 inch? Because you need to measure past 12 inches.
My guess is that your drivetrain was never/seldom cleaned. Don't expect great mileage when you neglect it that much.
 

Broadside

Guru
Location
Fleet, Hants
2500 does seem early to have done all that damage to the chainring. I tend to run the transmission in to the ground and then swap the chain, cassette and lage chain ring in one go, I've just done it on my bike after 7000 miles.

I wouldn't be too hastey going to the expense of swapping to an 8 speed system, I would replace what you need to now and try a KMC chain and see if that fairs better. It is the chain wearing prematurely that damages the other components. If you can find a less cheese like chain then the other bits will wear much better.
 
OP
Dogtrousers

Dogtrousers

Kilometre nibbler
Bike was given a thorough cleaning/relube after each & every ride, except when on tour.

The step that I forgot was the measuring of chain "stretch". All the same, stretched chain or not I think that's a rubbish performance. My suspicion is that I bought the wrong tool for the job in getting a bike with SRAM Apex. I'm guessing that it is maybe aimed more at racer types who want to go fast and they've compromised weight for cheesiness in the chainrings. Maybe it's the wrong thing for lugging 90kg of me repeatedly up Toy's Hill. Not that it really matters. I'm getting it sorted at the LBS. Staying 10sp for now.

The 8 speed swap I've put on the roadmap is only partly for longevity. It's also to enable reintroduction of friction shifters (I've tried friction shifting on a 10 sp cassette and it's too fiddly - 8 sp is fine). Maybe I'll do it, maybe not. That's for the future.
 
Last edited:

raleighnut

Legendary Member
Location
On 3 Wheels
Once you have got a chain that's at 0.5% stretch/wear replace it but do not bin it, keep it in a tub covered in oil. When you get to the point where a new chain will not ride on the cassette due to wear on the teeth guess what, that slightly worn chain will work fine and you may have 3 slightly worn chains that can be used to prolong replacing the cassette. There is no need for 'rotating' the chains as some have suggested just fit a slightly worn one and when it gets past 1% wear bin it and fit another 'part-worn' one until they are all gone then replace the cassette and chain and start again.
 
Top Bottom