I did the Exmoor Explorer ride on Sunday and about 12 miles in my non drive crank came loose. I had lost the crank arm fixing bolt which from memory is only done up finger tight anyway. The little plastic locking tab in the crank seems to have been damaged and I guess this is why the bolt was able to work loose.

Does anybody know where I can get a new locking tab from. I can find the bolt but not the locking tab. They are pretty much new Deore Cranks.

I obviously don’t want this to happen again as the next 13 miles pedalling very gingerly and not being able to stand on the pedal on the decents was a pain. Should I have thread locked the fixing bolt in place.

If both the 5mm blots were still in the cranks wont fall off. The plastic end cap is just a preload bolt to make sure the cranks are in the correct position before doing up the 5mm bolts.

You can buy the little tabs online, can’t remember name of shop tho…maybe something to do with “pedals”

Anyway – as mjsmke said above, the crank isn’t held on by the plastic tab or the plastic preload bolt thingy – there are two 5mm bolts holding it on….if they’re not there then you’re lucky to still be in 1 piece. Go back to the shop and kick up a fuss!

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My crank continuously worked loose when the preload thingy broke, even with 2 pinch bolts in place. So I’d say get a new one (I ended up with an alloy one probably off ebay

My understanding was wrong as I think a couple of others are that the end cap is just a dirt stopper come pre load device. The nice mechanics at the event all agreed that the splines are slightly tapered so without the crank arm fixing bolt the 2 x 5mm allen key bolts can’t hold the crank on. I did make it the end of the event just using the 5mm bolts but if you put even a small amount of lateral force onto the pedal the crank starts to move off.

I don’t live near a good bike shop so was hoping to order a new locking tab online but I still can’t find a name or part number that gives a search result, the closest I have come is a stopper plate.

Is this it: plate thingy

Well, that’s the one I got for my XT760 cranks. don’t know if the vary?

durfesneorama obviously no picture but it definetely sounds right and at that price will be worth a punt thanks.

The locking tab is not there to hold the crank in place. Its merely an indicator to show the crank arm is located on the axle sufficiently.
The two pinch bolts should be more than adequite foe holding the crank arm in place.
I run my XT & LX HT2 cranks without the tab, you should also be able to use them without the preload cap once the bolts are tightened up (in the same way as your stem cap can be removed once your stem is tightened up)

Bigyinn is correct. Any movement of the arm when the bolts are done up is usually an indication of spline damage. If the end cap was meant to be there to hold the arm on it wouldn’t be made of plastic.

You can buy metal end caps from crc.

No need for a metal cap, its no more load bearing than your stem cap. (when the aheadset was originally launched it came with a plastic cap) All it does is pull everything together and pre-loads the bearings. No massive torque on the bolt / cap required.

If that end cap was designed to hold the crank on it wouldn’t be made of plastic and would need to be done up much tighter than (recommended by shimano) just finger tight.

May not be designed to hold the crank on but without the flower cap the crank can and will come loose. happened a couple of times to different people that I know, never to anyone with one fitted.

The wee flat plastic idiot tab thing can hold the crank on for a little while- possibly long enough to mangle the splines. I’d sooner it just fell off.

well my plastic one:

a) broke
b) when it broke the crank kept on falling off

so I’d say:

a) it does have a function in hlding the crank on – rightly or wrongly
b) it shouldn’t be plastic in the first place

I doubt the crank fell off becuase the cap broke, it is more likely the cap broke because the arm was loose and pushed against it. Once the arm has come loose it is likely the spline in the arm is damaged and then it will keep coming loose.

Charliemort- did you replace it, and once replaced did it fix the problem?

[/url] link to pdf with parts…

The cap/bolt jobby does adjust bearing preload but also compresses when the actual NDS crank arm fixing bolts are fully torqued – try to remove the plastic bolt when the cranks are fully done up and it won’t (shouldn’t) budge. It’s made of plastic so it has these characteristics.

Thanks for the advice, I have ordered a new plastic bolt and locking tab will clean it all up and assemble correctly and will have to see if it will stay put or if I have just wrecked a 3 week old crank set. LH crank arms are pretty much the same price as a full Deore crank set so guess I might as well bight the bullet and get the whole lot if it does turn out I have damaged the splines.

FWIW I’m pretty sure my Saint cranks have a metal one.

Its not a locking tab. It will not hold the arm in place. Its only there as an indicator, nothing more. Sorry to be pedantic

XTR and Saint have metal ones but would you be happy with a plastic cap on an expensive crank?

Northwind – yup replaced it with an alloy one and no problems since. I have changed the bolts as well but not sure if that was at the same time

Mister P – think you may be right that the bolts loosened causing the cap to break, but as above no problem since replacing the cap

That’s interesting, cheers

My plastic end cap broke and off fell the arm. Now the splines may or may not be damaged, however I managed to ride it home by pushing back on and doing up tight. Replaced with a metal end cap as price is similar and its less likely to break (and is anodised blue :D). Used a torque wrench to fit so not on too tight. This was months ago and its all still tight which suggests to me that the splines are fine (hence did not cause it to come loose in the first place)!