Spokes loosening after rebuild (Shimano C24 W7950)

[freeflow]

A few months ago I replaced the hub in a shimano C24 W8950 rear wheel. The process was straightforward if a little long winded. Recently I've noticed creaking from the back wheel and on checking have found that all of the spokes have lost tension. When I rebuilt the wheel I checked tension with a park tools tension meter and the rebuild was in the same tension as the original wheel. This hasn't happened on other normal wheels that I've rebuilt. I'm a heavy rider (105 ish kg). Before I retension does anyone know if I need a threadlock on this wheel. Looking at the ends of some of the broken spokes there does appear to be some kind of coating on the threads. Prior to the rebuild I had no issues what so ever with spoke tension.

Advice gratefully welcomed.

[Brucey]

I think you need threadlock

cheers

[interestedcp]

Don't really know the model (did you mean W7950?). But try to find the Shimano manual online. Somewhere in it is the recommended spoke tension. For the W7950 model the max tension is 1400 Newtons (roughly 140 kgf) on the sprocket side. You should probably aim for a high spoke tension with so few spokes.

Be careful about twisting spokes when rebuilding the wheel, since it will reduce spoke tension when they unwind when the wheel is used.

I don't use thread locker myself, so no personal experience, but be careful if using a strong wicking thread locker like Loctite 290 together with alu nipples, since it allegedly is so strong that the force required to loosen the nipple afterwards may break the alu nipple. OTOH, it doesn't work very well if there is any residue oil on the threads. (probably a lot of thread lockers require the threads to be clean).
Too strong thread lockers may also make spoke twist a real problem with round spokes (bladed spokes can be fixated).

If the spokes accept standard nipples, then "DT Swiss Pro lock" nipples could be an option.

[Valbrona]

It is just that you riding it has stressed it. Normally the stressing is done by a machine.

[freeflow]

Tweaked the wheel tonight. The numbers I have from when I rebuilt the wheel (from Patk Tools Tensiometer) were average of 19.5 on drive side and 14.5 on non drive side. When I checked tonight the drive side wasn't too bad but the non drive side were all 10 or below with two spokes seriously untensioned (2.5 and 1!!). So no surprise as to why I was getting creaking noises from the back wheel.

I'll check again after tomorrows 100k ride to see how quickly spokes are unwinding.

And yes, the wheel is a 7950. My bad. Edited title to correct

[Brucey]

if you put some paint marks on the nipples you can see if they are backing off or not. I suspect that they are indeed backing off for the spokes to slacken dramatically as you have observed; I've seen it many times.

cheers

[Gearoidmuar]

105kg is heavy for e.g. racing wheels. I was 100kg for years and had constant wheel trouble. Since I got down to 82kg it seems to have disappeared.

I've built a lot of wheels in my time and a really stiff rim with a deep v-secion rim helps a lot. So does more spokes, getting them tight and even tensioned and finally stress relieving them by your heel pressure or some other technique prevents them fatigueing.
If they continually loosen, they're either not tight enough, or possibly sometimes, the rim isn't stiff enough for the weight of the rider/luggage.

[goatwarden]

Be careful about twisting spokes when rebuilding the wheel, since it will reduce spoke tension when they unwind when the wheel is used.

That depends entirely upon howthey "unwind" and what state the spoke and nipple threads were in.
It is unusual tto generate more than 90 degrees of wind-up on an individual spoke; more than this suggests stiff (damaged) threads or lack of care when tightening.
If there is any wind left locked into the built wheel, it will usually unwind via the nipple turning relative to the rim but staying in the same place on the spoke thread (this causes the pinging sometimes heard on new wheels when first ridden). Unwinding by even half a turn, without the nipple moving relative to the spoke, is unlikely to make a perceptible difference to the spoke tension or the trueness of the wheel.

[TonyR]

No you don't need threadlock and it should be banished from wheel building. What you need is more tension. What is happening is the spokes at the bottom of the wheel are loosing tension completely with your weight pushing the rim and hub together and that loss of tension allows the nipples to loosen off. Put more tension on and that won't happen. The heavier you are the more tension you need. You probably got away with it on the old wheel because the nipples had corroded onto the spokes or the threads had got gunged up with road muck

[Brucey]

No you don't need threadlock and it should be banished from wheel building....you need... more tension...

You couldn't be more wrong.

This is a heavily dished 20 spoke wheel. In order not to go slack the spokes would have to be half as tight again or twice as tight as per (say) a 30 spoke or 40 spoke wheel respectively. You just don't have that leeway with spokes, or rims come to that!

Most minimally spoked wheelsets come with threadlock on the nipples, and without it the most modest weight/strength riders can cause the nipples to unscrew; NDS first and the others later.

You can very easily work out what kind of lateral forces are likely to cause the NDS spokes to go slack and these forces are not that high; a strong rider can easily generate them. A heavy rider needs less lateral force to give the same effect.

If you use the right kind of threadlock it contains microspheres of adhesive which;

a) allows the threadlock to be applied weeks months or years before use (that is what comes on BB units etc) and

b) may allow some bond strength even if the locked parts are repositioned later; not all the microspheres break at once.

I have built many wheels with well lubricated nipples before now and (when using the best lubricants that provide long term assurance against seizure) to date I have not built a lightweight dished rear wheel where the NDS nipples definitely wouldn't unscrew in normal use with a strong rider. Most dished rear wheels need some friction between the nipple and spoke to avoid slackening, and the fewer spokes/more dish you have, the more friction you need.

cheers

[MikeF]

... Most dished rear wheels need some friction between the nipple and spoke to avoid slackening, and the fewer spokes/more dish you have, the more friction you need.

cheers

Do they? Is locking compound used on machine made wheels? I periodically give my spokes a tap to see if they are still "in tune".

[freeflow]

After yesterday's ride it looks like thread lock is required.

For info the spokes on these rear wheels are balded and straight (no elbow). You get two little spanners with the wheelset. One end has a slot to hold the bladed spoke the other end for the nipple. Hence no windup when tensioning.

What threadlock would knowledgeable folks recommend.

Also, is it a simple application (apply to tensioned nipples and it wicks in) or is it a remove nipple, clean thread apply threadlock etc.

[Brucey]

... Most dished rear wheels need some friction between the nipple and spoke to avoid slackening, and the fewer spokes/more dish you have, the more friction you need.

cheers

Do they? Is locking compound used on machine made wheels?...

on ones with a conventional construction and not many spokes, usually, yes.

cheers

[Brucey]

What threadlock would knowledgeable folks recommend.

Also, is it a simple application (apply to tensioned nipples and it wicks in) or is it a remove nipple, clean thread apply threadlock etc.

I did some calculations recently which suggested that even with moderately strong threadlock you would not need more than 2Nm of torque to shift a typical threadlocked nipple with 10mm engagement. I don't think that is enough to ruin an alu nipple (provided you use a decent spoke key, like a, er, spokey) and it is nowhere near enough to shear a normal spoke.

Use the stuff as per the manufacturers recommendations if you need the full strength, but otherwise it is fair game to use it in any way you like. The worst that can happen is that you need to take the spokes out, clean and reassemble if the locking action isn't enough.

You can get thick pastes and thin grades that are meant to wick into tight spaces, as well as strong and weak grades. Two obvious choices are strong wicking grades (if you want to try without much cleaning/ reassembling) or modest strength paste material if you are starting clean and fully disassembled. The factory application is to use the latter.

cheers