almost lost rear wheel at 40+mph

[curious]

Coming from a local convenience store I had to beat the coming thunderstorm so I went full throttle almost entire ride back. At home I decided to check temperatures of various parts and doing so looked at the rear wheel / motor holding nut. That thing almost fell of the axle ! Checked the other side - was loose too. The only thing that was holding the axle is my weight and a torque arm on one side. Was pretty close to a disaster at 40mph (normally I ride much slower).

I think part of the problem is regen braking which reverses torque on the axle moving it back and forward within torque arm play. BTW I had a thin second nut to jam the main one and it did not help. I guess next thing to try is blue loctite. If that does not help - perhaps some kind of a slotted nut would be needed.

 

[Microbatman]

To try to keep this from happening again.

Take a sharpie and mark a line on each axle bolt so you know thier position.
I maked a line on mine a the 12:00 oclock position so all I have to do is look down and see the shapie mark.
No sharpie mark=trouble.

That way before every ride you can do a quick "pre flight/ride" kind of check to make sure nothing has moved.

Just look at the sharpie mark before the ride to make sure it has not moved.

Will this prevent it from moving during the ride? Obviously loctite would help better.
But this will help you spot/see a problem BEFORE getting on the bike than after.

 

[curious]

Good idea about sharpie marks. But I think I need something more drastic - regen causes too much torque rocking. I mounted my x5 removing outer plastic wire protection sleeve and adding a pair of tooth lock washers on both sides of the frame. This is not enough in regen setup. Perhaps I should remove outer tooth lock washer and replace it with a plain one to allow the the axle with the nuts move a fraction of a degree relative to the frame. I need to think it over some.

Anyway seeing completely loose nuts on both sides today got my imagination running wild

 

[BVH]

What about drilling the ends of the axle and inserting some small cotter pins or aircraft safety wire. Drilling beyond the drop outs point of contact would not compromise the structural integrity of the axle. Similar to how non front wheel car front wheel bearing adjustment nuts are kept in place.

 

[ausGeoff]

Good idea BVH...

Castellated nut and split pin will make sure the nut ain't going anywhere.

Cheers.

 

[Reid Welch]

I agree with the initial respondent. Plus use locktite, such as green, because it is so convenient.

Castle nuts: require cotter pins. Henry used castle nuts EVERYWHERE, practically. I near bled to death on innumerable occasions; the slightest scrape-up of hand against a bent-over cotter pin.

Spring lock washers (split washers are NO GOOD for critical stuff. If soft, they don't dig in and grip.
If fully hardened, then tempered, they may be brittle, split and FALL OUT of the joint.
Don't use split washers for critical assembly.
drilling and safety wire, or castle nuts and safety wire, or loctite products are Ace, rickenbackers.

 

[BVH]

If you don't like the drilled axle ends and castellated nuts, try the external type of lock washers - the ones with many, many bent tabs around an internal ring - instead of the traditional split ring type. There's tons more surface contact area to bite into the nut.

 

[John in CR]

My answer has been to modify steel dropouts to almost 1/2" thick on each side, with dropout sizing that requires a rubber mallet to fully seat the axle. This makes the nuts serve the same purpose as on a regular bicycle and only to stop the wheel from falling off. On the 2 bikes I've abused regularly at 40-50mph for almost 2000 miles I've yet to have a nut budge.

BTW, I do like the sharpie line idea for a quick pre-flight inspection, just for the added safety, but my attitude it that I've never checked the lug nuts on any car or motorcycle I've owned, so I demand the same reliability in that respect with my e-bikes.

John

 

[curious]

I do not use split washers, I've got some hard steel tooth lock washers from mcmaster. Used four total - on each side of the frame dropout. But now I think that outer pair are making things worse. They should be replaced with something slippery such that inevitable rocking motion of the axle does not affect nuts.

Unfortunately I do not have a drill press and welding tool to modify either axle or dropout as suggested. (If I ever buy my own house I'll definitely get a small mill and a welder).

Anyway I put regular washers on the outside, applied generous amount of blue locktite to the axle, tightened the nuts and put the sharpie marks. This will give me some time to think of a "toolless" solution.

 

[fechter]

I agree that the outer ones will probably not help. I got some Audi lug nuts from the auto supply store that have the right threads. Lug nuts are taller and have more threads, which will allow a higher torque without stripping the axle threads. If you can get the nuts tight enough, there won't be any movement. Install the lug nuts with the cone side facing out.

 

[curious]

I'll try lug nuts if it fails again. I am using stainless steel nuts (also from mcmaster) instead of softer galavanized nuts. I actually tried to find deep lug nuts in mcmaster but there are none for this thread. Nice to know that Audi nuts fit.

Conceptually though it would be better to let the flat axle sides counteract the rocking torque rather than rely on axial contact surface. I guess an ideal setup would have axle flats squeezed between two hardened steel pieces by high-tensile bolts. Could be part of the torque arm or part of the frame. Could also serve as brake caliper mount. Wish I had tools to make one...

 

[monster]

i had regen on an X5 and it caused those problems too. i tried some 3mm mild steel plate torque plates but it ate them amd the drop-outs. i came to the conclusion that hard regen (the kind you need for stopping) is too much stress for the frame. you would propably need 1" steel torque plates or something! i went down the disc brake route and haven't looked back.

i could see a limited power regen setup working tho

 

[curious]

Once I've tried proportional regen (using DIY analog brake level sensor) I got hooked . It has an amazing feel of a boosted brake with very smooth and powerful action. Don't want to go back.

I do not think it causes any major global frame stress (max regen current in my controller is 0.5 of peak forward current). It is more of a local rocking effect that eats hardware and loosens nuts. The proper design should squeeze the axle flat between two hard steel pieces such that twisting force is dissipated in elastic deformation of the axle/arm rather than hitting contact spots on every torque reversal. I have few ideas but all of them require access to a decent mill.

 

[monster]

you need to use the surface area of the bolt as well as the flats on the axle, so tighten it up really strong.

maybe you could use 1" thick Al tool-plate to make torque plates. thats what i have for holding my rear disc adaptor and it looks strong but i wouldn't mess with regen again after my last experiences. what controller do you use and does it have regen -or did you DIY it ?

 

[curious]

what controller do you use and does it have regen -or did you DIY it ?

I use Kelly controller (with regen).

 

[Doctorbass]

I decided to directly cancel any potential problem lilke this!:

Use a PERMANENT WRENCH !!!


Low cost, very strong

Doc

 

[set]

a trick I learned while working on cars a while back is to use 2 nuts compressing AGAINST each other. If you still have thread space when you mount your axle to the dropout, simply get another nut and, using 2 wrench, torque the second nut over the "inside" nut. Use an opened-end wrench to hold the "inside" nut still. Torque to 20-30 foot lbs and I guarantee that "inside" nut is not coming off. No loctite needed.

 

[dogman dan]

Would love to see long axles that you cut to fit yourself later. Then you could use some mondo nuts and 150 ft pounds. A big fat torque plate with a heavy duty kick stand integrated would be cool too.

 

[curious]

a trick I learned while working on cars a while back is to use 2 nuts compressing AGAINST each other.

That is what I had - did not work. There is not enough length to put a pair of full size nuts so I used narrower nuts for locking. You can not apply a lot of torque to those narrow jam nuts.

I think Doc's solution is quite good. I may try that combined with fechter's lug nut idea.

 

[heathyoung]

You could also try nylocks - the ice bike guys use them due to motor vibration...

 

[dogman dan]

Higher power motors really should have a long enough axle to put all the big nuts and thick torque plates you want on it.

 

[curious]

Higher power motors really should have a long enough axle to put all the big nuts and thick torque plates you want on it.

I agree, but the axle design is poor in the concept. Bike axle joint is not intended to handle large torque. I understand that they had to do something compatible with existing bikes but I think they should have permanently integrated a pair of permanent torque arms with the axle instead of using those stupid flat spots.

 

[spinningmagnets]

I had a motorcycle once that on two occasions had the rear axle nuts loosen. I was concerned, but by DOT rules, they had pull-retainers that did two things, they were like a large fat washer that prevented the axle from slipping out of the drop-outs, and they also had threaded studs pointing back upon which nuts would be tightened to tension the chain and align the axle. Something like this:

Once properly set, the big axle nuts could be tightened. I drilled a small hole in the tip of the axle so I could insert a cotter pin. This way if the nuts came loose again, at least I wouldn't lose the axle nuts onto the road. I would feel it was riding funny, and just pull over to tighten them.

Here's a pic of a scooter axle-retainer. Each application may have some custom dimensions required, but something like this would be cheap and easy to make. Personally my concern is not so much that the axle nuts might loosen on occasion, but that as the OP stated, the axle might fall out at speed.