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Axle does not fit into dropouts perfectly

Posted: Nov 15 2019 4:20pm
by transposon
dropout1.png
dropout1.png (454.13 KiB) Viewed 920 times
Hi know this question has been asked here many times, but this is my first build and I wanted to see if filing down my dropouts was a good idea. It seems like I may not have a whole lot of material in the drop out. There is about 1-1.5mm of distance between the bottom of the dropout and the motor axle.

This is an aluminum Trek 4500 with a 1000W ebay hub motor. I am using a grin v4 torq arm on the other side of the motor. I wanted to use two torque arms, but my second v4 wont fit over the disk brake housing bolt.

Thanks.

Re: Axle does not fit into dropouts perfectly

Posted: Nov 15 2019 8:51pm
by E-HP
If you file them by about 2mm, then the center of your axle will rest in a the similar position as a normal bicycle axle would fit. You'd have more purchase for your axle nuts, and the rotor and caliper would line up as they were designed.

Re: Axle does not fit into dropouts perfectly

Posted: Nov 15 2019 9:07pm
by Balmorhea
E-HP wrote:
Nov 15 2019 8:51pm
If you file them by about 2mm, then the center of your axle will rest in a the similar position as a normal bicycle axle would fit. You'd have more purchase for your axle nuts, and the rotor and caliper would line up as they were designed.
Careful not to leave sharp inside corners on the axle slot. Those constitute stress risers that invite the dropout to crack and snap off at that point.

Best, I think, is to leave the dropouts alone and make a left side torque arm that screws to the eyelets. Carefully done, this takes all the prying forces off the dropout while leaving the dropouts with the structural integrity they were made to have.

Re: Axle does not fit into dropouts perfectly

Posted: Nov 16 2019 2:37am
by MadRhino
Torque plates, each side, 1/4 steel. Ideally 2 screws each to hold em on the actual dropouts, but one screw and glue is OK.

Re: Axle does not fit into dropouts perfectly

Posted: Nov 16 2019 7:59am
by dogman dan
Well, at the very least, one good torque arm is needed for sure. Try to modify the other grin arm so it can fit. Play with different ways to put it together, or grind a notch in it to go around that bolt.

I would file the drop out deeper, till the center of your motor axle matches where the center of your old axle was. This makes sure the disc lines up good with your calipers. But not too deep, too deep makes the nut fit better, but it then makes your caliper grind on the disc.

Re: Axle does not fit into dropouts perfectly

Posted: Nov 16 2019 10:06pm
by transposon
I posted pics of the torque arm on the other side in this thread:
viewtopic.php?f=3&t=103295

Re: Axle does not fit into dropouts perfectly

Posted: Nov 19 2019 1:15am
by wturber
I made these for my bike with the same (and very typical) issue that you have. It looks to me like this approach might work for you on the one side. This kind of thing is fairly easy to make.
viewtopic.php?t=26444&start=175#p1315521

Not filing the dropouts does keep the brake disc from sitting high enough for the brake pads to fully engage. That isn't a huge deal since it is only short by a millimeter or so. But you won't get the full wear out of your disc pads. I eventually switched to a 180mm rear disc and filed the 180mm adapter down by a millimeter or so to compensate. That resolved the disc pad/rotor depth issue.

Image

Re: Axle does not fit into dropouts perfectly

Posted: Nov 19 2019 9:27am
by kcuf
avoid regen