39mm Front End Axle Issues

[SuprltvCnspircy]

I bought a narrow 39mm front end, but it was missing a few pieces. I bought an axle that matched the width and ID dimensions of each axle tube. It fits perfectly and very snug, but on the larger end (the carb side), it wont fully tighten with the pinch bolt and slides through too much towards the nut side. On the nut side when the axle is fully pushed through, the nut and washer have way too much space to properly tighten the axle. Am I missing something? I've never had a front end this "new". I've tried to look up schematics to see what I'm missing but I can't figure it out. I'd appreciate any wisdom. Thanks!

[Sky]

Not sure why the pinch is loose
But you may just be jumping the gun by installing without the spacers...

[MOTher]

Your problem isn't just the 39 mm forks, it's a combination of those and the drum brake front wheel. You may have to have an axle custom made. I'm in the house in my pajamas now so I can't measure the diameter of the pinch side of the axle you'll need. If I recall, the bearings in that wheel are 17 mm (.669") at the axle, and the hole in the non pinch side slider is 3/4", so you'll have to have a couple sleeves made up to make it work. Custom axle, the right size spacer (probably also custom made, I don't know anyone who stocks various sizes of 17 mm spacers.) to center the wheel in the forks, and sleeves for the left side slider. It's not gonna be a bolt-on deal.

[TriNortchopz]

Did you get the right axle? Is it 3/4"? I see there are a couple different lengths for the 39mm fork depending on year;
9-5/16" long for '73-77 FX, '84-'87 FXR, then 9-1/2" for '77-'83 FX, all at 3/4" diameter. Could it be newer lower legs - metric?
Fork legs straight - triple trees not bent?

[MOTher]

TriNortchopz, fork is 39 mm so it's '87 or later The years you listed all use 35 mm forks. And he's using a hamburger drum wheel, which has 17 mm bearings.

[TriNortchopz]

TriNortchopz, fork is 39 mm so it's '87 or later The years you listed all use 35 mm forks. And he's using a hamburger drum wheel, which has 17 mm bearings.

Thanks, good to know; guess these guys got a typo in their listing:
39mm Forks FX 1973-1977

https://www.bikerdirect.com/tires-wheels-hubs/axle/axles?sort=20a&page=1&zenid=5790937q3p4cps2emvevu5adq6

[SuprltvCnspircy]

Here we go. So, with this drum wheel, I went and got new bearings to match this axle. Additionally, I did what I could to get an axle that would fit the shock tubes. My micrometer might not be 100%, but its pretty damn close, hopefully enough to give an idea of how close everything is. Lastly, I did build spacers for this axle wheel combo, you can see them below.

Spacers


Shock Tube - Big Side


Axle - Big Side


Shock Tube - Small Side


Axle - Small Side


Continued below...

[SuprltvCnspircy]

Wheel Bearing


Axle Length - 10"

[JBinNC]

You need a spacer between the shoulder on the axle and your backing plate, wide enough to move the axle to the right in the fork. Then you can pull the nut tight on the left side as it should be. The spacer you need should be the same diameter as the head of the axle, or a couple of thou smaller, and a light press on the axle, to make assembly of the wheel easier. I see this all the time with this mix and match stuff.

Jim

[SuprltvCnspircy]

You need a spacer between the shoulder on the axle and your backing plate, wide enough to move the axle to the right in the fork. Then you can pull the nut tight on the left side as it should be. The spacer you need should be the same diameter as the head of the axle, or a couple of thou smaller, and a light press on the axle, to make assembly of the wheel easier. I see this all the time with this mix and match stuff.

Jim

Are you referring to the spacer that also centers the wheel between the tubes?

[JBinNC]

Are you referring to the spacer that also centers the wheel between the tubes?

No, that is the left side spacer ONLY, the nut side. When you pull the axle nut up tight, it pulls the wheel assembly against the left fork leg, and the left spacer sets the position of the wheel. Right spacer, if any, or the shoulder of the axle, sets the position of the AXLE in the assembly. Right fork leg just clamps to the axle wherever it falls.

Jim

[SuprltvCnspircy]

No, that is the left side spacer ONLY, the nut side. When you pull the axle nut up tight, it pulls the wheel assembly against the left fork leg, and the left spacer sets the position of the wheel. Right spacer, if any, or the shoulder of the axle, sets the position of the AXLE in the assembly. Right fork leg just clamps to the axle wherever it falls.

Jim

JB, thank you very much for your help. I now completely get what you were saying because I found the right axle in my garage.

The left axle is what I was trying to use, the right one is exactly as you explained. Has a wider shoulder section to center the wheel. The only other difference is the diameter, but a few bearings will fix that quickly.



Thanks again for your help!

[Sky]

That's what I said! Lol
Need the right (left) spacer...

Looks like you got it figured out, the hive mind is a great thing!!
Think AI will be using our collective knowledge to build choppers in the future?

[SuprltvCnspircy]

That's what I said! Lol
Need the right (left) spacer...

Looks like you got it figured out, the hive mind is a great thing!!
Think AI will be using our collective knowledge to build choppers in the future?

Hahaha, I get your comment now, I was just thinking you were saying an additional spacer. This axel only works because it's the same diameter as the axel itself. Thanks for your input. Honestly, it would be great to have a collective mind for this stuff. Thats why I wanted to update the thread, so then next goon with the same problem can see the difference in the axles.

[Sky]

Credit where credit is due,
Jb, Tri, and Mot spelled it out better than I did, for sure.