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Discussion Starter · #1 · (Edited)
I've got a 2016 Fox 36 27.5" that I converted to coil (hacked together from old Van 36 parts), and two years ago changed the lowers to 29". Since then, the fork has not been working well. I have enormous amounts of shear force induced stactic friction, as much as 35lbs when pushing straight down on the handlebar with all the internals and seals removed from the fork. I've sent it back to Fox have the bushings resized several times, and each time it came back working well for one ride, then next ride awful and sticky again. The last time I sent it in, the bushings were replaced and then resized. Still only good for one ride.

I took the fork completely apart (again) and tried the lowers on with no seals. They go on with a bit of friction on the upper bushings, and then considerable resistance when the lower bushings engage. When I push the legs all the way on, it takes excess of 10lbs to pull them straight off (no shear forces). The old 27.5" legs come off with just a couple pounds of force, and a pair of Van 36 legs slide off by themselves.

If I only put one leg on at a time, they slide on considerable easier. I have left the axle off, to make sure the lowers are free to move. It seems the bushings are not only too tight, but also slightly misaligned.

Now, how does the bushing resizing happen? I recall having read about simply forcing a slightly larger tapered tube through the bushing to pry it more open. This seems like an amateur's approach to me, and not something that would give a permanent result. Or are they reamed prior to or after installation?

Can I expect Fox to be able to fix this? Maybe send in just the upper and lower legs, as well as the old Van 36 legs for reference of how good I expect it to be?

The last two years have been a frustrating experience, I have adapted to a fork that only partially responds to the terrain. Super smooth brake dive (very low shear forces then), chattery and rough on everything else. But I recently bought a new 2020 36, and put a Push ASC3 coil kit in it, and it is a marvel of a fork. Several rides in, and still buttery smooth. I am re-learning the joys of fast technical riding.
 

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Pushing a "tapered tube" through the bushings is the correct way to resize them, it is a very precisely machined piece of steel that is oversized by a few hundredths of a mm to set the clearance perfectly. A combination of tolerances however means some forks need to be slighty larger than others which is why I have multiple sized dies to get the ideal fit on any fork.

My guess is whoever did your bushings has just put the standard sizing tool through them and not checked afterwards, they should definitely not feel how you describe. I would expect them to either try a bigger size or advise you that the fork is possibly twisted.

At this stage I would find a better suspension specialist to deal with them

Fyi - info from the manufacturer of your forks bushings - https://www.bearings.saint-gobain.com/solutions/norglide/ptfe-bushing-sizing
 

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Discussion Starter · #5 ·
Pushing a "tapered tube" through the bushings is the correct way to resize them, it is a very precisely machined piece of steel that is oversized by a few hundredths of a mm to set the clearance perfectly. A combination of tolerances however means some forks need to be slighty larger than others which is why I have multiple sized dies to get the ideal fit on any fork.

My guess is whoever did your bushings has just put the standard sizing tool through them and not checked afterwards, they should definitely not feel how you describe. I would expect them to either try a bigger size or advise you that the fork is possibly twisted.

At this stage I would find a better suspension specialist to deal with them

Fyi - info from the manufacturer of your forks bushings - https://www.bearings.saint-gobain.com/solutions/norglide/ptfe-bushing-sizing
Interesting, so the bushing material actually gets compressed, not the whole bushing pryed apart. But is there a slow partial rebound to this? Since my fork has usually been fine for one ride, and then get tight again.

How much over the desired dimension is the tool? Would it be possible to heat up the inners, freeze the outers, and quickly force them them together to achieve better tolerances? Or clamp the outers with hose clamps where the busings are to compress the bushings?
 

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But in my case, the stiction also happens with everything removed, be it axle, internals, dust vipers.
I can't stress enough the need to be cautious while handling the dust vipers as I've heard they are highly venomous.
 

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Interesting, so the bushing material actually gets compressed, not the whole bushing pryed apart. But is there a slow partial rebound to this? Since my fork has usually been fine for one ride, and then get tight again.

How much over the desired dimension is the tool? Would it be possible to heat up the inners, freeze the outers, and quickly force them them together to achieve better tolerances? Or clamp the outers with hose clamps where the busings are to compress the bushings?
the PTFE material does spring back but its more or less instant. What you describe is just the oil/grease from assembly being wiped away during the first ride. If there is clearance there it will keep a film between them

The stanchions won't be hard enough to be effective I don't think, and possibly risk damage to them

The exact amount the tool needs to be oversized depends on your combination of upper & lower and not the kind of thing I would share online to be honest

If you slide a single leg on, would it slide off on its own?

Where in the world are you? If you can ship to New Zealand I can tell if you they're fixable or not ;)
 

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Interesting, so the bushing material actually gets compressed, not the whole bushing pryed apart. But is there a slow partial rebound to this? Since my fork has usually been fine for one ride, and then get tight again.

How much over the desired dimension is the tool? Would it be possible to heat up the inners, freeze the outers, and quickly force them them together to achieve better tolerances? Or clamp the outers with hose clamps where the busings are to compress the bushings?
Stanchions don't have the proper lead-in and the temperature difference required to create the size difference would be extreme.

Any shop equipped to size and burnish bushings can fix this for you.
 
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