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Changing travel on Fox F80/100 forks

46K views 82 replies 26 participants last post by  mtb_tico 
#1 · (Edited)
I remember this question coming up before, whether it was possible to adjust the travel on these forks. There was no certain answer and the best I got from Fox was that I needed to purchase a new assembly for the left leg (air spring side). Quoted at $30. Not bad, but not free. A while ago I picked up a used F80 RLT to use on my race bike. The frame was designed around a 100mm fork, but I figured to give 80mm a shot anyway, since it would drop the front end a bit and give faster steering. I didn't like the ride so I decided to open up the fork and check out the guts, and change the travel and oil. I was happy to see that the person who sold the fork to me did a complete overhaul prior to the sale and the oil inside was pristine. Anyway, onto the travel adjustment.

In Floats and Vanillas travel adjustment is as easy as a rearrangement of spacers. In Floats it is easierst, since there are less springs. In case of the F series forks, this is more complicated, because in order to save all possible weight there are no spacers, simply, the travel adjusters, if you will, which are pinned into the assembly.

In order to change travel, you don't need to touch the right leg at all, the one with rebound/lockout/threshold adjustment, only the left one, where the air spring is. Simply unscrew the bolt in the bottom of left leg with a 10mm wrench, and unscrew the top cap with a 26mm wrench. It will also help to remove the air valve cap before undoing the leg cap. Remember to let all the air out before doing any of this, otherwise you might have a little explosion of high viscosity oil. Let the oil drain out and remove the plunger assembly from the leg. This is also a good time to wipe down the inside of the slider and stanchion. The assembly will look like so:



Examining more closely you will see a hole obove a black ring, like this:



The black ring has a hole in it as well, through which a pin is inserted. In the picture it is sitting in the 80mm position. At first glance I was pessimistic as to my ability to do anything about it, however, I took a nail and flattened the end, inserted it into the hole in the black ring and banged at the pin with the hammer. (I would advise against a use of a sharp tipped object because the pin is hollow on the inside and the last thing you would want to do is to make the thing expand) After a bit of banging here's what it looked like:



and a closeup:



Now, just bang it out further until it almost comes out of the black ring. Try not to get it all the way out, because it might be difficult to insert back into the ring, but I am not sure. You will see when the pin leaves the shaft because the ring will be loose. Slide it to the upper hole and bang it back in:



Voila! Your F80 fork is now F100. To lower travel just do the reverse. Assemble your fork back up, fill with proper amounts of oil. 20ml in the bottom, 7wt oil, like Maxima. 5ml of Float fluid at the top, to form the air seal.

_MK
 
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#52 ·
Right leg is much different than the left. There is no pressure and no air spring, it is just the damper. You can just unscrew the top cap without any worries. You might end up having to release some air from the air spring, so that the negative spring compresses the fork some, before you can pull the top cap out enough so that you can add oil.

_MK
 
#53 ·
Any luck on figure out why the harsh rebound? Want to get as much inpute before this here non-mechanical person tries to take a wrench to fork.

Thanks

Der Blaue Reiter said:
Hey MK_,
I tried this with mine last night. I have the 2005 F80RLT and i noticed that mine has three holes on the leg(where spacer goes). I set on the 100mm one, put fork back together, but now it tops out harshly. Do the springs need any rearrangement?
I never touched the right leg, but was wondering if maybe I need to open it up to let the air equalize for the new length?

For the record, My fork was making clunking noice(similar to loose headset) when breaking.
I figure it is a bushing issue and plan on sending it for repair.
That's why I decided to at least take a look and try this modification.
Thanks!
 
#54 ·
First off, hats off to the original poster of this thread. Thank you!

I just totally cleaned out and put new enduro fork seals in my 2004 Fox F80 RL (the pictorial instructions on that site are amazing!).

When doing so I figured, why not - I'll change the travel to 100mm by moving the "pin" and spacer as per the instructions on this thread.

I haven't had much time to ride it yet, but so far it seems to have worked perfect. The stantions seemed plenty long to support the extra 20 mm (and I think the crown will hold up to the change as well).

I hope it works ( I need 100mm for the terrain here and my frame is built for 100mm of front travel). I'll keep you posted.

Anyone else have more feedback on this change?

K
 
#56 ·
slaw said:
Does changing travel change the AC height? I've just got a 2006 F100RLT to replace a rigid fork that has AC of 420mm. At 100mm it's a pretty dramatic change to the geometry so if I drop it to 80mm would that be better?
Naturally. You subtract the reduced travel amount from the AC.

_MK
 
#57 ·
It worked... almost

Hi,

This is my first post on this forum. I just bough a "used" Specialized SJ 2005 with Crossmax SL wheels and Hayes 9 carbon brakes to get back to mtb after 5 years spent mostly on the road.

Inspired by the original post of this thread (thanks a lot to this guy by the way :thumbsup: ), I went ahead and increased the travel of my F80 RL. (By the way, I used a 7/64" allen key to bang the pin out and it worked very well :thumbsup: ). So I thought everything was fine after putting the fork back together until I tried to compress the fork... When springing back after being compressed, it now makes a "klunk" when reaching the end of the extension. Its like there is nothing to smooth out the end of the travel (when releasing it). Any idea as to what I might have done wrong or what I could do.

Also, I had to lower the pressure down to 65 psig before being able to get 80mm of actual travel and a reasonable amount of sag (15-20 mm). I'm 160 lbs and 80-85 psig got me 65mm of actual travel and a 10-15 mm of sag before increasing the travel. Is this normal :skep:

Thanks for your help !
 
#58 ·
The fork broke before I had the chance to make the modification. However, I did talk with the guys at PUSH about doing the modification. I don't remember all the details, but do remember it was not a one for one modification. In other words, pulling the pin and putting it in a different spot does not give you RL 100. Yes you do get 100 mm, but you don't get all the functionality of a RL 100. There are some internal workings that are different.
 
#59 ·
Update

Thanks for your reply but I'd like to know if I can run my fork like this even if there is no solution for the sound.

BTW, I forgot to say (see original post above) that I have already tried every trick posted on this thread (servicing and fully extending the oil damper, adding more oil, etc.)

I also measured the extension of the oil damper at 100 mm which tells me that there should be no problem running the fork with that amount of travel.

Anybody got longer term experience with running the F80 with 100 mm travel ? Should I worry about the clunking top out sound or can I ride my fork like this without damaging it ?

Thanks again for your help.
 
#60 ·
cereal_monster said:
Thanks for your reply but I'd like to know if I can run my fork like this even if there is no solution for the sound.

BTW, I forgot to say (see original post above) that I have already tried every trick posted on this thread (servicing and fully extending the oil damper, adding more oil, etc.)

I also measured the extension of the oil damper at 100 mm which tells me that there should be no problem running the fork with that amount of travel.

Anybody got longer term experience with running the F80 with 100 mm travel ? Should I worry about the clunking top out sound or can I ride my fork like this without damaging it ?

Thanks again for your help.
My guess would be to look at the negative spring. See if you have two little coils below your air piston on the spring side. Make sure, also, that it is functioning properly.

_MK
 
#61 ·
MK_ said:
My guess would be to look at the negative spring. See if you have two little coils below your air piston on the spring side. Make sure, also, that it is functioning properly.

_MK
My air spring looks exactly like the one you took pictures of in your original post of this thread. Also, appart from the "clunk" at top out, everything is normal. The fork is smooth through its travel and before pumping air into it, I could feel the negative spring worked properly.
 
#62 ·
Info from Fox's rep.

He MK,

Here's some very interesting information that I recieved from a Fox rep. by email:

"Fox 80mm forks are not travel adjustable up to 100mm. You should not move the black negative spring stop from it's original position on the air shaft assembly. Moving the black stop back to it's original position will solve your top-out issue.

To convert your F80RL fork to an "official" F100RL, you will need to replace your damper cartridge as well as your up upper assembly. 80mm upper tubes have been lightened and are not intended for use at 100mm. Your damper cartridge is too short and is topping at full extension."


:skep:

What do you make of this ?

After riding some more with my modified fork, the harsh top out doesn't really bother me so I am just trying to figure out if I can run my fork at 100mm without risking damaging it.

Cheers !
 
#63 ·
cereal_monster said:
He MK,

Here's some very interesting information that I recieved from a Fox rep. by email:

"Fox 80mm forks are not travel adjustable up to 100mm. You should not move the black negative spring stop from it's original position on the air shaft assembly. Moving the black stop back to it's original position will solve your top-out issue.

To convert your F80RL fork to an "official" F100RL, you will need to replace your damper cartridge as well as your up upper assembly. 80mm upper tubes have been lightened and are not intended for use at 100mm. Your damper cartridge is too short and is topping at full extension."


:skep:

What do you make of this ?

After riding some more with my modified fork, the harsh top out doesn't really bother me so I am just trying to figure out if I can run my fork at 100mm without risking damaging it.

Cheers !
You can always put a couple mm of nylon washers between the black stop and the negative spring to drop the max extension to say 98 or 96mm to get rid of the top out.

_MK
 
#64 ·
MK_ said:
You can always put a couple mm of nylon washers between the black stop and the negative spring to drop the max extension to say 98 or 96mm to get rid of the top out.

_MK
That's the best idea I heard in a long time ! I'll find a way to lower the travel by about 5mm and that should do it.

The bottom line is that the damper cartridge is long enough to accomodate the 100mm travel but lacks a couple of mm to prevent harsh top outs.

As for the crown/steerer tubes assembly, the steerers are long enough to accomodate 100mm travel but something (either the thickness of the steeres or the design of the crown) is not as beefy as on the F100. But I am beting that the "reduced" stiffness will not be an issue for me as I don't ride that hard.

Case closed for me :thumbsup:

Thanks guys.
 
#65 ·
cereal_monster said:
That's the best idea I heard in a long time ! I'll find a way to lower the travel by about 5mm and that should do it.

The bottom line is that the damper cartridge is long enough to accomodate the 100mm travel but lacks a couple of mm to prevent harsh top outs.

As for the crown/steerer tubes assembly, the steerers are long enough to accomodate 100mm travel but something (either the thickness of the steeres or the design of the crown) is not as beefy as on the F100. But I am beting that the "reduced" stiffness will not be an issue for me as I don't ride that hard.

Case closed for me :thumbsup:

Thanks guys.
I think by steerers you mean stanchions. And I think Fox is full of sh!t in that department. But whatever.

_MK
 
#67 ·
ednino said:
Sorry to dig up an old post, but this does not work.

Moving the pin and washer up will not give you 100mm of travel if you started with 80mm. The damper cartridge on the f80 will limit your travel. A f100 damper is £126 from mojo
It certainly worked for me. What year fork were you working with?
It is possible Fox started making shorter dampers to save a few grams; that was not the case with mine.

Note: You should check the damper extends at least 20mm after unscrewing the top cap on the right side before you undergo the procedure.

_MK
 
#70 ·
Good thread. I did find this after I had done all of the above but was getting this knocking as the fork topped out.
I had a stuffed (staunctions & lowers) F100x but picked up a good F80x with the intention of putting my internals in, I just did the air chamber. It appears though that the F80x damper is very slightly too short, I solved this by putting a thin washer 3-5mm between the spring and the stop, only get 95mm travel now but no knock, so looks sorted.
I will be fitting the 100 damper soon so I will post the diff in lengths.
 
#71 ·
OK i would post a photo if i could be bothered to set up some photo hosting thing to link to the picture, BUT i laid the 2 dampers side by side.

This asumes you can visulise what the damper looks like - the main body of the 100mm is probably 50mm (2") longer than that of the 80mm, and fully extending the shaft out the 100mm is probably 25mm (1") longer. so thats why is knocks!

but problem can be solved by adding a washer as in the above post.
The lower legs and staunctions are identical in both.

I dont know the weight saving but it looks a lot of trouble for a few grams.
 
#72 ·
NZRob said:
OK i would post a photo if i could be bothered to set up some photo hosting thing to link to the picture, BUT i laid the 2 dampers side by side.

This asumes you can visulise what the damper looks like - the main body of the 100mm is probably 50mm (2") longer than that of the 80mm, and fully extending the shaft out the 100mm is probably 25mm (1") longer. so thats why is knocks!

but problem can be solved by adding a washer as in the above post.
The lower legs and staunctions are identical in both.

I dont know the weight saving but it looks a lot of trouble for a few grams.
Hi I was thinking of increasing my F80 to F100 to slacken my head tube angle and chanced upon your posting. If you had taken a pic of the 3-5mm thick washer installed, it would really give me great help. If you dun have the pic, could you let me know the inner diameter and out diameter of the wahser that you used? thanks.

Email: eugene.sim@kla-tencor.com
 
#73 ·
Wow, I was going to make a new thread about my adventures of travel adjustments earlier today, but since this one was bumped...

I have a 2007 F32 RLC that was set at 100mm. I wanted to go to 120+mm. Not worried about the weaker uppers, as I'm under 150 pounds.

I could tell the damper cartridge would not extend enough, but a friend had a 2007 TALAS RLC he converted to a Float set at 100mm...I figured we could simply swap dampers, but the top cap on my F32 was slightly larger in diameter, and would not fit into the TALAS leg. The TALAS stanchions have thicker walls...and apparently the top caps are machined to fit very closely. I should specify that the thread pitch and diameter is the same, but the area below the threads has a different diameter.

We ended up swapping only the lower section of the cartridges, which solved the problem. (The dark gray part, with the lockout threshold knob...)

The air piston rod was drilled for 100, 120, and...more than 140. (The last hole was more than 20mm from the middle one...25-30mm)

I also trimmed the air piston rod while I had it apart...removed 20mm, which seems to have increased the usable travel, as well as made the spring rate less progressive.
 
#74 ·
cossie said:
Hi I was thinking of increasing my F80 to F100 to slacken my head tube angle and chanced upon your posting. If you had taken a pic of the 3-5mm thick washer installed, it would really give me great help. If you dun have the pic, could you let me know the inner diameter and out diameter of the wahser that you used? thanks.

Email: eugene.sim@kla-tencor.com
The OD of the washer doesn't matter a lot, as long as it it smaller than the OD of the spring, stop collar, etc. The 20mm Fox spacers have an OD of 15/16", so anything less than that. The OD of the air piston rod appears to be around 3/8", so a washer meant for a 3/8" bolt is large enough. They're around 1mm thick, so you could stack as many as you need...or simply cut a section of plastic pipe to save weight. 1/2" PEX, perhaps? Or any other plastic tube shaped item...
 
#75 ·
kramnnim said:
The OD of the washer doesn't matter a lot, as long as it it smaller than the OD of the spring, stop collar, etc. The 20mm Fox spacers have an OD of 15/16", so anything less than that. The OD of the air piston rod appears to be around 3/8", so a washer meant for a 3/8" bolt is large enough. They're around 1mm thick, so you could stack as many as you need...or simply cut a section of plastic pipe to save weight. 1/2" PEX, perhaps? Or any other plastic tube shaped item...
As Kramnnim said, i just found a std washer and poped it on, once you have dismantled it it will all become blatently obvious and its a doddle.
 
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