40 Float issues?

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40 Float issues?
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flag droplover
Posted: Aug 28, 2014 at 21:10 Quote
How common is it for the 40 Float to sink into the travel due to the static weight of the bike? I'm not getting full extension (I only measure 185mm on the stanchion with the bike on the ground). With the bike in the stand, I have to put 85psi in the fork to measure the full 203mm on the stanchion. I then reduce the air pressure to 60psi and I can only measure 197-198mm. I'll put the bike on the ground again and push the fork down a few times and only measure 185mm again. With the bike in the stand, I can fully extend the fork with my hands but as soon as I let go, it moves again and I can only measure 185mm. Is this an issue or is this characteristic of a 40 Float? Thanks.
flag Chuvak
Posted: Aug 28, 2014 at 21:20 Quote
Fox 40 float utilizes coil negative spring (what is pretty funny for 2k$ fork). So you have a situation when positive chamber pressure is not enough to compress the negative spring to release all the 203 while bike is on the ground.

PS. Change the oil in the lowers. This will reduce risk of uppers damage and eliminate sticking. 5w30 motor oil will be good.
flag droplover
Posted: Aug 28, 2014 at 21:59 Quote
motor oil? I've never heard of that before
flag parkourfan
Posted: Aug 28, 2014 at 22:54 Quote
You *can* run motor oil in a fork. Does anyone actually think it's better? Not really. However, you don't need to run fox branded oil, motul or the like, as long as it's in the correct amount and weight (duh) will work great.

Pretty much all air forks will have a few mm of play. My lyrik, set at 170, sits at about 165 or so. Not because of the weight of the bike, but the internals. Chuvak is right about the positive/negative weight difference being the issue.

If the extra oil doesn't help, check out your LBS to see what's wrong with the internals. You should be able to run pretty low pressure in your float without it sticking down a la fox DHX air of old.
flag Chuvak
Posted: Aug 28, 2014 at 22:58 Quote
oil in the lowers and oil in the damper are different. oil in the lowers has only one function: lubrication. it must have good adhesion and be very slick. fork oil (for damper) dos not have these characteristics. every fork, that utilizes colsed-bath type damper, must have motor oil in the lowers. not fork one. also, manitou dorado manual tells about it too.
I know what I'm talking about. I've serviced hundreds of forks as I have hobby-workshop. 40 float was in my workshop too. I was changing oil in the lowers (coz fork felt very sticky) and in the air spring (7-10cc of 5w30 on the piston. before servicing due tu awful factory oil it was so stuck that I had to kick it out of the fork's leg with a hammer. after oil change I could move it with just 2 fingers).
flag parkourfan
Posted: Aug 30, 2014 at 6:51 Quote
Well if it works for you that's fine. All I'm gonna say is that while watching the pits at the WC, the RAD truck was pretty open about what they were doing in terms of visibility to the public, and all they had was fork oil, some of it not even fox branded-so clearly not an issue with branding. There's a reason why most fork manufacturers are so anal about using branded fork oil for everything. It's not just for them to make more $. Push used suspension oil in the lowers, and float fluid on the wipers on my friends 40, which is certainly more viscous and better suited to the wipers and bushings. Yeah, I've used SAE 5w-30 motor oil in an 02 boxxer. Sure, it worked, but it also didn't have a damper of which to speak. It'll work, sure, but a fork isn't going to heat up enough to make use of a variable weight oil anyways...so there isn't going to be a benefit of "adhesion". Straight 30w oil is onl recommended for older engines that 1. Don't call for variable weight and 2. Have damage that can be filled in by the high weight. So why not use 7.5 or 10wt straight suspension fluid for the added viscosity and float fluid or sumilar to service. Honestly.
flag droplover
Posted: Aug 30, 2014 at 6:52 Quote
thanks for the info...the guy at my LBS said the fork might be set at 7 or 7.5", is that possible? also, he is changing the oil in the lowers with fork oil...I hope that helps some
flag Gabber
Posted: Sep 1, 2014 at 10:35 Quote
It doesn´t matter which oil you put into the lowers as long it lubricates, but imo the best oil there is guiding way lubrication used in CNC machines as it reduces the stick-slip effect.
flag droplover
Posted: Sep 3, 2014 at 17:44 Quote
got the oil changed in the lowers today...the guy at my LBS told me the same thing about the coil negative spring...now that I know it's a setup issue per se, and nothing is damaged, I will just ride the hell out of it until the end of the season
flag huicho
Posted: Jan 18, 2024 at 12:57 Quote
So it's okey if the fork doesn't extend fully? Does that compromise performance?
Chuvak wrote:
Fox 40 float utilizes coil negative spring (what is pretty funny for 2k$ fork). So you have a situation when positive chamber pressure is not enough to compress the negative spring to release all the 203 while bike is on the ground.

PS. Change the oil in the lowers. This will reduce risk of uppers damage and eliminate sticking. 5w30 motor oil will be good.
flag Chuvak
Posted: Jan 21, 2024 at 3:45 Quote
That really depends on your fork, but in general, if we assume that all the greases and oils are relatively fresh and are of a proper type, these dead few millimeters are caused by small parasite friction of air piston seal plus almost equilibrium forces of pos and neg springs when the air piston is in the "rest" zone near the equalizing notch.

Anyway, different forks behave differently. I had Dorado 2014 and now I have Dorado 2023, they have around 3-4mm of dead travel (that never affected overall fork travel and damping performance). Most of Fox forks have a similar issue. RS before C1 generation - as well, but in C1 they moved the notch higher in the stanchion so this effect really mitigated.

Also there can be a number of other reasons for this effect, related to fork malfunction, improper service or service interval overrun. But described above assumes that fork is fine
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