Probably bad seal between positive and negative chambers. Recommend an air seal rebuild kit.
Mastadon freeze up
Happy winter riding fellow fat biker. Here in Maine we have great conditions but it’s been cold. During this mornings ride, (it was -12F) by Mastadon Comp fork sagged half way into its travel. Cycle it the fork accomplished nothing. Went to my LBS in which they aren’t very familiar with Manitou forks but the tech hooked up a fork pump to the valve on the lower left leg In which the fork immediately when back to full extension And functioned perfectly. The tech only assumed perhaps there was something that may have stuck between the positive and negative air pressure sides to the fork. I myself am not familiar with this fork at all. Any thoughts as to what might have happened. The fork was new this Fall.
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It’s a new fork.And it does work fine now.
I have two Mastodons. LOTS of mileage on both over the past 1.25 years, but mostly in winter. These have seen plenty of minus 20 C days, lots of winter rain (Fernie) and huge temp variations, but so far so good.
Commencing one week from now, my daughter and I hope to be on these bikes for 40+ days in a row, weather permitting. Needless to say, I will be watching this thread. The forks we are riding are 2021 Mastodon Pro, Dorado Air, 100mm Travel.
Commencing one week from now, my daughter and I hope to be on these bikes for 40+ days in a row, weather permitting. Needless to say, I will be watching this thread. The forks we are riding are 2021 Mastodon Pro, Dorado Air, 100mm Travel.
All that comes to mind is this bike gets ridden almost daily and it stays in my unseated garage. It has been very cold out the last couple weeks. Yesterday was -13 when I rode. There may be a small amount of condensation in the fork causing the neg/pos valve not to work properly and the fork went into most of its stroke and stayed there. When the tech at LBS hooked a fork pump to the valve on the lower left leg, even before pumping the fork came back to normal. There is a small nipple in the middle of that air valve that resembles a Schrader \valve but thicker. Once that nipple was engaged, the fork resumed normal operation. I’ll be going out for another ride tomorrow. We shall see.I have two Mastodons. LOTS of mileage on both over the past 1.25 years, but mostly in winter. These have seen plenty of minus 20 C days, lots of winter rain (Fernie) and huge temp variations, but so far so good.
Commencing one week from now, my daughter and I hope to be on these bikes for 40+ days in a row, weather permitting. Needless to say, I will be watching this thread. The forks we are riding are 2021 Mastodon Pro, Dorado Air, 100mm Travel.
Thanks for the further info. I will continue to monitor this thread.All that comes to mind is this bike gets ridden almost daily and it stays in my unseated garage. It has been very cold out the last couple weeks. Yesterday was -13 when I rode. There may be a small amount of condensation in the fork causing the neg/pos valve not to work properly and the fork went into most of its stroke and stayed there. When the tech at LBS hooked a fork pump to the valve on the lower left leg, even before pumping the fork came back to normal. There is a small nipple in the middle of that air valve that resembles a Schrader \valve but thicker. Once that nipple was engaged, the fork resumed normal operation. I’ll be going out for another ride tomorrow. We shall see.
To add a bit of context, our bikes are in our unheated garage 24/7. They see massive temp extremes. In the last month we have seen temps range from minus 33 C to plus 12 C (27 below zero F, to 54 above F). Zero issues so far with either.
Good luck, and please keep us posted.
There's a bit of discussion on this from the past couple of days in the other mastadon thread. Starting about here:
www.mtbr.com
Summary: you're not the only one seeing this issue.
Manitou Mastodon?
I've heard that Treks are being spec'd with this new fork from Manitou. Has anyone heard any details?
www.mtbr.com
Summary: you're not the only one seeing this issue.
I guess this is what you mean, right? Manitou Fork Rebuild KitProbably bad seal between positive and negative chambers. Recommend an air seal rebuild kit.
Yep. My main seals (fork lowers) are always wet when I come back from a ride. Like they are passing lubrication oil when it’s cold.There's a bit of discussion on this from the past couple of days in the other mastadon thread. Starting about here:
Manitou Mastodon?
I've heard that Treks are being spec'd with this new fork from Manitou. Has anyone heard any details?
Summary: you're not the only one seeing this issue.
I guess this is what you mean, right? Manitou Fork Rebuild Kit
I’ll keep an eye on those, thanks.Yep. My main seals (fork lowers) are always wet when I come back from a ride. Like they are passing lubrication oil when it’s cold.
Well, after working with these forks for several days, I’ve figured out that they don’t like temps well below 0F. It appears on the day that they malfunctioned it was -13F and the negative side air pressure depleted causing the fork to sag over halfway through its travel.
Upon bringing the bike inside where it is warm, I depleted all the air from the fork and started the preload process from scratch by pumping up to 25lbs, then cycling the fork several times and repeating the process 10lb Increment up to 100lbs. I rode the bike for several days, rechecking air pressure after every ride while the bike was cold and notice pressure had depleted 10-15lbs on the first couple rides. The last two rides the preload has stayed stable at 95psi (my prescribed preload).
So my recommendation is if you are bikepacking with this fork in the extreme cold, carry a fork pump and when you get a chance, bring the bike inside and keep it warm. Avoiding riding when it’s less than 0F is sometimes unavoidable, but if your going to ride when it’s that cold, expect this sort of thing to possibly happen and be prepared. As much as I like the fork, I’ll be going to a carbon fork in the winters.
Upon bringing the bike inside where it is warm, I depleted all the air from the fork and started the preload process from scratch by pumping up to 25lbs, then cycling the fork several times and repeating the process 10lb Increment up to 100lbs. I rode the bike for several days, rechecking air pressure after every ride while the bike was cold and notice pressure had depleted 10-15lbs on the first couple rides. The last two rides the preload has stayed stable at 95psi (my prescribed preload).
So my recommendation is if you are bikepacking with this fork in the extreme cold, carry a fork pump and when you get a chance, bring the bike inside and keep it warm. Avoiding riding when it’s less than 0F is sometimes unavoidable, but if your going to ride when it’s that cold, expect this sort of thing to possibly happen and be prepared. As much as I like the fork, I’ll be going to a carbon fork in the winters.
Just came across your thread; I've been having a similar issue with my Mastodon Comp on the cold weather. It seems to sag around -17C or colder; right around 0F. I've posted in the Mastodon thread that kbeefy linked above.
You had asked if other people were having the problem, but no, we are not. I've been using this fork around -25C fairly frequently and a few times even below that. A lot of other people ride this fork here and in similar places. I've had a few complaints, but this hasn't been one of them. I did notice when the cambers equalize when I hook up a bump I have to physically pull the fork apart to keep it from sagging, but reading into it, that appears to be fairly normal, the pump engages the valve which opens a path between both chambers. If your fork is starting at full travel, but sagging down, it's fairly obvious that a seal in between the positive and negative is malfunctioning. Our use of the fork or not having the issue isn't going to help you obviously. That seal rebuild kit and rebuilding everything on the air side would be the way to go. I found to make things easier, dremel/file down your own "thinwall" socket for the air valve and remember both footnuts (the airvalve on the air side) turn OPPOSITE directions compared to conventional threads, manitou threw this one in there for funsies for some reason. After doing that, you probably want to go for lighter bath oil (lighter at -40C, check viscosity).Well, after working with these forks for several days, I’ve figured out that they don’t like temps well below 0F. It appears on the day that they malfunctioned it was -13F and the negative side air pressure depleted causing the fork to sag over halfway through its travel.
Upon bringing the bike inside where it is warm, I depleted all the air from the fork and started the preload process from scratch by pumping up to 25lbs, then cycling the fork several times and repeating the process 10lb Increment up to 100lbs. I rode the bike for several days, rechecking air pressure after every ride while the bike was cold and notice pressure had depleted 10-15lbs on the first couple rides. The last two rides the preload has stayed stable at 95psi (my prescribed preload).
So my recommendation is if you are bikepacking with this fork in the extreme cold, carry a fork pump and when you get a chance, bring the bike inside and keep it warm. Avoiding riding when it’s less than 0F is sometimes unavoidable, but if your going to ride when it’s that cold, expect this sort of thing to possibly happen and be prepared. As much as I like the fork, I’ll be going to a carbon fork in the winters.
That seems poor that we would have to do a seal rebuild on a new fork... I wonder where the screw up is?: at the factory or the the supplier that modifies the fork for sale (from STD to EXT and 100mm to 120mm travel etc...).
What do you mean "supplier"? Did a shop modify your fork? In either case, it sounds like a warranty issue.
The place I bought the Mastodon fork from said "The supplier only brings a few models then modify the travel as I order them and also modifies them from standard to extended if needed". Yeah, I guess it does boil down to more warranty work; even though it's free; the downtime sucks.
I have a 2018 Pro Ext. Oil was a bit low when it came from the factory. Once that was solved I haven’t noticed any weird behaviour. A bit sluggish (but not bad) at -30 deg C. Performs wonderfully at the temperatures I ride most days (warmer than -20 deg C) No leaking, sticking, pressure loss or travel issues. My garage is slightly above freezing on cold days, so my fork doesn’t stay full cold all the time. Most other Mastodons in my town seem to be working fine as well.
Sorry to hear that others are having issues. Hopefully they get sorted!
Sorry to hear that others are having issues. Hopefully they get sorted!
I've contacted Hayes/Manitou about my sag issue in the cold temp. Here is what they said:
Worst case is you've got air passing past the seal from the negative to the positive chamber. But, we don't think this is likely and would require a rebuild to solve. You'd also see this at ANY temp.
The most probable cause is also the forehead slapper to me and a duh moment. The negative chamber is the smaller of the two internally. What I failed to realize (basic science) is that as the temperature drops there - the air in your (smaller) negative chamber is contracting.
So basically; I have to equalize the chambers any time the temperature drops below the temperature the last time the chambers were equalized. I also want to believe its not a bad seal (I haven't ruled it out completely) and it does seem to only happen when the temperature is below -17C or so.
Worst case is you've got air passing past the seal from the negative to the positive chamber. But, we don't think this is likely and would require a rebuild to solve. You'd also see this at ANY temp.
The most probable cause is also the forehead slapper to me and a duh moment. The negative chamber is the smaller of the two internally. What I failed to realize (basic science) is that as the temperature drops there - the air in your (smaller) negative chamber is contracting.
So basically; I have to equalize the chambers any time the temperature drops below the temperature the last time the chambers were equalized. I also want to believe its not a bad seal (I haven't ruled it out completely) and it does seem to only happen when the temperature is below -17C or so.
Just wonder if anyone is experiencing this? The cold weather riding will be here again.
Yeah, i ended up having it later in the season (after my post above). I replaced the air shaft seal a month ago, hoping it will help. Air is not a good idea for cold weather riding. It should be coil. And not having an equalizer notch like RS/Fox is also dumb.Just wonder if anyone is experiencing this? The cold weather riding will be here again.
Or a fella could use an inert gas in lieu of air.Yeah, i ended up having it later in the season (after my post above). I replaced the air shaft seal a month ago, hoping it will help. Air is not a good idea for cold weather riding. It should be coil. And not having an equalizer notch like RS/Fox is also dumb.
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