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Airline travel and disc brakes
 

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 4472
Location: Nashua, NH

7/7/19 1:50 PM

Airline travel and disc brakes

I have a bit of a mystery that I need the collective minds here to solve. We just got back from a 2-week trip to CA and we flew our bikes out with us. I carefully packed our bikes in a TriAll3Sports double case, as I've done before. I put pad spacers in all four brake calipers that were fairly thick and compressed the pistons slightly.

When we got there, I noticed that my rear brake lever went almost to the bar, but would pump up to a normal position if I squeezed it a few times (typical). Over the course of a few days use, it seemed to return to normal operation.

This morning when reassembling the bikes at home, I didn't notice any issues with Linda's bike, but I had to get it back together quickly so she could head home and reunite with her dog and cat (yeah, I'm sort of "third fiddle" in this relationship, but I'm fine with that).

I had the same issue with my bike again, but somewhat with the front brake, too. I bled both and got a few small air bubbles out of the rear lever and tiny bit out of the front lever, and everything seems normal, now. I also found some spots of what appeared to be brake fluid or mineral oil on the bottom of the case, but they were on her side. I didn't notice any leaks or fluid on either bike, which would have been pretty obvious since they were lightly covered with CA trail dust. I'm waiting to hear back from her after she looks it over.

Anyway, my question is if anyone has encountered any issues with disc brakes when flying. Obviously, lots of riders do it, so it shouldn't be a major issue. I don' recall having any issues with our MTBs when we flew with them back in 2008. Could the issue just be due to expansion of the tiny amount of air in my brake lines? I'm somewhat baffled.

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Sparky
Joined: 08 Dec 2003
Posts: 17412
Location: Portland, OR

7/7/19 2:50 PM

"encountered any issues with disc brakes when flying"

Do you mean with hydros and pressures at altitude, etc.?

Maybe upside down for the duration allowed for scant air bubbles to get together in the system. You either have a leak or don't. But if up at the lever compression fitting you may not have realized it until now. Given it spends it's lift in the non prone position. ;) My guess is that may be possible.

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 4472
Location: Nashua, NH

7/7/19 3:13 PM


quote:
Do you mean with hydros and pressures at altitude, etc.?

Precisely!

The case itself definitely spent time on it's side, but it's highly unlikely that it was ever upside-down. The bars were removed and re-positioned to fit in the case, though they were basically still upright. Everything was tied together securely, so they wouldn't have been flopping around.

I tend to agree with your point that it either leaks or it doesn't, but I have seen admonishments from MTB manufacturers about not storing bikes with disc brakes hanging upside-down. One would think that this wouldn't be an issue in a sealed system, but who knows?

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Sparky
Joined: 08 Dec 2003
Posts: 17412
Location: Portland, OR

7/7/19 4:09 PM

"One would think that this wouldn't be an issue in a sealed system, but who knows?

If there is inherently 'some' air not purchasable in the system even at the minutest amount. Design provisions are certainly in order to keep 'any' of it above the master inlet, etc.

Any way you can determine for sure one way or the other if the 'wet' spot IS mineral oil?

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 4472
Location: Nashua, NH

7/7/19 7:31 PM

The fluid that leaked was odorless and felt oily, which is true of both mineral oil and DOT brake fluid, so I can't tell which it is. Linda said she noticed something on one of her tires when I was assembling the bike, but she didn't mention it at the time. I suspect that it came from her bike and most likely from the levers, based on where it was in the case. This is going to take some sleuthing and I'll check my bike out on the trails tomorrow so I can rule it out.

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