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A friend is in the process of swapping brakes over from one bike to another. Rather than go through the palaver of routing a new hose through the frame, he's left the old hose in situ. While it was disconnected from the calliper and master cylinder, he used mineral oil to flush out the Dot 5.1 fluid in the old brake hose and has now reconnected the new mineral oil based master cylinder and calliper to it. I don't think he's bled the brake yet, but I'm really worried that there might be residual Dot 5.1 fluid contaminating his brake system.
Am I worrying over nothing, or is his bike going to explode into a fireball on an Alpine descent? My mate's pretty convinced that everything will be fine and I'm worrying over nothing. I'm pretty convinced that there's no way I'd fancy taking the risk, but I am a huge worry-wort. I've had a rear calliper failure on a descent, and it hurt. It hurt a lot.
Has anyone else added just a trace amount of Dot 5.1 into a mineral oil solution. Did you survive or die? I need to be convinced that everything is fine and I'm worrying over nothing. Or, I need enough evidence to stand up and say, "Chuck that in the bin, it's a liability"
Cheers
Mmmmm there's a question. That's a tricky one, but i'd have NEVER contemplated doing it like that... i'd have just fitted the new hose.
Back in the day i had a mechanic do a service on a KTM which was running Magura blood, he used Dot (not knowing it was Magura), i got about 100m before failure. But that was a full bleed rather than a residual/tiny amount.
I did similar on my old cube ebike. Swapped the Shimano brakes for my preferred hope brakes.
Flushed the hose about 5 times with dot fluid, attached the hope caliper and never had a problem in over 1000 miles of use.
The lbs said I shouldn't have done it, but they didn't want to swap the hose for me when I first got the bike.
I think at least some hoses offered online are good to be uses no matter if for DOT or oil... I would be reluctant to do it the other way (DOT -> oil) as DOT seems to be aggressive, but from DOT to oil. But I wouldn't do it on both brakes to be on the save side 🙂
I design brakes for cars for a living.
Mixing even a small amount of mineral oil with a DOT brake fluid is a recipe for eventual disaster.
The seals are made of different types of rubber to suit each fluid.
The different fluids attack the rubber for the other fluid and will eventually lead to seal failure and brake failure/loss of brake fluid.
This is an absolute NO in automotive circles.
Back in the day i had a mechanic do a service on a KTM which was running Magura blood, he used Dot (not knowing it was Magura), i got about 100m before failure. But that was a full bleed rather than a residual/tiny amount.
A mechanic did this to my cousin's Citroen Dyane which uses LHM mineral oil. That was an expensive mistake for him!
For the OP, I'd do what your mate did. Probably flush some mild solvent though and re-flush that as belt and braces but in principle flushing is fine and DOT hose will be OK with mineral oil. At the end of the day it's his bike and risk.
I'd not be doing that myself...if a system is filled with Dot then it only ever gets dot, if mineral then only mineral.
I'd be too worried that I hadn't flushed enough and the new fluid was chewing away at the seals (so 2 things I'd be worrying about).
Saying that, I have an incredibly unhealthy love affair with my brakes - I can't keep my hands off them! So I suspect I'm already primed to be worrying about that kind of thing!
It wouldn't be me. It's such a safety critical system that I'd do nothing that the brake manufacturer doesn't recommend. What do they say about this?
Put it this way, you mentioned the Alps, so am assuming he has a trip coming up. If he has a bad one in the Alps due to brake failure, do you think the manufacturer will accept any liability?
Being dumb here but... he took his DOT-based brake to the new bike and replaced the DOT with mineral oil?
Or he only took the old hose; and the new brake is mineral oil based? Cause if it's the former, I'd say he has more to worry about than traces of DOT in the mineral oil - like a whole load of mineral oil in his DOT...
If it's the latter, that's probably less bad, but still not ideal
I did it on my wifes ebike, swapping the rear hose looked like it was a motor out job so I drained the old fluid and then put the air line on it and blasted every last bit of dot fluid out. Luckily the hose was long enough to nip the ends off and fit the correct barb and olive before fitting the new lever and caliper. Been fine for the 18 months since I did it.
Big fat no from me.
It's not that difficult to swap the hose over even on the worst-designed internally-routed ones. Just need the correct tool for the job, a kit something like this for less than the cost of a pint: www.amazon.co.uk/Internal-Routing-Hydraulic-Professional-Mountain/dp/B0BJ15LM2Z/ref=asc_df_B0BJ15LM2Z
(pull the guide wire through the frame and you remove the old hose, then use the guide wire to pull the new hose in - easy, in theory)
@a11y I got a clever little 2 sided screw tool that connects the old hose to the new. It was a couple of quid off Amazon. I then simply pulled the old hose out and the new one was pulled through. It took a couple of minutes to setup and worked perfectly. We were swapping the Hope V4's from my old bike that he's just bought, onto my new bike, and the new Shimano brakes from my bike onto his. He just didn't want to bother running a new hose through the frame. I think I've convinced him to disconnect the system again and flush it all through with a good quantity of isopropanol, then flush again with mineral oil before connecting it all back up and properly bleeding it though.
I very much appreciate that I'm getting more risk averse as I age, and I've always been a worrier. In my head, just connecting the old hose that had contained Dot 5, to the mineral oil Shimano brake risks contaminating the system and has made it a bin job, but I very much appreciate that's just my scaredy-cat head talking.
What's the difference between the 2 kits listed above?
The hoses are compatible with both fluids. But one fluid (DoT i think) can contaminate the inside of the hose over time, which can cause issues if you then switch to mineral.
No, i don't know what the effect is. Or what the timescale is.
Thanks everyone. My mate has messaged me to say he's just bought a fresh hose and bleed kit. Again, he was probably right and everything would have been fine, but I personally wouldn't want to be second guessing my brakes, and I've been getting more and more anxious about it on his behalf. Time to have a nice relaxing G&T now, on his behalf.
This is the doohickey that I got. It's incredibly simple and works perfectly for feeding the hose through the frame.
Sorry, can't get the link to work. Just google 'threaded brake hose connector'.
Everyone I’ve ever spoken to has said that even the tiniest bit of DOT will trash the seals.
Won't any residual DOT fluid rot any seals in the lever and caliper? If so, won't he also have to replace them as well (and not just the hose)?
(Is it even possible to replace seals in Shimano brakes?)
All in all, seems like a bloody stupid* idea to re-use brake hose unless it's DOT > DOT or Mineral > Mineral...
*And expensive and time consuming
The different fluids attack the rubber for the other fluid and will eventually lead to seal failure and brake failure/loss of brake fluid.
Isn't it about time someone came up with a third kind of rubber that works with both?
Isn't it about time someone came up with a third kind of rubber that works with both?
It’s been like this for 50 years so it’s clearly not that simple 😮
Isn't it about time someone came up with a third kind of rubber that works with both?There are several that do both already. They're just terrible at high, or low temp, or water. Or possibly not very flexible, or they might be £100 for a set... Take your pick.