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Discussion Starter · #1 ·
So...long story short I found myself on top of a mountain in failing light with a fat bike in my hands with a completely flat rear brake. El cheapo Shimano M447's that came on my fatty. Not wanting to walk down, I decided to bleed it with the only thing I had in my bag, Finish Line Wet chain lube.

Finish Line - Bicycle Lubricants and Care Products - WET Lube

First off; it worked! No guff, I was able to force enough chain lube into the reservoir through the tiny bleed port to get a working back brake and get down the mountain.

Question is, is that brake garbage now? Can it be purged out and re bled? Have I damaged the seals, and stuff?
 

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Why so uptite?
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Just bleed them with fresh Shimano mineral fluid and see how it goes. I doubt they are trashed. If they are trashed it gives you a reason to upgrade.
 
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Yup many liquids can be used, olive oil, power steering /auto trans fluid so seeing as you macgyvered it to get down the mountain speaks to nearly anything being used in a pinch.
 

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Dang. Good job doing a fix. What's the worst that can happen at this point? You put $5 worth of mineral oil in to flush and re-bleed? If they work, you saved $100 on new XT brakes, if not, you aren't out much.


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Ripmo
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It seems to me, that flushing them with alcohol would be best. Perhaps the 70% rather than the 90% isopropyl alcohol. Then refill with Shimano mineral oil. Perhaps drain and refill with fresh mineral oil after a few rides. A call to Shimano couldn't hurt.
 

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Of course Shimano will tell you they're trashed. They don't know what the result of using unapproved fluid will be, which voids the warranty btw, and will be happy to sell you new ones.

There are many good reasons not to use random fluid in your brakes: It may damage seals, the bladder or other parts, be too viscous at low temperatures, boil too easily at high temperatures, create precipitates that clog orifices, etc...but you'll probably get away with it anyway.
 

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To the OP...what failure necessitated bleeding them?
That's what I was wondering too. M447's are usually pretty reliable and I can't see what failure would require a bleed and then not repeat itself if there was still an issue.
 

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I'd say that's a great McGuyver. Also curious of the ":why" it was needed and did not need to be repeated? As to if it damaged the seals, as everyone else said, no clue, but flushing it with something first before flushing with Shimano mineral oil would be a good idea, maybe 70% alcohol would do the trick. Personally, I'd strip it down, take the hose off and flush that separate and then do the reservoir and caliper, then put it back together and flush again and the flush with mineral oil.
 

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I agree to flush and refill with the approved fluid. I'd spend extra effort to flush it THOROUGHLY to make sure all the chain lube is flushed out. It's likely that negative effects of the stuff won't happen immediately, but rather will take some time (and will probably happen with the seals).

I liken this to the time a generic repair shop put gearbox fluid in the transmission of my manual transmission Ranger a long time ago. Fluid was too thick and I couldn't shift out of 1st. The shop tried to convince me that my transmission needed rebuilt. Ford dealer spotted the problem immediately and had to do a REALLY THOROUGH flush before using the correct fluid. Thankfully, the bill for that went to the shop that f*cked it all up.
 

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Discussion Starter · #12 ·
Thanks for the feedback, so what happened was the brakes started making a lot of noise. Contaminated pads kind of noise. They also started going flat, where I'd have to pump them lots. The pads were worn out, so I replaced the pads, sanded and lightly blow torched the rotors, and did a bleed.

I either have a leak at the pistons or messed up the bleed, (or both)whatever the case, at home the brakes felt perfect, but once I started riding (-15 degrees celcius) they started losing pressure, and again started squealing. I thought I could get through the ride but by the time I got to the top of the DH they had gone completely flat.

I tried pumping them a hundred times and was not able to build any pressure at all. I briefly though of just jamming my foot in the back wheel ghetto style but that proved very difficult to control. I tried the DH with only front brake and crashed hard when my wheel washed out so I was left with 2 choices; walk down, or bush fix.

I opened the bleed port and managed to get brake fluid into the reservoir by pumping the lever slowly until the drop of lube was pulled into the lever reservoir. It took a good 20 minutes to get enough pressure to control the brake but it worked.

Since then, I've drained the brake and forced compressed air into the line from the bottom up and just left it hanging from the rafters of the garage. I guess it's flush time.
 

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So let me get this straight, after everyone gave the advice to properly flush the system you still went ahead and did not and expected the brakes to work properly with a "bleed"? :???:

Thanks for the feedback, so what happened was the brakes started making a lot of noise. Contaminated pads kind of noise. They also started going flat, where I'd have to pump them lots. The pads were worn out, so I replaced the pads, sanded and lightly blow torched the rotors, and did a bleed..
 

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Discussion Starter · #14 ·
So let me get this straight, after everyone gave the advice to properly flush the system you still went ahead and did not and expected the brakes to work properly with a "bleed"? :???:
No, this is the back story as requested. Before the bush fix, before the issues with brakes going flat, I started having mushy brakes that started making a lot of noise.

I think what happened is that as the pads wore out the pistons eventually over extended and allowed fluid to leak onto the pads and rotors. I replaced the pads, and did a bleed and everything was cool until I got to the top of a big climb and realised all was not cool and I had no pressure.

Next I did a bush fix, got home drained the lines by force with a blow gun, hung them to dry, and then made a post on MTBR asking if I wrecked my brakes.

Beyond that I haven't done anything to them yet. I did however buy some XT M8000 brakes which as per usual had to be bled out of the box, and as per usual came with metallic pads which squeal like a banshee when wet (like when fat biking in the snow). I'm talking 100dB hearing protection required loud! So today I bought resin pads, will test out tomorrow.

As of today I still haven't tried to repair my M447's yet. I would like to keep them in working order. For fat biking in snow they are perfectly adequate. On dirt where speeds are higher they are way underpowered for 200 Lbs of me on a 35 Lb bike... Spare brakes are always good to have.

Anyway, thanks for the advice. I'll try a flush and see how they hold up. I forgot to ask the guys at the LBS today, will phone and see what they say as well.
 
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