Not sure which brake fluid for 2010 SLX

alienmuppet · Aug 14, 2023

Hi, I’m preparing my oldest bike to sell and noticed the back brake feeling spongy and weak. So I decided to bleed it. First thing I noticed was the oil was not the same pinky red colour of the shimano mineral fluid. Also it turns out the reservoir is blocked so I’ve ended up stripping down the lever.

I’m worried someone has stuck DOT fluid in there.

Is it likely it’s just old mineral oil and lost its colour?

it’s a Trek Fuel EX 8 2010, Shimano Deore SLX. It wasn’t that old when I got it so it’s more likely the original fluid..

I’m worried I’ll stick the Shimano fluid in there and it’ll fail at a later date.

Sparticus · Aug 14, 2023

From this Shimano website:

HTH.
=sParty

ljsmith · Aug 14, 2023

Mineral oil has no color. Shimano dyes theirs red, other companies use different color dyes. It is probably non-Shimano mineral oil that is not dyed. Or some cheap people use baby oil. DOT would dissolve the seals so it wouldn’t have worked very long.

Sparticus · Aug 14, 2023

Old mineral oil can get pretty dingy looking regardless what hue it once was.
=sParty

alienmuppet · Aug 14, 2023

Cool, thanks

J.B. Weld · Aug 14, 2023

It's typical for the old fluid to be nearly black when bleeding older Shimano brakes.

alienmuppet · Aug 14, 2023

That’s the thing, it wasn’t, it was just a light oil colour, though a little dirty. The reservoir had some gunk. Tomorrow I’ll get the circlip off the piston and see why it’s blocked.

NoCanSurf · Aug 15, 2023

I bought (and installed) SLX 4 piston brakes in May and had to bleed the front last weekend. These brake were ordered directly from Shimano (I work part time at a bike shop). The mineral oil in the front unit was a pale sickly light brown or tan-like color. The red color of Shimano brakes fluid seem to fade quickly, but still works.

You could drain and refill the system if you wanted 'wash out' the old brake fluid. There's really not much fluid in the system compared to a car or pick-up truck.

Jayem · Aug 15, 2023

I've used very light suspension oil in my shimano brakes, in an attempt to fix the wandering bite point issue. It was slightly better, but it didn't fix the issue. The suspension fluid was fairly clear. But fluid always comes out black or grey with shimano brakes, as the cast master cylinder scores the piston and seals over time.

mtbfree · Aug 16, 2023

If you are worried that 13 years old brakes will fail later, dismount them and sell without brakes. Buyer can easily buy new quality brakes quite cheap these days.
If there was DOT inside it probably destroyed seals.

davez26 · Aug 20, 2023

What does this mystery fluid taste like?
.
JK, a billion years ago my Chemistry teacher 'F' an assignment as I used taste as a determinant on an unknown chemical. 'you coulda killed yourself'...
anyway all above is accurate.
Blocked reservoir makes me think that maintenance was few/far between on this bike.
If it was DOT, this system should have failed by now.
Clear it, bleed it, should be gtg.

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Not sure which brake fluid for 2010 SLX

alienmuppet

Sparticus

ljsmith

Sparticus

alienmuppet

J.B. Weld

alienmuppet

NoCanSurf

Jayem

mtbfree

davez26

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