hydrolic brake bleeding

[madcyclist09]

I need to bleed my MTB brakes, I have been watching you tube.
There seems to be a couple of ways
One bleeding from the top just to get the air out
The other using the oil via the disc caliper
Using a syringe
I have never done this before so any advice would be very much appreciated

Thanks in advance

 

[KneesUp]

I did this for the first time recently by injecting oil at the caliper until the stuff coming out the lever was new oil (red not black in my case)

I then sealed it all and bounced the bike for a while to get the air to the top and repeated until the lever was firm. I’m by no means an expert but the brakes work. It’s not as difficult or fiddly as you might think, but it is the brakes so make sure the work!

 

[88robb]

The best method uses a syringe at the caliper. Push new fluid up from the bottom to force the air out the top.
Keep the lever reservoir full at all times. Never let it run dry or you'll get more air in.
Tap the hose and fittings to loosen stubborn bubbles.
Close the lever bleed port first, then remove the syringe.
Clean everything perfectly with isopropyl alcohol. Spilled fluid ruins your brakes.

 

[chriswoody]

The very first thing you need to do is determine which fluid your brakes use. There are basically two fluids, Mineral Oil and DOT 5.1. They require very different bleed procedures and DOT 5.1 in particular is very nasty corrosive stuff, for which you'll need isopropyl alcohol to clean everything and gloves on your hands.

Broadly speaking, SRAM brakes use DOT5.1 and Shimano use mineral oil, though there are exceptions! The best thing is to look at the brakes themselves, often the DOT fluid systems will have that marked on them, otherwise Google is your friend. Do not under any circumstances put the wrong fluid into your brake system!

For SRAM systems you'll need two syringes with DOT fluid, one attached to the caliper, one to the brake lever. You push fluid between the two until no more bubbles come out, then you lock the syringes and independently bleed the caliper and the lever reservoir. It is more detailed, but it's best you check out videos online.

Shimano I've never done, but I believe you just need a little bucket type affair to attach to the reservoir. DOT fluid is pretty hygroscopic, so SRAM brakes could do with a bleed every year to keep them tip top. Mineral oil is much better though and often will go many years before needing a bleed.

 

[Punkawallah]

Be aware that if bleeding does not improve the braking, you could be getting air in at the lever, and the cost of a lever service kit (if available) is not cheap. Got that t-shirt.

 

[figbat]

The very first thing you need to do is determine which fluid your brakes use. There are basically two fluids, Mineral Oil and DOT 5.1. They require very different bleed procedures and DOT 5.1 in particular is very nasty corrosive stuff, for which you'll need isopropyl alcohol to clean everything and gloves on your hands.

Broadly speaking, SRAM brakes use DOT5.1 and Shimano use mineral oil, though there are exceptions! The best thing is to look at the brakes themselves, often the DOT fluid systems will have that marked on them, otherwise Google is your friend. Do not under any circumstances put the wrong fluid into your brake system!

For SRAM systems you'll need two syringes with DOT fluid, one attached to the caliper, one to the brake lever. You push fluid between the two until no more bubbles come out, then you lock the syringes and independently bleed the caliper and the lever reservoir. It is more detailed, but it's best you check out videos online.

Shimano I've never done, but I believe you just need a little bucket type affair to attach to the reservoir. DOT fluid is pretty hygroscopic, so SRAM brakes could do with a bleed every year to keep them tip top. Mineral oil is much better though and often will go many years before needing a bleed.

It’s usually DOT 5.1 or DOT 4, in fact DOT 4 is more usual. Both are acceptable and interchangeable. Both are also bad for paintwork so need thoroughly cleaning up, but I wouldn’t describe them as “very nasty, corrosive stuff” - if they were then the brake systems would dissolve!

Mineral oil is not hygroscopic, no, but this means that any moisture that enters the oil tends to pool as free water at the lowest point of the system, usually the caliper, which can cause corrosion.

 

[chriswoody]

It’s usually DOT 5.1 or DOT 4, in fact DOT 4 is more usual.

It's a fair point, I should have said DOT fluid and Mineral. Personally I find 5.1 more common, whilst SRAM do say 4 or 5.1 is fine, 5.1 is referenced in their tech docs and more commonly available in the bike shops here in Germany. But it's irrelevant really, your right, 4 or 5.1 will do.

, but I wouldn’t describe them as “very nasty, corrosive stuff” - if they were then the brake systems would dissolve!

OK, fair point, probably a little hyperbolic. Still I would always advocate for gloves and keeping everything clean.

Mineral oil is not hygroscopic, no, but this means that any moisture that enters the oil tends to pool as free water at the lowest point of the system, usually the caliper, which can cause corrosion.

Good to know, I've never used mineral oil brakes so it's good to increase my knowledge.

 

[Drago]

Use whatever method the manufacturer of your brakes suggests.

 

[fossyant]

Epic Bleed Solutions do a very good step by step instruction sheet that you can print out and take to the bike when you do the bleed.

 

[midlandsgrimpeur]

Most of the relevant points are covered. The only thing I would add is to check whether your brake manufacturer says to not pump the brake whilst the bleed is in process (I have seen people on Youtube vids doing this to check if the brake lever is now firm). Shimano for example says specifically not to as it can let air back into the system.