Jump to content

Disk Brakes Service


Crytaan
 Share

Recommended Posts

Hi,

 

This is my first topic on the HUB, and I am fairly new to MTB. I would like to be able to service my own MTB.

 

I thought I start with the brakes - Shimano M575.

I would just like to know if someone can tell me how often should one bleed disk brakes. My disk brakes performance is going down. Might this be because of the pads.

 

Your help would be appreciated.

 

Crytaan

Link to comment
Share on other sites

Go to park tool's website. also youtube! they show some nice vids on all the how to's........ MAKE SURE YOU USE MINERAL OIL!

Link to comment
Share on other sites

Yes MIneralOIl only its a pink oil from shimano DO NOT use Normal Dot4 as this will mess up the internal seals.

 

 

Basic technique:

 

open reseviour cap on the lever make shure it is parallel to the ground, use a syringe with a plastic tube on the tip and put it over the bleed nipple, open the nipple, suck out the old oil and dispose of it properly.

 

Bleading is the same technique but in reverse pushing oil in from the syringe into the caliper through the hose to the lever. don't get any air in the syringe when you bleed as it may cause a nasty bubble and a dip in performance. if the reseviour in the lever get filled up suck some oil out with a different syringe.

 

 

Here are a few tips for you,

 

Remove the pads and don't get oil on the,

Push the pistons back into the caliper.

Bleed the brakes with new oil.

 

Close everything back up

Link to comment
Share on other sites

Thanks guys.

 

But my question is, why is it necessary, should I bleed the brakes at all? Where does the mineral oil, if there are no leaks, go to? Isn't it just the brake pads, have them for about 1000KM? Should I try clean them first or what?

 

I am trying to understand the logics behind it, and not just jump in and start changing things I don't understand why.

 

Thanks

Link to comment
Share on other sites

Hi C

 

Remember, when your brake pads are removed...NO NOT pump the brakes! It causes the pistons to move toofar out and it becomes a problem to get them back in and it opens the sytem up for air...

 

That being said, as your bake pads wear down...there is a need for more oil in the reservoir to basically produce the same amount of hydraulic pressure as before (i.e new brake pads).

 

So, as you pads wear down...like yours at ~1000km...there will be a need to top up with brake fluid...

 

It's a fairly straight forward exercize...just keep air out of the system..(use your logic!)and the rest is a breeze.

 

I find that pushing oil up from the bottom via a syringe works fine...the bubbles if any will foat to the top...

 

Good luck!

Link to comment
Share on other sites

There are a few things that can cause performance to dip.

 

1. The brake fluid degrades over time as a result of the heat generated by the braking itself the oil goes kind of watery and thin and looses its pink colour therefore needs to be replaced from time to time.

 

2. the pads wear down and the pistons stand further out as a result to make up for the pad wear the oil for this is taken from the reseviour slowly emptying it.

 

3.Small amounts of oil is lost through the seals as the oil also lubricates the seals

 

These are just a few reasons there can be many others.

 

I have a general rule of thumb, when my pads wear out over a long time (not as a reasult of one muddy race) I replace the pads and re-blead the system because you'll have to push the calipers pistons back anyway to accomadate the new pads with the thicker braking surface.

Link to comment
Share on other sites

Bleading is the same technique but in reverse pushing oil in from the syringe into the caliper through the hose to the lever. don't get any air in the syringe when you bleed as it may cause a nasty bubble and a dip in performance.

 

I bled my avid elixers last nite and some how a bubble sneaked in.

 

Half way in my rear brake lost alot of power and pulled to the bar,so always check your work with a small ride if I didn't test it it would have been a disaster in racing.

 

Also bear in mind that after you've drained the system some air could get trapped in the corners of the caliper or levers so alway alway check it.

 

One more tip when the pads are out put a small block of wood between the piston and then bleed them the block will stop the pistons sneaking outward and make the bleeding easier.

Link to comment
Share on other sites

Hi Guys,

 

Thanks for all the replies.

 

Okay so this is what I learned from this topic.

 

1. Keep air out of the system.

 

2. The mineral oil or brake fluid, because of the density it cannot be compressed as air can which makes the brakes responsive.

 

3. When the disk brake pads gets wears down, the pistons stand further out to make up for the pad wear mineral oil or brake fluid from the reservoir needs to enter the pipe system to produce the same amount of hydraulic pressure as before, which leaves the change of air entering the pipe system from the reservoir. This it why the mineral oil or brake fluid should be topped up in the reservoir.

 

4. Because of the mineral oil or brake fluid degrading over time as a result of the heat generated by the braking itself the oil goes watery and thin and looses its density and needs to be replaced from time to time by bleeding the system.

 

5. Small amounts of oil is lost through the seals as the oil also lubricates the seals, which is another reason why the mineral oil or brake fluid should be topped up.

 

Is this it or did I mis something?

 

Once again, thanks guys. I have a much better understanding on why disk brake performance degrades.

 

Cheers

Link to comment
Share on other sites

Hi Guys,

 

Thanks for all the replies.

 

Okay so this is what I learned from this topic.

 

1. Keep air out of the system.

 

2. The mineral oil or brake fluid, because of the density it cannot be compressed as air can which makes the brakes responsive.

 

3. When the disk brake pads gets wears down, the pistons stand further out to make up for the pad wear mineral oil or brake fluid from the reservoir needs to enter the pipe system to produce the same amount of hydraulic pressure as before, which leaves the change of air entering the pipe system from the reservoir. This it why the mineral oil or brake fluid should be topped up in the reservoir.

 

4. Because of the mineral oil or brake fluid degrading over time as a result of the heat generated by the braking itself the oil goes watery and thin and looses its density and needs to be replaced from time to time by bleeding the system.

 

Is this it or did I mis something?

 

Once again, thanks guys. I have a much better understanding on why disk brake performance degrades.

 

Cheers

 

Spot on!! 100%

 

So, your'e not a disc brake virgin anymore!! :D

Link to comment
Share on other sites

Spot on!! 100%

 

So, your'e not a disc brake virgin anymore!! :D

 

LOL, I understand it better, however, now its time to actually service these bad boys. Do you perhaps know were I can get the mineral oil used by Shimano disk brakes.

Link to comment
Share on other sites

A few thoughts to add.

 

All fluids break down over time and believe it or not do leak out as well as get contaminated, how? I don't know, so the fluid needs replacing.

 

Mineral oil can be purchased in 1 Lt containers from a brake supplier to the motor trade for less than R40.00/Lt.

 

Make your own bleed kit, mine cost R10.00 and works just as well as the Shimano kit for R1200.00.

 

All you need is the internet for tech tips. A bike stand to hold the bike in the right posistion, reservoir higher than the caliper, helps.

 

When you buy brakes from CRC you get the plastic spacers to keep the pads "open" when the wheel is removed, great help, try to get these from a bike shop if you can.

Link to comment
Share on other sites

A few thoughts to add.....

 

Would it possible to add some images of the kit you made for some ideas?

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

Settings My Forum Content My Followed Content Forum Settings Ad Messages My Ads My Favourites My Saved Alerts My Pay Deals Help Logout