How to: change/replace front brake fluid, Brembo

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Magic Wand
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How to: change/replace front brake fluid, Brembo

Post by Magic Wand » Tue Jul 12, 2016 9:18 am

Hi!

KTM SMT 990 2010, aprox. 30000 km (18640 miles). Brembo calipers.

I have changed the brake fluid in rear brake system, by using the traditional method, that is to repeatedly pump the brake lever and open the bleed valve to let fluid come through and keep an eye on the reservoir to fill it when necessary (without letting in any air in the system). I used 70 ml of new fresh brake fluid DOT 4+ which should be enough to change/replace all the fluid in the system.
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Now I´m going to change/replace the brake fluid in the front brake system.
I have read a couple of threads at different forums and also searched the "U-tube" for movies "how to", but can´t really find the answers of my questions about this work.

First, the bleed valve at the caliper is placed ON TOP at the banjo bolt, which gives that the old brake fluid will stay in the caliper if using the traditional method; pumping the brake lever and open the bleed valve. Right?

And also if using the method to demount the banjo to let the brake fluid "drop out" of the system by the law of gravity, gives by hand that the old fluid still will be left in the caliper. Right?

So, my question is: how do I get the old fluid out from the caliper? I don´t want to disassemble the hole caliper (!)

One theory is to demount the caliper from the bracket, take out the brake pads, open the bleed valve and at the same time slowly push the pistons in, equally. The brake fluid should come out through the valve hole. When fluid stops, close the bleed valve.
Use a syringe and a plastic hose attached to the bleed valve (be careful not to push in air). Open the valve and suck the old brake fluid out, keeping an eye on the reservoir and fill it when level gets low. I presume it´s a bit difficult to see when all old fluid has passed the system, but my guess is that aprox. 100 ml will be enough.
After sucking the old fluid out, mount the brake pads and mount the caliper back to the bracket. Press the lever to make the pistons move out.
Bleed at the valve on the caliper and also at the valve on the master cylinder. Just in case.

What do you think - will this work out?

/M
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Last edited by Magic Wand on Tue Jul 12, 2016 6:49 pm, edited 1 time in total.

Gary
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Re: How to: change/replace front brake fluid, Brembo

Post by Gary » Tue Jul 12, 2016 2:02 pm

I can't really answer your question. Service manual suggests the use of a pressure bleeding system. I'm not sure how that system defeats gravity, which is the source of your problem. I reverse bled the rears and it worked great. I'm planning to do they same on the fronts as well.

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Re: How to: change/replace front brake fluid, Brembo

Post by Magic Wand » Tue Jul 12, 2016 6:45 pm

Gary wrote:I can't really answer your question. Service manual suggests the use of a pressure bleeding system. I'm not sure how that system defeats gravity, which is the source of your problem. I reverse bled the rears and it worked great. I'm planning to do they same on the fronts as well.
Hi Gary!

Thanks for the reply.
Not blaming anyone, I don´t understand how "reverse bleeding" or pressure bleeding of the front brake system will get the old fluid out of the calipers... since the bleed nipple/valve is placed on top of the banjo bolt. Strange.

/M

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Re: How to: change/replace front brake fluid, Brembo

Post by Thirdway » Fri Jul 15, 2016 7:05 pm

Just bleed it normally. Start with the furthest point and just flush the fluid through using the age old loosen, squeeze, tighten, release method with a jar half full of fluid to prevent air entering. then go the caliper nearest the reservoir, then finally the lever bleed nipple.

You will want to empty the reservoir, but only just, then wipe a paper towel around it to get rid of any sludge. Push a full bottle through the system. Easy as that

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Re: How to: change/replace front brake fluid, Brembo

Post by Magic Wand » Fri Jul 15, 2016 8:37 pm

Thanks "Thirdway"

I understand how to bleed the normal way. But still I don´t understand how the old fluid in the calipers will come out, since the bleed nipple/valve is placed ON TOP of the caliper/banjo bolt...
When doing it the way you are describing, the old fluid in the calipers will stay in the calipers. Right?

/M

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Re: How to: change/replace front brake fluid, Brembo

Post by Thirdway » Fri Jul 15, 2016 9:04 pm

Magic Wand wrote:Thanks "Thirdway"

I understand how to bleed the normal way. But still I don´t understand how the old fluid in the calipers will come out, since the bleed nipple/valve is placed ON TOP of the caliper/banjo bolt...
When doing it the way you are describing, the old fluid in the calipers will stay in the calipers. Right?

/M
If you want to purge every bit of fluid you would have to remove and empty the caliper bodies. If you don't want to do that then the closest you can get is to remove the calipers, push back the Pistons and then use clamps to hold them in that position whilst you bleed them. Overkill unless you have contamination or have boiled the fluid.

If you have decided all the fluid needs to go, then I suggest you do a full overhaul of the Pistons and seals at the same time. It's a fiddly, but straight forward job if you have the patience. You can buy seal kits from KTM and the Pistons if any are damaged. Best to buy a little dental kit, Q tips, ty wraps and a head torch.

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Re: How to: change/replace front brake fluid, Brembo

Post by Magic Wand » Mon Jul 18, 2016 7:26 pm

Thirdway

I see. As I expected.
Probably I will do a full overhaul during winter time. For now I will use the method described by you.
Thanks!

/M

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Re: How to: change/replace front brake fluid, Brembo

Post by Thirdway » Mon Jul 18, 2016 9:02 pm

Magic Wand wrote:Thirdway

I see. As I expected.
Probably I will do a full overhaul during winter time. For now I will use the method described by you.
Thanks!

/M
One of the reasons not to bother using the DOT4 super fluid is that you can't avoid mixing with some of the older fluid anyway. Just use plain DOT4 as that's what DOT4 super becomes immediately it mixes with older brake fluid.

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Re: How to: change/replace front brake fluid, Brembo

Post by Magic Wand » Tue Jul 19, 2016 8:33 pm

DOT 4 Super fluid - don´t know what it is. I have bought DOT 4+ (I did use it for the rear brake), maybe it is the same thing?
Ok, I see what you mean about the mixing - thanks again.

/M

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Re: How to: change/replace front brake fluid, Brembo

Post by Magic Wand » Sat Jul 01, 2017 1:30 pm

Update 2017-06-30:

KTM 990 SMT 2010, with 46920 km.

I have neither used the bike in snowy conditions, nor on "salty" roads.

2 weeks ago 5 friends and I made a long travel in Sweden, Finland and Norway. We ended up at nearly 6000 km in 9 days!

Decided to take the brake calipers off and have a closer inspection to them.

Removed and emptied the caliper bodies.
Pressed out the pistons by using pressured air - no problem. Once at a time of course, and tied the 3 others up using binding wire (cable ties will work good as well).
The pistons were dirty on the outside, as I expected, but not a scratch or similar damage on the main surface.
Cleaned the inner surface using STP Brake cleaner (evaporates quickly).
The sealings were tight as well. No need to replace with new ones.

Noticeable:
The brake pads still have the thickness och 3.1 mm, compared to the new SBS ones I bought earlier; 4,5 mm.
So the original Brembos have a quite long living interval.

Decided to wait with the "overhaul" of the brake calipers until coming winter. Maybe I will put some new paint at them as well.
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When refilled with brake fluid I bled the system as it should be done, but still there are some air in the system I think. So I will do a new bleeding session later on today.

/Magic

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Re: How to: change/replace front brake fluid, Brembo

Post by Thirdway » Sat Jul 01, 2017 5:11 pm

You should really have changed the seals if you pulled the Pistons. Over time the brake fluid swells them, so when putting the Pistons back there is a greater chance of damage. Also, the dust seal gets full of grit - you only realise it when you prise the seal out-that means you may well have pushed grit into the caliper or the pressure seal. Remember that it only takes one faulty seal and you got no front brakes.

Before bleeding the system and adding fluid allow the fresh can of fluid to sit on the shelf 24hrs to get rid of any bubbles before using it. The place where the air hides is up on the master cylinder, just one tiny bubble makes the difference between soggy and great.

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