K13GT Bleeding brakes!

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Andrew
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K13GT Bleeding brakes!

Postby Andrew » Sun Oct 03, 2021 4:19 pm

I have replaced the pistons and seals in the front brakes on by K13GT with new ones because they were starting to get a bit sticky and difficult to retract. It was an easy job but now I can't fully bleed them. No more air bubbles come out of the calliper bleed nipples or from the master cylinder bleed nipple, only clean fluid. I have run the ABS bleed test using a GS-911 a number of times but it makes no difference. The lever pulls right back to the bars unless I pump it 2 or 3 times.

Does anybody else have experience of this problem and, if so, how did you resolve it?
BMW K1300GT, Sunbeam S8, Ariel VH

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Jaythro
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Re: K13GT Bleeding brakes!

Postby Jaythro » Mon Oct 04, 2021 9:19 am

Before I offer up advice

Are you aware that there are 6 bleed nipples that you have open in sequence

3 for the front and 3 for the back and If I recall the GT used the rear brake reservoir to supply the ABS chambers via two small hoses ?
"Put your Ass on a motorcycle and ride with an attitude and the "Grim Reaper" will ride in your shadow!"

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Re: K13GT Bleeding brakes!

Postby Andrew » Tue Oct 05, 2021 10:14 am

I haven't touched the rear brake this time and it is still working as it should. There is only one hose from the rear reservoir. I have done a lot of work on the brakes this year and all of it went without a hitch until now, just by following the instructions in the manual. A couple of months ago, I replaced the rear calliper and all it needed was to bleed the rear brake circuit from the nipple on the calliper itself. A few months before that, I had the ABS unit refurbished and that required a full bleed from a vast number of nipples on all four circuits, in several iterations through a sequence. Again, that went without a hitch. This time, I should only need to bleed the front brake circuit through the two calliper nipples and the third one on the master cylinder. However, in spite of the fact that I can find no more air in the system, the lever is really spongy. I have found that newly bled brakes are seldom as firm as they should be until the bike has been used on the road for a few miles. This time the sponginess is so bad that it wouldn't be safe to try it on the road.
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george baker
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Re: K13GT Bleeding brakes!

Postby george baker » Tue Oct 05, 2021 10:30 am

Hi
cable tie the lever back to the bars overnight?
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Re: K13GT Bleeding brakes!

Postby Andrew » Tue Oct 05, 2021 9:50 pm

Tried that. Actually, since you mention it, I have always been puzzled by that wheeze. When the lever is in its resting position, the valve in the master cylinder is open and air can escape through the reservoir. When it is pulled back, the valve is closed and air cannot escape. So how does it work?
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Re: K13GT Bleeding brakes!

Postby george baker » Tue Oct 05, 2021 10:32 pm

Hi
Magic?


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Jaythro
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Re: K13GT Bleeding brakes!

Postby Jaythro » Wed Oct 06, 2021 8:40 am

Tried that. Actually, since you mention it, I have always been puzzled by that wheeze. When the lever is in its resting position, the valve in the master cylinder is open and air can escape through the reservoir. When it is pulled back, the valve is closed and air cannot escape. So how does it work?
PXL_20211002_165403521 smaller 2.jpg
There is a secondary hole in the master cylinder (to the right in pic above, I hope)

It is tiny and inboard of the main fluid feed and needs to be clear its the size of a small needle

If it is blocked it will produce the symptoms you have described

Also If you have servo ABS I would do the full ABS front circuit bleed just to be sure

Often when you change brake pistons and seals they don't sit at the place that they are meant to and slip back because they are much freer than they were before
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"Put your Ass on a motorcycle and ride with an attitude and the "Grim Reaper" will ride in your shadow!"

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Re: K13GT Bleeding brakes!

Postby Andrew » Thu Oct 07, 2021 4:48 pm

Thank you Jaythro. Now, that has the ring of plausibility about it. However, what I see when I peer into the depths of the reservoir looks quite unlike the picture. Does the picture show what is underneath the reservoir?
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Jaythro
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Re: K13GT Bleeding brakes!

Postby Jaythro » Sat Oct 09, 2021 12:26 am

Andrew There are two holes

One is maybe 1 to 2 mm and is to the inboard side of the master cylinder reservoir this is where the brake fluid floods the master cylinder pump part

the other is to the outboard side but is only a pin sized hole

It is the pin sized hole that lets the air out of the actual master cylinder pump mech

If you still cant see it I will pop the lid off my 1150 tomorrow and get you a picture
"Put your Ass on a motorcycle and ride with an attitude and the "Grim Reaper" will ride in your shadow!"

Islandmagee in case you're interested?


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