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Problem with brakes after lines & fluid change 24 May 2023 10:48 #885129

  • katz
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Hello,
I have a 1985 ZL900 which has two single-caliper brakes on the front. I installed longer handlebars which required a longer brake line (the one leading to master cylinder). I filled both brakes/lines with brake fluid but brakes don't work, brake lever is spongy and nothing happens.
When I bled the brakes there was no air coming out, only brake fluid. I don't quite understand what's going on, how can you have both lines filled with fluid and no brake action? When I was refilling brake fluid I could squeeze the brake lever any number of times and fluid was getting pushed out of bleed screws but brakes didn't budge. This kind of boggles my mind, as if the brake fluid in my motorcycle suddenly became compressible, just like air.
I'd appreciate any help with this, I'd like to understand what's going on.
Thank you,

Katz
 

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Problem with brakes after lines & fluid change 24 May 2023 10:55 #885130

  • OKC_Kent
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Somewhere there must still be air in the lines. I suggest you squeeze the brake lever hard, against the grip and tape it in place overnight. The next day cut the tape and you might have a firm lever. 
Oklahoma City, OK
78 KZ650 B2 82,000+ miles

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Problem with brakes after lines & fluid change 24 May 2023 11:03 #885131

  • Nessism
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Did you mess with the calipers?  This sort of problem occurs when the caliper pistons are pushed back away from the disc.  The fix is to first make sure the caliper is clean and free of gunk.  Next, pump up the lever and tie it back to the handlebar for several hours.  This allows the pistons to creep out of their bores and move closer to the disc.  In extreme cases, you may have to do this a couple of different times.

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Problem with brakes after lines & fluid change 24 May 2023 12:54 #885135

  • Wookie58
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Worst case (especially if fluid changes have been neglected) is that there is a rust band in the master cylinder. When bleeding the piston is travelling further than normal so the seal could be damaged by corrosion build up. If the actions already suggested don't sort the problem you may have to look deeper into the master cylinder

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Problem with brakes after lines & fluid change 24 May 2023 14:53 #885139

  • Scirocco
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Hanging the caliper higher above the MC and the pistons all the way in blocked with a piece of wood to minimize the volume.
The remaining air bubble should travel up to the top end of the bleeder screws. SomeTeflon tape around the bleeder screws thead prevent air sucking in the system when releasing the MC lever!

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Last edit: by Scirocco.

Problem with brakes after lines & fluid change 24 May 2023 15:06 #885140

  • sf4t7
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I also use the method OKC_Kent suggested but I add a step:
Fill the master and leave the cap off.
Squeeze the lever and tape it to the grip.
Then open the bleed screws (with your clear hoses on so you don't make a mess) but don't pump the lever.
let the system sit open like that for 20 minutes or so, top off the fluid in the master if it goes down.
Close the bleed screws and let it sit overnight with the lever taped as OKC_Kent sugggests and you should have better brakes tomorrow.  Sometimes gravity bleeding first pushes some air out.
Good luck

Scotty
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1974 Z1A
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Problem with brakes after lines & fluid change 24 May 2023 15:15 #885143

  • TexasKZ
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When you put the new lines on. You introduced air at the top of the system. It may take quite a crew pumps to force that air down and out. Some folks claim that filling from the bottom up solves this problem. Use a large syringe and a short piece of tubing connected to the bleeder screw. Fill the syringe with fluid, connect it to the tube and push the fluid and air op to the master cylinder. You will need to do this with both sides and you will have to keep a close eye on the level in the master cylinder so you do not spill fluid all over the place.

Did you rebuild the master cylinder and calipers? 
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough
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Problem with brakes after lines & fluid change 24 May 2023 15:27 #885144

  • sf4t7
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Thanks TexasKZ
Filling from the bottom up sounds like a better way to bleed.  One of my tasks coming up in reviving my Z1A is new master, caliper and braided lines.  Perfect opportunity to try it.
"If you're not careful you might learn something new every day"

Scotty
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Last edit: by sf4t7.

Problem with brakes after lines & fluid change 24 May 2023 16:05 #885148

  • Scirocco
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To let the bleeder screws sit open did nothing! You need the break fluid pressure to reset the gasket ring travel!!!

  
 
 
 
 
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Problem with brakes after lines & fluid change 24 May 2023 16:15 #885149

  • Wookie58
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Something else you can try if you are struggling is after each pump of the lever close the bleed nipple before releasing the lever. Then pull the lever before opening the nipple again - keep repeating this process as it helps stop stubborn bubbles being drawn back towards the MC when you replease the lever
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Problem with brakes after lines & fluid change 25 May 2023 04:07 #885158

  • howardhb
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Something else you can try if you are struggling is after each pump of the lever close the bleed nipple before releasing the lever. Then pull the lever before opening the nipple again - keep repeating this process as it helps stop stubborn bubbles being drawn back towards the MC when you replease the lever
 
Wookie, that is similar to what my Dad taught:
Squeeze the lever, then slightly open the bleed valve... then, close the bleed valve just BEFORE the lever touches the handlebar.
 This way, positive pressure is always maintained. (Hydraulic "cup" seals don't seal well under vacuum)
Repeat until no more bubbles exit the bleed nipple.

I've always done it like that and never had a problem.

H.
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Problem with brakes after lines & fluid change 25 May 2023 04:25 #885162

  • Wookie58
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Also as previously mentioned, on old vehicles it is best not to use the full travel of the piston (maybe a little over half) to reduce the risk of tearing seals on corrosion in the cylinder

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