KZR's Bikes of the Month for 2024

Pressure Brake Bleeder on 82 GPZ750

  • Scirocco
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24 Jun 2022 16:08 - 24 Jun 2022 16:14 #869308 by Scirocco
Replied by Scirocco on topic Pressure Brake Bleeder on 82 GPZ750

I some times reverse fill the brake system using a 60cc syringe filled with brake fluid. Start with little or no fluid in the mc resiver and push the 60cc of fluid through the slave bleed port.
Good point ckahleer, a three Dollar 100 ccm syringe i use to bleeding the break system can vaccumise and pressurise the bleeding process of the brake system. No need to buy expecive special tools. You only have to to remove/clean the break fluid from the piston or the rubber part will swell up and sized in the syringe cylinder! 
Last edit: 24 Jun 2022 16:14 by Scirocco.

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  • Nessism
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24 Jun 2022 17:27 #869313 by Nessism
Replied by Nessism on topic Pressure Brake Bleeder on 82 GPZ750
A common problem when bleeding is getting the caliper pistons in the proper position, close to the disc.  Unless the caliper piston moves close, into its proper position, the hand lever will feel spongy.  Also, you need to prime the master before it will build pressure.  And, as mentioned by others, if the small return port is plugged, you will never have properly working brakes.

It's critical, with an old brake system, to de-crud the calipers on the inside by taking out the piston and descaling everything.  Also, replace the brake lines with new.  Preferably, teflon/stainless lines.  

If all this is done and the system still won't build pressure like it should, then pump the lever and tie it back overnight.  This will force the piston to creep forward, toward the disc, and then the lever will firm up.

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  • Scirocco
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24 Jun 2022 17:38 - 24 Jun 2022 17:49 #869315 by Scirocco
Replied by Scirocco on topic Pressure Brake Bleeder on 82 GPZ750
DoctoRod made a genius animated GIF to explain the MC operation, bleeding, relief port and piston seal ring reset over night.

 

Normal operation MC

 

Bleeding operation MC

 
Last edit: 24 Jun 2022 17:49 by Scirocco.
The following user(s) said Thank You: Mikaw

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24 Jun 2022 18:04 #869319 by martin_csr
Replied by martin_csr on topic Pressure Brake Bleeder on 82 GPZ750
How good does a speed bleeder work on the Rr brake?  It's what I use on the Fr & makes the job pretty easy.

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  • Scirocco
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24 Jun 2022 18:15 #869322 by Scirocco
Replied by Scirocco on topic Pressure Brake Bleeder on 82 GPZ750
Delta P does the magic of bleeding a system.....

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25 Jun 2022 10:02 #869331 by linuxrob
Replied by linuxrob on topic Pressure Brake Bleeder on 82 GPZ750
I just use a large syringe to create vacuum.

Small amount of ptfe tape on nipple threads too

1980 Z500 B2 owned from new 78260 miles
1980 Z500 B2 in bits since 1982 23000 miles
2004 GSF1200S Bandit K4
2000 GS125 ESD

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27 Jul 2022 20:39 #871173 by Irish Yobbo
Replied by Irish Yobbo on topic Pressure Brake Bleeder on 82 GPZ750
I've never had much luck using a vacuum system by itself. The best method I've found for motorbikes is to:
- Push the caliper pistons all the way in
- Open the caliper bleed screws, attach hoses/vaccum bleeder.
- Vacuum bleed the system as best as possible. If you don't have a vacuum bleeder you can just pump it as normal, but that's hard if the system is dry
- Take off the bleeder, and pump up the calipers until they are where they need to be
- Bleed the calipers once more, which should take out any remaining air in the calipers
- Check that the brake lever is firm. If it's not, there's air in the lines. Bleeding them against gravity is difficult so:
- Push the caliper pistons back in all the way (make sure you don't overflow the reservoir). Any remaining air in the lines should be pumped back up to the reservoir with the fluid, and because it's going up, gravity will assist this time. As you're pushing the caliper in, tilt the brake splitter junction (or tilt the bike if still attached) and tap it with something hard to dislodge any bubbles that may be sitting in there.
- Pump the calipers back up with the lever again. The lever should now be firm. If it's not, you may need to bleed the master cylinder (take off the lever and pump with the full travel of the piston with a pushrod of some sort), or there is a issue with seals or incompatible parts (eg using a 14mm master cylinder on a dual caliper KZ).

1981 KZ750 LTD
The following user(s) said Thank You: ThatGPzGuy

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