Author Topic: Brake bleeding problem rd400  (Read 500 times)

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Offline rd400greenhorn

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Brake bleeding problem rd400
« on: April 28, 2021, 09:54:46 AM »
Hi guys
So, this damn caliper ( front for now) is giving me a really Hard time.
Setup :

Brembo master with braided line for single disc
Refurb calipers wirh new ss pistons and fresh rubber.
I just Cant get it to garden up on the master. I can always squeese it in to the handlebar
Allthough the brakes are biting somewhat to the disc, Its crap.

What do I do from here?

I have already taken the caliper apart, Nothing seems to be of Any issue.
Also tried to check if the membran in the master is working, it squirts fluid up when i pump but it just never gets better.

Help

And yes ive tried with vacuum and bleeding from cylinder to master as well, no luck

Offline rodneya

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Re: Brake bleeding problem rd400
« Reply #1 on: April 28, 2021, 10:06:15 AM »
Try bleeding with the caliper higher than the master.
Bleed it at the Master banjo first, then the caliper.
If that does not work you could give it a few pumps and then ziptie the lever against the bar and leave it overnight and then try bleed again. No idea why this really works, but it is common to do on KTM dirtbikes and it worked for me.

Offline m in sc

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Re: Brake bleeding problem rd400
« Reply #2 on: April 28, 2021, 10:27:11 AM »
zip tie: It does work. what it does is put everything under compression, the air will 'congregate' and then rise to the top burping itself.  i do that every time i work on the brakes with the fluid. just to get the possibility of air in there out.  Actually, did it last night on the 72 R5.   :toot:
« Last Edit: April 28, 2021, 10:38:33 AM by m in sc »

Offline rd400greenhorn

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Re: Brake bleeding problem rd400
« Reply #3 on: April 28, 2021, 10:30:52 AM »
Well damn.. So i Will zip tie that lever in to the bar and leave it for a day and try again 🤷‍♂️👌👍

Offline elliottles1

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Re: Brake bleeding problem rd400
« Reply #4 on: April 28, 2021, 01:08:44 PM »
hi,

just had the same problem exactly with a brand new master cylinder.

i could feel just a tiny bit of pressure occasionally, but then it would release and go to the handlebar, as if fluid was slipping by the seal. i kept on pumping and pumping until i got some pressure and then cable tied it back under pressure and it improved in no time.

i think the new seal was "dry" and under pressure it lubed and expanded up, works a treat now.

les.
« Last Edit: April 28, 2021, 01:10:29 PM by elliottles1 »

Offline murphywv

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Re: Brake bleeding problem rd400
« Reply #5 on: April 30, 2021, 05:27:36 AM »
I have a 300 KTM that is damn near impossible to bleed the front caliper. The best method I found for it his to reverse bleed it. Get one of those big syringes they use on cattle and connect a hose to the bleeder on caliper. Fill it up, crack the bleeder and push fluid back until it comes out the fitting on the master. Works on that monster.
1974 RD350 not stock
KTM 300 XC-W
Beta 500R-SS
And a big ol' chopper

Offline SoCal250

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Re: Brake bleeding problem rd400
« Reply #6 on: April 30, 2021, 11:49:24 AM »
I have a 300 KTM that is damn near impossible to bleed the front caliper. The best method I found for it his to reverse bleed it. Get one of those big syringes they use on cattle and connect a hose to the bleeder on caliper. Fill it up, crack the bleeder and push fluid back until it comes out the fitting on the master. Works on that monster.

Agreed.  I follow this procedure: Fluid Removal & Reverse Bleeding - Brakecrafters

A lot of other good brake tips here: https://www.brakecrafters.com/blogs/hints-tips-and-other-brake-motorcycle-brake-information
79 Yamaha RD400F     77 Yamaha RD400D     
75 Yamaha RD250B     75 Yamaha RD200B (project)
75 Yamaha RD125B     75 Yamaha RD125B (project)
89 Yamaha FZR400      05 Yamaha FZ6
91 Yamaha TZR250R    02 Aprilia RS250 Cup (sold)

Offline rd400greenhorn

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Re: Brake bleeding problem rd400
« Reply #7 on: May 03, 2021, 06:08:55 AM »
This thing just wont bleed out. Tried the zip tiez No difference

Offline ~JM~

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Re: Brake bleeding problem rd400
« Reply #8 on: May 03, 2021, 09:44:31 AM »
Well damn.. So i Will zip tie that lever in to the bar and leave it for a day and try again 🤷‍♂️👌👍

Try zip-tie the lever halfway through its travel & let sit overnight.

Offline 1976RD400C

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Re: Brake bleeding problem rd400
« Reply #9 on: May 04, 2021, 07:43:17 AM »
I think you should try the syringe connected to the bleeder on the caliper. Remove cover on master cylinder, open bleeder, push syringe, watch for air coming up and out the master cylinder reservoir. 
'76 RD400 green  '76 RD400 red   '84 RZ350

Offline 85RZwade

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Re: Brake bleeding problem rd400
« Reply #10 on: May 04, 2021, 09:13:43 AM »
Vibrations can help, too. I've heard of an automotive product that vibrates the brake line to encourage bubbles to migrate upwards. Maybe an electric engraving tool or something from a lady's bedside table temporarily applied to the brake line would work. Seriously.
Rubber side down!

Offline teazer

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Re: Brake bleeding problem rd400
« Reply #11 on: May 04, 2021, 11:48:39 AM »
Not sure about borrowing someone's vibrator, but tapping the brake line with a wrench or screwdriver usually helps to dislodge air bubbles so they can rise.

Another thing to check is the caliper mounts.  It is common on RDs for the caliper to mount out of square.  Simple check is to loosen the caliper mounting bolts so the caliper can move easily and then try the brake lever, if it's not firm, slowly tighten one mounting bolt and watch the caliper as you squeeze the lever.  You should be able to see it flex as the pads try to grip the disk.

Shim the gap between caliper and fork leg as required to get it to fit square.