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Brake Bleeding question

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Ben Robertson
(@14898)
Posts: 10
Active Member
Topic starter
 

Hello. I'm replacing the under tank master cylinder on my R75/6 and have access to an electric pressure brake bleeder with an adjustable pressure regulator. I was wondering if anyone might know what an approximate pressure would be to set the pressure bleeder to?

 
Posted : 04/22/2017 16:11
Richard W
(@wobbly)
Posts: 2585
Member
 

You don't need anything nearly that fancy. I fill these systems from the caliper end using a dedicated hand-held oil can that's only used for brake fluid. A small length of 3/16 tubing is slipped over the spout that fits tightly onto the bleed nipple.

Fill the can, loosen the nipple, slowly pump fluid up to the reservoir, close the nipple, done.

May I make some other suggestions while you're in this far....
Really consider using a "stainless steel" brake line in place of the OEM black rubber line. Your braking effectiveness will increase remarkably !!
• Consider converting over to "DOT5 Silicone" purple brake fluid to reduce system maintenance and prevent spoiling your paint. Your local auto parts store will have it. (We can talk more about this if you like.) Download: http://php-junder.rhcloud.com/wp-content/uploads/2015/09/dot5.pdf
• Whether you are "bleeding" traditionally, or pushing the fluid up from the caliper, you will want to manually lift the loop in the flexible line so that air isn't trapped in the high point formed by the line looping downward. Bubbles will naturally work their way up to the master cylinder reservoir if the line has a constant upward slant.
• If your under-tank master cylinder is being replaced due to leakage of any type or amount, you need to carefully look at all the electrical connections directly under the master cylinder. Due to the lean caused by side stand, especially the LH side. The very corrosive nature of DOT4 brake fluid will have an adverse effect on the brass connectors in that section of your electrical system. Washing everything in that area (including the bottom of the fuel tank) with HOT soapy water is a good place to start.

Hope this helps.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 04/22/2017 21:22
Ben Robertson
(@14898)
Posts: 10
Active Member
Topic starter
 

Thanks for all the suggestions! I will definitely take a close look at all the electrical connections below the master cylinder, as I am replacing it due to leakage. I did get a stainless steel brake line as well, so I'm glad to hear that was a good investment. I did clean the frame with hot soapy water. I appreciate the bleeding tips! I'll let you know how it turns out.

 
Posted : 04/23/2017 10:35
Richard W
(@wobbly)
Posts: 2585
Member
 

Then the only step needed for conversion to DOT5 Silicone would be to clean out the caliper. That's very easy.

On my ATE calipers (which were left mounted in place), the bleed nipple was removed and 80 psi compressed air forced though the brake line (before installing the stainless line). All the caliper fluid came blowing out and continued to mist out for about 90 seconds. Then I reinstalled the nipple and brake line to make things water-tight and washed the whole front end with hot soapy water. This to remove any trace of the corrosive DOT4 from the front end.

Then I pumped in my DOT5 Silicone as suggested above.

• No more worries about corrosion.
• No more worries about destruction of painted surfaces.
• No more annual brake fluid replacement.
• No more concerns about leaking master cylinders.

Hope this helps.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 04/23/2017 21:17

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