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Discussion Starter · #1 ·
Hi All: I have a 1986 450 Nighthawk. I've rebuilt the Master Cylinder & Front Caliper & drained all the old brake fluid out. Using / connecting the same brake hose, I'm now squeezing the brake lever (20-30x) to try & gain pressure but the lever is flowing freely & not building up pressure. I've "bench tested" the Master Cylinder to make sure it's creating pressure & displacing fluid & that seems to be ok.

I've never bled brakes before, so I assume I'm doing something wrong. Any ideas what I'm doing wrong?
 

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Assembled with the washers on each side of the hose? Bleeder valve cleaned and tightened? It can take a bit for the fluid to work thru and push the air out of the system. Slowly squeeze the lever with the bleeder open, tighten bleeder and release the lever. These masters don't "pump up" by squeezing fast or multiple times.
 

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Discussion Starter · #3 ·
Assembled with the washers on each side of the hose? YES
Bleeder valve cleaned and tightened? YES

I've read elsewhere that a hose replacement is a must on such an old bike (with the original hose), so I'm going to order a new hose. Once I get it, I will take your advice & squeeze level w bleeder open, then tighten bleeder & release lever.

Thanks for the reply.
 

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likely you have air bubbles in your brake line and this will take a while and a lot of pumping to get them all out. Easiest thing you can do would be to drain the brake again and then do a reverse bleed on the brake.

 

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I am having a similar issue but I did not rebuild anything. I get no pressure but brake oil is freely flowing. Where did you look to get parts to rebuild your caliper? I'ma go ahead and just do that because mines are old anyways.

Sent from my Moto Z (2) using Tapatalk
 

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I am having a similar issue but I did not rebuild anything. I get no pressure but brake oil is freely flowing. Where did you look to get parts to rebuild your caliper? I'ma go ahead and just do that because mines are old anyways.

Sent from my Moto Z (2) using Tapatalk
It would help if you told us what bike you are working on and whether the caliper is stock or not.
That said I have had good experience getting mine from 4into1

https://4into1.com/search.php?search_query=brake+caliper&Search=
 

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I think the best way is the reverse bleed. Just make sure you loosen the handle bars to point the MC up to eliminate the bend. That makes no possible place for air bubbles to hang up.
 

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I did this not too long ago and had no problems, it just takes a while to fill the hose and the caliper with fluid but at first I thought nothing happened when I pulled the lever multiple times.
I always make sure the master cylinder never gets empty. I also have a cheap tool which helps alot: (swedish site, I'm sure you have simlar tools and even more in the US)
https://www.biltema.se/en-se/car---mc/car-tools/brake-tools/brake-bleeders/brake-bleeder-2000017001

One guy on a motorcycle forum really had trouble getting the air out and bought this tool which easily got it out:
https://www.biltema.se/en-se/car---...lics/brake-callipers/brake-bleeder-2000031634
 

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Discussion Starter · #9 ·
Update: I didn't replace with a new hose - just used the existing one. Looked good enough.....

Did it the old fashioned way:

1) made sure bleed valve was closed
2) squeezed brake lever
3) keep lever squeezed: opened bleed valve 1/4 turn, then closed it
4) release brake lever

Did this 25x or so & I got pressure. Very nice.

Looks great now, except I'm getting a small 1-2 drips of brake fluid on the bottom of the caliper each night. Is this normal? If not, any suggestions?
 

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Not normal....
Big O ring on piston:.... incorrectly installed (pocket not adequately cleaned), or piston surface marred....
Hose:.....banjo bolt loose/warped sealing washers, or flair fitting loose....
or bleeder valve not tightly closed/sealing...
 

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likely you have air bubbles in your brake line and this will take a while and a lot of pumping to get them all out. Easiest thing you can do would be to drain the brake again and then do a reverse bleed on the brake.

I had the exact same problem as the OP. Rebuilt master cylinder and caliper, and would not build pressure. Reverse bled it and worked perfect after that. Should have done that in the first place and wouldn't have wasted so much time pumping the brake!
 
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