Front Brake Drag

[2017EX_imp]

"I did not even know that the small hole existed and only found out after a clear picture of it on the net." Max, do you still have/did you save the picture of the infamous tiny hole under the stainless deflector? If so could you post it please, or a link to it on the web? My mechanic saw it, but I didnt, so I am curious as to what the situation actually looks like. I had no clue it was there, as I imagine most other members dont either.

[max]

Sure, here is what i found when i searched "motorcycle master brake cylinder hole" in google and opened the results a new tab;

1; a drawn picture someone talented drew showing the inner workings of a master cylinder;
http://www.howmotorcycleswork.com/articl...cle016.htm

2; The series of explanations that leads to the picture under "howmotorcycleswork" site;
http://www.howmotorcycleswork.com/sitemap.htm

3; another clearer cutaway diagram of the parts;
https://www.accessnorton.com/NortonComma...ing.22837/

4; an article about the hole and you can see the hole clearly when you click on the picture twice to magnify it for a closeup;
https://www.reddit.com/r/motorcycles/com...turn_port/

5; a good article pretty close to what we have in our bikes;
https://motofaction.org/motorcycles/hond...d-part-01/

The first time i looked at mine i thought the hole was drilled by mistake and left there, only after seeing what it was supposed to look like did i find the obstruction and when i cleared it out all the air escaped when i worked the handle slowly and the pressure buildt up correctly wnen all the air bubbles worked themselves slowly to the top of the cylinder, even a small amount of air in the line can compress and stop the brakes from building enough pressure to engage normally.
This system is very simple and reliable and requires minimum maintenance but because the brake fluid is hygroscopic ( it absorbs moisture from the air ) it needs to be replaced regularly otherwise the moisture builds up inside the system and corrodes the parts inside.

For the same reason i push the caliper pistons all the way back into the calipers after cleaning them on the outside and empty the lines to expel as much old fluid as possible when i replace it with fresh fluid.

How quickly does it absorb moisture? in my sample ( a soda bottle cap ) it took 15 minutes to activate the first led and was unusable ( red led ) after 1,5 hours at 4%, much quicker than i had thought, if you pause at 14 sec. you can read the results of two tests;
https://www.youtube.com/watch?v=HPCvEoPlNlU

Here i use a small trick to replace the seal on the piston and show what's involved if you're interested;
https://www.youtube.com/watch?v=9tC9qYyv-OM

Just select which part you're interested in.

[2017EX_imp]

Thanks Max, Lots of really good info, particularly the last link with the close up pictures.

[dave]

Thank you very much Max. I am reconditioning a 1992 VFR800 I picked up on eBay that was left sitting outside for over 7 years. I just completed draining all of the hydraulics, cleaning all of the brake calipers (removed and cleaned all 9 pistons), and refilling and bleeding the system. It's a real job on this bike because it has linked brakes, ABS, two separate pressure regulators, and a third (secondary) master cylinder attached to the LH side front caliper. Everything looks good, except the rear brake drags. I guess I'll try cleaning the small hole in the rear brake master cylinder; maybe I'll get lucky and not have to bleed the entire system again (the air from this area should go up and out the reservoir by itself). What do you mean by the "banjo bolt" - the plastic connector to the master cylinder?

[max]

Hi Dave, most connections on brake lines use a hollow bolt and a round fitting to allow the fluid to operate, these are called a "banjo fitting" because of the way they look when disconnected, on the picture of the rear brake cylinder the bolt can be seen sticking out at the top of the cylinder which is also the highest point and should not be overlooked in the bleeding process when pressure is not building up as it should.

[dave]

Thanks Max. I just didn't see a banjo bolt in the picture you provided because it was removed, and I thought you might have been referring to something else. It doesn't look like I have to take the banjo bolt off - just the plastic junction that attaches the line from the reservoir to the master cylinder. I might get lucky and not have to bleed the entire system again. Thank you Max.

[dave]

Max, thank you so much for all great information! I viewed all of the links you posted. From one of the links I discovered that I put the "protector" in up-side-down on my VFR800 clutch master cylinder. The protector was sitting loose in the bottom of the reservoir when I drained it and I guessed which way it went back in. Wouldn't you know it - I had a 50-50 chance of getting it right, and I got it wrong! The clutch seems to work fine, so I'll just wait until the next time I change the fluid to correct it. Just one little hint, that I discovered works very well: Put a dab of grease on the surface of the piston where it contacts the lever - it works wonders. You applied grease to the rubber cap when you installed it, so some of it likely covered the top of the piston. I had to purchase special snap-ring pliers to reach deep enough to remove the snap-ring. I owned 8 or 9 pairs, but none of them were small enough, yet long enough to reach the clip.