FZR front master cylinder help

[kpke]

Brake help please. I'm almost ready to start this project bike but would like to have front brakes available in case it runs.

Short version is front MC won't pressurize and little bubbles come up thru the little hole in the base of the MC. All parts are fresh rebuild or new. Long version below.

From my notes and a post on the RZ forum (with no response)...

11/9/20
Yesterday still having troubles with getting pressure in the front brakes. The rear is holding up fine.

Here is a nice diagram of this type of MC.

I think the calipers are not leaking. There is no fluid dripping off after 2 days. Earlier that fluid was (more I think) a result of opening the bleed screw. I am getting bubbles coming up into the reservoir. www studies indicate this is a MC problem. Unfortunate because I used a Yamaha rebuild kit on this thing.

I’ve adjusted the lever adjust screw all the way in to get max throw to no avail. Removing the splash plate on the bottom shows the bubbles coming out of the tiny hole closest to the lever. Next I’m going to take the bike off the lift, put it on the side stand, turn the bars full left, hoping to get any high spot out of it. I don’t think this will help.

Then I suppose I’ll change out the MC/lever assy to a 2005 R6 one I have in stock.

Anyone know what to use to purge the DOT 4 out of the R6 MC before putting the DOT 5 in? Alcohol?


Edit: I’ve tried this trick a few times to get air bubbles to purge up. It has not helped.

 

[DannoXYZ]

Hopefully you're using DOT-5.1 and not DOT-5? Otherwise completely rinse out system with alcohol. Military is really only ones using DOT-5 for it's longevity and durability. And they've got procedures in place and discipline to make sure it's done right.

You're fighting physics, because bubbles in line are rising faster than you can push them down with squeezing lever. Heck even with vacuum-bleeder like MityVac, it's difficult to out run bubbles rising in lines.

Make it easy and have gravity help you move bubbles in direction you want; towards caliper. So take calipers off and place them higher than master-cylinder. Usually I just set ladder up over front-wheel. Then put board between steps of ladder to make flat platform for calipers. Also convenient place to hold bottle of fluid and catch-can for old fluid.

Then bleed as normal, but with calipers above master. Really easy, 3-6 squeezes and you're done.

 

[Maddevill]

Or get a syringe and push brake fluid up from the bleed screws in the calipers. I was having trouble with air in the system and that cured it.

Mad

 

[motomania2007]

When I usually do is pull the caliper off make sure the pistons are clean and then I can press the pistons and push the fluid that's in the caliper all the way up the line and push all the air out of line while I'm at it. And I do it to both lines on both calipers.

Then I let it sit for a little while and then add fluid to the master cylinder, reinstall the calipers, and then pump them up. Worst case scenario I've had to do this cycle three times. But mostly once or twice is All that is needed.

 

[bobl]

Or get a syringe and push brake fluid up from the bleed screws in the calipers. I was having trouble with air in the system and that cured it.

Mad

This. Easiest and fastest. Use DOT 3 or 4 that the system was designed for.

Edit: Drain the master cyl. before pumping from the calipers up, as the increased fluid level may over run the reservoir. Also, place a rag over the top of the reservoir to prevent spray from landing on your paint or other place you don't want it. The syringe to use is a large one used for irrigation, etc., not a needle type for injection. Probably available from a vet supply.

 

[GPzPop]

OK, may I suggest checking if any and all banjo fittings from lever to caliper are good and tight?

Don't ask me if from recent experience I know to ask this.

 

[Lucytriple]

To add to the great advice above, give each banjo fitting a nice rap with a screwdriver handle to dislodge any trapped air. The small bubbles are what you want to see coming to the top, sometimes it just takes a long time. Turn your handlebars so the res is as high as possible.

 

[kpke]

Thanks for all the replies. I have to take about a week long break on the brakes :laughing I'll report back when I get back on it.

 

[kpke]

Thanks again for all the helpful comments above :thumbup

Has it been a week yet?

Today I took the bike off of the stand out to the driveway. I parked it on the side stand and turned the front full left. This leveled off the master cylinder considerably. I fought it for a long time, tapped on the banjo fittings, bled just the master by loosening the banjo there, bled the calipers more, and was just about ready to give up when I started feeling pressure in the lever.

I think I can claim success at this point. Of course the bike has not been ridden yet and that will be the true test. But the lever feels pretty solid and pushing it down the driveway the brakes worked. Happy days. I should be starting this project bike soon.

 

[GPzPop]

winning !
--S

 

[Lucytriple]

Hahaha! It really made you work for that. Sounds like you're good to go. Congrats!