Topic: bleeding the brakes - where is that damn air hiding?

[superchode]

spent some time both today and yesterday working on getting the air out of my brakes and getting it on the road - but not having the results i was hoping for.

it's a '78 750F, it's got a VFR master cylinder on the front and the stock on the back. the front is really pissing me off. can't get anything but brake fluide out of either bleed nipple - no air bubbles to be found... i've tried letting out the screw at the top of the connecting manifold above the wheel to see if there's air in there... i've opened the cap of the m/c to see if anything's bubbling up that way... can't find any more bubbles, but the brakes are spongy. real spongy. i wouldn't ride the bike as is... the front lever comes all the way in to the bar.

the brakes on my VFR are tight within 3/8" - part of that is stainless steel lines, but the 750F just won't tighten up.  the rear isn't as bad, but it's not where i'd like it.

any advice? i'm making no progress.

[SohcCBs]

What does the brake feel like?  Does it pump up at all, depress a certain amount and get hard, or otherwise?

If you're not getting any fluid out of the bleeder then it can't be full of fluid.  Maybe it's clogged.  You might need to pull that line and blow it out....try and clear it...or see if it's clear.  I do the same for all three lines.

[superchode]

i can get fluid out of both front calipers just fine... what i can't get is air bubbles. got a bunch out initially - brakes tighted up somewhat... but the lever can still be fairly easily depressed all the way to the bar.

i kept at the bleeding procedure for a while... but it just pushes more fluid out each time... no more bubbles. and i can't get the lever any tighter than it already is.

[SohcCBs]

Did you have the bleeder fully opened?  You might try having it barely open so it takes a good bit of pressure to puch the fluid out.

[superchode]

i generally crack it a touch... then open it wider if i can't get anything.  since i can never get any bubbles... the procedure is pretty much crack nipple slightly, then wider every time.

would i be better off cracking it just a touch every time?

[SohcCBs]

I'd try that.  Maybe it'll force some bubbles out that are deeper in the system.  Loosen it just barely enough for fluid to come out, no more....that'll increase the presure in the system.


Otherwise it's rebuild or new lines.

[Jugghead]

Also, I would add (after bleeding my front brakes 2 times)
To make sure that the end of the bleed hose attached to the nipple is submerged in fluid, and that the bleed line is always full of fluid. And only crack the nipple a tiny bit.
This seems to draw the air out of the claiper consistently.  Make sure the hose is full of fluid and the non-nipple end of the hose is submerged in fluid, so it can't draw air back up the tube.
In all honesty, I worked at this for two days.  And I still got some bubbles, but then affter no perceptibly bubbles, I closed it off all the way, squeezed the lever and it was pretty hard, and micro bubbles finally coagulated and worked their way up to the MC to bleed off naturally.
I now have a firm, hard lever that can easily bring me down from 65 MPH in (reasonable) distance.  I never checked against the manual's stopping distance, but I guess Ishould.
I can't lock the front,tho. (it still has the original black rubber hoses) but also have not applied 100% ass-pucker force to it yet.
Good luck and keep us posted.

[Weatherman]

Have any of you folks had problems with your front brake light after this procedure? I drained and replaced my fluid, bled the system and have a nice solid feel when I pull the handle, but now the brake light doesn't work. I have power to the switch, but nothing downstream when I apply the brake.

Thanks,
Dennis

[SohcCBs]

Have any of you folks had problems with your front brake light after this procedure? I drained and replaced my fluid, bled the system and have a nice solid feel when I pull the handle, but now the brake light doesn't work. I have power to the switch, but nothing downstream when I apply the brake.

Thanks,
Dennis

Either there's left over junk in the switch....or it just decided to quit on you, unless you accidentally unplugged a wire somewhere while you were bleeding.

[OldSchool_IsCool]

Does it pull to the bar straight away or does it fade down to the bar?  Is it soft at first then hardens up after pumping?  <<insert penile joke here>>

[superchode]

it's certainly stiffer than an empty system - the brakes actuate, but not enough.

pumping them doesn't cause it to get any more stiff then it already is.  it's about even pressure on the lever all the way to the bar.

[Rhonda750F]

Get a pistol grip pump speed bleeder $20-25.  I spent 2 days trying to bleed those bicthes the old fashioned way, and they still seemed soft.  Picked up a bleeder and less than 5min later their rock hard.

Weatherman, As for your brake light not working, unhook the brake light switch from the lever and pop it open, I bet you broke something inside.  this happened to me wile bleeding the system.  Those plastic swithces get brittle with age and can also get gummed up with junk.   

[superchode]

after seeing what it would cost to put speedbleeders on the 750 and the VFR... i'm just going to buy a proper vacuum bleeder. less investment and the VFR service manual actually specifies a vacuum bleeder as required due to the linked braking system.

hopefully that tool turns bleeding into a very quick job.

[SohcCBs]

If the VFR manual states it's required for that brake, then that's probably the whole deal.  Good thing you've got that manual, they often point out little details like that.

[cafehonda]

Bleed the master cylinder. Pump the lever 3 or 4 times and crack the bolt that holds the brake line on.The master can hold a bubble of air and will give you a spongy lever but still pump fluid at the wheel cylinders. I've had this happen several times until I learned to bleed the master first every time. This will also usually fix the "my brake light doesn't work" syndrome. Good luck.

[Weatherman]

Thanks. I'll give it a try.

[superchode]

picked up a vacuum bleeder... i'll give it a go tonight and let you fine folk in on the results.

[superchode]

ok, i spent another night on this... and now i'm really starting to get pissed off.

picked up a vacuum pump and had another go at the system.  it became clear early on, when using the vacuum pump, that there was a problem with the bleed nipples. they didn't seem to be sealing properly... so i applied teflon tape all around and sealed those up.  after this, i was expecting a short trip to tight brakes... but it didn't happen.  i was able to tighten up the rear a bit - and it's likely acceptable now - but i'm getting nowhere on the front.

i can apply vacuum at either nipple on the front and pull clean fluid with little or no tiny air bubbles in it - but the brakes never become stiffer than they were shortly after i added fluid to the system.  i can still easily pull the lever all the way to the bar.  repeating this process is getting me nowhere - other than almost out of brake fluid from having bled off small increments of fluid so many godamn times.

just in case i'm comletely retarded, i'm going to outline what i've been doing - and hopefully someone can point out a mistake or give some advice on another procedure.

1. pull cap off master cylinder, make sure there's plenty of fluid in there.

2. apply tubing connected to resovoir and vacuum pump to bleed nipple. apply vacuum. crack nipple a small increment until fluid starts to be pulled out (hopefully with some air bubbles along with it - but not bloody likely).

3. repeat. repeat. swear at futility of life. repeat. while doing all this ... make sure fluid level in master cylinder isn't down to nothing. top off as necessary.

4. move to other caliper. do same #$%* over again until you can actually hear the bike laughing at you.

[Bob Wessner]

With all the posts about having problems bleeding brakes, I have to conclude I was just lucky. But, just in case it might work for you, I started with a completely dry system (front) after rebuilding the master cylinder and cleaning the caliper and inserting a new piston seal. I poured fluid into the reservoir and completely removed the bleed screw. I used my thumb over the bleed screw hole, using the usual sequence until fluid reached and filled the caliper. Then I inserted the bleed screw and used the usual method described in most manuals. I ran the tube from the bleed screw into a small plastic ketchup bottle, the small hole in the cap seemed to control any movement of the tube that might pull it out of the brake fluid better than just sticking it into a jar. It only took a few cycles to bleed it and firm it up. It's been solid for two years now and as a matter of fact, probably needs draining and refilling so I guess I'll get a chance to see if this was just a fluke.

[techy5025]

You might try pressure bleeding the brakes from the bottom.  This requires a device
similar to a doctor's syringe that will hold a reasonable amount of fluid...no needle of
course..just the bare syringe. You connect it to the hose coming out of the bleeder
and then, being careful not to introduce more air bubbles, force the fluid from the
bottom.

I had to do this once and it is much faster and moves the bubbles in the direction
that they naturally want to go.

Jim

[SohcCBs]

Yes, it sounds like it's getting to you!!!  I've never used a vaccum bleeder, and have always had success doing it one of two ways, but mostly the first:

1. Fill master if needed and close.
2. With bleeder closed, pump brake and hold in down position and open bleeder just a little (do not let brake up)
3. Close bleeder
4. repeat........
5.Recheck master level

....and more lately
1.Fill master and close
2.place box end on bleeder and attach tube
3 place tube in bottle of Dot4 and raise bottle to bleeder level (the tube most absolutely be sealed on the bleeder even if small hose clamp is needed).
4. Open bleeder and pump the heck out of the brake.
5. Close bleeder
6 Recheck master level

[supersport_CB400F]

I also had no problems, I had the bike on the main stand and the calliper was straight and level, I also hope I have the same luck when I flush it through next year.

[OldSchool_IsCool]

What concerns me is your statement that you can pull the leaver to the bar.  Does the leaver come to the bar at the same speed no matter how hard you pull?  I'm suspicious of leaky internals in the master cylinder.

[superchode]

yeah, i'm getting suspicious of both my lines and the master cylinder.

i do have an identical spare for the master cylinder... may just swap it in to make sure i'm not wasting my time with this one. the one that's on there right now isn't leaking or anything... but i suppose that doesn't necessarily mean it's actually working.

[mic-57]

It sounds like the master cylinder is worn and needs a rebuild. I had the same type of problem with mine, I bled and bled and bled until I broke down and rebuilt the master cylinder, now all works fine.

[lsutton]

Are you sure  you have air in the system?  What if your hoses are old and weak and expanding when you pull the lever? Or what if your master cylinder is worn and passing fluid past the piston?  Just some possibilities.  What I usually do after bleeding is to pull the lever back as much as I can and tie it to the handlebar and leave it over night.  This opens the port in the master cylinder and any air bublbles left in the system rise to the reservoir.

[supersport_CB400F]

I forgot to add I also replaced all the parts in the MC/caliper and it worked 1st time.