Topic: Brake fluid not making its way from the res.

[Teach]

I've searched and have found nothing like this:

I tried filling the rear brake on my 78 750F today and the brake fuid is only barely making it's way from the reservoir to the the master cylinder.  I filled it about 2/3 full and now it's only about gotten down to about half full, with no sign that the fluid has made it's way into the line or brake caliper.

I have rebuilt both the caliper and the MC, and have installed a new braided line, and Goodridge speed bleeder.  I'm using DOT 5 fluid.

Is this typical?  I've seen a few air bubbles come to the top of the reservoir so I know it's doing something, but it's going terribly slowly.  When I remove the bleeder nipple and cover the hole with my finger and depress the pedal there is a small amount of pressure built up (a slight hiss when I remove my finger).

Should I wedge something in to keep the pedal depressed overnight, or should a leave it in the up position?

[scondon]

If you have rebuilt everything and there is no fluid to begin with in the line and caliper I would expect a full reservoir to become nearly empty before fluid starts to come out of the bleed nipple on the caliper. Keep bleeding and topping off the fluid as you go.

[mick750F]

  As Scondon has said..If you're starting out with a completely dry system it will take a while to bleed the brakes. I recently did a complete rebuild of the brake systems, front and rear, on the same bike and it took a long time to bleed both systems.

Mike

[HondaMan]

The 750 caliper is real bad about this, because of the union on the steering head.
If you can find a large syringe (like the ones auto body shops use for paint mixing and matching), try inserting the end into the bleed hole on the caliper and pulling the air OUT, which will pull the fluid IN. This will "wet" teh system and let you finish the job easier. Otherwise, it can be 2 days before enough dribbles down the line into the caliper to "wet" the system.

You can also crack the banjo at the steering head to get it started that far, but chances are you'll get DOT5 on the paint and ruin it if you do...   

[MRieck]

If the piston is pushed all the way into the caliper(bottomed) you will have problems because of the lack of space for fluid to go to. If you take low pressure air and push the piston out just a little it will go easier.

[dusterdude]

getcha a vacuum bleeder kit and pull the fluid thru the line to the caliper

[KB02]

Okay, Teach, I have a question (and this is mostly for my own understanding): Are you just filling the MC and then letting it sit? Or are you actively trying to push / pull / suck the fluid down into the caliper? The way your post reads, it sounds like the former, which WILL take a long time.

Take DUSTERDUDES advise and get a vacume bleeder. I have one of these that I bought pretty cheap at a local auto parts store. It really helps sped along the process.

[Teach]

I filled the res. and then worked the pedal up and down many many times...sometimes slowly, sometimes quickly, neither of which seemed to make a difference.  I'm gonna go check on it today and I'll let ya'll know if any more of the fluid seeped in overnight.

[jtb]

Teach,

It took a hell of a long time to bleed my brakes after rebuilding them.  I probably did everything that you did, except the stainless lines.  Even after I finally got fluid to come through the bleed nipple, I still got bubbles for a long time.  Sounds like you're moving fluid, just not much.

John

[dusterdude]

kb,you know it brother.that bad boy saved my ass when i did my brakes

[Teach]

I dissasembled the master cylinder today to make sure everything was put together properly and they are according to the manual.  How in the world is fluid supposed to go from the inlet (where the hose from the res. attaches to the MC) to the outlet (where the brake line connects) if air won't go through when I blow into it.

What am I missing here, guys?

[scondon]

I dissasembled the master cylinder today to make sure everything was put together properly and they are according to the manual. How in the world is fluid supposed to go from the inlet (where the hose from the res. attaches to the MC) to the outlet (where the brake line connects) if air won't go through when I blow into it.

What am I missing here, guys?

If you could blow air through it it would be broken. The cylinder needs to "force" fluid from the reservoir through the line. If it were an open path you could blow through then what's to stop the fluid from just backing up the reservoir. At the moment I lack the words to explain the mechanics but hope this helps put your mind at ease that you did the rebuild correctly.

     It really does take a lot of pedal work to get a dry system bled and I think your doing it correctly but let me outline the process just in case.

1)Fill reservoir
2)depress brake pedal 5-6 times and then hold down
3)open bleed nipple,close bleed nipple
4)release brake pedal

repeat steps 2-4 until your arm/leg falls off. Repeat step 1 as needed, do not let the reservoir empty.

      It takes a while of seemingly getting nowhere before you actually get somewhere so be patient. Your original post states that you noticed a small drop in the reservoir level, if this is the case then I believe you are doing everything right, just keep at it.

[Teach]

Alright I had an epiphony.  I had the nut that the rubber boot is connected to threaded too far up on the pushrod, therefore not allowing for a full stroke of the piston in the master cylinder.  I spun it out, and voila!  Still slow going but at least there's visible progress being made.  Thanks everyone for your patience!

[cbcoker]

why are you running DOT5? It isn't always compatable with brakes meant to run DOT 3 or 4.

[KB02]

to my knowledge, DOT's 3 and 5 are compatable, but DOT 4 is the odd ball out. Right?

[Teach]

why are you running DOT5? It isn't always compatable with brakes meant to run DOT 3 or 4.

Because it doesn't absorb water and isn't as hard on painted surfaces.  I've found several post where people have used DOT 5 without any problems.  I've also found a couple of posts that say "whatever you do, don't use DOT 5, but I have no idea why not."  The only incompatabilities I've found are ABS brakes (the ABS on my '78 doesn't work anymore anyway), and if there was previously another type of fluid in the system that wasn't properly cleaned out.

[Gordon]

The compatibility issue is with the fluids themselves, not the type of brake system.  Since you rebuilt both the master cylinder and the caliper, and replaced the brake lines, you won't have any problems with mixing of the incompatible fluids. 

[dusterdude]

right on gordon!!!

[n9viw]

Another thing to pay attention to (considering your 'slow going') is whether the piston cup is mounted the right way round... one way it goes on very easily... the other way is correct. I made this mistake on my 550, and finally figured it out on my own.
Also, make sure both reservoir holes in the MC are clear- if the bleedback hole (the smaller one) is clogged with even the slightest bit of grit, you'll have a heck of a time bleeding the system. Also, bleed the MC to itself before you bleed the line, otherwise you can wind up with an air bubble trapped between the MC and the line that won't move for love or money.

[brockj]

I am having the same issue with my 72.  With the MC off, should I be able to push fluid out through the hole or not?  Seems like a big newB question but I am thinking I need a rebuild on the MC?

[Teach]

I finally got the brakes bled today!  I talked to a mechanic friend today and he recommended loosening the banjo bolt at the MC, and pump till fluid came out then tighten it back.  I did that, then I did the same at the caliper end of the line, then I bled them in the normal way.  I'm still getting tiny bubbles out of the bleeder nipple, some I'm gonna work on it again tomorrow once the air has time to settle.  Even so, after rebuilding the MC and caliper and fitting braided lines, the pedal is firmer on my '78 CB750F than on my three year old Harley.