Topic: 1978 CB750F Brake Problems

[LiquidYogi]

So one of the pads won't fit into it's slot and I'm wondering...is it such a bad idea to just file down the edges to get it in there? Thoughts?

[TwoTired]

Depends on where you are filing.

[LiquidYogi]

Depends on where you are filing.

Where the edges are...not the contact point of the pads but the edges on the outside that extend past the pad. It simply would fit into it's proper slot so I need to do something.

[TwoTired]

Honda pads or aftermarket?

[LiquidYogi]

Honda pads or aftermarket?

Nissin. I got them from the same place I got all the other parts to rebuild the caliper. Also the one against the piston totally fits...it's the other one that doesn't.

[TwoTired]

There is a SS anti rattle insert at each end.  Is that where the interference is?  If so then file to fit.  I'd put a thin thin coat of HVG on the bit that was filed to arrest rust.

[LiquidYogi]

Soooo I finally got back around to the bike. Brake is on and rebuilt and in good shape. I got a small do it yourself Bleeder kit and some brake fluid so I'm good to go. Fill up the little reservoir and hook up the bottle to the bleeder valve bolt thingie and start pumping. Nothing happens, just some bubbles come up. Keep pumping 100 times, the liquid won't pump itself to the caliper, I even take off the bolt and try to see if it's going in and just blocked. Nothing doing still won't work, and I'm encountering no resistance from the pedal.

So obviously I'm doing something terribly wrong that I imagine you guys know right away what it is. Please help, here's some pictures of my set up.

[BeSeeingYou]

Your brake line could be blocked.  The best option is to get a new one but failing that remove it and use a 16th inch diameter piece of braided wire and push it through the brake line to clear the obstruction.  You need a nice clean cut on the wire.  Worked for me on my bike that sat for many years.

Did you rebuild the master cylinder?  If not you really need to do that too.  The F rear MC's are easy to get apart.  Do both of these suggestions and it should be good to go.  It's just something that should be done on an old bike where you do not know the maintenance history, has been sitting a length of time, or has brake problems.  These somewhat primitive early systems that do not take neglect all that well.

[LiquidYogi]

Your brake line could be blocked.  The best option is to get a new one but failing that remove it and use a 16th inch diameter piece of braided wire and push it through the brake line to clear the obstruction.  You need a nice clean cut on the wire.  Worked for me on my bike that sat for many years.

Did you rebuild the master cylinder?  If not you really need to do that too.  The F rear MC's are easy to get apart.  Do both of these suggestions and it should be good to go.  It's just something that should be done on an old bike where you do not know the maintenance history, has been sitting a length of time, or has brake problems.  These somewhat primitive early systems that do not take neglect all that well.

Thank you soo much, I'll just order a new brake line and be done with it. Yes I rebuilt the whole thing, new piston and other innards. Thing is really smooth, but if it's not getting any fluid into it, kinda defeats the whole purpose of it.

[TwoTired]

Did you clear the tiny bleed hole in the master cylinder?  Have you primed the master cylinder?
Do you have a mity vac, to suck the fluid from the master to the caliper via the bleed nipple?

[BeSeeingYou]

On my 76F there is a bolt on the master cylinder that when removed allows easy access to the send and return holes so you can clear them if needed.  The later F's have a different master cylinder and I am guessing that access to those two holes may be behind the "nipple" fitting that the hose from the fluid cup is connected to.  This is removable.  The send hole is large enough to see easily but the return is very tiny, smaller than a needle.  When I had mine apart even though I knew where it was I could not see it if I was looking up into the bore with the piston out.  Maybe someone with the same bike can confirm the access to those two holes but I think I may be correct in that.

[madmtnmotors]

  The later F's have a different master cylinder and I am guessing that access to those two holes may be behind the "nipple" fitting that the hose from the fluid cup is connected to.  This is removable.  The send hole is large enough to see easily but the return is very tiny, smaller than a needle. Maybe someone with the same bike can confirm the access to those two holes but I think I may be correct in that.

You are indeed correct.

[LiquidYogi]

Did you clear the tiny bleed hole in the master cylinder?  Have you primed the master cylinder?
Do you have a mity vac, to suck the fluid from the master to the caliper via the bleed nipple?

Hey Two Tired...if prime it you mean put some brake fluid in the reservoir than yes I did. If not, you're gonna have to explain it to me better because I really don't see where I can prime it. I don't have a mity vac, I'm thinking that I'm gonna have to spring for a more expensive bleed kit. Most bleed kits I see have a pump of some kind, mine doesn't, it's just a bottle and a tube.

[TwoTired]

Did you clear the tiny bleed hole in the master cylinder?  Have you primed the master cylinder?
Do you have a mity vac, to suck the fluid from the master to the caliper via the bleed nipple?

Hey Two Tired...if prime it you mean put some brake fluid in the reservoir than yes I did. If not, you're gonna have to explain it to me better because I really don't see where I can prime it. I don't have a mity vac, I'm thinking that I'm gonna have to spring for a more expensive bleed kit. Most bleed kits I see have a pump of some kind, mine doesn't, it's just a bottle and a tube.

No priming a pump means getting fluid on both sides of the pump check valve(s).  The master is, in effect, a pump. 

I will ask some fundamental questions:

Does your bleeder kit apply any sort of suction to the bleeder nipple?  (I use the Mity vac (hand help vacuum pump) for this.
Are you opening the bleeder nipple/valve while you are trying to bleed the system?
Are you certain that the master's actuating piston is fully retracted when the brake lever is up?
Did you assemble the master's piston cups in the correct order, and did you place the one with the hole in the center approximately midpoint on the piston shaft?
See:
http://www.westernhillshondayamaha.com/fiche_section_detail.asp?section=2037015&category=Motorcycles&make=HONDA&year=1978&fveh=123330

The pic below is exemplary for showing internal parts orientation (particularly the center cup), even though it is actually a Cb550 Master piston.

[LiquidYogi]

Did you clear the tiny bleed hole in the master cylinder?  Have you primed the master cylinder?
Do you have a mity vac, to suck the fluid from the master to the caliper via the bleed nipple?

Hey Two Tired...if prime it you mean put some brake fluid in the reservoir than yes I did. If not, you're gonna have to explain it to me better because I really don't see where I can prime it. I don't have a mity vac, I'm thinking that I'm gonna have to spring for a more expensive bleed kit. Most bleed kits I see have a pump of some kind, mine doesn't, it's just a bottle and a tube.

No priming a pump means getting fluid on both sides of the pump check valve(s).  The master is, in effect, a pump. 

I will ask some fundamental questions:

Does your bleeder kit apply any sort of suction to the bleeder nipple?  (I use the Mity vac (hand help vacuum pump) for this.
Are you opening the bleeder nipple/valve while you are trying to bleed the system?
Are you certain that the master's actuating piston is fully retracted when the brake lever is up?
Did you assemble the master's piston cups in the correct order, and did you place the one with the hole in the center approximately midpoint on the piston shaft?
See:
http://www.westernhillshondayamaha.com/fiche_section_detail.asp?section=2037015&category=Motorcycles&make=HONDA&year=1978&fveh=123330

The pic below is exemplary for showing internal parts orientation (particularly the center cup), even though it is actually a Cb550 Master piston.

No no sucking it's just a bottle that has a magnet on it so it can stick to something metal. Can you suggest a better kit that I can use, maybe there's a specific one I could order? Or what I should be looking for in a bleeder kit? Mity vac, sounds like something I could use actually and I'm looking into it now. I didn't rebuild the master just the Caliper. The Master had no problems with it that I could tell, it worked perfectly fine when it jammed the piston into the brake disc and locked it up on me.

[LiquidYogi]

http://www.mityvac.com/pages/products_hvpk.asp

How about the MV8000? Could that work for a motorcycle?

[TwoTired]

http://www.mityvac.com/pages/products_hvpk.asp

How about the MV8000? Could that work for a motorcycle?

I don't see why not.  Looks quite similar to my 20 year old one.

[LiquidYogi]

http://www.mityvac.com/pages/products_hvpk.asp

How about the MV8000? Could that work for a motorcycle?

I don't see why not.  Looks quite similar to my 20 year old one.

It works GREAT! It just proved to me that there's definitely a blockage so I'm taking off everything now. Yippie! This wouldn't be so annoying if I had a garage with lights and not a flashlight and a curb.

[TwoTired]

Get your self one of those LED headband lights.  There are many different kinds.  But, here is an example to get the idea.
http://www.alliedelec.com/search/productdetail.aspx?sku=70145445

[bollingball]

Get your self one of those LED headband lights.  There are many different kinds.  But, here is an example to get the idea.
http://www.alliedelec.com/search/productdetail.aspx?sku=70145445

That has been #1 on my tool list for my bike and car. Really handy or no handy
Ken

[LiquidYogi]

Get your self one of those LED headband lights.  There are many different kinds.  But, here is an example to get the idea.
http://www.alliedelec.com/search/productdetail.aspx?sku=70145445

Good call...I look like a dork all the time anyways.

[TwoTired]

I guess it takes hard work and vigilance to be fashion worthy at all times.  But, to insist on such while wearing blackened nitrile gloves or with road grime hands, I hadn't even considered before now.

You can also have baseball caps equiped with LEDs for spot lighting, or get the halo type for general lighting.  For the latter, leave out a tip jar for passersby. 
http://www.thefind.com/sports/info-led-hat-cap-light-flashlight