Topic: cb750k4 Front Brake Work

[Ujeni]

Hi everyone. Man am I glad I found this forum...super useful! Thanks for all the info...i'll be around here for a while!

I have a 74 cb750. Been slowly getting it running better. After getting the carbs, electrical system and the engine happy, i am now focusing on the front brakes. Even after bleeding the brake system, the pads would not retract from the rotor. I looked around and found that I needed to grease the sides of the pads. Now I need to get the piston out to take a closer look at it. I tried to hook the brake system back up and re-bleed the system to force the piston out...but now i have nothing...the brake lever goes limp. What have I done here? I did manage to take the boot off the master cylinder, but i never got the master cylinder out (silly circlip problem). I put the boot back on and tried again...but something is wrong. no pressure. have i damaged the master cylinder?

Thanks for your help. Hopefully in a few months I'll post the before and after shots of my bike...exciting!

[gerstle]

mmmm.... fun with brakes.  I'd have to say that this is one of the more enjoyable (by enjoyable i mean a #$^%ing PITA) projects involved in keeping these bikes running.  You've probably got some gunk built up in the master.  Either that or you've just got an amazing amount of road gunk and dirt built up around the piston that's making it difficult to get out.  I remember fighting with mine quite a bit the first time i removed it.  While you're doing this, i would recommend taking your rotar to someone who can clean all the burs off and drill holes in it.  Squeeling like a banshee is a very common problem with these brake systems, and drilling will help a lot with that.

good luck

casey g

[turnenwheels]

Try Boiling them...the pressure will pop them right out!  Lets us know

[turnenwheels]

Pop the piston that is...

[Ujeni]

mmmm.... fun with brakes.  I'd have to say that this is one of the more enjoyable (by enjoyable i mean a #$^%ing PITA) projects involved in keeping these bikes running.  You've probably got some gunk built up in the master.  Either that or you've just got an amazing amount of road gunk and dirt built up around the piston that's making it difficult to get out.  I remember fighting with mine quite a bit the first time i removed it.  While you're doing this, i would recommend taking your rotar to someone who can clean all the burs off and drill holes in it.  Squeeling like a banshee is a very common problem with these brake systems, and drilling will help a lot with that.

good luck

casey g

I thought about the gunk in the master cylinder possibility....but the system worked (at least it pushed the piston out) before i took the caliper off. maybe dirt moved in during the process.

I do have a master cylinder rebuild kit arriving today (hopefully). Maybe that will solve the problem. Now to find a tool to get the circlip out.

Thanks for your help.

[Ujeni]

Try Boiling them...the pressure will pop them right out!  Lets us know

you mean boil the caliper unit? really?

[turnenwheels]

Yeah, Cleans it up real nice...After the boil, lube up with brake fluid on the inside. 
This is also, a great way to really clean your carbs... Minus the gaskets of course. 

[nobrakes]

Just rebuilt my m/c last night so thought I'd throw this out there - make sure the m/c (not the brake line) is bled first.  I started trying to bleed from the caliper first, but since I did open the m/c up to pop in the new kit, there was air between the reservior and brake hose bolt.  After a few squeezes of the lever and turns of the hose bolt the handle started feeling snug and I was then able to bleed the brake line.  Before that, though, similar symptoms - limp handle, no pressure, etc.

If you do this, be sure to wrap an old shirt or towel around the m/c bolt to keep brake fluid from getting all over your tank...

[frostypuck]

IF you can get the bleeder screw out of the caliper, you should be able to find a grease fitting that'll turn right in. Then hook up a grease gun, give a pump or three and the pad (and piston) will come out like a rocket. Then just dump out the grease that's inside the caliper.
Clean the inside of the caliper, replace the rubber seal (it is mostly responsible for retracting the piston) and reassemble. Fill the caliper about 2/3 full with brake fluid, place the piston back inside with it's new seal, and press in with a C-clamp. Do this with the cap off the master cylinder, but with a rag over it to catch the shooting fluid.
Then most of the system's air will have been displaced by the fluid in the caliper. Then go ahead and bleed as per the instructions, but it won't take nearly as long.
Good luck,
Chris in Boston

[Ujeni]

OK, in the interest of good documentation for those with similar problems in the future...here's what happened.

I tried boiling the caliper to loosen the piston to no avail. Evenutally I gave up trying to get it out and decided that I would push it out via the brake system itself (I have no grease gun at the moment). Replacing the master cylinder was a bit of a challenge. I followed some advice I found on this site and purchased a set of plyers from Sears (tool # 47385). They didn't fit perfectly, but with a little grinding, i was able to fit them into the the tiny area needed to remove that pesky circlip. By the way, I found that the ring clip that is supposed to hold the boot was lodged above the circlip. Once that was removed, i have an easier time getting to the circlip.

My master cylinder was a wreck. Worn. Even sandy in places. Glad i decided to replace it (30 bucks at the old bike barn).

Hooked everything up, bled the brakes and the piston came right out. Wow, i thought the master cylinder was bad...the piston and the back of the caliper literally had sandy/muddy chunks all over them. I cleaned everything out (I will evenually get a stainless steal piston) and reinstalled it. Finally, I applied to grease to the edges of the brake pad and the inside of the caliper.

Re-bled the brakes and wa-la...i have brakes again!

Thanks for everyone's help!