CB750k Front Brake Help

[CivilPenny]

1978 Honda CB750k
Hey guys,
So in my front brake caliper, the piston is seized and irremovable. I've tried compressed air, heat, and even the high pressure of grease. I do not want to spend over $100 on a stock one that might later end up with the same problem, so I was curious if any aftermarket brake calipers could be used? If anybody knows what calipers can work on 750's let me know!
Thanks
-Dom

 

[dirtdigger]

I would just look for a good used one that is not seized and rebuild it before you put it into use. If you flush fluid on a regular basis you will keep the moisture out of the system and will help keep the piston from locking up. Moisture is the worst thing you can have in a brake system.

 

[amc49]

How dedicated was your grease setup? If done correctly I have never seen one that that would not remove and I've done some absolutely horrible ones. If grease coming out where you fasten the grease gun to you haven't got it sealed well enough, done right there will be zero grease coming out there. You should be able to get like 2500 psi there with a good sealing grease gun.

Look at '79-'80 DOHCs, some Ks may use the same caliper.............

 

[CivilPenny]

I didn't mention my pad is still in there as well as the piston. Can't seem to get the pad out...there's still a hollow circular pin through the pad going towards the piston. Do I need to remove that to get the pad out? I just assumed it should come out easily

 

[madmtnmotors]

I didn't mention my pad is still in there as well as the piston. Can't seem to get the pad out...there's still a hollow circular pin through the pad going towards the piston. Do I need to remove that to get the pad out?

No. The top of the pad is notched. The pin is only a guide pin to prevent the pad from turning.

Compressed air is weak and dangerous. Once the piston starts to move it still has all that compressed air behind it. It can drive the piston out like a bullet. The master cylinder or grease gun method uses hydraulic pressure. Since fluids can't be compressed, the pressure is limited to the length of the stroke of the master lever or grease gun handle. You can also generate much higher force hydraulically as amc49 has indicated. Did you block off the brake hose inlet and loosen the bleed screw before connecting the grease gun to the bleed screw?

 

[Dave]

I don't know of anyone manufacturing new calipers for old Hondas. If you want new you'll probably have to do a fork conversion.

Your location says "Lansing", I assume that's MI? There's a lot of motorcycle salvage yards in MI. and and there's always Ebay.

 

[grepper]

Yeah, there's Slick's Motor Sports in Dansville (South of Lansing), but I've found them to be expensive. The pad should come out with some work. You might try putting it in a vice and getting the piston to go in a little just to get it moving.

 

[amc49]

'...and dangerous.'

X2, I've seen a piston go a hundred foot before it touched the ground powered by air.............put a fat wad of rags in there to take the hit and still stand back.

Grease works better as you can go much higher on the pressure but it builds up slower to control it...............usually. Consider the forces involved and don't be silly about it.

 

[AlabamaCB750]

amc49 is absolutely correct, grease will build up more pressure without the danger of compressed air. Like he said, a brake piston becomes a large bullet when it comes loose with high air pressure behind it. I like to put mine inside 2 or 3 layers of old socks when using the grease gun method to keep the piston and grease from flying everywhere when it does let go. Sometimes I even put it in a wooden box for extra insurance.

 

[tctreppin]

Nice ... you guys are very knowledgeable