Front Brakes NOT working properly

[ScottinNY]

I have an 81 CB750C that I got as part of a trade deal. The bike had been sitting for a few years. All original. 7K miles. When I got it, the calipers were stuck, and you couldnt move the front tire. Got it home, pulled the calipers, cleaned them, didnt change anything. The rubber and pistons looked good. Threw them back on the bike, and before I attached the lines, I put the lines in a bottle and pulled the brake to verify that fluid is getting to the calipers. All looks good. I reattached the brake lines to the caliper and bled the brakes. The bike is on a bike stand, and I spun the tire and pulled the brake. It kept spinning. I pumped the brakes a few times, and then it stopped. I bled them again, and same thing....you have to pump the brakes before they actually kick in. I changed the master cylinder, bled the brakes, and same deal. I pump them 2 or 3 times before they work.

since doing brakes is all new to me...what am I missing??

 

[dirtdigger]

Do you have to pump it every time you hit the brakes or just the time right after bleeding? Sounds to me like you still have air in the system or you have a small leak letting air into the system.

 

[ScottinNY]

It has to be pumped at least 3 times, every time, before it actually stops the tire. I wiped all the lines, master, and calipers...but I don't see any fluid leaking anywhere.

 

[dirtdigger]

I would have used new seal in caliper, you could be getting air in by the seals. You can get air in the system and not have a fluid leak. How are you bleeding the system?

 

[ScottinNY]

A hose to the bleeder going into a bottle. Open the bleeder, pull the brake, tighten the bleeder, release the brake. About 20 times on each side. *Keep in mind I'm new to brakes. I saw this method on youtube

 

[dirtdigger]

If you open the bleeder will brake fluid free flow out of the bleeder? I usually let fluid gravity flow from the bleeder then go about the method you used above. Every couple of times pull the brake lever very fast a couple of time and let the lever snap back...it helps to break loose any air bubbles caught in the system.

 

[ScottinNY]

No..it kinda dribbles out. Far from a good free flow. I did try the snap back a few times, but I'm scared that brake fluid will go flying everywhere. When i open the bleeder and pull the brake, if I pull too fast, the master cylinder looks like a water fountain and fluid goes all over.

 

[dirtdigger]

A dribble is about right. Put the cap on the master cylinder when you snap the brake lever.

 

[ScottinNY]

While bleeding, I leave the cap off, correct? What do you suggest..taking the caliper apart and putting all new rubber? Pistons?

 

[dirtdigger]

Keep the cap on then you wont shoot fluid all over, just check the level after ever time you open and close the bleeder, the only reason some people leave the cap off is to watch the fluid level. I would bleed it snapping the lever then let it set over night then bleed it again. If it still isn't working as a last ditch effort...pull the lever harder than normal...sometimes it will force air out or force a leaking seal to seal correct. Nothing to loose if you blow out a seal because it sounds like there is a seal issue or air trapped. I would say try a different master cylinder but you already did that.

 

[tommycarl]

When I've come across a contrary system I've sometimes had better luck by bleeding at the banjo bolts. Start at the master cylinder and just slightly loosen that banjo bolt while squeezing the lever to let out any air that might be trapped there. Naturally be sure to tighten it again before letting off the lever. Do the same at the bolts at the connections under the headlight.

Pay close attention to the position of the master cylinder to be sure it's at the highest point... for example, turning the handlebars to the left might make the master cylinder higher. All depends on the handlebar style and rotation. Turning to the left should also get the junction under the headlight to be high on the RH end, so that might help when bleeding that banjo.

I have much better luck sucking the fluid with a vacuum pump, although bleeding by pumping the lever should work fine, just not always as easy.

Are you sure it has the stock master cylinder? If that has been replaced and doesn't have sufficient capacity for the twin front calipers, that could be a reason it needs pumping every time.

 

[ScottinNY]

It is not the original master. (I do have the original). I purchased a new master cylinder..made 10000% sure that its compatable for twin front calipers before buying them. There is nothing wrong with the stock master, I just wanted a new one. Again..never did brakes on a bike. I figured if i buy a new one, I can take the old one apart and learn about how it works and I can rebuild the stock one. If I mess it up, I still have the new one, so no big deal. So the new one is on the bike. I also have a spare set of calipers. I took the spare set apart, cleaned every nook and cranny, and threw some paint on them. The pistons are in great shape. I ordered new caliper and piston seals and once they get here, im going to take the calipers that are on the bike off, and put the ones I cleaned on..and try again. With a new master cylinder, and rebuilt calipers, thats a good start. Once I do that, I can rebuild the other calipers, and end up with a spare set of calipers and a spare master. I tried everything that you guys recommended, and im having no luck. Its fustrating. Some else suggested that instead of pulling fluid through the bleededer, try pushing fluid into the bleeder up to the master. not sure how to do that. As soon as the new rubber gets here, I will pop those calipers on and try again.

 

[tommycarl]

No offense meant, but you sound a bit like me a couple of years ago... (fortunately you don't know how bad that can be).

I had a CB900C and a friend had a VW-Goldwing trike. I needed a master cylinder and so did he. I bought 2 very nice ones that were for twin calipers and couldn't get either one to work. Could pump them up, but like you. had to do it every time. Bleeding did no good. I checked with the seller and was assured that it was the right master cylinder.

I put one on my '75 750 with a single caliper and it worked great. Put the second on the 750... great. Put my leaking stock MC on the 900... great. Put his leaking MC back on his trike... great.

By coincidence I was on another forum and saw that a fella in Florida had bought the same MC for his 900... didn't work.

A couple of months later I was for some reason looking at that MC again to buy another for another 750... things changed and the literature no longer said it was for a twin caliper bike... go figger.

My point is... maybe you should check 10001% on that new MC. Not to be a smarta$$, just letting you know that you aren't the only one that's been frustrated by similar situations, and it may not be your fault.

 

[dan1951]

Honda did on some models incorporate the rear brake to the rt. front caliper, Drove Me crazy on My first goldwing giving Me the same problem Your describing. I do not know if this system is used on Yours or not check the rr. lines to see if it is. Had to bleed the rear and rt. frt. first, Probably not the case but just a thought.

 

[ScottinNY]

I thought of that as well, but there are no brake lines going to the back from the MC. Also, I did put the stock MC back on just to see if it would make a difference, but same deal. I bled the lines with the stock MC, and the exact same result. Id have to pump the brakes 3-4 times before they stopped the tire. I put the new MC back on, repeated the bleeding, and same deal. Theres air someplace.

 

[ScottinNY]

Heres a question..since i changed the MC, and rebuilding the caliper..why not new lines as well? Im looking at Galfer Steel Braided Lines. Any thoughts on this upgrade? **keep in mind, doing brakes are all new too me.