Topic: help with brakes please

[juntjoo]

front brakes https://imgur.com/a/CmQxW

hey, so I've done this like once about 20 years ago, and either it wasn't this difficult or there's something defective here. I can't build up any pressure after rebuilding the master cylinder and both calipers. I've ruled out my hand vac I'm using and I've confirmed brake fluid flows all down to where the line connects to the calipers. pressure slowly drops from the hand vac connected to the bleeder valve. I think I can find an M8 bolt or whatever they are to isolate the lever/master cylinder and the calipers themselves then pump the brake to test it and hand vac the calipers to test them. Is that a good route to go from here? Last but not least I painted them with that really rich red. How about I paint the tank and seat likewise and remove the decals? Thanks

[evinrude7]

did you get all the air out?

[Yamahawk]

Sometimes you have to prime the MC, take out the banjo bolt, put your thumb over the MC outlet and pump the lever until you feel pressure, and all the air bubbles sift out the MC reservoir holes. Then, hook up the brake line and the banjo bolt, and start bleeding them again. I like the Mighty Vac for sucking air out of the lines, or when I flush the nastys out.
Charlie

[juntjoo]

Sometimes you have to prime the MC, take out the banjo bolt, put your thumb over the MC outlet and pump the lever until you feel pressure, and all the air bubbles sift out the MC reservoir holes. Then, hook up the brake line and the banjo bolt, and start bleeding them again. I like the Mighty Vac for sucking air out of the lines, or when I flush the nastys out.
Charlie

i googled mighty vac, and it's what I'm using! okay, so why can't I just keep using my mighty vac then? take too much time? but again, my mighty vac has the slow leak connected. Is that how it's supposed to behave when a lot of air is in there? theoretically then shouldn't I just have to keep pumping the vac to get the air out?  I'll try in the morning. thanks

[Flyin900]

Did you clean the tiny return hole in the master cylinder body when you rebuilt it and confirmed it was clear? It is somewhat normal for the brake bleeder to leak down pressure slightly after you pump up the pressure. Sometimes the small bleeder tube over the brake bleeder connector will pull air in once you get a bit of pressure built up.

[Yamahawk]

^^^^^ +1
Charlie

[juntjoo]

okay, something is wrong with the right caliper I believe as I'm able to pull air and fluid through the left one, but barely through the right and the pressure drops faster in the right.  I think at this point I should empty the fluid out and test each component right? I'm sure I did a good job on the MC. I couldn't quite touch the hole down there with anything, or the entire passage really so I suppose it could be partially blocked but it is passing fluid good enough it seems. As far as testing the calipers what should I do? plug the banjo bolt hole and see if I can maintain a certain amount of vacuum pressure at the bleeder hole? If there was a leak I should find fluid leaking though right? So if everything is good and sealed why would right caliper be giving me these problems? I'll get to it later tonight(EST) but any ideas til then anyone? Thanks again

[pjlogue]

If you are applying vacuum to the system via a bleed screw, you are going to be sucking air past the threads for the bleed screw any time the screw is loosened.  The best way I have found to get the air out of a brake system is to use pressure and drive the fluid (and any air bubbles) up.  Gravity is your friend.  Any "T"'s or couplings in the system is where tiny air bubbles will get trapped.  The MC will trap air too.  The tiny hole in the bottom of the reservoir  is where air needs to be purged.  Make sure it is at the highest point in the system.  Once you think you have most of the air out of the lines let the bike sit for a day with that tiny hole oriented so it is at the very top of the system.  The next day gently and slowly pull on the brake lever just a small amount and you should see bubbles come out of the tiny hole.  You don't want to pull on the brake lever so much that you drive the air back down into your lines.  Just a few mm is enough to "burp" the air out.

-P.

[PeWe]

My CB750 K6 has dual brakes, DSS MC. I took it apart and put it together again a week ago since I restored the fork. Brakes very easy to fix. Filled MC with brake fluid. (I have covered tank and all painted areas around MC with old sheets.
Opened the bleeding valves on calipers. An let it flow. Press the brake lever a little. Then did one caliper each time. I used a 20 cm long hose on the bleeder valve to get the fluid to  flow away from bike and a little bit upwards so I can see the bubbles in the clear hose. Opened bleeder, press brake lever and keep it pressed. Tighten bleeder valve, release brake. Open bleeder valve and press again. Do this a few times until no more bubble is to be seen in the hose on bleeder valve. Do the other side.

Refill MC with fluid in time. Be aware of it will squirt brake fluid from MC when you press brake lever. I do it without cap so I can refill in time. Cover with a this cloth to avoid the fluid to hit fresh good paint.

This is a 10-15 min job once started.
I have never had any problem to bleed my front brake on my CB750, stock as with dual brakes. The only problem was to mount right caliper bracket correct wich must be mounted AFTER fender bracket. (Fork leg 5mm spacers, fender bracket, caliper bracket.
8 mm bolt has 7mm spacer. Stock side has fork leg, caliper bracket, fender.

[Scott S]

 If the LH caliper works and retracts, then the tiny return hole in the master cylinder is probably OK. That kinda points to the RH caliper as the problem. Did you pull the pistons and check/clean/replace the piston seals?

 Other tips for bleeding (but I think you have a caliper issue):

 Turn the forks so that the caliper you're working on is on the "high" side. Same thing with handle bars when doing initial bleeding on the master. You want any trapped air bubbles to "float" to the top and not get stuck in a low point.

 Gently tap the calipers, and brake tee's, fittings, etc., lightly with a rubber hammer. Dislodge any trapped air bubbles so they can float up or out  to the bleeder.

 If you have a particularly finicky system, slowly crack each banjo bolt/fitting and see if any air escapes there. Protect your paint.

 Sometimes, I'll get to 95% and just can't get the last little bit of sponginess out, even though I'm not getting any air from the bleeders. Wrap a rubber band or zip tie around the brake lever and turn the bars/forks so that all air can go UP and out the little bleed holes in the master. Walk away and let it sit overnight.


 BUT....if you have one caliper working and one not, focus on that caliper.
 

[Yamahawk]

I have been successful in adding fluid by pressure from the bleeder on each caliper like this:
Get a cap off of a gear lube bottle that has the cone spout, and just cut the tip so that you can attach a clear tube to it, of the size needed to go over the bleeder on the caliper. put the cap on your bottle of brake fluid, (I like the quart size Valvoline synthetic DOT4)  and Crack the line at the MC. Now with the line banjo bolt loose at the MC, squeeze the bottle and fill the line until you see fluid coming out the junction of line and MC at the banjo bolt. (Do not let the bottle go as it will suck air back into the line at MC) Tighten the bolt, tighten the bleeder, and remove hose. Do the same for the other caliper. When this is completed, follow PeWe's instructions to bleed any trapped air out of the system. You may have to pump the lever several times, then open the bleeder at the caliper, and then tighten it while still holding the lever in, and have a hose off the bleeder into a bottle or container with a little fluid in it so the hose end is in fluid. If you still have no pressure at the MC, you will have to do what is called 'bench bleeding' of it. It can be done on the bike, but is a little messy, so be sure you cover the painted areas of your tank, etc with a piece of plastic or a rag. Remove the banjo bolt and line with the two washers (one on each side of the hose fitting), and then hold your thumb over the MC hole, and slowly squeeze the lever until you feel pressure on your thumb, Then install the line making sure your washers are both installed correctly. Repeat the PeWe procedure.

Charlie

[juntjoo]

thanks for all that. I'm still reading, trying to at least before I fall asleep. Long day at the riding class. A lot of fun. Rode this suzuki 250 something. smaller looking cafe racer type bike I think. anyway, Im not getting any piston action on either caliper. The left one I can just pull fluid from whereas the right side I cannot. So I took that as I've got an issue with the right one. I'll keep studying up this subject and report back tomorrow. thanks

[juntjoo]

bleed valves https://imgur.com/a/72HNX

one is the one I'm using, the other is a new one from my kit but they had to custom pack my kit because apparently my brakes are rare. And I don't think there is anything wrong with the valves, I think the threads in the right caliper are stripped since it has noticeable wiggle once loosened hence my inability to apply suction to it. So I think first I'll try coating the internal threads in the caliper with epoxy then re-tap the hole. If for some reason that doesn't hold or even work I can tap it to the size of the valve. Does this sound like a good plan? I just learned the epoxy trick in here I think for scratches in mating surfaces and it sounds like a possible solution for loose threads. Anyway, let me know if you've got other ideas.

[juntjoo]

https://imgur.com/a/XSNzu

this seems to have fixed the issue and I've been bleeding the right side now for a long time but I still get no resistance at the lever. But the cap is off, so the displacement of fluid in the MC piston would be done in the atmosphere right? So then in order to test the brakes you'd have to close off the MC cover but what about that little bit left at the top? what am I missing here?

[juntjoo]

so I've been working at this for a while now. How long is it supposed to take to get the pistons to release into the pads? I've got totally free play with the lever. otherwise it appears to bleed correctly

[DaveBarbier]

so I've been working at this for a while now. How long is it supposed to take to get the pistons to release into the pads? I've got totally free play with the lever. otherwise it appears to bleed correctly

What do you mean “release into the pads”? The pistons should be pushed out against the pads after a couple lever pulls.

Unsure if it’s been said, but vacuum bleeders can pull air through the threads on the bleeder making it look like you’re not fully bled. I prefer doing what Charlie said to make sure the MC is bled first. Then I connect the lines to the MC and remove the bleeders from the calipers completely and use my finger to plug and unplug the hole as I squeeze and release the lever. If the system is dry it seems like it needs more help then just a cracked bleeder.

Don’t use epoxy in the threads. The bleeder will wobble a bit in the threads when you loosen it. If you’re worried they’re stripped take a look at them.

[juntjoo]

so I've been working at this for a while now. How long is it supposed to take to get the pistons to release into the pads? I've got totally free play with the lever. otherwise it appears to bleed correctly

What do you mean “release into the pads”? The pistons should be pushed out against the pads after a couple lever pulls.

Unsure if it’s been said, but vacuum bleeders can pull air through the threads on the bleeder making it look like you’re not fully bled. I prefer doing what Charlie said to make sure the MC is bled first. Then I connect the lines to the MC and remove the bleeders from the calipers completely and use my finger to plug and unplug the hole as I squeeze and release the lever. If the system is dry it seems like it needs more help then just a cracked bleeder.

Don’t use epoxy in the threads. The bleeder will wobble a bit in the threads when you loosen it. If you’re worried they’re stripped take a look at them.

I'm not sure what you guys mean about bleeding the MC. use my finger? at the point I connect the banjo bolt to it won't I be allowing air back in (along with making a big mess)?

[DaveBarbier]

https://imgur.com/a/XSNzu

this seems to have fixed the issue and I've been bleeding the right side now for a long time but I still get no resistance at the lever. But the cap is off, so the displacement of fluid in the MC piston would be done in the atmosphere right? So then in order to test the brakes you'd have to close off the MC cover but what about that little bit left at the top? what am I missing here?

If you squeeze the lever too quickly with the MC cap off, you’ll get a stream of brake fluid in your face

You can bleed with the cap off, once the MC piston is pushed past the supply hole in the reservoir it seals and pressurizes the lines...in a working system.

[DaveBarbier]

so I've been working at this for a while now. How long is it supposed to take to get the pistons to release into the pads? I've got totally free play with the lever. otherwise it appears to bleed correctly

What do you mean “release into the pads”? The pistons should be pushed out against the pads after a couple lever pulls.

Unsure if it’s been said, but vacuum bleeders can pull air through the threads on the bleeder making it look like you’re not fully bled. I prefer doing what Charlie said to make sure the MC is bled first. Then I connect the lines to the MC and remove the bleeders from the calipers completely and use my finger to plug and unplug the hole as I squeeze and release the lever. If the system is dry it seems like it needs more help then just a cracked bleeder.

Don’t use epoxy in the threads. The bleeder will wobble a bit in the threads when you loosen it. If you’re worried they’re stripped take a look at them.

I'm not sure what you guys mean about bleeding the MC. use my finger? at the point I connect the banjo bolt to it won't I be allowing air back in (along with making a big mess)?

I bleed it on the bench over the trash can. Yeah, I get fluid all over the MC. I hold my finger over the hole (or stick a rubber plug in there if you’re smarter than me) where the lines go until I get it bolted to the handlebar. Then I quickly connect the lines and bleed as I explained above.

Edit: of course always keeping the reservoir full. Once the reservoir gets low allowing air back in the system you have to start over.

[juntjoo]

oh.. okay, I think I got it. had to visualize it. when the lever is depressed I can let go of the hole, or unplug it without concern for air coming in,THEN reattach banjo bolt. lemme try again...

[DaveBarbier]

oh.. okay, I think I got it. had to visualize it. when the lever is depressed I can let go of the hole, or unplug it without concern for air coming in,THEN reattach banjo bolt. lemme try again...

I just unplug the hole and quickly connect the lines as fluid slowly leaks out. It won’t pour out, just drip. I have rags handy. If you don’t know, brake fluid will eat your paint.

[juntjoo]

so... lol, still trying to visualize this. I plug the hole, check, then depress lever once, hold, the loosen plug/bolt slightly to release the air =to one squeeze of the lever? and there will be a combination of fluid AND air escaping? what if I detach the handle bar (easy?) and turn hole up? will that push out JUST air first before I reconnect the line? Thanks pal for hanging out with me here

[DaveBarbier]

When bench bleeding the master cylinder I fill the reservoir and squeeze the lever. Then plug the hole with my finger and release the lever. Unplug the hole and squeeze the lever. Keep doing that until you decide it’s fully purged of air. Doesn’t take more than a handful of squeezes. Yeah, you can tip the master cylinder up so the hole is higher but don’t spill all the fluid.

Then I hold my finger over the hole to prevent fluid from dripping out and mount to the handlebars and connect the lines. Sometimes, once the lines are connected, and the bleeders cracked or removed completely, gravity will pull fluid to the calipers and you’ll see fluid coming out the bleeder holes. If that doesn’t happen I bleed the calipers as I said in my earlier post. Finishing with regular bleeding. After that you should have decent lever feel.

When I’m all done, I zip tie the lever back turn the handlebars to the left while the bike is on the kickstand and leave it overnight (that makes the MC the highest point in the system). In the morning I come back and release the lever quickly. I’ve heard that helps firm up the lever. I think I notice that it helps.

[Flyin900]

If your still struggling with this back to my original suggestion on the master cylinder. Did you verify the small hole in the bottom of the master is clear? There are two holes down there a larger one, although still small and a really tiny one that usually needs special attention.
If the very tiny hole is plugged you will get the symptoms you are experiencing in not being able to bleed your brakes.

[juntjoo]

When bench bleeding the master cylinder I fill the reservoir and squeeze the lever. Then plug the hole with my finger and release the lever. Unplug the hole and squeeze the lever. Keep doing that until you decide it’s fully purged of air. Doesn’t take more than a handful of squeezes. Yeah, you can tip the master cylinder up so the hole is higher but don’t spill all the fluid.

Then I hold my finger over the hole to prevent fluid from dripping out and mount to the handlebars and connect the lines. Sometimes, once the lines are connected, and the bleeders cracked or removed completely, gravity will pull fluid to the calipers and you’ll see fluid coming out the bleeder holes. If that doesn’t happen I bleed the calipers as I said in my earlier post. Finishing with regular bleeding. After that you should have decent lever feel.

When I’m all done, I zip tie the lever back turn the handlebars to the left while the bike is on the kickstand and leave it overnight (that makes the MC the highest point in the system). In the morning I come back and release the lever quickly. I’ve heard that helps firm up the lever. I think I notice that it helps.

spill the fluid? don't you have the cover on the MC?

so plug hole w/ finger, fill it up MC as much as possible. install cover. squeeze the lever til I feel pressure on my thumb then hold lever in.

NOW tilt hole(I'll loosen the lever/MC assembly on the handle bar) upwards release lever and squeeze again then hold and repeat?