Author Topic: Front brake. need help please (Read 2393 times)

import_tuner13 · « **on:** November 08, 2010, 04:37:44 PM »

got a 77 cb750 front brake setup (the one with the stoplight switch on the brake halfway down with the joint connector) and it was bone dry with a clean (looked like it ) functional brake lever. put brake fluid in, and it does nothing, just sits in the resevoir. tried pumping brakes to get the fluid down to the caliper, got a couple little bubbles, and that's it. doesn't go down to the caliper. think it's clogged? also, have a 20 year old brake pad stuck in the front caliper. any ideas on how to get that out? think i will have to rebuild the caliper? thanks!

Dan

TwoTired · « **Reply #1 on:** November 08, 2010, 04:46:23 PM »

Two holes in bottom of fluid reservoir; one large, one with a tiny hole in the tapered bottom.

The lines get charged from the tiny hole. If plugged, no work, and air can't escape there (and it needs to).

Want more details? The search function will likely return more posts about this than you'd care to read.

Cheers,

import_tuner13 · « **Reply #2 on:** November 08, 2010, 04:54:42 PM »

got it. now how do i remove that brake pad from the front caliper? it's seated in there pretty good. when i get fluid moving to it do you think i can just pump it outta there?

cookindaddy · « **Reply #3 on:** November 08, 2010, 04:55:45 PM »

You did slightly loosen the bleed screw on the caliper?

As TT said, you will find plenty of info here on bleeding and, if necessary, rebuilding your brakes.

BeSeeingYou · « **Reply #4 on:** November 08, 2010, 04:56:20 PM »

Maybe a bit more info. Has the bike been sitting for a long time? It is common for the flexible brake lines to develop a clog from long storage. Take it all apart and get a short length of 1/16th wire rope from the hardware store. If you get a nice clean cut it won't unravel and it is flexible enough to get it through the banjo fitting and pushed down the brake line. Get your MC and lines working first and then you can use that to force out the piston in the caliper. I would rebuild the MC and the caliper at a minimum. If your budget affords it you could spring for new flexible stainless steel lines too. You don't know the condition of the rubber seals. The caliper has only one rubber seal but you will need to check the piston for excessive pitting. The parts are readily available and there is plenty of info on the site on how to do this. Just do a search.

Kevin400F · « **Reply #5 on:** November 08, 2010, 05:05:20 PM »

Once the tiny hole in the floor of the master cylinder (nearest the outlet port) has been opened up with a very fine wire as Lloyd suggests, a useful trick is to fill the reservoir, install the cap, remove the hose and use your thumb over the outlet port as a "check valve". Squeeze the lever with your thumb "off" the port, then seal the port tightly with your thumb before releasing the lever. This will help create a vacuum within the cylinder bore to draw fluid down from the reservoir. It is usually best to do this away from the bike, in case you spill or spray fluid, and once it starts filling, holding it with the port straight up will help "prime" the master cylinder fully.

TwoTired · « **Reply #6 on:** November 08, 2010, 05:09:32 PM »

Quote from: importtuner13 on November 08, 2010, 04:54:42 PM

got it. now how do i remove that brake pad from the front caliper? it's seated in there pretty good. when i get fluid moving to it do you think i can just pump it outta there?

Yes. I've been able to pump out any stuck piston/or the brake pad by getting the master to work first.

Cheers,

import_tuner13 · « **Reply #7 on:** November 08, 2010, 05:14:15 PM »

dont worry guys, i know how to use the search button. I figured it would be easier to ask instead. i will try cleaning the return hole tonight. and yeah it's been sitting a looooong time. thanks kevin for the tip if i can't get it flowing easily i will try that. the master cylinder looks like it's already been rebuilt. god knows about the caliper. the bike only had 10k on it.

Kevin400F · « **Reply #8 on:** November 08, 2010, 06:04:48 PM »

No probs, Tuner. The way I see it, if everyone found all the answers to all their questions by quietly searching, we wouldn't have much conversation in here, would we?

But, since I only have a little over 400 posts, I'm not too tired to answer a question or offer some useful advice.

import_tuner13 · « **Reply #9 on:** November 08, 2010, 07:25:34 PM »

update: return hole was clogged. pair of sharp tweezers from work opened it right up. managed to pump the old brake pad out too. before that, caliper was seized up so couldn't roll the front wheel. assuming it needs a rebuild if it doesn't retract, right? at least i have everything down to the caliper working now lol. how can i tell if it needs a rebuild though? PS nobodys ever called me tuner before lol it's Dan.

The_Crippler · « **Reply #10 on:** November 08, 2010, 07:36:47 PM »

A word on the steel lines: There's a guy on here (services section, I believe) who makes them. High quality, and good price. I highly recommend them.

MoMo · « **Reply #11 on:** November 09, 2010, 06:24:48 AM »

If the caliper piston is pitted you'll need a new one, plus the new o=ring

import_tuner13 · « **Reply #12 on:** November 09, 2010, 09:45:41 AM »

caliper piston has a total of 15 pits

yes i counted them. brought it to the stealership near me, and was told by a parts guy that it could be re used. none of the pits are major. removed the o ring inside the caliper, had a ton of junk in it, scraped it all out with a pick tool/flathead screwdriver (gently, of course). so a new seal is the same thing as that o ring inside the caliper? didnt see many moving parts. also, small little plastic washer fell out of the caliper? where does that go?

MCRider · « **Reply #13 on:** November 09, 2010, 09:56:49 AM »

Quote from: importtuner13 on November 09, 2010, 09:45:41 AM

caliper piston has a total of 15 pits yes i counted them. brought it to the stealership near me, and was told by a parts guy that it could be re used. none of the pits are major. removed the o ring inside the caliper, had a ton of junk in it, scraped it all out with a pick tool/flathead screwdriver (gently, of course). so a new seal is the same thing as that o ring inside the caliper? didnt see many moving parts. also, small little plastic washer fell out of the caliper? where does that go?

If the pits are on the outside of the seal, and don't pass under the seal, should be reusable. seal=Oring= Square ring (it has a square cross section, not an O), plastic washer = ?

TwoTired · « **Reply #14 on:** November 09, 2010, 11:14:34 AM »

The plastic washer goes between piston and friction pad.

import_tuner13 · « **Reply #15 on:** November 09, 2010, 11:44:26 AM »

if it has 1 or 2 pits inside the seal is it considered garbage then? because that sucks. i'd need to get a new one. yeah weirdest thing for that plastic washer, goes between piston and brake pad who knew. any ideas for cheap new piston?

MCRider · « **Reply #16 on:** November 09, 2010, 12:07:20 PM »

Quote from: importtuner13 on November 09, 2010, 11:44:26 AM

if it has 1 or 2 pits inside the seal is it considered garbage then? because that sucks. i'd need to get a new one. yeah weirdest thing for that plastic washer, goes between piston and brake pad who knew. any ideas for cheap new piston?

That's my opinion re the pits. I just bot new phenolic ones from a forum member: kevin400F. You'll have to PM him for availability and price. Other than that the usual suspects: dealers, motogrid.com, partsnmore.com etc.

I thought that about the washer but wasn't sure. Some models don't have them. They reduce vibrations and hence squeal, hopefully.

MCRider · « **Reply #17 on:** November 09, 2010, 12:08:31 PM »

Quote from: importtuner13 on November 09, 2010, 11:44:26 AM

if it has 1 or 2 pits inside the seal is it considered garbage then? because that sucks. i'd need to get a new one. yeah weirdest thing for that plastic washer, goes between piston and brake pad who knew. any ideas for cheap new piston?

Ytou could use the piston, and if it leaks it will be obvious and replace it then. But leaking fluid is not cool. Did it leak before the teardown?

What can happen is as the pad wears down, more of the piston is exposed. Then it sits with the pad worn out, for 20+ years and gets a pit in the chrome. Then the new owner puts new pads in and pushes the piston back in for clearance, and now the pit is on the inside of the seal, where it never was before. As the pit slides back and forth under the seal, it chews away at it and it begins to leak, but that could be much later.

import_tuner13 · « **Reply #18 on:** November 09, 2010, 12:10:55 PM »

it seized before teardown. like, tons of pressure, piston did not retract, could not move front wheel. i suppose that would equal not leaking, because the pressure would eventually dissapear. brake handle was solid

The_Crippler · « **Reply #19 on:** November 09, 2010, 12:12:58 PM »

Quote from: importtuner13 on November 09, 2010, 12:10:55 PM

it seized before teardown. like, tons of pressure, piston did not retract, could not move front wheel. i suppose that would equal not leaking, because the pressure would eventually dissapear. brake handle was solid

Basically, you found the secret "Immovable Object" setting. Now, you just need to mod your engine to "Irresistible Force" levels and see what happens.

MCRider · « **Reply #20 on:** November 09, 2010, 12:15:13 PM »

Quote from: importtuner13 on November 09, 2010, 12:10:55 PM

it seized before teardown. like, tons of pressure, piston did not retract, could not move front wheel. i suppose that would equal not leaking, because the pressure would eventually dissapear. brake handle was solid

Yeah, that symptom is usually a blocked return passage in the master cylinder, very common. Sounds like it wasn't leaking. If this was all recent and not the aged scenario described above, you could maybe get away with your piston, but i didn't say so.

import_tuner13 · « **Reply #21 on:** November 09, 2010, 12:54:50 PM »

don't know if the master cylinder would have a blockage though because i was able to bleed/flush the brakes successfully. started with dry system, that was sitting for at least 10 years. will try the old piston, worst case scenario it leaks and i notice....bike doesn't run anyways. always have the rear brake if the front fails, right?

MCRider · « **Reply #22 on:** November 09, 2010, 01:08:28 PM »

Quote from: importtuner13 on November 09, 2010, 12:54:50 PM

don't know if the master cylinder would have a blockage though because i was able to bleed/flush the brakes successfully. started with dry system, that was sitting for at least 10 years. will try the old piston, worst case scenario it leaks and i notice....bike doesn't run anyways. always have the rear brake if the front fails, right?

If the brake clamped onto the disk and wouldn't let go, i still vote for the return passage in the MC. Bleeding the brake would involve pushing fluid towards the caliper. The return isn't needed.

Once the brake is bled, to operate the brake, fluid must go towards the cylinder to clamp the brake. But then it must be allowed to return to the master cylinder via the return passage, so that the pad can withdraw itself from the disc. That's where the problem likely lies. It sounds pretty lame I know, but the only thing pulling the puck away from the disc when you release the lever is the springiness of that seal. Which is puny at best and weaker still if its really old. So any blockage in the master cylinder return will keep the puck up against the disc.

Its the small hole in the reservoir, nearest the banjo bolt. It can be cleaned with a thin wire, often I've heard guitar strings are used. If its been sitting dry, it could easily have dried crud in it.

The_Crippler · « **Reply #23 on:** November 09, 2010, 01:18:25 PM »

I gotta say, this is all resonating with me as well. Bike I picked up a few weeks ago has mostly locked front brakes, and I was also just assuming buggered caliper...even after seen posts month after month about cleaning that little hole in the MC, my brain still refused to consider that.

Looks like I know what I'm doing this weekend.

import_tuner13 · « **Reply #24 on:** November 09, 2010, 01:35:42 PM »

just remembered. fluid was pushing back through the return hole because it was shooting out of the resevoir !!!!!!!!!!!! so its not clogged. it was clogged at first used a pair of fine tweezers to clean it out. but that caliper was seized too had to have been. and the brake lines weren't filling up because the return was clogged. will update when i get a new seal later on this week.

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Author Topic: Front brake. need help please (Read 2393 times)