Topic: help with brakes please

[juntjoo]

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.

okay. I'll give davebarbier's suggestion a try and if no luck I'll empty it out and check again. I remember though it was difficult to impossible to get to those holes because there is this plastic cover over the bottom with a hole in it's center to go under it, and I don't know if it's directly lined up over any of these holes you're talking about. we'll see...

[Flyin900]

Back on post 15 you indicate the caliper pistons aren't releasing the pads and that is a symptom of the very tiny hole being plugged, as that is its purpose. The pads should release the rotor after every release of the brake lever, if not then you have an issue with the return pressure hole in the master cylinder.

I have never had to resort to these measures of pre bleeding the master cylinder, although I do have a brake bleeder tool which does make it a lot easier to pull vacuum through the system and remove trapped air.

+1 on tying back the brake lever overnight once you get it sorted, as it does help purge any remaining air and firms up the feel of the brake lever.

That plastic housing can be removed from the lower metal base, as it is press fit with a large o ring as a sealer. Look up a parts fiche of the front brake master assembly and it will show you the parts orientation and breakdown. The removal will be hard as they usually become sealed up in there with old dried brake fluid.
If you do need to take it apart I recommend removing all the internal parts and boiling the assembly in hot water for 10 mins. this will soften the dried crud and allow you to twist back and forth and break free the upper plastic cover from the base.

It's been a few years since I have rebuild a plastic topped master, yet I am surprised that they don't allow access to both holes through the bottom of the plastic reservoir without removing it from the base.

[juntjoo]

Back on post 15 you indicate the caliper pistons aren't releasing the pads and that is a symptom of the very tiny hole being plugged, as that is its purpose. The pads should release the rotor after every release of the brake lever, if not then you have an issue with the return pressure hole in the master cylinder.

I have never had to resort to these measures of pre bleeding the master cylinder, although I do have a brake bleeder tool which does make it a lot easier to pull vacuum through the system and remove trapped air.

+1 on tying back the brake lever overnight once you get it sorted, as it does help purge any remaining air and firms up the feel of the brake lever.

That plastic housing can be removed from the lower metal base, as it is press fit with a large o ring as a sealer. Look up a parts fiche of the front brake master assembly and it will show you the parts orientation and breakdown. The removal will be hard as they usually become sealed up in there with old dried brake fluid.
If you do need to take it apart I recommend removing all the internal parts and boiling the assembly in hot water for 10 mins. this will soften the dried crud and allow you to twist back and forth and break free the upper plastic cover from the base.

It's been a few years since I have rebuild a plastic topped master, yet I am surprised that they don't allow access to both holes through the bottom of the plastic reservoir without removing it from the base.

thanks. Sounds like you're on to something. Although this plastic tub has no screws in it that I can see. I vaguely remember trying to pull on it. It must just pop in there with a gasket as you say. I guess I didn't completely rebuild it.  oh no, that's another week to get an expensive part. oh well. almost done....

[Flyin900]

Usually no need to buy any parts for the top section. It may have a little tit on the bottom of the plastic housing that aligns it to the metal base housing, so you may not be able to spin it and will need to pry it off the base.
It is stuck on there from age and old fluid that has seeped past the O ring slightly and cemented it in place. So the best bet is to boil it in water as noted to soften the crud and release the top.
You can usually just reuse the O ring if there isn't any leaking going on around the base area, yet if you want to buy new parts then go for it.
Is the bottom of that plastic housing not open to the metal base and are both holes not exposed down in there for the fluid to exit and return back to the master reservoir? As I said it has been awhile since I did a plastic housed one and sometimes I forget what I had for breakfast these days. 

Also make sure you really clean up the slotted area where the O ring sits once you do get it apart, so it doesn't leak after you re assemble it. A small single wire cut from a metal bristle brush is usually small enough to probe and clear the very tiny hole that is plugged.

[DaveBarbier]

As I said before, you can bleed with the master cylinder cap off.

I agree that something else could very well be the issue, especially if you didn’t fully clean or rebuild the system. I’m just trying to make sure your process is correct and thorough.

[juntjoo]

alright, so I went in and cleaned that little hole. not quite sure if it was plugged up as I started poking at it before I cleared all the fluid out of the area. but before I moved on I confirmed it was clear. Yeah, that tub just pops off and on easy enough. Anyway, so I bled on with no luck. No pressure at all on the pistons/pads after bleeding both sides a couple times and no leaks anywhere. What now? shall I try again and take a video?

[DaveBarbier]

Clear pictures and video helps.

[Bodi]

There's not much magic in hydraulic brakes. You say you've bled them twice but have no pressure. I don't understand exactly what you mean, bleeding them requires some pressure unless you do it with a vacuum or pressure bleeder. Is your MC pumping any fluid ever? Just putting a finger blocking the outlet will prove it works, pressure will be enough to get past your finger on lever pull, and plugging the outlet lets the piston draw in from the reservoir.
Air in the lines or caliper cylinders will effectively eliminate pressure - pulling the lever compresses it a bit and releasing the lever lets it just flow back: end result no fluid pumped in and no change.
Dual disk setups are more challenging to bleed but not impossible.
Are the caliper cylinders full? You can fill the cylinders (if unmounted) before inserting the pistons, the unavoidable air also in there is easily pushed out but pointing the inlet up and pressing the piston in. If you get the cylinders full enough this way you can connect the lines and then force one piston in all the way, that pushes fluid up the line to the MC and back into the reservoir. Once that's done, that side's caliper and brake line is definitely close to air-free. Repeat for the other. The hydraulic system should then be purged of air sufficiently to get the MC pumping so you can move on to final bleeding and eliminate any air pockets in the calipers or lines.

[juntjoo]

There's not much magic in hydraulic brakes. You say you've bled them twice but have no pressure. I don't understand exactly what you mean, bleeding them requires some pressure unless you do it with a vacuum or pressure bleeder. Is your MC pumping any fluid ever? Just putting a finger blocking the outlet will prove it works, pressure will be enough to get past your finger on lever pull, and plugging the outlet lets the piston draw in from the reservoir.
Air in the lines or caliper cylinders will effectively eliminate pressure - pulling the lever compresses it a bit and releasing the lever lets it just flow back: end result no fluid pumped in and no change.
Dual disk setups are more challenging to bleed but not impossible.
Are the caliper cylinders full? You can fill the cylinders (if unmounted) before inserting the pistons, the unavoidable air also in there is easily pushed out but pointing the inlet up and pressing the piston in. If you get the cylinders full enough this way you can connect the lines and then force one piston in all the way, that pushes fluid up the line to the MC and back into the reservoir. Once that's done, that side's caliper and brake line is definitely close to air-free. Repeat for the other. The hydraulic system should then be purged of air sufficiently to get the MC pumping so you can move on to final bleeding and eliminate any air pockets in the calipers or lines.

thanks. great walk through. I meant I was not producing any pressure by the lever after bleeding with hand vac, ultimately not getting the air out OR something is up with the MC.

So I'll start from scratch. The pistons are already in and I'd rather not try to take them out (plus I can't remember how I got them out in the 1st place as they hadn't been touched in decades) but what I think I'll do is

1)test the MC itself. (still wondering what should happen when I squeeze the lever. will it like fart past my thumb? lol)

2) test one caliper at a time, connected directly to the MC! Most genius thing I've thought of this month.

3)carefully detach calipers from MC and replace to their original positions on the T junction whatever that part is called, then

4) bleed system and if problem still persists there must an issue with either the 1st line running down to the T or the T itself or I didn't get past step 2 and one of both calipers are bad somehow. can't see why. I replaced all their rubber and pistons look like new

if there's something I should know feel free to share. otherwise like the terminator I'll be back.

[juntjoo]

oh and I'll reiterate that this bike is old including the brake system so the lines should be replaced but first I wanna get this working somewhat just so I can better understand what I'm working with here. UNLESS anyone tells me bad brake lines could cause this problem but i can't imagine why atm. thanks!

[juntjoo]

well I could not bleed the MC. It just kept squooshing. thats an onomatopoeia  . I would point outlet up to bring air up, squeeze and hold lever while loosening plug bolt in outlet, just a bit to let out air then tighten quickly, release lever, rinse and repeat to no avail. then I believe I found a leak at the dust boot around the end of the piston which I didn't find a trail from to anywhere else like the outlet, so I'm guessing either something wrong with the metal parts, fitment or age, or my faulty installation. So either I go digging into it or just order a new one for $30-40. IDK, maybe I shoule at least spend a few minutes inspecting the parts. maybe ill get lucky and find something repairable

[juntjoo]

so the seal on the MC piston felt like it fit but maybe loose, I'm not sure, and I found the rubber cap on the end of the spring mangled. In the vid I show how I've got some extra parts but none of which are to replace the mangled cap. I removee thed old seal and compared to the others, not in vid, and they look the same size.

what do you think? How should the piston fit in there? tight?  wait a sec... it just hit me: without a seal at the end of the spring, basically the front of the action pushing the fluid, that would case fluid to leak back while piston being pushed forward no? which is ultimately the seal for the piston? both? How might I have mangled that cover? if no one has a better idea ill just bite the bullet and order a new MC and lines, but geez, it would be great if i didn't have to spend another $150 for at least a few months!

might I had(grammar?) installed that piston seal incorrectly?

oh I just realized in the vid I put the piston in backwards lol. oops. I'm just getting a new one.

[juntjoo]

any recommendations on any of these aftermarket ones? are they all the same? aside from mine there are solid metal ones with little fluid level windows and there are round shaped ones. does it matter? I think I've looked into ss lines and found some for $100. any tips/recommendations on those?

[juntjoo]

and id still like to know what went wrong with mine, at least so if I sell my left overs for someone who's got that cap and just needs the rest for cheap, I can sell it in good faith and knowledge of what I'm selling. or just chuck it? I friggin bought that lever by itself as the original had broken from PO dropping bike. So people still look for cheap parts even tho a whole new assembly is <$40

[Flyin900]

It helps if you either take pictures of the parts as you disassemble and also use a Honda parts fiche for orientation of the new parts if you are not sure how they fit. This has been an odyssey for sure and it is clear that something is off as with a brake bleeder you should have had no issues.
I would consider one of the cheaper aftermarket complete brake masters that 4 into 1 sells, as he has them for around $45.00 and shipping should be cheap in the US for you. Lube the new parts if you do decide to go the replacement rebuild kit again with brake fluid before you reassemble back into the master cylinder bore.

If you decide to buy a replacement then the master cylinder bore is the determining factor for the correct size, so it will be either 12mm-14mm-16mm as three possible size options. More than likely 14mm if you have twin front rotors as a best guess.

[juntjoo]

I just saw a vid on rebuilding a different MC, similar but had two seals on it. now I believe mine calls for one but you may have noticed in all ive got four of those seal total and I bought only two kits(injured the dust boot on the 1st kit) so they both came with two which I found interesting. idk, might be worth trying to put one of those extra seals on the other side of the (flange?). maybe it's one of those things where maybe your after market one is a bit off or your original is old and an extra seal thrown in can make up for some micro leak? that cap on the end of the spring, maybe I originally put it in wrong hence the mangle-ation. and maybe it is not to seal but just to pad against the piston.... a sleuth I am!

[juntjoo]

I bet you I put that spring in backwards! i gotta check the film as i forget how it came out

[Flyin900]

There are two seals inside a master cylinder; one is the small cap the you mangled that sits on the end of the spring and the other is a round seal that fits in the middle of the metal part that is about 1.5" long and that seal also faces a specific direction too.

[juntjoo]

well I hope my mangled seal is the culprit but I don't see how as it's not even as wide as the part of the piston it touches. anyway, i put two seals on this time and same thing, bleeding just transfers the fluid to the hand pump and the lever never stiffens. I'll just order a new one. wish I knew exactly what the problem was, that's usually my reward for struggling with this stuff

[Flyin900]

You probably have the wrong kit for your master, as the top hat rubber seal should be a tight fit into the bore if it is loose in there then it is the wrong kit.

[scunny]

The 650 front brakes are a pig to bleed for some reason. Saw you had a vac of some sort but have no clue as to there use.
I just hook up a 50mil syringe to the bleeder and have at it. problem over. Do the same to my cars.

[PeWe]

I assume a DSS MC for a CB750 will fit your bike too. Cost less than a restore kit for Honda MC. Work fine.

[DaveBarbier]

This is a stock master cylinder, right? Do you not have a manual that has an exploded parts diagram?

[Yamahawk]

+1 on purchasing a new MC, the all metal ones with the sight glass would be my choice.
Charlie

[juntjoo]

thanks for the replies. just installed new (cheap!) MC. still working at it. 2 questions:

1) with bleeding often occurring through bleeder valve threads, is there a risk air can reenter and if so what is the best speed to let the bubbles pass through to take rather than give air?

2) I'm so close, but I can't get any more air from them. they squeeze onto the disk barely.  So how far are the pistons supposed to be able to push towards the disks? do I just keep trying to bleed them? I should be able to push 'to infinity' right?

steps I take:

I secure the lever in place(if it's even necessary with the mighty vac, idk)
turn the caliper out/frontwards,
bleed from above with MV adjusting valve to get least fluid more air possible,
tighten valve when bubbles are tiny,
repeat on other side
release and check lever action
rinse & repeat.