Rear brake caliber dragging

[SpencerPJ]

So, I've been having some rear brake issues.  First it started as air introduced in the rear system.  Bled the top at proportioning valve, fixed it.  Couple days later, bled again(not much), really had nice rear brake again. Today, left for a ride, 5 miles in, I did hit rear brake harder than usual, but not terrible at all; at my next stop (2 miles) I noticed the rear caliber was dragging.  I immediately pulled off, and I had to release the pressure with the bleed screw to take it home.  (Could have been much more ugly than it was).  So I get it home, cooled down, figure I'd start by a thorough cleaning, took rear caliber loose, and I could move pistons back and forth, cleaned up well, but for the life of me, I could not press them both into their innermost rest.  I had to loosen the bleeder to allow fluid out.  Is this normal?  Seems whenever I've changed rear pads, little prybar and each would move back.  Tomorrow I plan on a flush whole system with brake fluid, assuming the mityvac is acceptable.  Any other suggestions or things I should look for?  Thanks, I'm not the most knowledgeable around bikes.

 

My other thread about air in rear lines.  I felt I should get this under Tech Talk and not watering hole.

[Squidley]

It sounds to me like the return orifice in the rear master cylinder is clogged. It won't allow the brake fluid to return to the reservoir when it heats up and starts to expand. That will lock up a back brake fast, been there, done that, on an 86.

[SpencerPJ]

12 hours ago, Squidley said:

It sounds to me like the return orifice in the rear master cylinder is clogged. It won't allow the brake fluid to return to the reservoir when it heats up and starts to expand. That will lock up a back brake fast, been there, done that, on an 86.

Is this something I can clean?  What part might I be looking at?

 

[Squidley]

Paul,

It can be cleaned, the master cylinder is at the bottom of the page you have posted. It's where the #2 assembly, a seal rebuild kit goes into. The #4 oring that goes on to the unnumbered elbow is where you want to look at. You'll see a tiny hole inside the body of the master cylinder and that's your return orifice hole. I usually clean them with a single wire on a wire brush. I would suggest that you purchase the seal kit, #2 in the picture and rebuild it while you have it apart. If you have any questions my number is (936) 232-9299.

[saddlebum]

I agree with Squidly =, If your pulling it apart you may as well get the rebuild kit #2 but before you do make sure the master cylinder bore is free of any imperfections, even the slightest imperfection can compromise the brake system. Also check the proportioning valve which attaches to the rear master and divides the brake fluid between the rear and left front caliper. They are notorious for building up crud inside and cleaning up the master as per Squids instructions could be a wasted effort if you do not address this part as well because that crud will just plug the orifice again.That's Item 20 in the picture it is the piece the two brake lines attach to and is mounted on the master.

 

Edited August 5, 2021 by saddlebum

[SpencerPJ]

Thanks guys, I'll be back. Digging in this afternoon.  

[SpencerPJ]

Got disassembled, things pretty dirty. I did not find a ‘culprit’, rather how was this even working this long. I just ordered a #2 rebuild kit from a local shop, 3-4 days and no shipping, partly because when I took the snap ring clip off master cylinder, like a rocket sailed into oblivion into the yard, lol.  There were little black rubber marbles inside the bore, so I'm not upset, and rebuild kit comes with new clip. Bore cleaned up nice so feel good about it. I feel like I’ve got the mess cleaned up, I feel I should give the rear caliber a good cleaning considering the junk I found in the reservoir.  While it’s apart, anything else I should throw money at?

[Squidley]

The 2nd pic is your culprit, that tiny hole encrusted with crap is the return orifice. Clean all that really good and you'll be in good shape.

[Pasta Burner]

@SpencerPJ its worth noting here to be Very careful removing the fill plug from the reservoir, the housing can break rather easily.  You’ll notice there are nice flat spots on the reservoir neck to hold with a wrench while you remove or install the plug.

[Marcarl]

46 minutes ago, Squidley said:

The 2nd pic is your culprit, that tiny hole encrusted with crap is the return orifice. Clean all that really good and you'll be in good shape.

Hey!! I was going to say that!

[SpencerPJ]

10 hours ago, Squidley said:

The 2nd pic is your culprit, that tiny hole encrusted with crap is the return orifice. Clean all that really good and you'll be in good shape.

I thought that as well.  I took the elbow off while on bike, saw that, was certain I was just going to need to take apart and clean.  Then the stupid snap ring clip loss made me need to order the rebuild kit.  Anyways, look at the two pics.  That hole we all think is plugged, well it does not go through to the inside of the bore. Only the obvious one goes through.  Maybe this is the design of an 83?

 

[Marcarl]

There be a hole there,,, keep cleaning!! It's not near clean enough yet.

[SpencerPJ]

Thanks for the persistence Marcarl 

So the hole will not even allow me to push a stick pin through it, only a couple fine wires.  Does that seem correct? Also, any ideas on what will get some of the gunk off, I hate to sand and brake cleaner not effective enough.  I did sand bore slightly with 1500 wet/dry sandpaper, wrapped around a dowel rod. 

Thanks

 

 

[saddlebum]

3m abrasive pads or extra fine steel wool. If using steel wool make sure you rid the cylinder of all debris. Maybe follow up with brake clean and an abrasive or scotch brite pad. You don't want any steel reside left behind because steel an aluminum can chemical react to each other. you can also follow up with ultra fine crocus cloth. and brake clean.

Edited August 6, 2021 by saddlebum

[Pasta Burner]

That’s the hole, it’s not as large as the area that is bored out.  I want to say it’s the size of a high E guitar string.  This thread may help you. It helped me a while back,

 

 

[SpencerPJ]

@Pasta Burner Thanks for that link and confirmation.

[Squidley]

That's all the big that return orifice hole is, very tiny, but makes big problems when it's clogged.

[windrider1983]

This was all good info - I had seen other posts on the MC rebuild a few years ago but couldn't find them, so this was quite helpful (I also had a rear brake lockup recently). Thanks to Squidley for the conversation also. I was wondering if anyone knew why there was not a diagram that showed the parts inside the proportioning valve portion of the MC?  And if there is a rebuild kit for it? I was able to clean mine up - the rubber boot on the copper piece still seems good, as well as the o-ring on the big 19mm cap bolt. What if those were rotted or if the spring was too rusty to clean up?  Or has everyone been lucky and not needed to replace any of these? Or have they just scrapped it at that point and split the rear from the front brake and eliminated the part altogether?  Just curious...

[MoonShine]

Great job on the repair and all the info!

I did the same repair with the help of the good folks on this forum.  
I later switched to a 2000’s Royal Star Venture MC and reservoir for convenience.  It pretty much bolted right in without too much trouble…

[saddlebum]

I like that conversion plus you get to see were your fluid level is at.

[Marcarl]

Get a mixture of water and original tide (you know, the stuff you do laundry with) mix well, bring it to a boil and dunk in the parts. Probably 1 hour on simmer will clean up those parts fantastically.

[saddlebum]

3 hours ago, Marcarl said:

Get a mixture of water and original tide (you know, the stuff you do laundry with) mix well, bring it to a boil and dunk in the parts. Probably 1 hour on simmer will clean up those parts fantastically.

Just don't do it in the kitchen. Don't ask how I know

[Marcarl]

2 hours ago, saddlebum said:

Just don't do it in the kitchen. Don't ask how I know

Achhh do not worry about that too much, things will smell nice and clean and all will be happy. Might have to clear out the clean smell though.

[videoarizona]

On 1/9/2022 at 3:15 PM, MoonShine said:

Great job on the repair and all the info!

I did the same repair with the help of the good folks on this forum.  
I later switched to a 2000’s Royal Star Venture MC and reservoir for convenience.  It pretty much bolted right in without too much trouble…

Well, Moonshine...that is pretty neat! Thanks!

Question....you said it bolted in without to much trouble. Care to elaborate?

I'm fighting a new to me issue with my rear master cylinder...and if I'm going to go in and rip it apart, I might as well add your modification as well...

Thanks,

david

[MoonShine]

Ok.  I have been going through my records and cannot find the make model of what bike this part came off of…. I’ve attached a few pictures after unbolting that might help.  There are 2 bolts mounting the MC and 1 for the reservoir.

There is also another outlet that I capped off as my front and rear brakes are separated now.

By bolting up fairly easily, I mean that the brackets on the frame lined up pretty well with the new set up.  I may have had to drill a hole?  I believe I only had to adjust the slack after bolting in.

Apologies for any confusion.  I will keep researching to find the bike model and year for you.