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Discussion Starter #1
Hey guys, I need some serious help.

I'm working on a project, an 86 gl1200i, and I've done everything, timing belts, carb clean, fluids, oils, final drive, battery. She runs like a top, all carbs in sync, perfect idle, no issues, my only issues are, and the last thing...the brakes.

Both front calipers and the rear calipers when applied, the pistons don't come back in, and the brakes hold the rotors and have to be knocked off.

I bled the lines multiple time with fresh brake fluid, and blew air through the lines.

It gets good suction and good flow from what I can tell, but after doing a flush, the calipers still apply to the rotors and hold, they won't release.

I pulled the pistons on all 3 calipers, o rings, bleeder valve, theres barely any build up, theyre in great shape no visible rust etc.

I'm about to reassemble the calipers..but before I do that..and waste another 32 oz container of brake fluid flushing the brakes.....what on earth else should I check to get my brakes to work?

Decent life on the pads, good looking rotors, fresh fluid bled with no air, and they grab hold and down let go.

Please help me, I want to take this thing on her inaugural ride.

Thanks
 

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Did you check the "return hole" in the bottom of the master cylinders. If clogged, that will keep pressure applied to the calipers....!!

Some options are:

Pistons not moving freely.

Brake lines partly clogged up.

Return holes clogged up.
 

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The master cylinders have a very small fluid return port . That needs to be cleaned out so the pressure/fluid can return to the reservoir . If you look in bowl of the front master this hole is in the bottom. A single wire strand from a wire brush is is about size needed to clean this out. The rear master has the same type system I believe its where the fluid supply line connects to the master cylinder.
 

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Discussion Starter #4
The master cylinders have a very small fluid return port . That needs to be cleaned out so the pressure/fluid can return to the reservoir . If you look in bowl of the front master this hole is in the bottom. A single wire strand from a wire brush is is about size needed to clean this out. The rear master has the same type system I believe its where the fluid supply line connects to the master cylinder.
Heres the photos of the cylinders, where would they be?

Thanks
 

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Discussion Starter #6
Okay I took the metal tab off and blew air through there but literally a strand of speaker wire wont fit through it.

How about the rear. The rear only has the one hole

Thanks
 

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If the small wire won't fit through (I use a high G string from a 12 string guitar set), then it is still plugged. You might have to pull the reservoir on the rear to get at the hole.
 
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The rear one is in the master cylinder . Where the reservoir hose attaches. Umm two screws hold the hose adapter ? its under there.
 

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I failed to ask in my first reply, are all three calipers locking up ? The rear and right front are both actuated by the rear master cylinder in the "Unified Brake System" . The front master only does the left front caliper.
Another thing.... when you had the calipers apart did you do a thorough cleaning of the seal grooves? Sometimes you need to take like a dental pick to really get the seal grooves clean .
 

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Discussion Starter #11
I failed to ask in my first reply, are all three calipers locking up ? The rear and right front are both actuated by the rear master cylinder in the "Unified Brake System" . The front master only does the left front caliper.
Another thing.... when you had the calipers apart did you do a thorough cleaning of the seal grooves? Sometimes you need to take like a dental pick to really get the seal grooves clean .
I have the calipers right now, I polished everything nice and clean and pulled the rings to clean the seal grooves, i did have to use picks to get all the dried gunk out.

I can't tell you if the front right does (which I know is activated by the rear brake), but the front left brake (front) and rear caliper, both do it. So yes, essentially all 3 lock up.

So to clean the return on the rear, I have to pull the master cylinder off I guess, which is below that res.

I don't think the caliper seals or pistons where the issue, as they were already pretty clean inside, however I gave them a brass brush scrub with brake cleaner.
 

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You could briefly loosen the bleeder screws on the front two calipers to see if the brakes release or not. This would confirm calipers OK and master cylinder return hole is plugged.
 

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Check that the brake pedal pivots freely and returns to the proper height to foot peg and the MC push rod length is correct per the "specs" in the manual. Remove the metal deflector cover inside the front MC and see if it squirts fluid/bubbles through the hole while squeezing the lever and if it does, the port is open. Jack the front tire off the ground while trouble shooting the left rotor so you can spin it. Smack the caliper side with a rubber mallet if the pistons stick or open bleeder if that releases them ?
 

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For what it's worth the return hole is also the feed hole.
In other words if you can pump fluid through the system the hole ain't plugged.
 

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Caliper piston is usually the problem. I had to make a scraper tool out of an old spoke. Bent and Flattened the end. Ground it to the right shape to reach every part of the seals groove. It has to be cleaned of all gunk or the o ring will be too tight.

Sent from my SM-J320V using Tapatalk
 

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Both front calipers and the rear calipers when applied, the pistons don't come back in, and the brakes hold the rotors and have to be knocked off.
On a 1200, the Lt frt is on the handle bar right side hand control master …
...the Rt frt is operated by the rear foot operated master cylinder, the systems are totally separate. There is no way for a single plugged port or other malady to cause all three to fail to release, other than operator holding all applied.
 

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I had that problem with the back brakes on my GL1200i and I just put some oil on the outside of the pistons so they would slide smoothly and have not had the problem again..
 

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Port

The port everyone is talking about is called the compensation port. Although there are other names I have heard it called as well. I have had that problem on my 78 and it takes a very very small wire to clean it out.
 

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Personally, I once had an issue like yours on an old car. Turned out to be that the inner hose lining had separated and would only allow the fluid to flow out to the caliper, but not back in to release pressure. I could drain fluid out through the bleeder, but not add fluid back through the same bleeder, or through the caliper end of the hose.
 

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I just cleaned my rear MC on the '79 tonight. The "compensation" port (separate from the feed port) is behind a separate plug on the MC. Remove it (14mm head) and look straight in, you will see a ~2mm depression - the hole is in the bottom of it. I had to clean mine out with a 12-string guitar high G in a pin vise. Then I flushed it well with brake cleaner.
 
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