Front brake bleed on '79 GS550L

[tbrand69]

In your picture you have the spring the wrong way round...

the primay cup (rubber bit) goes toward the piston...

Johnny Boy, if that works I'm going to mail you a box of chocolate covered macadamia nuts.

 

[tbrand69]

Okay, so I flipped the spring around, bench bled the MC, and reinstalled. Definitely an improvment. I can see and feel the caliper move when I depress the lever, so the piston is engaging, which is good.

When I bleed the line with the MityVac a lot of frothy bubbles come down the line. The MC reservoir drains rather quickly now, so I have to keep topping it off every 15 or so seconds. I wish the MityVac had a larger catch can, because it fills up very fast. I bled the line like that for about twenty minutes or so.

In the end, the lever pull was greatly improved, the caliper worked, but I would only get tension in the lever after it had traveled 3/4 of the way back. I can slightly touch the handgrip with the lever. No amount of bleeding improved that feeling.

I'm happy the brake actually kind of works now, but I smell an oldrookie issue cooking up.

 

[oldrookie]

Great, I have a syndrome named for me now. It does sound all too familiar.

 

[john82q]

So for 20 mins you useed mityvac vacuum to draw fluid from the bleeder, experiacing lots of frothy bubbles the whole time?

If thats the case the vacuum is drawing air in. Are all the fittings tight?

Put the mityvac aside and try it the old fashioned way.
- pump lever 3 times and keep squeezing the lever on the last stroke.
- crack the bleeder, (only open a little, so theres some pressure)
-just before the fluid stops flowing, close the bleeder
-repeat about 10 times, keeping the resivour full.


report back...

 

[tbrand69]

So for 20 mins you useed mityvac vacuum to draw fluid from the bleeder, experiacing lots of frothy bubbles the whole time?

If thats the case the vacuum is drawing air in. Are all the fittings tight?

Put the mityvac aside and try it the old fashioned way.
- pump lever 3 times and keep squeezing the lever on the last stroke.
- crack the bleeder, (only open a little, so theres some pressure)
-just before the fluid stops flowing, close the bleeder
-repeat about 10 times, keeping the resivour full.


report back...

Reporting back. I did what you said and there seems to be slightly more force behind the lever pull, but it is still localized near the end of its travel. I'd say the first 2/3 of pull are nothing.

I re-tightened the banjo bolts to make sure, and they were a little loose. Afterwards i threw the Mity-Vac back on to see if anything changed, and I didn't get any frothy bubbles this time. Strange. I have the bleeder lined with anti sieze, so that should be air sealed.

Hmmmm...

 

[john82q]

I am a little perplexed by your oldrookie syndrome, but it interests me.
If I was a gazillionaire, I jump on a plane and come see for my self...but alas I am not, so some proxy thinking for you. I do not know 100% the answer.

The current symptom you describe, should indicate you still have air in the system.

So hit me with some info;

During the the old fashioned bleeding you just did, did any air come out?

Right now;
If you pump the lever a few times quickly does the position improve?
Indicates air in the system

If you squeeze it hard does stop hard or keep moving slowly/slightly?
Indicates leaks, either external, internal to the MC, or sticky caliper
piston or brake pad pins.

I think your bike has 1 caliper, No? Is your brake line a single piece, or does it have a T or L fitting, or other joiner on the triple tree?
If so while squeezing against the closed bleeder crack it loose,
maybe air will come out. (fluid will so be prepared)

More things to try;
Try squeezing the brake lever has hard as you can and tie it here with rag or better yet a bungee cord, and leave it overnight.
this can let air out the MC piston cup.

When you set up the above inspect the entire system for leaks, a piece of paper held up is a good indicator, as it can spray really fine.

And of course you could try the bleeding again, and dont be frightened to get violent with the pumping, also flick and shake the line so as to dislodge bubbles. Also change to a different colour fluid so you know its gone right thru. A L model (american cruiser styling) may have a section of the hose on the handle bar that is higher than the MC while bleeding hold or tempory tie this lower than the MC (bubbles get traped)


Otherwise fxxx knows!

 

[tbrand69]

I am a little perplexed by your oldrookie syndrome, but it interests me.
If I was a gazillionaire, I jump on a plane and come see for my self...but alas I am not, so some proxy thinking for you. I do not know 100% the answer.

The current symptom you describe, should indicate you still have air in the system.

So hit me with some info;

During the the old fashioned bleeding you just did, did any air come out?

Right now;
If you pump the lever a few times quickly does the position improve?
Indicates air in the system

If you squeeze it hard does stop hard or keep moving slowly/slightly?
Indicates leaks, either external, internal to the MC, or sticky caliper
piston or brake pad pins.

I think your bike has 1 caliper, No? Is your brake line a single piece, or does it have a T or L fitting, or other joiner on the triple tree?
If so while squeezing against the closed bleeder crack it loose,
maybe air will come out. (fluid will so be prepared)

More things to try;
Try squeezing the brake lever has hard as you can and tie it here with rag or better yet a bungee cord, and leave it overnight.
this can let air out the MC piston cup.

When you set up the above inspect the entire system for leaks, a piece of paper held up is a good indicator, as it can spray really fine.

And of course you could try the bleeding again, and dont be frightened to get violent with the pumping, also flick and shake the line so as to dislodge bubbles. Also change to a different colour fluid so you know its gone right thru. A L model (american cruiser styling) may have a section of the hose on the handle bar that is higher than the MC while bleeding hold or tempory tie this lower than the MC (bubbles get traped)


Otherwise fxxx knows!

Info:

1) I couldn't really tell if air came out with the old fashioned bleeding. The last squeeze while opeing the bleeder would send a small rush of fluid out, but I did not catch any bubbles going with it.

2) Yes, if i pump the lever right now the feeling will get better and more positive. By the fouth and fifth pump it is nice and tight during its last 1/3 of its travel.

3) If I squeeze the lever really hard, it will eventually come to a stop and not move anymore. However, I know the piston required a lot of force to push into the caliper. Even when coated with brake fluid I had to use a flat piece of wood that I laid over top of the piston; I then pushed on both ends of the wood so the piston would be recessed evenly on all sides. Yes, I put in a new seal for it.

4) Yes, there is only 1 piston in the front, and the brake line is a brand new SS one from Earl's. All the fittings are brand new, as are the banjos and crush washers, which are from Suzuki.

 

[2BRacing]

Info:

However, I know the piston required a lot of force to push into the caliper. Even when coated with brake fluid I had to use a flat piece of wood that I laid over top of the piston; I then pushed on both ends of the wood so the piston would be recessed evenly on all sides. Yes, I put in a new seal for it.

I am perplexed by your problem, as I have rebuilt the calipers on my 850 a few times and never experienced such acute problems.

Forgive me if this has been mentioned in one of your earlier posts, but was the new caliper piston rubber seal a genuine OEM Suzuki one? If the recess into which that seal fits is nice and clean (no crud in the groove) the seal can seat properly without "high spots" caused by any crud. I have never had to use much force to get a piston into a caliper fitted with a OEM seal. However, I cannot say the same for other makes of replacement seals.

I think that your piston cannot move freely enough and is maybe "hanging up" on a rubber seal which either does not have the exact OEM dimensions, or is located in a groove which is not properly clean.

Hope you get this sorted out!

 

[john82q]

It shouldnt take much pressure to install the piston, The pistion, caliper, and the seal groove in the caliper were meticulously clean when you did it... wernt they?

You said in another post you can see the piston moving so maybe its alright.

You can test it is working OK with the mityvac, you should be able to pump the pistion out, say about half its depth, and draw it back in fully with the hand pump alone.

So try that and set it right if not.

And it sucks to say but, bleed it again...

 

[tbrand69]

I am perplexed by your problem, as I have rebuilt the calipers on my 850 a few times and never experienced such acute problems.

Forgive me if this has been mentioned in one of your earlier posts, but was the new caliper piston rubber seal a genuine OEM Suzuki one? If the recess into which that seal fits is nice and clean (no crud in the groove) the seal can seat properly without "high spots" caused by any crud. I have never had to use much force to get a piston into a caliper fitted with a OEM seal. However, I cannot say the same for other makes of replacement seals.

I think that your piston cannot move freely enough and is maybe "hanging up" on a rubber seal which either does not have the exact OEM dimensions, or is located in a groove which is not properly clean.

Hope you get this sorted out!

Yes, the seal was an OEM Suzuki part. I'm also thinking that the piston is getting hung up in there.

It shouldnt take much pressure to install the piston, The pistion, caliper, and the seal groove in the caliper were meticulously clean when you did it... wernt they?

You said in another post you can see the piston moving so maybe its alright.

You can test it is working OK with the mityvac, you should be able to pump the pistion out, say about half its depth, and draw it back in fully with the hand pump alone.

So try that and set it right if not.

And it sucks to say but, bleed it again...

Yes, I dipped the caliper and piston in chem dip, actually. I even took a Dremel with a wire wheel and scrubbed the seal's groove. However, I did do it a little lightly since I was afraid of getting a little overzealous and messing something up. The piston itself had some pitting, which is visible on another one of my posts in this thread. I did sand down what I could, but there's no way of knowing if that has had an effect. Unfortunately, no one supplies that OEM piston anymore, otherwise I would have replaced it.

I'll disassemble the caliper and check the groove again, maybe scrub it again, too.

 

[oldrookie]

BWRinger fixed mine. He said he'd post up what he did in my thread later.

Basically, the piston was hanging up. Going to pick it up later this afternoon.

 

[tbrand69]

BWRinger fixed mine. He said he'd post up what he did in my thread later.

Basically, the piston was hanging up. Going to pick it up later this afternoon.

So I tried BWRinger's little fix on the piston seal. Well, it worked: I now have a front brake with very positive lever feel. I can barely pull it half way in now. I am very happy and satisfied.

However, it looks like I might have a piston seal leak now.
It looks like I was a little too aggressive with my shaving of the rubber seal. I appear to have taken too much material out. However, that is a quick fix with a new seal, and now I know I have to be a little more gentle with it. But I'm not worried at all.

 

[oldrookie]

Good to hear that you are on the way to getting the thing fixed right! Brian did say he took it very slowly and fitted it three times until it "felt" right. The trick is in getting the experience to know when it "feels" right.

Good luck with the next seal!

 

[tbrand69]

Quick update:

After letting the bike sit for a little and pumping the brakes as I walked by every now and then I can safely say that the front piston seal is not leaking. I jam my fingers up underneath the caliper and they come out dry everytime.

So yay!

 

[oldrookie]

Excellent!