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post #1 of 31 (permalink) Old 10-08-2007, 09:35 AM Thread Starter
 
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Help me trouble shoot my brakes

Why is it that I am always asking questions about the same freaking subject?


Ok, to combat brake fade I decided to go for a complete rebuild again.

I replaced the master cylinder piston and 2 seals, and all seals and wiper in the calipers, cleaner everything with degreaser, wiped, dried and re assembled.

Then I went and got one of those nifty vaccuum assisted bleeding tools. Its a hand operated vacuum pump that hook to the bleeder nipples thru a reservour.

Keep in mind that the system is completely dry, and has lots of air in it.

In the begining I was getting tons of bubbles, while cycling fluid over and over (we are talking about gallons worth here). Part of that prooved to be the threads on the bleed nipples. After I got some teflon tape on them I could get clear fluid to come out, with no bubbles, but only as long as I dont actuate the brake lever.

As soon as I actuate the lever, bubbles start coming out. The greater the vacuum, the more bubbles. It doesnt matter how much liquid I cycle thru, the bubbles stay as long as I work the lever.

I think, this is because the seals on the master cylinder are one way, designed to hold liquid in. When there is a vaccuum on the liquid side, and the seals move back and forth, air can enter the system.

But I still have the worst spungy brakes ever. I get some resistance, but I would be hesitant to ride down to the store, much less go on the track.

My thinking is that there is a giant bubble in the master cylinder, around the banjo bolt, that refuses to move, and the liquid just seeps around it. If there was a leak in the system, I woudlnt get any pressure at all, and I wouldnt be able to draw liquid thru the system, right?



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post #2 of 31 (permalink) Old 10-08-2007, 09:57 AM
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Re: Help me trouble shoot my brakes

Quote:
Originally posted by Vash
Why is it that I am always asking questions about the same freaking subject?
Perhaps someone "upstairs" hates you

Quote:
Then I went and got one of those nifty vaccuum assisted bleeding tools. Its a hand operated vacuum pump that hook to the bleeder nipples thru a reservour.

Keep in mind that the system is completely dry, and has lots of air in it.

In the begining I was getting tons of bubbles, while cycling fluid over and over (we are talking about gallons worth here). Part of that prooved to be the threads on the bleed nipples. After I got some teflon tape on them I could get clear fluid to come out, with no bubbles, but only as long as I dont actuate the brake lever.

As soon as I actuate the lever, bubbles start coming out. The greater the vacuum, the more bubbles. It doesnt matter how much liquid I cycle thru, the bubbles stay as long as I work the lever.

I think, this is because the seals on the master cylinder are one way, designed to hold liquid in. When there is a vaccuum on the liquid side, and the seals move back and forth, air can enter the system.

But I still have the worst spungy brakes ever. I get some resistance, but I would be hesitant to ride down to the store, much less go on the track.

My thinking is that there is a giant bubble in the master cylinder, around the banjo bolt, that refuses to move, and the liquid just seeps around it. If there was a leak in the system, I wouldn't get any pressure at all, and I wouldn't be able to draw liquid thru the system, right?
When I've used those Mightyvac systems, I just pulled with the actuating pump, not the lever too. Sounds like you did that, sealed it up, and still have a problem, right?

So perhaps you have a bubble at the banjo. Is it tight? Obviously you do get some pressure in the system which you proved when you didn't have the bleed nipples sealed with teflon. I assume you've tried "rapping" on the various high points (like the caliper itself) with a screwdriver handle or such to ensure the bubbles got some jarring while you were doing the bleeding. Only have one bleed valve? My brake's got one at the master cylinder as well as on the calipers.

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post #3 of 31 (permalink) Old 10-08-2007, 11:15 AM Thread Starter
 
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Crap, I forgot to give my offering to the god of brakes. Let me go slaughter a lamb.

I got a bleeder screw on each caliper, but nothing on the master cylinder. My next plan is to take the cylinder off the bar, and rotate it in such a way so that it is below the calipers, with the banjo bolt pointing up (or should it be down?)

I tried tapping on everything, but its no help. I think moving the lever was a mistake, I was just hoping to dislodge whatever bubbles were in the system.



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post #4 of 31 (permalink) Old 10-08-2007, 12:55 PM
 
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Two things to think about, V. - first, the bleeder bolts. Experience has taught me that if you open the bleeders more than a fraction of a turn, they will let air in. Seems you addressed that with the teflon tape, but creating too much vacuum may be overcoming the tape. I've noticed the air problem can be significant when not applying any vacuum over that caused by the return stroke of the master cylinder.

A slight amount of sponginess will usually disappear with use as the bumps and repeated brake use allow the air to make it to the reservoir and be replaced in the lines by fluid.

I would avoid using the teflon tape on a bolt which must be loosened and retightened. Its good for something like the fan switch, but considering the possibility of a piece of tape breaking off when the bolt is loosened and tightened again,and working its way up to the m/c and possibly clogging a pressure relief orifice makes me apprehensive.

Over the years, I've noticed four issues that affect brake feel & performance:


1) The accumulation of brake dust and dirt around the exposed circumference of the caliper pistons. Whenever I change pads, and sometimes more often depending on what I see, I take a toothbrush, cloth, and brake cleaner and remove all dirt from around the pistons. I do this by forcing each piston in turn ALMOST completely out of its cylinder. When you can rotate each piston by hand, it is out far enough. Make sure it is clean completely around its circumference. If this has never been done before, you will notice a fair amount of corrosion on the piston. If the corrosion is too bad, the caliper will never feel like new, no matter what else you do.

2) Burrs, raised edges or deep indentations on the rod which guides/supports the brake pads.

Cleaning and a few strokes with a points file will keep your brakes feeling good for the life of this rod. Good cleaning keeps this rod in the game for about 40k miles replace after that or when the indentations become too deep.

3) Pad contamination. The pads can be contaminated from any number of fluids, including things thrown up from the road. Replacement is the best option.

4) Old fluid. You being you, I'm certain this doesn't happen on your bike.

Gallons of fluid through the system? I've read your posts for years, and I have no doubts about your mechanical proficiency. In this case, I feel there may be a flaw in your bleeding process. I'm sure you'll get to the bottom of it.

I've never had to replace a m/c, and I've replaced one caliper on all of the 11 bikes I've owned. This with ~ 1 million total miles. It is from this I arrived at the knowledge I write here, not from any special brake knowledge or training.

You'll figure out a better way to remove air from your brakes, that's just the way you roll!....
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post #5 of 31 (permalink) Old 10-08-2007, 01:25 PM Thread Starter
 
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Thanks guys. This has been incredibly frustrating, and as of today, I missed the sign on date for a track day due to this issue.

Let me go over each of rundog's points

1. I cleaned the caliper halves with degreases, steel wool and an old toothbrush. There was some signs of brake dust/ road grime that I couldnt get off, but they look almost new.
I took the pistons out of each caliper completely, and carefully cleaned each one. On one, there is still a very light line left by brake dust against the viper seal that does not come off, and I'm afraid to go after it with anything too abrasive becuase I might screw up the seal. Anyways, it very light, and its outside of the oil.
2. If I understand your next point right, you are talking about the rods that attach to the body of the caliper, and pass thru the pads. They are strange set screw looking things on this model. They are clean, and lubed with white lithium grease (being carefull not to get the grease on to the pads)
3. Pads might have gotten some brake fluid on them by now, everything else has. I've been spraying brake cleaner pretty liberally hoping to clean it off, and I'm hoping whats left will burn off when the pads heat up. If they remain contaminated, I should still have firm lever feel, just less braking action, sort of like trying to brake after washing the bike, right? If thats the case, I'll get new pads once the hydraulic system is fixed.
4. No, old fluid is definetly not the problem.

I should explain the gallons comment. The bleeder pump has a reservour on it, which allows me to recycle fluid. So I would pour the fluid back into the system, over and over again. I started out with 3 new bottles of brake fluid, and I'm down to one, from the tiny bit that gets spilled each time I pour the fluid from one bottle to the other. I literally bled brakes from 9am saturday to sometime past nightfall. Talk about the least fun way to spend a saturday!

Here is the procedure I follow.
1. Open master cylinder reservour, move the handle bars to the reservour is level, and top it off with fluid. Find a bystander, hand him a bottle of fluid, and threaten him/her with bodily harm should the reservour go empty.
2. Attach hoses to both bleeder nipples (I have a T hose setup) and to the vaccum pump.
3. Pump to achieve 15-20" of vaccum.
4. Open one of the bleeder nipples, allow the pump to draw fluid. Pump to maintain vaccum, and allow sufficient fluid to pass thru the system to eliminate all bubble. Tap on all the banjo bolts, the caliper bodies, the cylinder body while fluid is flawing. This is also the time I used to work the lever back and forth which might have been a mistake. After fluid comes out with no bubbles, cycle another bottle of fluid, just to be on the safe side
5. Close the bleeding nipple, and open the other one. Repeat step4.
6. Open both nipples and bleed both calipers at the same time. I have 2 hoses running from the master to each caliper (instead of the factory hose over setup) so I dont see the harm in bleeding both simultaniously.
7.Close both nipples, and work the lever untill some pressure becomes apparent (takes forever), continue working the lever untill back pressure does not increase.
8. Curse
9. press the lever, and with it pressed open one of the nipples, for an old style hand bleed. Repeat with the other side.
10. Test pressure
11. Curse some more. Kick a chair. Call the dealership to check the price of a new bike. Take a break and drink a beer.

Go back to step 1.



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post #6 of 31 (permalink) Old 10-08-2007, 07:10 PM
 
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ok, you missed a few steps at the end there. first of all there are way more step 8's, and i have found that if you keep yourself at a certain level of intoxication you can do no wrong....at least untill the next morning when you try to find out what was right in the ass backwards thinking of the previous day. but now you have done all the wrongs you could possible do therefore everything done from now on has to be right...right?....Wrong, everything now isnt necessarily right, its just not wrong. now you can move on with what ever your doing knowing full well that you can do no wrong....and let me tell ya....thats a great feeling

sorry i am no help with the breaks cause everything i would have done has been said and more.

Last edited by Meat_Shield; 10-08-2007 at 07:17 PM.
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post #7 of 31 (permalink) Old 10-08-2007, 09:25 PM
 
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I'm no expert at bike brakes, but it should be similar to cars.

When bleeding, pump the brakes until they're stiff ( ), hold the lever, open the bleeder, let air out, close bleeder, release lever. Repeat for other calipers, repeat all until lever is firm straight away.

Don't release the lever with the bleeder open, it'll just let air back in.

I prefer the traditional method to vacuum bleeders and all that jazz


Also, have you bled the master cylinder?
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post #8 of 31 (permalink) Old 10-09-2007, 05:04 AM
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Quote:
Originally posted by Vash
Here is the procedure I follow.
1. Open master cylinder reservour, move the handle bars to the reservour is level, and top it off with fluid. Find a bystander, hand him a bottle of fluid, and threaten him/her with bodily harm should the reservour go empty.
2. Attach hoses to both bleeder nipples (I have a T hose setup) and to the vaccum pump.
3. Pump to achieve 15-20" of vaccum.
4. Open one of the bleeder nipples, allow the pump to draw fluid. Pump to maintain vaccum, and allow sufficient fluid to pass thru the system to eliminate all bubble. Tap on all the banjo bolts, the caliper bodies, the cylinder body while fluid is flawing. This is also the time I used to work the lever back and forth which might have been a mistake. After fluid comes out with no bubbles, cycle another bottle of fluid, just to be on the safe side
5. Close the bleeding nipple, and open the other one. Repeat step4.
6. Open both nipples and bleed both calipers at the same time. I have 2 hoses running from the master to each caliper (instead of the factory hose over setup) so I dont see the harm in bleeding both simultaniously.
7.Close both nipples, and work the lever untill some pressure becomes apparent (takes forever), continue working the lever untill back pressure does not increase.
8. Curse
9. press the lever, and with it pressed open one of the nipples, for an old style hand bleed. Repeat with the other side.
10. Test pressure
11. Curse some more. Kick a chair. Call the dealership to check the price of a new bike. Take a break and drink a beer.

Go back to step 1.
Wait, wait, hold the phone here. This seems overly complicated. If I were you I'd go right back to basics. Bleed only one side and don't use the Mightyvac (or whatever). Bleed only until you see no more bubbles and stop. Follow the steps listed by jakkyl. Then do the other side.

The setup is odd to me but I suppose shouldn't matter all that much. Did you take the hoses off the master cylinder? If so, its possible there is a leak there and when you release the lever it pulls in a small amount of air that rests as a bubble and when you pull on it the air gets released through the same location. It just seems unlikely.

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post #9 of 31 (permalink) Old 10-09-2007, 06:25 AM Thread Starter
 
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kanwisch:

If there was a leak by the master cylinder, wouldnt it leak brake fluid out preventing me from ever building up pressure?

Jakkyl: There is no bleed screw on the master cylinder. Anyone know where I can get one of those nifty banjo bolts with a bleed nipple on them?



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post #10 of 31 (permalink) Old 10-09-2007, 06:43 AM
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I do syringe bleeding, I gave up on my vacuum pump a long time ago.

there's hope in the words and emotion in the eyes
it's so easy to be misled by the savvy gentle guise
and like fools we trust the delivery
but it's all just drunk sincerity
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