Black streaks in brake fluid??

[Colin Green]

Hi all,
I have just re-kitted (cleaned & installed new sets of original Suzuki pistons and seals) in my calipers and installed new braided lines (Goodrich). I have recently re-kitted the master cylinder. I also plugged the various caliper bolt and bleed holes with rags then painted my calipers in shiny black epoxy paint.

Have run 2.5 liters (84 Fluid ounces) of Motul dot 5.1 fluid to clear the air (and streaky black clouds that keep squirting through with the air bubbles)... finally got all the air out and had nice clean fluid. I left it for 5 minutes then ran some more through only to see the black streaky stuff squirting through... WTF?

The lever travels 40% before engaging (though starts squirting fluid through the M C return hole immediately when the lever is touched).

Anyone have any ideas as to what the black streaky stuff in the fluid is? It seems dissolve pretty quick. I hope it isn't the lines... it cant be paint cause even if a tiny amount had gotten into the first couple of thread spirals, it should have long since disappeared.

Any ideas on a way to get the lever to engage further away from the bar would also be appreciated, as I don't like having to pull the lever hard back to the bar to stop. ( a bar riser to throw the whole MC & lever assembly further from the bar, or different lever perhaps?)

 

[Big T]

Well, I can't speak to the black streak issue, but my single disc GS 1000 has braided lines and you can't move the lever 40% no matter how hard you squeeze.

The fluid in the MC shouldn't squirt until you release the lever. You may have something wrong in the assembly

Take the calipers off their mounts and let them dangle for a while to confirm a lack of air bubbles in the line

 

[Colin Green]

Well, I can't speak to the black streak issue, but my single disc GS 1000 has braided lines and you can't move the lever 40% no matter how hard you squeeze.

The fluid in the MC shouldn't squirt until you release the lever. You may have something wrong in the assembly

Take the calipers off their mounts and let them dangle for a while to confirm a lack of air bubbles in the line

Thanks BT.

"the fluid shouldn't squirt till the lever is released??? Is anyone else able to confirm this?

 

[Stefnwolf]

Thanks BT.

"the fluid shouldn't squirt till the lever is released??? Is anyone else able to confirm this?

Hi
Yes, the little squirt of fluid rising from the hole nearest the exit of the master cylinder should not happen untill the lever is released.

Also, I noticed a while ago while searching the forum for brake system information that DOT5 fluid was not recommended, but I can't remember why. I know I decided to use DOT4.

 

[Snowdiver]

DOT 5 is silicone based and not compatible with any other brake fluid.

 

[Colin Green]

Opinions needed please

Opinions needed please

Hi
Yes, the little squirt of fluid rising from the hole nearest the exit of the master cylinder should not happen untill the lever is released.

Also, I noticed a while ago while searching the forum for brake system information that DOT5 fluid was not recommended, but I can't remember why. I know I decided to use DOT4.

Thanks Stefnwolf.

The fluid squirting out of the smallest hole (nearest the exit of the MC) seems to be a point of disagreement between members of the forum.

It would be really helpful if other members can comment on this issue as I believe it is Key to my lever travel problems.

I do not see how (when I pull my lever in) any pressure can be applied to the caliper pistons/pads/disc until the MC piston seal has passed and blocked off the small hole in question, if the fluid simply flows out the hole into the reservoir.

in my other thread...
http://www.thegsresources.com/_forum/showthread.php?t=141261
Nessism states that the fluid should flow out of this hole when the lever is pulled in. My problem is that approx 40% of my lever travel is gone before the piston seal passes this hole..


I do not believe that air is the problem (apart from the fact that I have bled and banjo cracked til I have blisters, taken lever off and pushed MC piston all the way in using a screw driver, to clear air and used at least 3 lires of fluid... I no longer have any air bubbles)... If air was the problem the lever would firm up when pumping the brakes.. this does not occur

DOT 5 is silicone based and not compatible with any other brake fluid.

Thanks Snowdiver, I have previously looked into the dot 5 issue. I am using dot 5.1 (which is ok). As I understand it, the silicone based Dot 5 can cause some rubber seals to expand and cause brake lock. Dot 5 is not recommended for this reason.

My understanding that none of the different dot grades should be mixed (differing brands ok to mix, but not different viscosity/grade)

 

[49er]

Colin, it's normal for fluid to squirt upwards until the piston seal passes that small relief hole. Re-check the distance from the seal to the piston end where it contacts the lever. Compare this to the original one. If it's shorter, your lever and seal will have greater distances to travel before building any pressure in your braking system. Some after market brake levers have adjustable screw stops to reduce this travel to a minimum. To be effective, the seal needs to just clear the hole on it's return after you release pressure on the lever.

The black streaks in the fluid could be your seals/piston rubbers dissolving in your new brake fluid. I hope I'm wrong, it might even be be remnants of the new paint!

 

[Colin Green]

Thanks 49er.

Nice to see another Kiwi here.

Gee I hope you are wrong about the black streaks

I don't have the original piston as I did the Master cylinder re-kit about 6 or 7 months ago. I had been previously experiencing differing lever action and thought to resolve it with the re-kit but found it was worse (but thought it was probably the lines.. doh!)

The seal appears to sit about 4 to 5mm short of the hole when the lever is released. I suspect that I might have received an incorrect piston. I might have to look at shaping a 4mm thick plastic button (or some such flat spacer) to insert between the piston and seal to see if that solves the problem.

Colin, it's normal for fluid to squirt upwards until the piston seal passes that small relief hole. Re-check the distance from the seal to the piston end where it contacts the lever. Compare this to the original one. If it's shorter, your lever and seal will have greater distances to travel before building any pressure in your braking system. Some after market brake levers have adjustable screw stops to reduce this travel to a minimum. To be effective, the seal needs to just clear the hole on it's return after you release pressure on the lever.

The black streaks in the fluid could be your seals/piston rubbers dissolving in your new brake fluid. I hope I'm wrong, it might even be be remnants of the new paint!

 

[Colin Green]

Just checked the length of the metal piston. It's 41mm ( 1 & 5/8" ) long.

Does anyone have a spare master cylinder from a GS1100G that can be checked.. please pretty please

 

[Nessism]

Just checked the length of the metal piston. It's 41mm ( 1 & 5/8" ) long.

Does anyone have a spare master cylinder from a GS1100G that can be checked.. please pretty please

The piston in my 850 is the same length, and the 1100G piston is the same as the 850.

Regarding the master cylinder squirt, I don't recall exactly at what point in the lever travel the fountain occurs, but I'm sure it occurs during while applying pressure.

Regarding the black streaks, did you reuse your old banjo bolts and line splitter? If so, there could be some old fluid grunge contaminating your otherwise clean system. Nothing to worry about though I think.

 

[TooManyToys]

The hole that you're getting the geyser from is the compensating port. At the M/C rest state, it should be open with the M/C piston retracted behind it. As you apply and initiate actuation of the brakes, the piston will travel past this port, but during so there will be some fluid that escapes compression through this path of least resistance. Once the seal is past the port and you have a closed system, your braking under pressure. Upon release, as the M/C piston retracts there can be another push of fluid from the system as the port is exposed to the fluid under pressure.

The compensating port is there to supply more fluid volume that is needed as the friction material wears, i.e., compensating for wear.

A 40% travel to engagement sounds like a lot, but of course would be dependent on the bike design. Is it possible that a replacement lever was installed due to a drop? If not exactly the same, it might be the cause of the excessive travel.

On cars and trucks, the pushrod that goes into the master cylinder usually has an adjustment screw to compensate for differences in manufacturing, both OE and aftermarket. Obviously it doesn't sound like your bike has an adjustment screw on the lever as some do.

As far as the black in the fluid, it doesn't take much black paint to show for a long time. The carbon black used in paint does not dissipate too easily. Although it's not uncommon to see black traces after installing new hoses. There is carbon black used in rubber to color it as well as it's not entirely encased into the rubber matrix. I would not worry too much about that.

 

[Colin Green]

The piston in my 850 is the same length, and the 1100G piston is the same as the 850.

Regarding the master cylinder squirt, I don't recall exactly at what point in the lever travel the fountain occurs, but I'm sure it occurs during while applying pressure.

Regarding the black streaks, did you reuse your old banjo bolts and line splitter? If so, there could be some old fluid grunge contaminating your otherwise clean system. Nothing to worry about though I think.

Thank you very much for your time Nessism. I will relax a bit about the black streaks.

The hole that you're getting the geyser from is the compensating port. At the M/C rest state, it should be open with the M/C piston retracted behind it. As you apply and initiate actuation of the brakes, the piston will travel past this port, but during so there will be some fluid that escapes compression through this path of least resistance. Once the seal is past the port and you have a closed system, your braking under pressure. Upon release, as the M/C piston retracts there can be another push of fluid from the system as the port is exposed to the fluid under pressure.

The compensating port is there to supply more fluid volume that is needed as the friction material wears, i.e., compensating for wear.

A 40% travel to engagement sounds like a lot, but of course would be dependent on the bike design. Is it possible that a replacement lever was installed due to a drop? If not exactly the same, it might be the cause of the excessive travel.

On cars and trucks, the pushrod that goes into the master cylinder usually has an adjustment screw to compensate for differences in manufacturing, both OE and aftermarket. Obviously it doesn't sound like your bike has an adjustment screw on the lever as some do.

As far as the black in the fluid, it doesn't take much black paint to show for a long time. The carbon black used in paint does not dissipate too easily. Although it's not uncommon to see black traces after installing new hoses. There is carbon black used in rubber to color it as well as it's not entirely encased into the rubber matrix. I would not worry too much about that.

Wow 'TooManyToys' Thank you for your in depth answer.

My lever isn't adjustable and is not original either. A difference in size could be the problem but as it appears to engage the piston immediately when touched, it would need to be pushing the piston part way in when at rest to make a difference.

With the feed back I have had from all you guys at least the issue of whether the squirt should be occurring at the start of lever travel or end is settled (both). It appears to me that for some reason too much (40%) of lever travel is required before the seal closes the system and applies pressure to the caliper pistons.

I think I will try inserting a 3 or 4mm packer between the end of the master cylinder piston and the seal. I believe that if the distance from the seal to the port is reduced (but not closed) my lever travel problem will be resolved. (I hope)

I will post my conclusions when I have done the deed, as it appears that excessive lever travel is not entirely uncommon and it may prove to be the answer for others with the problem.

Thanks again to everyone who has replied to my queries.

 

[49er]

Thank you very much for your time Nessism. I will relax a bit about the black streaks.






Wow 'TooManyToys' Thank you for your in depth answer.

My lever isn't adjustable and is not original either. A difference in size could be the problem but as it appears to engage the piston immediately when touched, it would need to be pushing the piston part way in when at rest to make a difference.

With the feed back I have had from all you guys at least the issue of whether the squirt should be occurring at the start of lever travel or end is settled (both). It appears to me that for some reason too much (40%) of lever travel is required before the seal closes the system and applies pressure to the caliper pistons.

I think I will try inserting a 3 or 4mm packer between the end of the master cylinder piston and the seal. I believe that if the distance from the seal to the port is reduced (but not closed) my lever travel problem will be resolved. (I hope)

I will post my conclusions when I have done the deed, as it appears that excessive lever travel is not entirely uncommon and it may prove to be the answer for others with the problem.

Thanks again to everyone who has replied to my queries.

Hey Kiwi, don't fit that plastic button between the lever and the piston. It may dissolve with the brake fluid, but more likely, will crush with the pressure exerted during braking. Use a piece of aluminium, or better still, let those moths out of your wallet and fit an adjustable lever. :-\\\

 

[Colin Green]

Hey Kiwi, don't fit that plastic button between the lever and the piston. It may dissolve with the brake fluid, but more likely, will crush with the pressure exerted during braking. Use a piece of aluminium, or better still, let those moths out of your wallet and fit an adjustable lever. :-\\\

My wife doesn't appreciate being called a 'moth'

Too late, I custom machined a spacer from billet plastic (cannibalised of son's boogie board) cut with hacksaw on leatherman and precision ground using the concrete floor. Looks good so far .

In my haste to reassemble I broke the brake switch

As it's 11:15pm, I decided to leave it until I get a new banjo bolt with brake switch incorporated. Will have to wait til tomorrow for outcome.

 

[Steve]

The compensating port is there to supply more fluid volume that is needed as the friction material wears, i.e., compensating for wear.

Another function of the compensating port is to compensate for liquid volume due to heat expansion. It is natural for the claipers to get warm while riding, due to the pads dragging ever so lightly on the disks. This warms up the brake fluid, causing it to expand. If the compensating port is blocked, the only way the fluid can expand is to press on the pads, dragging them harder. Dragging harder adds heat. Heat adds expansion. Expansion drags the brakes harder.

Would you believe that even a 1300cc V-4 Yamaha Venture in first gear can not overpower a locked rear brake to make it the last 200 yards to home?
Had to get out the Leatherman and open the bleeder for the rear brake to get home. :-\\\

Moral of the story: whenever cleaning the master cylinder, poke something through that hole to make sure it's open.


Colin, now to your lever travel problem:
There could be an air bubble trapped in the master cylinder. Remove the lever, use a large Philips screwdriver to push the piston in. It will travel farther than the lever can push it, usually getting rid of that troublesome space at the end of travel inside the bore.

If that doesn't work, there is one last-ditch method. Rotate the handlebars so the output of the master cylinder is the lowest point of the assembly. Squeeze the lever, tie it to the handlebar to keep it squeezed, leave it overnight. I have talked to several guys that have done this to allow the air bubbles to migrate up, through the assembly on its own, but it does take several hours to happen.

.

 

[Colin Green]

Thanks Steve,

Re the lever removal to push the piston in further... had already done that (see post 6).

Re the turning of the bars and taping the lever hard in.... I have/had done both and also note that if the lever is tapped a hundred times and pulled in hard half a hundred times while the bars are turned hard left and then right, the combination of lever vibration and master cylinder angle will also clear the trapped air. Pays to cover the MC with glad wrap (cling film) held in place with a rubber band, to avoid squirting fluid all over the tank etc.

I tried installing a 3.5mm by 13mm dia plastic spacer and found that it was too big to allow MC priming. I ground it down to 2.5mm and re-installed. It works great. My previously huge (and prolonged) fluid fountain is now a mere squirt. Lever travel is now fine. It was about 35 -45mm of travel before engaging and is now about 13 - 15mm. (not perfect, but close)

I haven't taken it for a ride yet to bed in the new organic pads (which don't appear very sticky) but am confident that I have resolved the lever travel.

Once sure that all is well I will post an explanation of how the modification can be used to address at least some excessive lever travel issues.

Another thing I noticed was that the piston can be slightly depressed in if the brake lever assy is moved too close to the throttle grip assy (preventing the heel of the lever from fully returning). This could be problematic if it resulted in the seal being prevented from clearing the relief port.

Another function of the compensating port is to compensate for liquid volume due to heat expansion. It is natural for the claipers to get warm while riding, due to the pads dragging ever so lightly on the disks. This warms up the brake fluid, causing it to expand. If the compensating port is blocked, the only way the fluid can expand is to press on the pads, dragging them harder. Dragging harder adds heat. Heat adds expansion. Expansion drags the brakes harder.

Would you believe that even a 1300cc V-4 Yamaha Venture in first gear can not overpower a locked rear brake to make it the last 200 yards to home?
Had to get out the Leatherman and open the bleeder for the rear brake to get home. :-\\\

Moral of the story: whenever cleaning the master cylinder, poke something through that hole to make sure it's open.


Colin, now to your lever travel problem:
There could be an air bubble trapped in the master cylinder. Remove the lever, use a large Philips screwdriver to push the piston in. It will travel farther than the lever can push it, usually getting rid of that troublesome space at the end of travel inside the bore.

If that doesn't work, there is one last-ditch method. Rotate the handlebars so the output of the master cylinder is the lowest point of the assembly. Squeeze the lever, tie it to the handlebar to keep it squeezed, leave it overnight. I have talked to several guys that have done this to allow the air bubbles to migrate up, through the assembly on its own, but it does take several hours to happen.

.

 

[TooManyToys]

Another function of the compensating port is to compensate for liquid volume due to heat expansion. It is natural for the claipers to get warm while riding, due to the pads dragging ever so lightly on the disks. This warms up the brake fluid, causing it to expand. If the compensating port is blocked, the only way the fluid can expand is to press on the pads, dragging them harder. Dragging harder adds heat. Heat adds expansion. Expansion drags the brakes harder.

Would you believe that even a 1300cc V-4 Yamaha Venture in first gear can not overpower a locked rear brake to make it the last 200 yards to home?
Had to get out the Leatherman and open the bleeder for the rear brake to get home. :-\\\

Moral of the story: whenever cleaning the master cylinder, poke something through that hole to make sure it's open.
.

The brakes on any vehicles should be able to develop enough torque hold back the motor. The ability to decelerate a vehicle from top speed at high g's is higher the motor torque plus multiplication out of the drivetrain.

Your brake lock-down is kind of the chicken-egg debate, but in my opinion goes back to the blocked port issue. When we had thermocouples in the brake pads on vehicles under off-brake conditions such as long distances on highways without brake applys, would have the brake pads only at 80-100F, and the caliper pistons and fluid would be cooler then that. If the calipers are working correctly, and the pads are free in their brackets, there should be 0.010 to 0.015" clearance between the pads and rotors. If the O-Rings have lost their compliancy, then the roll back will not be as much. But that is a problem with older brake parts or those that have gotten very hot, the rubber hardens.

Anyway, if there was the clearance necessary then the fluid should not have expanded from heat. But if you've got a blocked port, with some good braking I'm sure the heat did have a factor and the fluid expansion just applied the brakes harder. But just going down the road should not be heating up the fluid.

 

[49er]

The brakes on any vehicles should be able to develop enough torque hold back the motor. The ability to decelerate a vehicle from top speed at high g's is higher the motor torque plus multiplication out of the drivetrain.

Your brake lock-down is kind of the chicken-egg debate, but in my opinion goes back to the blocked port issue. When we had thermocouples in the brake pads on vehicles under off-brake conditions such as long distances on highways without brake applys, would have the brake pads only at 80-100F, and the caliper pistons and fluid would be cooler then that. If the calipers are working correctly, and the pads are free in their brackets, there should be 0.010 to 0.015" clearance between the pads and rotors. If the O-Rings have lost their compliancy, then the roll back will not be as much. But that is a problem with older brake parts or those that have gotten very hot, the rubber hardens.

Anyway, if there was the clearance necessary then the fluid should not have expanded from heat. But if you've got a blocked port, with some good braking I'm sure the heat did have a factor and the fluid expansion just applied the brakes harder. But just going down the road should not be heating up the fluid.

True, there should always be some clearance betwen the pads and rotors. That is the very reason I fitted up a set of o rings instead of trying to replace the rubber sleeves that are fitted to one pin in stock calliper configuration. The new setup provides instant and complete release. I've run the bike this way for a couple of years now.

The other thing that can happen when that port is blocked, is the brake fluid will expand in the system just through sitting in the sun. I had this happen on a couple of very hot days after work, and had to release the pressure at the banjo, just to ride the bike home (a short distance so no dramas).