Pressure test a caliper

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Dec 11, 2020
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Sunshine coast. Qld. Australia
Hi all,

2010 S10
Anybody know if its possible to pressure test front calliper to see if it has a leak or air trapped somewhere in it??
How would I go about it??
I have a firm brake line up until with only minimal lever movement up until the adding the callipers into the system. I clamp above the callipers and its hard and once its released the lever sinks to the handle bar.
Am I on the right track with assuming my problem lies somewhere in the callipers? Recently serviced both with new seals etc.
Have even tried putting old seals back in which made no difference.

I cant see any leaks from the callipers.
Have put litres of fluid through them to no avail.

Been fighting this for over a month now, good thing the weather has been lousy for riding.

Cheers,
Dave.
 

Jlq1969

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"It is probable" that the air bubble is closer to the pump than to the caliper. So, instead of pumping to get that bubble out through the caliper (since the ducts are downward, the bubble resists going down), try "backwards" ... remove the calipers, pump at once and stop. tap the pipe that descends from the pump to make the bubble rise again. After doing it a couple of times, and with the caliper piston far enough out, it “pushes the pistons in”… .and continues tapping the pipe so that the bubble detaches from the walls. It is easier to try to get the bubble up (towards the pump), than to push it down to the caliper… .when you pump with the calipers on, the path of the liquid in the pipe is “minimal”, scarcely 1 centimeter…. If the bubble is trapped in the first centimeters of the pump outlet pipe, it will always tend to go back up ...... all this would be "if the bubble is in that section of the descending pipe" ... ..and withdrawing liquid from the reservoir to avoid a spill when you push the pistons in again
 

Don in Lodi

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Are the pads making contact with the rotors? Jlq has it I think. I've tied the levers to the bars for both the clutch and the brake and left them set over night and it has cleared that last bit of air.
 
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Explain this. I don't understand exactly what you're saying.
Attempting to isolate where the air might be trapped causing the soft lever.
I placed a clamp on the brake line just below master cylinder and the lever is immediately rock hard, surely this means the master cylinder is working and not the source of trapped air.
Next i placed the clamp on the brake line decending to the first caliper, again a small movement of the lever and then rock hard, in my mind this eliminates the abs module as the source of the trapped air.
Next i placed the clamp on the crossover brake line between the calipers and immediatly im back to soft brake lever. So to me that would mean there is something causing sponginess within the caliper. Either air somehow trapped which wont come out using any method ive tried or some sort of fault with the caliper. Idk.

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Joined
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Messages
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Location
Sunshine coast. Qld. Australia
Are the pads making contact with the rotors? Jlq has it I think. I've tied the levers to the bars for both the clutch and the brake and left them set over night and it has cleared that last bit of air.
Yes they appear to be. If i roll bike forward and gentle start appling the lever i can hear the the pads starting to rub on rotor but they have no bite until lever is compressed almost all the way in.

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Joined
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Messages
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Location
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"It is probable" that the air bubble is closer to the pump than to the caliper. So, instead of pumping to get that bubble out through the caliper (since the ducts are downward, the bubble resists going down), try "backwards" ... remove the calipers, pump at once and stop. tap the pipe that descends from the pump to make the bubble rise again. After doing it a couple of times, and with the caliper piston far enough out, it “pushes the pistons in”… .and continues tapping the pipe so that the bubble detaches from the walls. It is easier to try to get the bubble up (towards the pump), than to push it down to the caliper… .when you pump with the calipers on, the path of the liquid in the pipe is “minimal”, scarcely 1 centimeter…. If the bubble is trapped in the first centimeters of the pump outlet pipe, it will always tend to go back up ...... all this would be "if the bubble is in that section of the descending pipe" ... ..and withdrawing liquid from the reservoir to avoid a spill when you push the pistons in again
Willing to give anything a go. Just not sure i understand all the steps you suggest.
Are you saying bleed it off the bike with the piston moving out? What if the pistons pop out??

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OldRider

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Pull both calipers off and place something solid between the pads. I use a couple of tire irons. Pull the lever and see if you get a solid feel. If you do, I think the problem is that something isn't lining up straight between the calipers and disc. Maybe something is in a bind. Did you have the wheel off any during this repair?
 
Joined
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Sunshine coast. Qld. Australia
Pull both calipers off and place something solid between the pads. I use a couple of tire irons. Pull the lever and see if you get a solid feel. If you do, I think the problem is that something isn't lining up straight between the calipers and disc. Maybe something is in a bind. Did you have the wheel off any during this repair?
Yeah i replaced a warped rotor and wheel bearings. Did the caliper service while i was at it. I have them both off at the moment suspended from a rope attempting to gwt any bubbles to rise. I just have a block of wood inbetween the pistons to stop tgem popping out. Its still just as soft on the lever

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Jlq1969

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Willing to give anything a go. Just not sure i understand all the steps you suggest.
Are you saying bleed it off the bike with the piston moving out? What if the pistons pop out??

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is that we do not know, "why" you lost braking pressure, from "what action" that you performed, you lost braking pressure ... but, if you detached and turned the handlebar, the air in the container may have entered the pump ... and when operating the brake lever, "introduce" that air into the line ... in that specific case, it is easier to remove that bubble by pushing it up (towards the pump), than to try to bring that bubble towards the bleeders of the calipers, passing through the body of the abs ... it would be a bit more complicated ... yes, it is "supposed" to prevent the pistons from coming out, but if they are withdrawn enough, you can use them as a pump to push the bubble to the nearest place of escape. "It is common" the entry of air to the line, when the handlebar is loosened and rotates ... and the fault is usually that the brake lever is free, after a few pumps, it has pressure again, but not enough, and If you leave it unused for a couple of hours / days, the same thing happens again… .the lever is free… a couple of pumps and it has pressure again, but not enough…. what happens is that the bubble is in the first centimeters of the line after the pump and when it is stopped, it goes up to the pump “but it does not come out” to the reservoir, then when you pump, you put it back into the line
 

OldRider

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You've done went and got some air in the abs pump and lines. Get a service manual and follow it step by step to bleed the system and the pump.
 
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