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Tires,Wheels,Suspension,Brakes Info about Tires, Wheels, Suspensions, Brakes, etc. |
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#1 |
IT'S ALIVE!
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Just finished doing a 929 MC and booster swap into my '89 GXL. The booster is a used unit and the MC is a new aftermarket unit from Raybestos. Bench bled the MC until the piston couldn't move <1/16" with the ports plugged. Installed the MC on the car and bled all the lines in the proper order and guess what, squishy pedal! I've since removed and bled the MC again (with the same results), reinstalled and bled each line probably a dozen times with no perceived change. Every now and then I'll get one tiny, tiny bubble from one of the lines. So do I just have a stubborn air bubble somewhere or is something else up?
Other info: 1) Using a Motive Pressure Bleeder. 2) Brake fluid is probably >2 years old but it wasn't opened until last week. 3) Booster plunger has maybe 1/4" inward/outward play (pedal movement before the plunger starts to move, not distance between plunger and MC). I'm not sure if this is normal or not because is my first experience with a double-diaphragm 929/TII booster. 4) Pumping the brakes does nothing for feel. There's no engine installed in the car and it's possible the check valve is bad. I would think pumping the brakes would make the pedal stiffer. Other thoughts? |
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#3 |
Lifetime Rotorhead
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On the Motive power bleeder, what kind of adapter are you using to rig it up to your MC? I love my power bleeder, but I quickly found out that the universal adapter that comes with the basic kit is useless on an FC, as I could never get it to seal the MC all that well.
To get mine to work right, I picked up a spare MC cap from the boneyard, drilled a hole thru its center and inserted a brass nipple fitting in, then sealed it to the cap with epoxy. Hooked that up to the Motive bleeder and it works great. If bleeding is stubborn like you described above, I just pump up the pressure a wee bit more than they recommend and it seems to purge out that last stubborn bubble without harm. |
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#4 | ||
IT'S ALIVE!
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The fluid was sealed. Never even cracked open until last week. Quote:
Also, regarding the check valve I found one that worked and still no luck. Same pedal feel. Last edited by infernosg; 06-05-2013 at 06:08 PM.. |
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#5 |
Rotary Fanatic
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I have used them in the past and got great pressure reading etc. But still had the same issues you're having. Went back to the old tried and true and got a few bubble out.
It shouldn't have picked up much water then. Just sucks that the fluid attracts water so no shelf life for it at all. |
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#6 | |
Lifetime Rotorhead
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Normally for a fluid flush & bleed, I'll dump a full quart of fresh brake fluid into the power bleeder tank, and it will take almost all of it to get to the point of zero bubbles and a solid pedal. To avoid the mess at the end, do the following when you're satisfied the last brake has been fully bled: 1. Tilt bleeder tank such that the feeder tube at the bottom is no longer under fluid. 2. Crack open the bleeder screw on that last line, and let it slowly bleed out until the fluid level in the MC drops to the full line, then close the bleeder screw. 3. Carefully depressurize the bleeder tank by *slowly* loosening the pump piece from the tank. Make sure the tank is still tilted at this point so the feeder tube at the bottom is not immersed in fluid. 4. Now you can remove the adapter from the MC without the mess. Last edited by Pete_89T2; 06-05-2013 at 06:34 PM.. |
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#7 | ||
IT'S ALIVE!
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#8 | |
IT'S ALIVE!
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#9 | |
Lifetime Rotorhead
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I'll normally pressurize the tank to 10~15psi. When opening the bleeder screws, I just crack them open slightly at first, then slowly open them up a little bit more until I get a steady flow out. When the flow of bubbles seem to be slowing down, I'll close the bleeder and then wait a minute or two. Then I keep repeating this open/close process until nothing but fluid comes out. After bleeding each wheel, I'll check the tank pressure and pump it up as necessary to keep it as close to the pressure I started with as possible. |
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#10 | |
Lifetime Rotorhead
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#11 | |
IT'S ALIVE!
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The top bleed screw is the correct one to use for the rear calipers, right? |
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#12 |
RCC Addict
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For dual bleed screws on brake caliper...
1) Bleed mostly from top screw to eliminate air. 2) Bleed a little more from bottom screw to eliminate debris. I think you should wait till the engine is in the car and running. Due to physics... Pressure is defined by mass divided by area - i.e. pounds per square inch. You have effectively increased the "area" side of the equation due to the larger brake master cylinder bore. Now you have spread pressure over a larger area... Thus, the feedback pressure is going to be less back to your feet - i.e. softer pedal feel. We need the brake booster to be operating to see how effective the whole system is under working conditions. I think you're just wasting brake fluid and labor at this point. ![]() -Ted |
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#13 | |
IT'S ALIVE!
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However, before I install the MC permanently and bleed the brakes I want to set the brake booster pushrod clearance properly. The FSM calls for a specific SST, which I obviously don't have. Is there another way to do this or does anyone have access to the SST I can borrow? |
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#14 |
IT'S ALIVE!
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Bumping this thread with a stupid question. Does anyone know where to get those plastic threaded plugs that come with new/remanufactured MC's? I've lose mine and need to plug the MC ports to remove it from the car because I don't want to lose all the fluid. Autozone doesn't have 'em separately and I can't seem to find anything online.
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