Another brake bleed/MC/Booster problem thread

[infernosg]

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?

[JL1RX7]

Use the good old pump pump hold. The power bleeder's have been know in the past to not get all the air out.

Also was the fluid sealed? Might be worth getting new.

[Pete_89T2]

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.

[infernosg]

Originally Posted by JL1RX7

Use the good old pump pump hold. The power bleeder's have been know in the past to not get all the air out.

Also was the fluid sealed? Might be worth getting new.

I guess I don't understand how a pressurized bleeding system would leave air in the system. Also, if it were air in the system wouldn't pumping the pedal rapidly stiffen it up, if not just briefly? No matter how many time the brake's pumped the pedal is the same. I'll still try the old fashioned method but I'm not optimistic.

The fluid was sealed. Never even cracked open until last week.

Originally Posted by Pete_89T2

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.

I have the universal fitting. Yeah, it sucks but I've gotten it to hold 20 psi of pressure. I regularly bled the brakes at 15 psi when the car was still running. The one thing I don't do is fill the bleeder with fluid. That just makes a mess so I just leave it empty so air is pushing down on the fluid in the reservoir. Think this could be an issue?

Also, regarding the check valve I found one that worked and still no luck. Same pedal feel.

[JL1RX7]

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.

[Pete_89T2]

Originally Posted by infernosg

The one thing I don't do is fill the bleeder with fluid. That just makes a mess so I just leave it empty so air is pushing down on the fluid in the reservoir. Think this could be an issue?

It could be, are you saying that you don't put any fluid in the bleeder, and just use it to pressurize the fluid in the MC reservoir & system? You'll never manage to flush out all the air in the system with that small a volume of fluid.

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.

[infernosg]

Originally Posted by JL1RX7

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.

I'll give it a try. I'd think with the amount of pedal movement I'm getting there'd be a pretty big bubble somewhere.

Originally Posted by Pete_89T2

It could be, are you saying that you don't put any fluid in the bleeder, and just use it to pressurize the fluid in the MC reservoir & system? You'll never manage to flush out all the air in the system with that small a volume of fluid.

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.

Yep, that's what I've been doing. I'll let the fluid in the reservoir get to the "LOW" mark and then fill it up again. I've certainly flushed more than a quart through the entire system by now. What pressure are you using with the Motive bleeder? Also, how much are you opening the bleeder screws? I've used anywhere from 5-20 psi and I've let the fluid come both rushing and slowly trickling out.

[infernosg]

Originally Posted by Pete_89T2

It could be, are you saying that you don't put any fluid in the bleeder, and just use it to pressurize the fluid in the MC reservoir & system? You'll never manage to flush out all the air in the system with that small a volume of fluid.

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.

So I just went out and did this - spent an entire hour on the right rear. I have to have flushed the fluid in that particular line 3 times through now. However, I am periodically getting streams of small bubbles, which is a change. I don't think I'm sucking in air anywhere. Using a pressure system I'd think I'd generate a leak before drawing air into the system. I just find it hard to believe I've run so much fluid through one line and haven't gotten all the air out. And yet, despite all those bubbles, the pedal feel is the same. What is going on? I've never had this much trouble bleeding brakes before!

[Pete_89T2]

Originally Posted by infernosg

Yep, that's what I've been doing. I'll let the fluid in the reservoir get to the "LOW" mark and then fill it up again. I've certainly flushed more than a quart through the entire system by now. What pressure are you using with the Motive bleeder? Also, how much are you opening the bleeder screws? I've used anywhere from 5-20 psi and I've let the fluid come both rushing and slowly trickling out.

Every time you open the MC to add more fluid, you introduce another opportunity for air to get into the system. As you pour in fresh fluid, sometimes the simple act of pouring can snag a bubble or two of air along the way.

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.

[Pete_89T2]

Originally Posted by infernosg

So I just went out and did this - spent an entire hour on the right rear. I have to have flushed the fluid in that particular line 3 times through now. However, I am periodically getting streams of small bubbles, which is a change. I don't think I'm sucking in air anywhere. Using a pressure system I'd think I'd generate a leak before drawing air into the system. I just find it hard to believe I've run so much fluid through one line and haven't gotten all the air out. And yet, despite all those bubbles, the pedal feel is the same. What is going on? I've never had this much trouble bleeding brakes before!

That is odd, although the right rear line is always the most difficult to bleed, since it's the longest line length. Only other thing I can think of is maybe the bleeder screw threads have worn out, or perhaps the new MC is defective? Sloppy bleeder threads would allow air to sneak in and would show up in the bleeder tube while you're bleeding it, but since it's a pressure bleeder, I don't think that air could get pulled into the system from that point or effect pedal feel.

[infernosg]

Originally Posted by Pete_89T2

That is odd, although the right rear line is always the most difficult to bleed, since it's the longest line length. Only other thing I can think of is maybe the bleeder screw threads have worn out, or perhaps the new MC is defective? Sloppy bleeder threads would allow air to sneak in and would show up in the bleeder tube while you're bleeding it, but since it's a pressure bleeder, I don't think that air could get pulled into the system from that point or effect pedal feel.

You're telling me. I've never had this much difficulty bleeding brakes and I've probably done them 100 times on this car. I have no external leaks whatsoever. I suppose the MC could be bad but when I bled it I could push the piston in <1/16" using all my strength. I guess I'll pull it off again tomorrow to see if anything is leaking internally. Beyond that I'm out of ideas.

The top bleed screw is the correct one to use for the rear calipers, right?

[RETed]

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

[infernosg]

Originally Posted by RETed

For dual bleed screws on brake caliper...
1) Bleed mostly from top screw to eliminate air.
2) Bleed a little more frombottom 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

Pressure is force per unit area. There's a finite amount of fluid in the system so if the MC diameter is increased it moves more fluid per unit of displacement so less pedal travel for a given amount of braking force. Either way I removed the MC again after systematically plugging off the ports. Even with all the ports plugged I was getting the same pedal feel so I somehow got air in the MC. I've bled the MC again and it's nice and firm installed with the ports plugged. I'll bleed the system the old fashioned way this time around to avoid any issues.

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?

[infernosg]

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.