Technical Bleeding a stubborn brake system

Here is what I have:
4 wheel disc system, Baer four piston calipers on the front and Baer Iron Sport single piston calipers on the rear. The master cylinder is from Master Power Brakes and is installed using a MPB combination valve, both items were spec’d by MPB using the brake system components mentioned above. The system is plumbed using 3/16 NiCopp line, the rear brakes are supplied by a single line split with a T mounted near the rear end housing. The flex lines from the frame to the calipers are braided hose that was supplied with the calipers directly from Baer.
The pedal system is factory stock for this vehicle (‘64 Comet), the rod from the pedal to the master cylinder is adjusted correctly. Every fitting is sealed, no leaks anywhere.
The problem is that after bleeding the system using a pressure bleeder, a vacuum bleeder, and the old fashioned pedal pumping method I still has a soft pedal for the first few pumps. I have gone through the trouble shooting guide on the Master Power Brakes web site, and have come to the conclusion that there is still air trapped in the system. They claim that is the most common problem with the symptoms I am experiencing. I figured the power bleeder would push the air through, but it has not. I pumped the pressure to 25psi on the tank hoping it would do the trick but no luck. I am open to ideas.
Thanks!

 

Are all the calipers mounted with the bleeder screws facing up? Did you bench bleed the M/C? Is the M/C pushrod adjusted properly?
That’s where I would start.


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Thanks for the reply.
Yes to all of your questions. I feel that I have covered every potential issue that is why I have turned to this forum for suggestions.

 

The last time I got into one like this it turned out to be a caliper leaking.

 

Bench bleeding is most important. Takes more than just a couple of minutes.

 

Be sure to check the free play on the pedal rod to the master! I just went through this on my '39 Coupe project and couldn't get good brakes. I discovered the rod was adjusted to tight, and no free play in the pedal, so it wasn't quite returning to full travel on the master cylinder piston. I backed it off a tiny amount, and bled the brakes again, and now they're great!

 

Thanks for the suggestions.
I bench bled the master.
I have seen no sign of a leaking caliper, I also inspected all of the bleeders to make sure they were not leaking.
The last time I bled the system (with 25lbs in the Motive pressure tank) I saw no air bubbles at all. ( I use clear tubing and bleed into a small container with a small amount of fluid in the bottom, so no air will be suctioned back into the system.

 

I have manual brakes, no booster. Do you have a booster?

 

Do you have any through frame fittings? There have been some styles that have been said to trap air. What other components are in your system? Valves etc.


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On private aircraft (small planes) the brakes have the master cylinder by the cockpit and the brakes are down by the wheels so you can imagine how hard it could be to get all the air out of the system. The solution is to use the power bleeder (or a pump style oil can) on the caliper/wheel cylinder side of the system. Connect the hose to the bleed screw and pump fluid back toward the master cylinder. Air rises and now the air is being pushed uphill so you are no longer fighting this tendency . Remember to have the master cylinder reservoir cap off before you start and the fluid level in the reservoir should just cover the master cylinder inlet hole (to allow space for the fluid you are pumping from the wheel cylinder/caliper bleed screw. You will also want a second person monitoring the master cylinder reservoir fluid level so it doesn't overflow.

 

No residual valves, only the combination valve that was part of the master cylinder package from Master Power Brakes. When I bought the master cylinder I gave MPB all the information about my system and they spec’d the Master and combo valve.

 

Are you still running a brake light pressure switch? When I did my conversion I fought with bleeding the front brakes for an hour or so until I figured out the new pressure switch that came with the kit was leaking internally. I swapped in the switch from the old master cylinder and was able to bleed it.

 

Master cylinder bore size too small? My Chevy II seems to prefer a 1 1/8" master w/manual front discs contrary to everybody and their brother saying it requires a 1" bore. Went through the whole deal with at least 2 new masters, valves, hoses, calipers, bench bleeding and wasting gallons of fliud. No self retracting metric calipers, deflecting brackets or loose wheel bearings. Might want to ask Baer what they recommend.

 

No, the light switch is mounted on the brake pedal, I am using an original FoMoCo type that I have on other vehicles.

 

The master cylinder is 15/16” and was spec’d by Master Power Brakes for my vehicle. Maybe a call to Baer might be a good idea. Thanks

 

I had a similar problem on car a few years back. Musta put 2 gallons of fluid through it. Same thing, just barely any pedal at all.
Like you, I tried all of the methods, nothing worked. Yes, I had all joints tight, yes the calipers were placed correctly, no leaks, etc., etc.
I figured that the tall hump of the rear hose over the rear axle is where the problem was, but didn't know how to "fix" it.

Anyway, continuing, then all of a sudden, while doing the same thing (one man, hand pumping into a half full can of fluid) for the 301st time...I had full pedal..! No slow pump up, no indication that I'd be there soon, nothing, until, I was, suddenly...done.
Been great ever since (a few years) with no problems.

Mike

 

I'm with Macromadness on this. Back bleed the system starting with the furthest brake nipple from the master cylinder and working to the nearest. Have found that this works when other ways have failed.

 

Don’t you wish brake lines were see thru?
That would be smart.
If it were possible you’d be able to watch the fluid and make sure brake fluid was following the law and doing what it’s supposed to be doing in the lines.

 

You must have got the final fart of air, ( even if it was 301 times) locked the bleeder down then got a pedal. Right?

 

If master cylinder is replaced and bench bleed. All components correct and installed correctly. I have always had success getting air out of an air locked system . Open the bleeders at all 4 wheels hold the pedal down ,close the bleeders ,repeat till pedal feels firm and then bleed wheels one at a time.

 

This guy can probably out smart some brake fluid.
Very Nice post @garyf.

 

Make sure the master cylinder can be fully stroked (open systems) before the pedal hits the floor.
Power bleeding * is the best method, imo. Use slow full pedal strokes for each caliper while circling the vehicle at least 3 times. When you have a good pedal, "stand" on the pedal (150-200lbs or so) for 10-15 secs. to check for leaks/weeps after using isopropyl or denatured alcohol to clean fitting, fluid spillage, hands etc. This makes it much easier to find and repair leaks. One or two more rounds of bleeding after the system sits for awhile is recommended if no leaks are found.
* Power bleeding is the best method, but only when using a brake pressure bladder that completely isolates air from the fluid. A cheap "garden sprayer" bleeder forces air into the fluid, something you want to avoid. I know the "correct" bleeders are not cheap, just pointing out the differences.

The recommended 15/16" master will give you a better non-power pedal with 4-wheel discs, but may be marginal in volume. That's one problem with 4-wheel discs, and is why most are power-assisted with larger bore masters.
I would also ditch the combo valve and simply use an adjustable proportioning valve, period. Your car/system is custom, so no fixed value combo valve will match yours like it should.

 

You may have a bad (faulty) master cylinder

 

Thanks for all the suggestions. One note I failed to mention: when using the Motive bleeder system it puts pressurized fluid into the system, I pumped it to 25lbs to try and push the air from wherever it was trapped. Once while doing this procedure I pushed down on the brake pedal, it had a perfect pedal!! I disconnected the sealed cap from the master which removed the 25lbs of pressure from the master and the pedal went back to the soft feel for a few pumps, then the next pump had a more firm feel. ???

Also a question for “Marcosmadness”: if I was to pressure bleed from the bleeders back to the master how would I stop the air in the bleeder tube from entering the system before the brake fluid fills the tube? How would I purge the tube without blowing fluid all over my fresh suspension pieces?
Thanks You everyone!

 

is the master cylinder reservoir lower than the bleed nipples, if so you can still gravity bleed by raising the car on stands , connect a piece of clear tubing ( eg from a fish tank) from each bleed nipple to individual jars at floor level with some clean brake fluid in each jar. the open end of each tube must be submerged in the brake fluid. Crack open the nipples on all four corners, push the brake a couple of times to start the siphoning action. DO not let the master cylinder reservoir run dry or you will be doing this again, as the open tubes are lower than the master cylinder gravity will slowly pull fluid through the system, it will take a few hours no rush just ensure that the master does not run dry. I have used this method, which is very old school to bleed brakes on Land Rovers and Lotus 7 type cars, this method will yield results in cases where others have failed.
You may also try to bleed conventionally starting at the wheel furthest away from the master cylinder, cracking open each union on the way this can only be a last resort method as it is very messy and can result in leaky or broken off brake lines.

 

Maybe I should be knocking on wood here but I’ve never ever had this kind of trouble EVER bleeding a brake system. I will say that I’ve alway had help though, experienced or 10 year old kid, think I might have grabbed a crackhead more than once to help. That’s because I tried the prop stick and it pissed me off.

I would kinda like to use a power bleeder once because it sounds cool but so far there’s not been a need.

Here’s some of the rules I follow. Maybe they will help you guys. All of this I learned from my dad before I graduated high school.

#1, I don’t do or make anything like this so I won’t have these elementary air locks. (yeah I posted some of this in the smart fluid thread.




When you let the pedal back up,,,, where does the fluid go and how does it get there?


don’t go up and over an obstacle.


does anyone see that as a brake line on a frame rail?

#2 I know about the shuttle valves in a combination valve, how they work, how to check them and how to reset them.

#3 I use the tip mentioned by Garyf or a variation of it.

#4 who ever is pumping the pedal is told to use their toe to pull the pedal back up after every stroke.

#5 I understand how a bleeder port is machined and that even though the little nipple thing looks dead on up it may not be in the up position. The seat of the bleeder (the part you can’t see) needs to be at the top.

#6 IF by some chance I’m forced to deal with an issue found in # 1 that I can’t eliminate and @garyf tip didn’t work , I can usually see the best place to tap the line move the air.

# 7 I’m not worried, concerned or avoidant about lifting one end or one side of the vehicle much higher than the other when doing this. Yeah it kind of a PITA so what.

 

My power bleeder Is a cheap electric fuel pump and enough hose to get the fluid back to the master cylinder. Hook it to the bleeder and put the hose in the reservoir turn on the pump and let it circulate for a few minutes and then go to the next wheel. You do not want a big pump. I don't know if it is necessary but I run a little fuel through it after I'm done.

 

Had the same problem on my Willys for years. Took two pumps to start stopping the car. Finally got sick and tired of it and decided to lengthen the master cylinder push rod. Worst that could happen is plunger blocked the bleed hole and the brakes lock up. Turned out I got perfect brakes. Lengthened the rod til the plunger was always slightly depressed.

 

I remember having this problem on a friend's truck way back when I was a lot younger. Went so far as to cut half the brake pedal off in order to get more brake pedal travel past the steering column. Finally ended up making an adjustable push rod for the master cylinder like willys36 and problem solved.

 

No booster on mine, all manual. But it doesn't really matter as either way they have a operating rod to move the piston in the master.