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Every now and then I get stumped, this is one of those times....

Fault: Cannot get any pedal

Have bench bled the master cylinder.....I am on the 2nd new master cylinder  thinking that was the issue.  Also checked all fittings for leaks, have manually bled the system numerous times with helper pumping the brake pedal ( 5 and hold)  Decent fluid pressure at rear wheel cylinders, a bit less at the front cylinders ..but no pedal at all.



New: Lines, hoses, wheel cylinders, master cylinder

New Shoes & they are adjusted as well as the E' brake

Pedal push rod to master cylinder is the correct length at 5.433 with pedal rod having 3/16 free play measured at the top.

Ok brain trust what say you ? 

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Ok Al I'll throw this out there and see if this might work. I had the same thing happen on a Hot Rod years ago. There is air in the lines and my problem was the air was trapped in the brake calipers. I had the car on jack stands while trying to bleed them. I couldn't force the air bubbles out. So I jacked up the front of the car so the front brakes were higher then the master cylinder and used a power bleeder I borrowed from a friend. Got a good firm pedal or as Stan would say, "Bob's your uncle"

I had that happen on my car until I realized that I had the front calipers on upside down with the bleeds on the bottom.    

I also had that happen after a new MC on someone else's car - Nothing we tried worked (including a bench bleed, which usually cures it) until I finally borrowed a pressure bleeder and bled them with that.  That finally got a decent pedal.

The weirdest brake bleed was a 2.5 ton chevy truck. Two wheel cels per wheel. Set at a 45 degree angle. Bleeder screw centered on each wheel cylinder. Air would be trapped in the area above the bleeder.  I would stick a .002" feeler gauge in past the piston and cup at the top of the cylinder.  This created a tiny air/fluid leak that allowed the air trapped there to leak out.  The manual called for removing the backing plate bolts and rotating the entire brake assy so that the wheel cylinders were vertical and all the air would be bled out.  If the brake bleeder had too much pressure it would blow the pistons out.  Real stupid procedure but we figured out an easier way.......Bruce

The brake fix:   I borrowed a better quality hand pump bleeder this morning and wasted an hour as I still had no pedal... I even tried jacking one end of the buggy at a time.   Ended up dragging it over to a friend's shop, I used his air powered bleeder system, that still took and hour plus then we had half a good pedal and knew we were onto something. Then bleed all four cylinders pumping the pedal and that finally did the trick. Bottom line was a lot of trapped air in the new  system., never ran into that this sever in all the builds. No more drum brakes for me even on a classic Meyers Manx..............  Thanks for all the suggestions !

I’ve posted this before but when I replaced my single circuit M/C with a double, I couldn’t get a decent pedal until I used both my Motive brake bleeder* on the reservoir and a suction bottle at the rear wheel cylinders, followed by an aggressive manual bleed with a helper like Danny suggests.

*Neither suck (rear cylinders) or blow (motive bleeder) worked by itself, but the combination seemed to work.

Where it's practical,  I just cap off the M/C reservoir  (full of fluid of course) , pressurize it with shop air pressure  (approx, 120 psi)  and start bleeding.  I check the reservoir after each wheel to refill it,  then go to the next wheel.  That amount of pressure usually does it and I get a fairly good flow of fluid out of the bleeder fittings at the wheels insuring that the flow carries the trapped air with it.  You don't need a helper to to this but it is nice to have one standing by in case we have to resort to "violence" method .......Bruce

@aircooled

HOLY BALLOON-BUSTER, Batman!

Re-read your last post.

Did you really mean 20 psi on your pressure bleeder, not 120 psi?

I’m a “Wild and Crazy Mechanic” but I only run my bleeder at 10 - 12 psi or so.  I would think that 120 psi would cause the reservoir to rupture.  

I made a Motive-style bleeder out of a garden sprayer for about $20 bucks, pressure gauge and all.  It works great.

Last edited by Gordon Nichols

Gordon....Your comments scared me too !  I wasn't using a pressure bleeder.

In my old tool box is a Brake bleeding tool made by Owatona Tool Corp which consists of a flat plate with one side covered in rubber and the other side has an air hose connection. Theres cinch chain attached as well.  In my old flat rate days I used this to bleed brakes. I didn't need anyone's help and I didn't need to go to the tool room to check out a bleeder. That's time saved to work. So I removed the cover on the M/C, filled the reservoirs to the top, placed my trusty (OTC) bleeder on top of the M/C, clamped it down with the attached cinch chain   (rubber side towards the M/C sealing surface). Connect my air hose and  "voila", 120 psi pushing down on the fluid in the M/C and anything behind it, all the way to the wheel cyl.

When you've estimated that you've bled out as much fluid as you dared, you stopped.  This is so the M/C doesn't go  dry and start blowing air into the lines.

Anyway, this can be done only where the fluid reservoir is integral with the M/C and made of substantial material.  However, I have done it on plastic reservoirs as well but only up to 25psi. The 25psi number is not scientifically derived. It is only what number I dared to go to. My thoughts were that I needed to have a higher pressure than the residual valve, if any.   I guess that makes it an empirical  number ?  Arrived at with no substantial data collected either !

So,  Gordon .... I'm glad that you raised a few flags on my comment. Perhaps even save someone from trying to do what I suggested. Perhaps someone who may not have the experience to recognize some of the pitfalls of taking shortcuts. Thank you for that......Bruce

Ahhh….   OK, that explains stuff.

When I was working on my Dad’s school buses they were all GMC buses, all had power brakes and all had the metal reservoir as integral to the master cylinder - The MC casting was much taller so the reservoir (on top) and the MC were all one piece.  That version (used all over the place but not on our cars) would certainly tolerate 120 psi air pressure.

That said, we “bus mechanics” had a portable pressure bleeder that was a metal tank with a pressure gauge on it.  You dumped a gallon or so of brake fluid into it, sealed it, pressurized it to 20 - 30 psi, attached the proper MC bleed cover (there were a bunch for different MCs), open the valve and start bleeding farthest to closest.  If the pressure in the bleed tank got down to 10 psi-ish then you could re-charge the tank.  Easy-Peasy.

Of course, a side effect of using a painted metal bleeder tank was that, eventually, the brake fluid splashed onto the tank while filling it ate all of the paint off of the tank over time.  

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