"Warning" Don't Bench Bleed Me

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dibbons

dibbons

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The '65 Valiant Raybestos master cylinder has conflicting literature included. One item is a description of Method "A" and Method "B" options that may be chosen to bench bleed. The second item, is a printed red warning that states: "Do not bench bleed this master cylinder--you will damage the cylinder" I guess they are worried about pressing the plunger too far during the stroking process (must be some idiots out there messing these things up).

The recommended new procedure is: basically says to open all the wheel cylinders and pump away, then close the cylinders and release the pedal. Repeat.

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That method does works on a single; BUT; you have to keep the air bubbles moving until they come out somewhere. If you stop pumping, the bubbles will stop moving, aaand if the angle is favorable, then they will turn around and backtrack to find a trap or backtrack all the way to the master, where they will be trapped in the high spot, at the front of the M/C...... and drive you crazy trying to solve a soft pedal.
So to overcome that, if I suspect it, I crack the fitting at the front and let the air out, lol. Sometimes I get a helper to push the pedal down enough to cause the brake shoes to go out at the back. then when you crack the fitting, the return springs will force the fluid back to the M/C and since the pedal is still partially down. the returning fluid has to force the air out for me. Course it will make a mess, so deal with it, lol. Then close the fitting and release the pedal.
It has happened to me that I just couldn't get it, so let it sit overnight. The extra time allowed the bubbles to accumulate at the top and the next morning I cracked the fitting and released the air, and BINGO.
As for me, I hate pumping bubbles downhill, so I bench-bleed everything. If the Front of the M/C is uphill from the firewall, I might "benchbleed" on the car; it's easier but does require a helper. Sometimes the fluid wants to just shuttle back and forth and the bubbles never come out. In this case you have to pinch the bleeder hose off on the return stroke, so that the returning piston draws properly thru the Compensating port.
Don't forget, brake fluid eats paint so if you make a mess, stop everything and clean and flush the area.It's not instant so don't panic.
 
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I cut old fittings off an make then "&" shaped. Mount the MC in the car, attach these fittings and pump the fluid back up into the ports just like on the bench but your using your foot and the proper brake rod. Once its pushed in about 10 times, reattach your real lines and proceed with any remote bleeding you feel necessary. The make one way check valve bleeders too, nnice for the back when your alone.
 
That because you use short strokes like a chinamen does. Lol

My advice to people and what I do...is put it in the car and do it with the pedal....short quick....then more pedal front port then rear in other words iirr.
 
I quit bench-bleeding masters over 25yrs ago, fill 'em up & top 'em off 'till it's running free out both(or all 4) ports/bleeders, put it in the car & repeat w/the lines attached but loose. Finish with easy 1/2pumps & a helper, in My case at home, a pedal depressor/chunk of wood. I have a real nice Thexton bleeder kit with anodized fittings, tubes & check valves etc., just a conversation piece now.
 
I was taught, you mount everything up, fill the reservoir, pump with short strokes till you get a peddle, then start bleeding with a flexible line attached to the bleed valve submerged into a clear jar of brake fluid (so you can see the bubbles). USE A BOX END WRENCH to open and close the bleed valve and close it after each down stroke before releasing the peddle until you don’t see bubbles. (Basically a two person job) Start at the wheel farthest from the MC making sure you keep the reservoir full.

However (there is always an exception) when I did the brakes on an old Honda Odyssey I owned, the Haynes manual said to start at the wheel closest to the MC.
 
Short strokes makes sense to me, if you ram it past the polished bore I could see it trashing the piston. Thanks for the advice guys, I’m new to the site, so happy to get MOPAR information, not Austin or Volkswagen or chebby/fraud. Now I’m getting my wheels under me I’ll drive you all crazy with my silly questions!!! This is so great, I wish I’d found it sooner!!
 
if all else fails
pumping fluid in from the wheel end can occasionally work.

you need a hose tail/barb with the same thread to replace the bleed nipple
and if your pump is powered rather than hand activated a friend to watch the level in the master cylinder whilst occasionally slowly pumping the peddle.

a last resort for the frustrated man who wants to go inside because its now dark and rain is hammering on the roof...... but....i'll just give it one more try

PS if you have drum brakes bleed the brakes with the shoes adjusted up tight against the drum and the hand brake off. if you get a hard paddle that slowly sinks well has to be master cylinder or a leak, can't be anything else.

if you get sinking peddle after you then adjust the brakes properly again look for a problem (wet) wheel cylinder

don't top off the master until all is good


dave
 
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Lectro said:
Short strokes makes sense to me, if you ram it past the polished bore I could see it trashing the piston. Thanks for the advice guys, I’m new to the site, so happy to get MOPAR information, not Austin or Volkswagen or chebby/fraud. Now I’m getting my wheels under me I’ll drive you all crazy with my silly questions!!! This is so great, I wish I’d found it sooner!!
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That's even more important on an older unit when bleeding the brakes period, trash & possible corrosion builds up past the normal range of travel, guys get in & start burying the pedal in the carpet wrecking the seals & getting trash all over. Let it gravity bleed & easy does it when it's time to pump. Not to mention pounding the pedal can pop the pressure differential over & old ones sometimes won't move back, making it impossible to bleed or get a good pedal.
 
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