[NoVa-Corvairs] Fwd: <VV> RE: Bench bleeding

[novacc-list@corvair.org]

Thanks very much, Bryan.

The concern I have is that the brake pedal on my '65 is so floppy -- that is, there's no resistance whatsoever.  I made sure the plunger went through the master cylinder boot, but it doesn't feel like it's engaging anything inside the master cylinder.  I replaced the master cylinder on the '63 I used to own, but that was may moons ago so I can't recall if I had to do anything special.  

Thoughts?  I'd check the instructions once again, but I'm emailing from Queens.


----- Original Message -----
From: "Bryan Blackwell" <bryan@skiblack.com>
To: "nova Corvair" <novacc-list@corvair.org>
Subject: [NoVa-Corvairs] Fwd: <VV> RE: Bench bleeding
Date: Thu, 25 Nov 2004 19:37:31 -0500

> 
> Since we were just talking about bench bleeding, here's a great post on 
> the subject from VV:
> 
> Begin forwarded message:
> 
> > From: Dennis & Debbie Pleau <ddpleau@earthlink.net>
> > Date: November 24, 2004 7:48:46 PM EST
> > To: "virtualvairs@corvair.org" <virtualvairs@corvair.org>
> > Subject: Re: <VV> RE: Bench bleeding
> >
> > My feelings about bench bleeding.
> >
> > It is required for dual master cylinders (although there are ways 
> > around it that are probably more trouble than bench bleeding).
> >
> > When you put a dry dual master cylinder on a car, hook up the lines 
> > and start bleeding, this is what happens.  You fill if with fluid and 
> > have someone pump up the system and you open the bleeder on the 
> > passengers side rear, you let some air and get some fluid into the 
> > rear circuit.  and you repeat until the line and cylinder of the right 
> > rear circuit is bleed and full of fluid, and then you do the left rear 
> > until it has no air.  Now you move to the passengers side front and 
> > try to bleed it.  Since the rear circuit is completely full of fluid 
> > the pedal only goes part way down and you get some air and fluid out 
> > of the right front.  You do this a few times and all you get is fluid, 
> > so you move to the left front and you bleed all the air you can out of 
> > it.  Now when you open any bleeder you get nothing but fluid, but the 
> > pedal still feels like there is air in the system, BECAUSE THERE IS 
> > and no matter how much you bleed one wheel at a time it will never be 
> > bleed out.
> >
> > The air in my description is trapped in the front brake circuit bore 
> > of the master cylinder (usually the back towards the firewall).  When 
> > you bleed the back brakes, the piston went full travel in its bore 
> > because you were compressing air in the front brake circuit and air 
> > compresses and the front brake circuit did not stop the master 
> > cylinder travel while you were expelling the air in the rear circuits. 
> >  When you switched to the fronts after the backs were properly bleed, 
> > the hydraulics pressure of the back brakes stopped the piston 
> > movements in both font and rear circuits before they bottomed out.  
> > Consequently some air is still in the front circuit bore of the master 
> > cylinder.  Since you will never be able to bottom the piston in the 
> > cylinder of the front circuit bore, you will never get all the air out 
> > resulting in a spongy pedal.
> >
> > When you bench bleed, you filling both the front and rear circuits 
> > with brake fluid and getting all the air out both circuits, this way 
> > when you have bleed you have no air trapped in the master you can't 
> > get out.  Remember the proper way to bleed a master cylinder is to put 
> > it in a vice and bend tubes from the outlets until they are in the 
> > reservoirs under the fluid level.  This way when the air is expelled 
> > it rises out of the fluid.  When the cylinder starts its return stroke 
> > and sucks back its sucking back nothing but fluid.  On a bench you can 
> > get all the air out of the master really quickly.
> >
> > One way to bleed a dry cylinder on a car is after both reservoirs are 
> > filled, have your assistant pump the brakes and hold them.  Open the 
> > bleeder on both the right rear and right front before they let off the 
> > pedal and then go back and close both bleeder before they let up on 
> > the pedal.   Now both pistons have gone full travel in there 
> > cylinders.  Do this three or four times and you have all the air out 
> > of the master cylinder and then you can bleed normally.
> >
> > Some day I'll make a few drawings and submit this as a tech tip to the 
> > Comminque.
> >
> > Dennis
> > _______________________________________________
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