Reproduction 1966 Disc Master Cylinder

Assuming you've covered all the other problem areas I don't think you have anything to lose by bench bleeding the M/C.

 

if after bench bleeding you still have the ptoblem it pretty much is likely to be the m/c having an internal leak. In that case the vendor should replace it.

Z. Ray

 

Just a warning, you may have a problem if you bench bleed the
M/C and tell the supplier. He may not warrant you a replacement
if you didn't follow the instructions.
Texas Swede

 

I agree with Swede about not saying anything about the bench bleeding. But, I'd love to have him argue with my old shop teacher, right up to the point where the teacher got all red faced and clintched up......

 

Yep, bench bleed but don't tell.....

 

Well, I have replaced many master cylinders, both single and dual
brake systems 65, 66 and 67's and never bench bleed any of them
and always got perfect brakes with no spongy pedal.
Texas Swede

 

Yes, I just have somebody handling the brake pedal
and I started with right rear wheel, then left rear wheel
right front and left front. With the 67 I had to resettle
the warning light by opening one of the bleeders and
my helper pressing the brake pedal until the light went out
and then I tightened the bleeder.
Texas Swede

 

Same here as Tx Swede. I have replaced many master cylinders in many types of cars and have never bench bled a master and never needed to. Same procedure as Tx Swede.

 

I have reconditioned my original 66 disc brake master cylinder several times over the last 35 years, and I've never bench bled it. Never had a problem. I don't see how bench bleeding would be any more harmful than bleeding it in the car, though.

 

I agree with your logic, I just replaced my master cylinder with a dual unit, it also said to bench bleed but not to push in more than 3/4" for some reason. I already had the unit installed when I read about the bench bleed. I called the distributor and asked if that was a problem, they said no just more air in the system that needs to be bleed out.

I bled my brakes by myself using 1/4" ID tubing, a drinking bottle with about 1/2" of brake fluid in it. I put the tubing on the bleeder screw and the other end in the bottle making sure the end of the hose was in the brake fluid. I started with the right rear, then left rear, right front and finally left front. The brake pedal is firm and the brakes work great.

 

I accept replaced abounding adept cylinders, both individual and bi fold anchor systems 65, 66 and 67's and never bank drain any of them and consistently got absolute brakes with no absorptive pedal.

 

"Bench" bleeding is not necessary, although it is useful if you are working alone. Clutch masters bleed well by just cracking the bleeder on the slave and letting gravity do the work. If there is air in the master after bleeding it, you can just loosen the nut on the line on the master and squirt some brake fluid into a shop rag, then tighten it before sucking air back into the master. This is a two person job.

Take the advice of others, don't let the supplier know that you bench bleed it.