Bench bleeding single circuit master cylinder?

[Norris W.]

So I bought a new/repro master cylinder from my favorite Corvette parts vendor for my '65 non power brake roadster. In the box was a large warning card: Do not bench bleed master cylinder or damage will occur.

My question: Why not? What can it possibly hurt, and I think it'll take more doing to get a decent pedal WITHOUT bench bleeding it. What am I missing?

[Tim S.]

Re: Bench bleeding single circuit master cylinder?

They must feel it's too easy to bottom out the piston and thus damage the seal. I've done it before with no issue, but perhaps I got lucky?

Tim

[Edward J.]

Re: Bench bleeding single circuit master cylinder?

Norris it really does not make any sense about not being able to not bench bleed your master cylinder, sense you have to bleed the system some how, if you don’t have a vacuum or pressure bleeder. What I would try is to fill the cylinder and see if gravity will do the work for you.if it will not starting dripping out of fitting, you may need to push plunger in a couple of times while holding your finger over fitting on the return stroke. To start the process.

[Bill M.]

Re: Bench bleeding single circuit master cylinder?

Norris I changed my 65 master last summer I bought the cylinder from a major Corvette parts supplier I bench bled it. I do not recal a warning. If you have time you can gravity bleed like Ed says. I did a dual master on my 67 that way. I left over night.

[Gary B.]

[Bill M.]

Re: Bench bleeding single circuit master cylinder?

Norris I changed my 65 master last summer I bought the cylinder from a major Corvette parts supplier I bench bled it. I do not recal a warning. If you have time you can gravity bleed like Ed says. I did a dual master on my 67 that way. I left over night.

[Leif A.]

Re: Bench bleeding single circuit master cylinder?

When manually bleeding or bench bleeding a master cylinder, you should not push the piston too far in because it can cause the primary piston to stick. When the pedal is fully depressed, the primary, and in some cases. the secondary pistons move to their furthest forward position. However, the piston can get stuck even though springs are trying to push it back into place. This can happen because the cylinder bore and seals are lubricated during assembly to create a positive seal, and air trapped in the system can cause a vacuum lock in the cylinder. When the piston is stuck in the applied position, the ports that supply fluid are blocked, preventing the cylinder from filling and operating properly.

[Norris W.]

Re: Bench bleeding single circuit master cylinder?

Thanks everybody. I think I' got it. I just took part of an old line, put clear tubing on it and stuck it in the reservoir and then had my wife mash the pedal about half way down until I couldn't see any bubbles in the tubing. When I had the ship in 80's and 90's we did dozens or probably 100+ of Corvette brakes with 4 calipers, hoses, master cyl's, etc and we never had issues, but now, since I no longer have patience or attention span seems like everything has a challenge. I usta' ALWAYS use DOT 5 and now everybody swears it swells the rubber parts. I'm a little skeptical to be honest.

[Gary B.]

Re: Bench bleeding single circuit master cylinder?

... I usta' ALWAYS use DOT 5 and now everybody swears it swells the rubber parts...

Norris,

Not necessarily. To be informed of the latest information, please read these two threads.


https://www.forums.ncrs.org/showthre...697#post949697


https://www.forums.ncrs.org/showthre...502#post946502


Gary