Bench Bleeding (1 Viewer)

[cb97angler]

So I am bench bleeding the master cylinder on my 74fj40, just bought a brand new aisin. I have the fittings on, clear tubes running into a container with fluid covering the ends instead of back into the resevoirs, I get endless bubbles so there's a problem, but also, should the fluid be flowing out while it is just sitting and I'm not pushin on the rod should it remain level not flowing out at all. Sorry of this is a dumb question, I have been fighting with this thing for hours.

 

[pbgbottle]

i think it needs to go back into the resevoir when bench bleeding .but i could be wrong
here is some info i posted awhile ago on bench bleeding in a wrong thread . the poster was asking info on the clutch master . not brake master.
but anyways . the link posts to info on bench bleeding.

https://forum.ih8mud.com/40-55-series-tech/156411-bench-bleed-clutch-master-cylinder.html

 

[Rockets2000]

If your containers are lower than the MC, fluid will flow into them. The brake system is closed-loop, meaning there is no place for fluid to go and no place for air to get in. You need to loop your plastic return tubes back into the reservoir and keep them filled with fluid so gravity cannot suck it out of the system. Then keep pushing slowly until the bubbles are gone. The tricky part is when you remove the tubes and hook up your lines.

 

[Huroneymoose]

Be sure your plastic lines are tight to whatever fittings they are attached to. It is possible they might suck a little air after each stroke if they are not tight or sealed. I don't know how probable it is but one more glich you can prevent. When I bench bled a new MC for my truck, I bought fittings and made two short hardlines that looped up and dumped the fluid back into the reservoir with the ends beneath the fluid level.

 

[Jacket]

I can't recall ever having it "perfect" after bench bleeding. But like others have said, ensure your fittings are tight and your looping back into the reservoir. Try tapping on the MC with a screwdriver in a few places as well to help dislodge any air pockets or bubbles in the chamber. Once you get good flow with minimal bubbling, go head and move it over to the truck and finish the job. You'll still have more air to push out once installed, so don't kill yourself with the bench bleed.

 

[82HJ47]

This is the method I followed:

At this point, it is time to prepare the new replacement master cylinder for installation. First, the master cylinder must be "bench bled." This process bleeds the air out of the brake master cylinder [BMC] before it is installed. The master cylinder is clamped into a bench vise and the reservoir is filled with clean brake fluid. Bench bleeding kits that consist of hoses and threaded fittings can be purchased at most auto parts stores. Run the hoses back into the master cylinder's reservoir. Activate the cylinder's piston by pushing it all the way forward with a large phillips head screwdriver. Watch the fluid as it cycles back into the reservoir. Keep pumping the fluid through until the large bubbles no longer appear in the fluid - it is now primed for re-fitting.

Once all of the air is bled from the master, it is time to install it. Slip the master onto the studs of the booster and install the retaining nuts and any additional items that were fastened to it. Tighten the 4 nuts, then go to the steel fluid lines and connect them.

Once installed, the master will need one more bleeding procedure. With the aid of an assistant in the truck, push the pedal slowly all the way to the floor while opening the bleed nipple at all 4 wheels in turn starting at the furthest point working to the closest point. Any excess air will be bled out at this time. Be sure to tighten the bleed nipple before the assistant releases the brake pedal. Top up the brake fluid in the reservoir to the "FULL" line and that's it! Be sure to test the feel of the brake pedal prior to a test drive. If the pedal still feels soft, additional bleeding at the master cylinder or wheels may be needed.

See 1st pic taken off the net to illustrate method.

NOTE: The use of clear plastic hose is better for visibility so that you can make sure that all the air bubbles are removed – see 2nd pic

These are the pipes I made up to bench bleed my BMC.

 

[Rockets2000]

This is the method I followed:



See 1st pic taken off the net to illustrate method.

NOTE: The use of clear plastic hose is better for visibility so that you can make sure that all the air bubbles are removed – see 2nd pic

These are the pipes I made up to bench bleed my BMC.

That's it!

 

[Pin_Head]

Bench bleeding is over rated. The MC needs to be bled, but the bubbles come out any way when you are bleeding it installed on the booster. This is based on experience with hundreds of master cylinders.

 

[desertpat]

In my opinion, bench bleeding is totally unnecessary on a '40 brake master.
The '40 brake master has the discharge ports orientated on top where air bubbles would naturally sit.
The master cylinder is just a hydraulic pump and as with all pumps, they need to be "primed".
When you stroke the pump the air will exit the cylinder - nevermind if its in a bench vise or installed in the vehicle.
I suggest that you will bleed all air from the system if you just install the master cylinder in the vehicle and proceed to "bleed the brake system".
You will see / hear the air bubbles exit the wheel cylinder nipple.
Bleeding the entire brake system should to be done in any case, to purge all air from the system...