Hot mess, a 1967 CJ-5 restoration

[davide]

I did not bench bleed the master before installing it, I did that after mounting it to the frame. After hooking up the single steel line and filling the reservoir with fluid, I then cracked the steel line while applying pressure on the pedal. This should have done the same as a bench bleed.

Last night I bled the wheels again and am still seeing the fountain pop-up. I understand that I should see fluid movement, but that only happens when soft, subtle pressure is applied to the pedal. I can redo the master bleed again as described above as I did not do this after changing out the stop light switch.

KW parts insists I am over filling the reservoir, but is sending me another.

[bmorgil]

There should not be a "fountain" or stream of fluid squirting out of the reservoir when pressure is on the pedal on any master cylinder.

When you "Bench Bleed" the master, you should run a line from the port directly up and back into the reservoir. As you stroke the piston, the fluid will be sucked back and forth thoroughly saturating the valves and purging all the air from them. This process is important. If you don't bench bleed there is a good chance you will pump a great deal of air into the system because the valves are not properly primed. You must be sure all the air is cleared from the piston before you hook it up.

https://www.onallcylinders.com/2018/...ster-cylinder/

Do you have a single or dual master cylinder?

[davide]

Hi Bob. It is a single cylinder master, which bolts to the frame under the driver-side feet. When discussing how I bled the system to KW, they said that no bench bleed was required on this particular master and normal bleeding of the wheel cylinders would also bleed the master. He even discouraged me from bleeding the master via the single exit compression line.

There has to be something else going on as the new brake light switch is inop. The brake pedal does feel spongy after my last bleed and I'll go back and do it again to see if anything changes.

In the meantime, I got my high-tack adhesive in the mail today and will get the t-case finished. With any luck, I'll also get the engine supported and ready to remove the tranny.

[bmorgil]

Davide, you always bench bleed a master cylinder regardless of how many ports it has. Cracking a line does not do the same thing. You need the cycling of fluid back and forth, and a full stroke of the piston to clear the valving and end of the piston bore from air. The pedal does not stroke the master cylinder far enough. You may never get all the air out any other way. It sounds like Mike may have misunderstood. I am not sure which Mike you spoke to but, I will try to give them a call and clarify.

I don't know how to make this any clearer, if the fluid is squirting out of the master cylinder when there is pressure on the pedal the master cylinder is leaking internally. It is allowing pressure through the valving to return to the reservoir. This can't happen or there will be little to no brake pressure. This may not allow enough pressure to activate the the brake light switch and/or, there could be air trapped at the brake light switch.

[LarrBeard]

Well, you learn something every day if you look and listen. I'd not heard of bench bleeding a master cylinder before. Thanks Doc Dana.

[gmwillys]

I agree with Bmorgil on the bench bleeding. It is a necessary step that should always be performed before the installation of the master cylinder. As a clarification of the fountain of fluid, are you seeing it when the pedal is pressed or when you release the brakes? As Bmorgil said, the fountain is definitely a bad cylinder due to internal piston leakage if it happens when depressing the pedal.

[davide]

Master cylinder update...
The bench bleed is complete as well as all the wheel cylinders again. The fountain is even grander now. Imagine standing in front of the Bellagio in Vegas.
bellagio.jpg

[bmorgil]

Davide, when you were bench bleeding did it settle down and stop squirting? You bench bleed until the fountain goes away. When you were done bench bleeding there should have been no fountains when done, just like the video. You need to take some photos of this. We must not be communicating something. As you are pushing on the pedal you have a fountain? There should be a corresponding drop in the pedal. As the fountain squirts, the pedal should drop. If the pedal is slowly dropping as the pedal is depressed and a fountain is appearing, you still have a leak in the valve. If the pedal is slowly dropping there will be less brake pressure. Whenever you apply pressure to a master cylinder piston and the air is out of a sealed system, if the pedal slowly drops the master cylinder is leaking internally.

Make sure you aren't mistaking air for fluid. Notice in the video while he is bleeding the master, it looks like a fountain till the air is gone. Use the plugged port method he demonstrates. Plug the port and apply pressure until there are no bubbles. If it squirts a fountain when you are pushing on the piston with the air out and the piston slowly sinks in, the piston is leaking. If this is the new Master, it could be two bad ones in a row. To test a Master Cylinder you apply pressure with the port blocked. The piston should not move once the air is out if the port is blocked.

[davide]

Hi Bob. I used the return tube method to bleed and the fluid did settle down when pushing the rod in after a couple times. I continued to give a few more pushes. At this point there was no air in the master and I was not getting the fountain effect. I reconnected the brake line and bled all wheel cylinders in order of longest fluid run to shortest (RR, LR, RF, LF). A few bubbles were pushed out and the fluid was clean from all wheel cylinders.

My master never ran out of fluid during the process and is topped to 5/8" from the bottom of the cap threads. This is still the original master from KW and I expect to see the replacement this week. Labor Day may add a few extra shipping days too.

The Website does not appear to accept video clips, but I was able to get a screenshot from a video. Note that the fountain has shot over the visible area and is at least an inch higher. Very little pressure was applied from my hand to create this stream and it is without a doubt all fluid. Foot pressure would have been much worse.
IMG_2639.jpg

[gmwillys]

I would stop at this point and await the arrival of your replacement master cylinder. You are currently seeing a tear in the piston or an imperfection in the casting on the master cylinder bore, allowing pressurized fluid to come out the inlet of the reservoir.