I have a small hydraulic leak somewhere. A leak does not show on the tires (rig sits more than I wish it did) so it does not appear to be a wheel cylinder. I knew of the leak and had kept it topped up; well thought I had. Recent though I was not aware it had leaked down to an empty resevoir.
I moved the Mog from my yard to its new covered Mog Port. By the time I got there I must have been sucking air thru the system cause I had no brakes and the air assist mechanism was hissing at idle. I discovered an empty resevoir once I poped the hood.
This weekend I tackled the job of bleeding things out with a cheap "Mighty Vac". Plan was to get the Mog ready for a camping trip next weekend. It was a dismal failure. Only one wheel (drivers rear) has no air in it. The air assist mechanism seems to have no air in its hydraulic side either. Everything else the "Mighty Vac" pulls vacuum on just sucks air and a little brake fluid. I did have to refill the Mog Brake resevoir about two and a half times total
Bleed procdedure used:
.Air assist mechanism first; rear most nipple blead first, then front bleed, (Good fluid)
.Followed by passenger rear brake (mostly air)
.Driver rear brake, (good fluid)
.driver front brake, (mostly air)
.passenger front brake (mostly air)
Repeated several times.
Brake pedal is to the metal still.
Any suggestions?
Can you bleed the Master cylinder? Honestly I didnt look at it to see if you could.
RE: Pedal to the Metal, buttt.. its the brake pedal
I have no clue as to the specifics of the 404's braking system, but to bleed a master cylinder in the vehicle, you can just crack open the line's flared fitting like bleeders while someone is pressing on the pedal.
However it sounds as though the leak that is allowing your fluid out also lets in plenty of air. I don't know how the master and pressure booster are arranged in your system, but for a leak that is not externally evident, I would suspect something like a worn piston cup that leaks out the rear of the master cylinder(or air assist mechanism) and into the booster. The cups are not designed to hold much vacuum but to seal better under pressure. A small fluid seep could allow alot of air to be pulled in.
Hard to make an accurate guess as I don't really understand how the assist mechanism is plumbed.
RE: Pedal to the Metal, buttt.. its the brake pedal
UPDATE:
Well, I dont know why but using the standard one man brake bleeding method* seemed to work just fine. Yet, the vacuum method of sucking some fluid thru the system with a might vac was worthless. I know the Mighty Vac was working properly**. Anyone have an idea of why the Mighty Vac type brake bleeder would not work?
*= hose into a glass of brake fluid, open bleed nipple and pump brake a few times)
**= air would not get pulled in, and the vacuum gauge held steady if I sucked on a closed nipple. (proves hose and pump was air tight)
RE: Pedal to the Metal, buttt.. its the brake pedal
Here is a responce from another source
Quote:
Bleed the master cylinder first. The bleeder is on top of the cylinder. Bleed all THREE bleeders on the auxilary master cylinder next (BTW, is that where the leak is?), then right rear wheel, left rear, right front, and left front.
I can probably dig up the part number for a rebuild kit for that aux
cylinder if you need it. Michael Smith managed to find one for me.
Ron DePugh
RE: Pedal to the Metal, buttt.. its the brake pedal
If the threads of the bleeder were of a loose enough tolerance it may have been easier for the vac to pull air through the bleeder threads instead of pull fluid throught the entire system. You could try packing grease around the bleeder screw if using that tool again.
RE: Pedal to the Metal, buttt.. its the brake pedal
The hand held vac tools love to suck air around the bleed nipple. There is a chance you could have torn your cup on your master cyl, or even the booster. Is it leaking anywhere around the master cyl or the air assist ? Rebuild kits are available for the system you have on your truck.
RE: Pedal to the Metal, buttt.. its the brake pedal
On a mog, with new lines and hoses, you can gravity bleed the system. If I crack any bleeder, fluid streams steadily out, bubbles and all. As to air around the bleeder, wrap a small bit of teflon tape around the threads. If you have obstructed lines, or collapsed hoses, the vac pump will pull air from around the wheel cylinder cups. Pressure seals them, a strong vacuum will pull right past them if there's a problem in some other line. HTH, Seth
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