Master cylinder question

[Beacher425]

I have a new master cylinder and brakes have been bled (by a local auto restoration shop that installed the complete new brake system including lines and wheel cylinders). The brakes are still soft. I opened the master cylinder to check fluid and it is fine. With the top open, I depressed the brake pedal and saw a jet of brake fluid coming up presumably from the intake port causing a little fountain at the surface. Is this normal? Or does it mean my master cylinder is not functioning correctly? Looking at the diagrams of master cylinders in the manuals, it looks like the piston and primary cup should pass the intake port fairly quickly on depressing the pedal so that the pressure is transmitted down the brake lines. It looks like I can depress the pedal a fair distance and still get back flow through the intake port or at least the pybass port, causing the fountain and decompressing the pressure that should be transmitted down the brake lines.

Is this line of thought correct?

Thanks

[53a1]

When I rebuilt mine I bench bled it then I plugged the outlet holes, apply pressure and checked to see if fluid was slipping past the cup. This gives you a pretty good indication that the master cylinder is working. You may be able to trouble shoot yours in a similar way.

I have always bench bled my MCs so I can't tell you how hard it is otherwise to remove the air but it may be a PITA. Do you have a bleeder kit for the wheel cylinders? They prevent sucking air back into the system and they are very cheap.

And remembering back to when I bench bled mine I think you will get a fountain on the return stroke.
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'53 M38A1 X2

[rwbow1969]

If you have 2 people its not so bad. Press the brake pedal very slowly and you can control the fountain from shooting up so high. I had a freind help who has done over 10 restorations. An empty can, small length of hose to slip over the nipple at each wheel and a wrench to open the valve at each wheel to pump the air out. Good Luck.
Rob
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1951 M-38
1951 M-100
M1919A4

[RimfireJim]

The little squirt, or fountain, of fluid at the beginning of the stroke is normal. It is not the cause of your soft brakes. If too much was coming out at that point, you would run out of MC stroke, but the brakes wouldn't be soft.

Soft, or spongy, brakes = air in the system. If you paid the shop for a complete, functioning brake system, take it back - they should never have considered the job done if the brakes are still soft. Or bleed them yourself, which, in my opinion, is a skill anyone who owns and drives old vehicles like these should have.
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Jim M.
1952 M38 son-father project
Discovering more worn out parts, one assembly at a time

[artificer]

The squirt has nothing to do with the air still in the system [if you have a spongy pedal.] Put the top back on while you still have some paint around the master cylinder.
If you paid to have the brakes done properly take it back.
These brakes are very easy to bleed so why they did not do it right escapes me.
_________________
John GIBBINS
ASE Master Medium/Heavy Truck & Auto Technician 2002 USA
Licensed Motor Mechanic NSW # MVIC 49593 Current
YOU CAN'T TROUBLESHOOT WHAT YOU DON'T UNDERSTAND

[BullRun]

One more thing. It may be the brand of brake fluid and the kind it is too. Maybe they put in the wrong grade?

From my own experiance it sounds like bubbles or something like a foam has formed in the system.

This is tough to fix by yourself as it requires a large quantity of fluid to flush out the system. One to push the pedal and one to watch for bubbles to stop and turn the bleed screw shut while the fluid is being pushed out if done manually.

[Oldsalt]

Is your jeep a M-38 or is it an A1? If it is an older model with the 4 point adjusters, those can be hard to get adjusted correctly. Having the shoes poorly adjusted can make getting a really hard pedal very difficult. One end of the shoe can contact the drum before the other end if they are not adjusted evenly. A mechanic who is not intimately familiar with that system will probably not get it right. The newer A1's have a modern brake adjustment system that keeps the shoes solidly on the drum.

[Beacher425]

Thanks for all the replies. I have a 1955 A1. They used DOT 3 brake fluid. When I jack up the front wheels and spin them to adjust the brakes as described in the servie manuals, the wheels spin and then grab and spin and grab. I may need to have the drums turned as well as all the other adjustments and rebleeding the system. You are right about brake bleeding being a skill I will need, so I will give it a whirl.

[DJ]

Simple way to bleed brakes alone. If you got a vented cap put a pipe fitting in the cap that the male end of your air hose will screw into,put the air hose on it with about 5 lbs pressure and open the bleeder. Keep checking mc so it doesn,'t go dry. I've done 5 vehicles this way. If the cap is solid get an extra one and put a threaded hole in it.

[wesk]

Turning the drums is not the answer to soft brake pedal. Don't turn the drums unless there is a need to do so such as extreme grooving or out of roundness. When drums have to be turned it presents a new problem. The shoes must be shimmed or thicker linings used to make up the increased inside diameter of the drum. Don't buy off on re-arching the brake shoes. If you remove .003 from the drum then add .003 shims to each shoe.

As for what and who pertains to qualifications and skills I have an opinion here. If the system's malfunction on the road can kill you or some other innocent person then the person making the repairs to that system must be qualified to do so. The three most important systems that can get you killed are the steering, the brakes and the suspension. If you don't thoroughly understand how it works, where the correct service data is and how to make the repairs then hire it out or get yourself qualified.

Tasks that are simple to one person may not be so simple to the next. I have been rebuilding, adjusting and bleeding brakes since 1960. It is simple to me but for someone who has never done it, has never read how to do it and doesn't even have the correct tools this can be daunting to say the least and suicide to negligent homicide on the highway if you screw it up. So use some common sense and try not to let ego's get in the way of safety.
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[RimfireJim]

Excellent points, Wes.
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Jim M.
1952 M38 son-father project
Discovering more worn out parts, one assembly at a time