Bleeding the Master Cyc

[Somemedic]

I read through some old threads about the master cyclinder being bled and didnt recall doing this when I first rec the deuce from Shelby. I had bled the wheel cyclinders and noticed that the brakes seemed a little firmer (when i pick the truck up - months ago) but never did the MC. So when I went to do the master cyclinder sunday it went to the floor and several tiny bubbles (Don Ho song here) began flowing from the tube. Now you can pump it all day and the bubbles keep on coming through the bleed tube. My assistant, daughter Madeline, said it felt "very loose, daddy" and wasnt getting better. She likes the truck and wants to go for a ride soon but the stopping thing is important.

Brake pedal is mushy now. Im under the impression Ive itroduced air into the MC and would like for it to be gone. Whats my next move??

 

[ida34]

Are you closing the bleeder screw while pumping?

 

[wsucougarx]

did you bleed the air pack as well?

 

[Somemedic]

Holy crap... The air pack??

Yeah I closed the bleeder screw when she was pushing down. I still got some bubbles upon opening it up though. I went through what I thought was the correct tm proceedures but I'm realizing its not the case. I saw a zerk on the air pack but not a bleed screw, cougar. Can you point a brother in the right direction?

And the order I bled the brakes would be 1) furthest wheel cycs from the mc then 2) the master cyc then 3) the air pack?

The reason I'm doing the bleed is that early in a trip the brakes are ok feeling but as the trip progresses the brakes begin to feel firmer. I figured there was some air trapped someplace and when I did the wheel cyclinder bleed and didn't know I had to do the master cyc I could finally have the pedal feel I need. Now its worse.

 

[wsucougarx]

The air pack bleeder can be seen on the passenger side of the unit at the 12:00 position just in front of the air reservoir. Looks like a zerk but that is your bleeder. It is at a 45 degree angle. The order should be MC, airpack,furthest wheel cylinder

 

[Somemedic]

im on it...

 

[Keith_J]

If you don't have a pressure bleeder, you can buy all the parts needed at Home Depot. What you need is an airline regulator (about $25), 1/8 NPT male fitting to compression tube and 1/4 NPT male to tube fittings. Set the air regulator to about 10 PSI, connect to the master cylinder cap and it will keep 10 PSI on the master cylinder. Fill the master cylinder, pressurize and then bleed. You need to refill the master every wheel, don't drain more than about 8 ounces per wheel.

This setup can be used to pressurize a suitable container, like a yard sprayer, to function as a bleeder reservoir.

 

[Speddmon]

it's real easy and inexpensive to build a pressure bleeder from a garden sprayer. The one using an air regulator like Keith_J described works well, but like he said you need to stop and fill the MC after each wheel.

With the garden sprayer that is not necessary. Fill the sprayer with about 1/2 gallon of brake fluid and pump it up some and off you go...Here is a post about the one I build for something like $20 or so...Bleeder.

All I do is pump up the sprayer and do the MC, and airpack and when I crawl from under the truck, pump it one or two more times....do the rear axles and on the way to the front, pump it one or two more times again and do the front...done in like 10 to 15 minutes.

 

[rlwm211]

Having recently gone through my brake system on my deuce I see some great ideas here in making the job of bleeding the system easier.

The small volume of the master cylinder is a drawback while manually bleeding the system and having a pressurized system can be a problem if you do not fill the resevoir as recommended in this thread.

no matter what, Bleed the master first.
Next as you look at the line from the master to the airpack, you see a bleeder pointed forward on an angle on the top of the front part of the airpack (it may look like a zerk). Check TM TM9-2320-209-20-3-2 chapter 13 for the illustrations.

After you bleed the airpack, start with the right rearmost rear, left rearmost rear, right foward rear, left forward rear, right front and then left front.

REMEMBER...REFILL THE MASTER AFTER EVERY WHEEL CYLINDER!!!!!!

If you do not do that you will waste a lot of time and silicone brake fluid.
Been there...done that!

The TM is complete in chapter 13 for manually bleeding the system.

You can get this manual from this link:

Deuce - Steel Soldiers::Military Vehicles Supersite


This is in the Deuce forum FAQ section...good luck!

 

[Somemedic]

Keith

Does the protective cap on top of the master cyclinder pull off somehow? It has to come off for me to hook up an air line to the the vent. I'd really like to not jack that cap up if I don't have to.

I went to the store to get the garden sprayer/power bleeder parts but these guys didn't have everything. I may go to autozone and pick up their 30dollar vaccuum pump that sucks the brake fluid through the bleed screw. That way I don't have to keep taking the mc cap apart.

 

[Keith_J]

The fitting on the MC cap is 1/8 NPT, pipe threads. Some have a check valve, others have an air line fitting. Either way, it is pipe threads. With the garden sprayer bleeder, get a 1/8 NPT male to 1/4" tube compression fitting. Home Depot has these in plastic bag packaging, it contains a brass insert for plastic tube. Depending on the sprayer, you might be able to fit it to the hose.

 

[cranetruck]

If you are lucky enough to find one of these and TM, you can do it the military way.
(From old site PS mag section)

 

[spicergear]

There's another way too. Take a small electric fuel pump 3-5 or 5-7psi and connect a piece of brake line into the vent fitting on the top of the MC. Connect via clear rubber tube (makes seeing the fluid easiest) to the line going into the top of the MC and the other side of the pump into an open container with a decent amount of brake fluid in it. Connect the pump to a battery...jumpers work to one truck battery...and let it go. That will pressurize the system and you can go and hit the MC, Air Pack, and wheel cylinders. I did this on the airpack style and on the Hydro-Max unit. Run some diesel or gasoline through the pump then when you're done and it won't get hurt at all. Yeah, disconnect it from the vent line first-

 

[rlwm211]

The master cylinder cap is threaded into the master cylinder. It takes a 3/4" wrench and use the shortest open end wrench you have as there is not much room to swing it with the pedal assemblies and such in the way. When I am only checking my brake fluid, I simply loosen the breather and it acts as a "keeper" as the breather pipe will spin in the fitting as you loosen the master cylinder cap and then the pipe will hold it as you check the fluid. Be careful to not "bend" the breather pipe as it will hold the cover exactly where it needs to be when you put it back on. If it gets out of place, it can tilt the cap, so you have to carefully "refit" the breather pipe by gently bending the breather pipe it until the master cap fits in square to the threads. The bleeding of the brakes is well explained by others here in this post so I will not elaborate any further on that.
Good luck

 

[Somemedic]

So after weeks of rain... I finally got to really delve into the bleeding preocess and I will tell you my findings.

Im realizing no 2 deuce break systems are the same.

My friend Mike (has several trucks and jeeps) assisted me and said theres no way for me to bleed the MC, theres no bleeder screw on it. Only thing that I can bleed is the air pack, which has only 1 bleeder screw. I was told theres sometimes 3 bleeders or maybe its an 5 ton air pack.

My MC cap has a one way valve on top of it and is not connected to an airline like some systems. I see where the cap used to connect to a hard steel line (maybe a vent that ties into some other vents?) and always wondered what the line went to.

I had a loose bleeder screw in the air pack which complicated things. If you tried to bleed the pack with the hand vacuum pump it would draw air from around the threads. Fixed that with some thread tape.

I was going to lubricate the air pack but wasnt able to locate the plug supposed to be found on the rear of the pack, only a large mounting bolt. Theres a plug on the front where I replaced the brake light switch with the up graded brake light switch kit. However, when i did remove the plug there was some brake fluid that leaked out. I was under the impression there was supposed to be air inside there, not brake fluid.

Brakes are now more consistent but Im not sure theyre 100%.

 

[rlwm211]

Sounds like you found the problem. I may have neglected to explain that beelding the MC is usually done on the bench before returning the MC to the vehicle. You simply make sure the bore is full of Brake fluid. It can be done on a vehicle by cracking the lines on the MC while pushing the brake pedal down and then close them before letting the pedal up. If the system is full of air, and the piston in the MC cannot get filled with fluid, it cannot displace the air. SOrry for the misunderstanding.

 

[Garandfan]

I think I have the master cylinder bleeding to a science. Even if the lines are bled the pedal can get mushy. Pressure bleeding through the master doesnt take care of air in the master. I have used my method on 3 different dueces. 2 with brakes bled and 1 with a bone dry master cylinder.
1. Make sure the air tanks are empty
2. Unscrew cap, if there is a copper line from the let off on the top, just unscrew (3/ it and pull it off so you can unscrew the master cylinder cap. Use a small crescent wrench on the master cap.
3. Start pumping the pedal all the way up and all the way down. It will start to build pressure.
4. Every 10 or so full cycles, press the pedal from the top to about an inch from the top. You will see air bubbles coming in the reservoir. Do this a couple more times until the bubbles are gone. Then go back to pumping at full cycles.

 

[Garandfan]

The brake pedal will get harder, higher off the floor. The master does not get bled with a pressure bleeder. It doesn't evacuate the air in the master cylinder itself. It basically stays trapped. The only way to bleed is manually with cap open and pumping until the air bubbles stop. should take about a half hour for a bone dry reservoir and about 10 mins normally to ensure no air any other time. I guarantee it works.

 

[Somemedic]

http://www.steelsoldiers.com/deuce/41560-soft-brake-pedal-when-not-running.html

If the first post is true it would appear I still have problems.

Ive followed the TM, Im not seeing fluid leaking from any wheel cycs and although Im not truely in my right mind (I mean look at the trucks I drive) the pedal still doesnt feel right.

WHERES THE AIR AT, DAMMIT!! Sorry, I was "venting"

 

[BugEyeBear]

...My MC cap has a one way valve on top of it and is not connected to an airline like some systems. I see where the cap used to connect to a hard steel line (maybe a vent that ties into some other vents?) and always wondered what the line went to.....

When I look thru the access panel in the driver's floor at the brake master cylinder I also see a disconnected hard steel line with a threaded fitting just to the passenger's side of the MC that connects to NUTHING.

Is this supposed to be some sort of vent line for the MC?

If so, where does it run? What else does it connect to (if anything)?

Mine is just sitting there unconnected to anything near the MC. Should this be capped?

-Bear-