Help: ID brake line placement

[Big Z]

Got my new brakeless truck home a couple weeks back. I've known about this problem since I got it: there's a brake line hanging off the top of the T fitting to the right of the master cylinder. The t-fitting is in the frame crossmember. Does this line serve any purpose, cause the only place I can figure it goes is into a plug on the side of the master cylinder. The TM pics are a shade blurry on where this goes, it looks like the top of the MC but I only see the plug fittings on the side. I included a pic of the cap on my MC because I understand that there is more than one type, and I kept reading about a vent line on the cap.

 

[doghead]

That line was the original vent line. Originally it was tee'd into the vent line you see there, from the Airpack or fuel tank(I don't recall at this time which).

At some point, the Military had a MWO to separate the 2 vent lines(cross-contamination was possible) They were supposed to add a new vent line up near the airfilter housing.

The vent cap in your MC fill plug causes a problem. You need to remove it and vent the MC properly.

 

[Heavysteven]

I saw that on a friends deuce.

On my master cylinder and air pack meet at that tee then run around the frame pickup the tank and finally end at the slobber tube.

DH What issue can be caused by using a spring vent? Just curious.

 

[doghead]

As the shoes wear, the fluid level gets lower. The vents(that particular style vent) only let air out, not in. This creates a vacuum in the master cylinder. The master cylinder needs to be vented to function correctly. Several people have reported brake issues, only to find they have that exact vent, has been incorrectly installed by the military.

 

[Big Z]

So, I traced the other lines in the T-fitting in the picture. Indeed, the passenger side line of the t-fitting goes up by the air filter, and the driver's side line is the air/hydraulic cylinder breather line.

I remain unsure of what to do with the line that's hanging off the top of the tee. I've been looking through TMs, and either I'm missing something in the 250 pages written on brakes, or they just don't have what I'm looking for. All I see written is whenever work on the master cylinder is done, you start by unscrewing the "hydraulic line" from the elbow on the cap. I must have the old style cap, so I'm assuming I would ignore this. Sooo, if I got the threaded elbow for the MC cap, would the line that's hanging there go into it and voila? Or... does that line need to be removed and plugged and the MC venting done some other way?

 

[doghead]

You can just get the correct fitting and put the old line back on the master cyl cap.

 

[Heavysteven]

Go to the hardware store and get a threaded 90. Attached the vent line back to the mc cap. Thread is 3/8" I believe.

Put the spring vent in your tool box.

 

[Heavysteven]

Or if you feel like upgrading cap the tee, remove the line, and install a remote brake resievor.

 

[DieselBob]

I second the advice of adding the remote reservoir. I added one to my truck and love the idea of it taking only a few seconds to verify the brake fluid level.

 

[bones1]

Or if you feel like upgrading cap the tee, remove the line, and install a remote brake resievor.

I did exactly this to my truck. Much better being able to see the fluid level before driving it.

 

[Jake0147]

So, I traced the other lines in the T-fitting in the picture. Indeed, the passenger side line of the t-fitting goes up by the air filter, and the driver's side line is the air/hydraulic cylinder breather line.

That's the vent for sure. I can recall a senior member of this site (rest his soul) referring too that chunk of plumbing as a "common vent", and while not correct, it was very clear to all members what he was referring to.

I remain unsure of what to do with the line that's hanging off the top of the tee.

Attach it correctly (I'll get there), or plug it with a standard (non-"T" union, a plug at the union, or a cap on the line. All can come from the hardware store, there is no pressure to require any consideration here.

I've been looking through TMs, and either I'm missing something in the 250 pages written on brakes, or they just don't have what I'm looking for.

You're missing it. You can (and should) read, read, and read again. The way the information is presented is at such a "step by step" level, that the big picture of the overall assemblies and systems is easy to loose. Your question is more of a "big picture" issue than a pinpoint repair. (Although the "fix" is most definitely a pinpoint fix). Trouble is, the manual can't tell you what to do when somebody's modified the system, so you have to know ALL of that system in order to spot something out of place like you have.

All I see written is whenever work on the master cylinder is done, you start by unscrewing the "hydraulic line" from the elbow on the cap.

It's called that more than once. "hydraulic line" is a poor choice, although in another perspective it is proper. The tubing is multipurpose and often used for fluids, and the fittings primarily used on hydraulic applications, so the assembly (tube and fittings) is called "hydraulic", even though it's use here is not hydraulic.

I must have the old style cap, so I'm assuming I would ignore this.

No. The little plug on your cap is a unit level retrofit. It's been done very often, but it comes at a cost. Searching this site will find discussion of that, but here's the short version. The cap (if working) will allow the pressure inside the brake hydraulic system to drop below atmosphere. The cup seals only seal in one direction. What ends up happening is with sudden temperature shifts it can actually draw miniscule amounts of air into any or all wheel cylinders and the master cylinder fluid area, which builds up over time to give a mushy pedal. You really should have a vent plumbed in correctly. Unscrew that little mushroom cap assembly from your master cylinder cap, and screw in a pipe thread to brake line adapter. Check the threads (or bring it with you), the post above suggested 3/8 pipe thread, and while I surely can't argue I am pretty confident that 1/8 pipe thread and 3/16 tubing is how mine is equipped...

Sooo, if I got the threaded elbow for the MC cap, would the line that's hanging there go into it and voila? Or... does that line need to be removed and plugged and the MC venting done some other way?

Exactly. That line goes directly to the elbow in the master cylinder cap. It should be verified as being able to breathe in case bugs made their nest there, but yeah, it's just as easy as a pipe to brake line adapter, and you're done.

Or, go with the remote reservoir. I've given my thoughts on those in a couple of the more recent posts on the subject. Very worthwhile in my estimation if you're confident in your ability to do so. Just convert that cap to a nipple or tube fitting, run your hose or tube to a reservoir, and that's that. Make sure it's higher, and gravity will take care of the rest. Air and or bleeding does not apply to that part of the system, your master cylinder might bleed it's self by gravity, but if not, it's supposed to have an air space in it anyhow.

 

[frank8003]

slobber vent hydraulic line brakes fuel axels

Just got a M35A2 to home. Goto bleed the brakes to find the Master Cylinder with a sealed fitting on top and another tube nearby not attached to anything.
Meaning the original 90° fitting is there but it is plugged and the line dangling is 1/8" female NPT.

I read hundreds of pages about brakes in the TM's and don't find the awnswer. I find the answer in SS. within an hour!

It is duh slobber tube connection!

Recently a new Master C was installed and the brakes bleed. The vent was not reattached and the sealed 1/8" fitting was left in place. I'll fix that.

Maybe thats what killed the Master Cylinder that had to be replaced.

Now I know that the lines from the axles, the fuel tank, the airpack, and the MC all the way to the slobber tube must be blown out.

Thank you all.