Master Cylinder Vent

[cten]

I had a long talk with LH7 on Saturday and found how important it is to make sure the MC is full.


Can anyone tell me by looking at these pictures which is the vent and which is the filler hole?



I'm just not seeing a vent hose here.



Thanks everyone.

 

[Recovry4x4]

How interesting! I see that someone in the past has done away with the 3/16 metal line and installed what apears to be a vent from a differential housing. As far as getting in there, use a 3/4" wrench on the square head and that will remove the filler cap. Wipe the area down good before this and blow it off. Rummage around in there and see if you see a small metal line floating around the area. That vent will probably work just fine as long as you don't try any fording. It certainly makes access easier. LH7 is so right. The single most responsible thing the deuce owner can do is to pretrip inspect that brake fluid. I'm not a methodical as I should be. Little late but lets make a New Years Resolution to check the brake fluid in pretrips. Think I'll buy a cheap 3/4" wrench and attach it in the area

 

[cranetruck]

Here are a couple of scans from a 1983 PS magazine that show you how to separate the vents from the fuel tank and MC/Air Hydraulic cylinder.

http://imageevent.com/cranetruck/psmagazineimages

If you can't read the copy, let me know and I'll do it over here.

 

[cten]

There was about 1" of fluid in the MC and I put more in.

I plan to check it in a few more days to see if the MC needs more and give it time to see if there is an issue.

No need to bleed, right?

Regards,

 

[MVtrucker]

Be careful of that vent on the master cylinder. I got a truck in and the brake pedal was all the way down to the floor, no brakes. Figured the master was bad, but I was wrong. Unscrewed the cap to have a look inside and when I did, a vacuum was released and the pedal popped up. Brakes were fine, as was the master cylinder. The check valve type vent prevented the master from venting air in, so as the fluid level dropped some and the pedal was pushed a vacuum was created in the cylinder. I suppose an early warning would be shown by the brake pedal not fully returning as you use the brakes over time. Luckily, the vent line was still there, so I replaced the vent with an ell and reconnected the original vent line. Seems kind of odd that the brakes were not locked. I guess some fluid in the wheel cylinders did manage to return and/or the lack of air pressure allowed the brakes to drag as we rolled the truck off of the rollback.

 

[cten]

Anyone have a picture that I could see to know what I need to do to correct this?

Thanks

 

[Lee Alessi]

my brake master cyl has no vent line at all. hmmm...

 

[Longhunter7]

CTEN,

The reason many vent lines were disconnected is obvious! It is a pain in the butt to disconnect the vent line before you can remove the cap on the master cylinder!

I had to take a cheap 3/8 " open end, box end wrench, and cut off the box end! The wrench needs to be short enough to clear the cross member above the nut on the vent line, so it can be removed!

Once the vent line is removed, it's easy to check the master cylinder!

See attached picture!

 

[cten]

Met a guy who use to be a mechanic for the National Guard for 18 years full time and then worked for Greyhound for some time.

He said to leave the vent unless I was planning to show the vehicle to get it to its original specs or for fording.

I do not plan to win ribbons and I have not immediate intentions of fording for now.

I'll keep this for a future project as time goes on.

Regards,

 

[Monster Man]

ughhh.... just checked mine (I know, I kow, I need to have my deuce driving priveleges REVOKED for not checking my fluid, but it's always been good on the brakes)
and I got that dang vent line. Could they make these things any harder to check? I think I'm going to rig up something like Stefos had, a remote fill tube/level checker

 

[Nomad1]

View attachment 779431View attachment 779432so this is how my vent line is hooked up. I couldn't find any pictures of other trucks vent system. So it goes from the top of the master cyclinder back to this block where the other lines are. Is this correct can I just diconnect the vent line at master cyclinder. Then unscrew the plug and check the fuild level and not have to bleed it provided everything is up to snuff?

 

[oboyjohn]

Up here in Canada, we did away (sort of) with the vent line for the MC. We installed a remote reservoir on the engine firewall and the line fed the MC through the original vent hole in the cap. This way the MC is always full and at a glance under the hood you can tell if the oil level is good or if has dropped. So much easier to fill up too! With the remote reservoir so much higher on the truck, close to level with the hood line, just the cap needs to be vented.

 

[Nomad1]

I know they make a remote but that's not my question. The vent looks like it hooks back in to the brake system so unlike other master cylinder that just have a cap how does it not introduce air into the brake lines when you undo it to check the level. Thanks for the response though.

Up here in Canada, we did away (sort of) with the vent line for the MC. We installed a remote reservoir on the engine firewall and the line fed the MC through the original vent hole in the cap. This way the MC is always full and at a glance under the hood you can tell if the oil level is good or if has dropped. So much easier to fill up too! With the remote reservoir so much higher on the truck, close to level with the hood line, just the cap needs to be vented.

 

[frank8003]

my brake master cyl has no vent line at all. hmmm...

It will fail without a vent

 

[frank8003]

Can't do any better than this
first part of second page
View attachment master cylinder remote roscommon nn17.pdf


Not much can be done. The preview (thumbnail) is generated with a 3rd party app. It tries to take a "screenshot" so to say of the PDF. Some PDF's work fine, others simply blackscreen when it tries to do it, but they will open with a click

View attachment Tm 9-1827cBrakesWagnerLockheed1944.pdf

 

[Nomad1]

Soooooooooo..... upon further investigation that indeed does go to a vent system under the hood and not back into the brake system as it appears a first glance. Now it makes more sense to me. Well if anybody doesn't have vent line and is wondering how it's suppose to be hooked up I know

View attachment 779431View attachment 779432so this is how my vent line is hooked up. I couldn't find any pictures of other trucks vent system. So it goes from the top of the master cyclinder back to this block where the other lines are. Is this correct can I just diconnect the vent line at master cyclinder. Then unscrew the plug and check the fuild level and not have to bleed it provided everything is up to snuff?View attachment 779519View attachment 779520