master cylinder without vent line?

[gene]

As is the case these days I was reading my TM's before bedtime and I noticed that under the brake bleeding section there is a diagram that shows the master cylinder filler plug with a vent line leading into it. Funny, when I was cleaning off the top of my deuces master cylinder yest in prep for the upcoming work I noticed that my filler plug does not have a vent line, only a brass plug.

The gent who sold me the truck also gave me a new brake boost since the truck requires more peddle pressure over time in order to actuate the brakes. "After several hours of driving up on the logging roads the peddle is damn near impossible to budge." He indicated that he had asked about what would cause a stiffening brake peddle and he was told he needed a new brake boost. Now that I find a master cylinder without a vent I am wondering if this could be the prob. Before I dive into replacing the brake boost I figured I'd ask those who really know about such things.

As always, any help or advice is much appreciated.

Gene

 

[WillWagner]

I'll give this a shot. The original design had the MC and, I think the tank vent, going into the road draft tube...I think it was for fording?? That is how my truck still is. There was a modification to remove the vent from the M/C due to fumes from the fuel tank...again, if I remember right...That's why you have a plug in the top. If i'm suffering from CRS, I'm sure someone else will have the right answer.

 

[acetomatoco]

A, the MC needs to be vented.. B, your vent line is probably bent up out of the way by some poor mechanic... C. take out the brass plug and put in a differential vent, it will serve the same purpose.. without the vent, air cannot get in to replace the fluid that is moved into the cylinders when you apply the brakes, and vice versa when you release them. as you drive the fluid heats and expands and the air compresses in the cylinder with no place to go....D, use a civvy cap with a built in vent...and finally if you push your pedal to the metal and it doesn't work you will have to peddle the wreck to the local junkie...and pedal a bicycle home.. (your problem with hard pedal is probably related to the fact that you have no vent in the MC.)

 

[hndrsonj]

Remove the vent line. Install a vent from a rear axle, and install a remote brake resevoir. You will be alot happier and they are simple to check/fill.

 

[ken]

Mine was vented untill i drove it through deep water "just over the hood" during a tropical storm. After flushing the brake system i plugged it off. And it's been that way since 2001. I wouldn't think it will hurt anything.

 

[sermis]

Mine is plugged off too. I am going to add a remote resevoir up in the cab behind the seat to just make it eaiser to see and fill. I had pedal issues when I bought the truck. it had been sitting for some time. Pulled the master off and there was a lot of dirt and junk in the bottom that was stopping the plunger from moving and releasing the brakes. there was still assembly greese inside. Reassembled and all has been fine.

 

[acetomatoco]

they need to be vented to allow the moisture to escape when heated as vapor...honest!!!! and pedal still is spelled pedal... to peddle is to sell....

 

[gene]

thanks for the advise all. add one remote resevoir with a vent on the list!

gene

 

[Recovry4x4]

I'm not conviced that I would use the differential vent. They are designed to let pressure out. You also need to compenate for dropping fluid level as you apply the brakes and they wear. The diff vent won't let makeup air in.Just my

 

[hndrsonj]

When you remove the vent line to install the remote resevoir, it leaves an opening where the line was. The system is still vented; the axle vent just keeps out water/dirt. The remote resevoir cap is also vented it is really a slick system, check/fill only takes seconds.

 

[FormerNewMVGuy]

Just looked at mine and it has an axle vent on it and my brakes work fine.

 

[bugei]

so my m35 master cylinder has a vent, and is blowing fluid out to a vent in my engine compartment (center of fire wall, pretty high up). enough to empty the m/c pretty quick, and make a big freakn mess. i was told to block it off, but i would like to find the problem. is it the hydrovac needs rebuilding? any other thoughts?

 

[11ACR-LT]

Ace is right, the m/c has to be vented, my M37 has a needle valve in the vent line which was closed, ( I never checked it) brakes worked fine on short runs thru town, the first time I took it out on a15 mile run on with a few more brake applications than it was used to, the pedal got very hard, and the pressure in the cylinder was appling the brakes on it's own.

 

[ken]

I got in the hannit of checking brake fluid each time i drive it. I had the brakes fail before and i check it to keep me from wondering each time i hit the pedal. So i guess the air has a chance to get in or out when i pull the cap.

 

[gene]

Ken, checking my brake fluid with each pre-drive check list now as well. Have a vented cap on the way and eventually will mount a remote reservoir behind the drivers seat. also gonna build a pressure bleeder, redo wheel cylinders and replace airpack and brake shoes as needed. the wife always knows where to find me!

 

[maxim]

Any pictures of a remote vent/reservior? Are there transparent type remote reseviors which makes a quick check to the fluid level possible with out having to take off the floor plate get, 3 wrenches out and then make sure no debris gets into the thing while you are checking it? You have to admit they are a pain to get a wrench on the vent. Seems to me the remote reservior could be plumbed right through the vent hole. This would leave the master full at all times but free to expand and contract into the remote.

 

[hndrsonj]

Remote resevoir is clear and is plumbed thru the vent line. Mine is mounted in engine compartment and just have to drop side cover to check. I will try to post a pic on sunday when we get camera set up. (maccus has the photo I sent, if he see's this)

 

[Recovry4x4]

Do a search of Roscommon Equipment Center. They have an article with pics on this very mod.

 

[houdel]

Link to the Roscommon remote reservoir:
http://www.roscommonequipmentcenter.com/news_notes/nn17.pdf

Link to Kenny's home made pressure bleeder:
http://www.steelsoldiers.com/index.php?name=PNphpBB2&file=viewtopic&t=3439

 

[oifvet]

I looked at the set-up, and called Wilwood Engineering pretty much immediately. They have a kit already assembled, but has two fittings that do not apply, and only 30" of hose. It is part number 260-8742, and the price is $64.74.
I ordered everything minus the the two fittings and got 6' of hose instead of the suggested 4'. The total price, $60.40. I suggested that they assemble the parts into a kit for M35A2s. It would be easier than having to take down all the part numbers every time someone calls about a deuce kit.

************************************************************************

I finished the install. Here are the pics. Easy project! I found the best location for me was on the left (driver's) side, just behind the engine service panel. (see pics)