Master Brake Cylinder Upper Fitting?

[ammoman]

Hello!

After months of researching and reading thousands of posts on this forum, I finally purchased my first M35A2! Its a 1966 AMG that was rebuilt in 1992 and has only 400 hours on the engine.

As I've been going through everything, I saw something very peculiar that I'm pretty sure isn't right - I'm going to install a remote brake reservoir to monitor the brake fluid better, and when looking at it I discovered there is a fitting on the passenger side of the master brake cylinder towards the top that was completely unscrewed! I followed the tube down and it met up with a T-junction for what I believe are the front brakes. But I'm really confused because I drove it all the way home and didn't have any issues. (300+ miles over multiple mountain passes) I also contacted the previous owner (who is a mechanic by profession) and he said it had always been like that since he purchased it 2 years and a few thousand miles ago.

I tried looking through quite a few of the manuals and searching the forums, but I couldn't find anything that clearly explained what this is. So couple questions - what is it for? And do I need to hook it back up? Seems to me that dirt and grime could have entered the master cylinder, which might require a rebuild or at least a really good cleaning...

And sorry for the dirty pictures - a fuel line cracked on my drive home and sprayed diesel fuel everywhere! I repaired it for the drive home but I haven't cleaned it up yet.

Top view: (you can see to the left there is the fitting that is loose)


Opening for fitting on master cylinder:


This is where the loose tube connects:

 

[gimpyrobb]

That is(was) a vent line that tied into the fuel vent and then went up to your slobber tube. It has been found that fuel fumes will damage the master cyl(there is an MWO -modification work order - to fix that), so they separated the lines. Your brake line should go to the "air pack" and then to your brakes. I'm pretty sure the port you THOUGHT it goes to, is where the winch PTO shifter bolts to.

 

[NDT]

Picture #2 is not a pipe fitting, it is a threaded hole for when the MC is side mounted like in a CCKW!

 

[Floridianson]

I would remove the copper master line vent tube at the T on the frame and put a plug there. It's an inverted flair so NAPA brake line plug should do the trick.
Then the new MWO would be a new copper line installed into the master cyl. and routed up on the firewall as high as the govener and a U turn on the line then it gets capped with the same vent that is on top of your master now.

 

[welldigger]

If your wanting to install a remote brake fluid reservoir then simply plug off that copper line that isn't attached to anything. You should be able to remove the line at that tee fitting and plug it with a brake line plug. Then remove that bobble head vent from the m/c cap and screw in a barbed fitting. Then attach your rubber line to your remote reservoir.

That threaded hole in the side of the m/c doesn't lead to anything. It's a blind hole. Disregard it.

 

[ammoman]

Thanks for all the great feedback! I feel a lot better now knowing there isn't a missing brake line!

 

[gimpyrobb]

Thanks for all the great feedback! I feel a lot better now knowing there isn't a missing brake line!

Just a screw loose behind the steering wheel.

 

[ammoman]

Just a screw loose behind the steering wheel.

My wife sure would agree with that! When I first floated past her the idea of buying a deuce, well, let's just say she was less than thrilled!

 

[brianp454]

Napa 204-3

I think you are asking about NAPA 204-3, pic attached.

 

[gimpyrobb]

I think you are asking about NAPA 204-3, pic attached.View attachment 482645

Yup, thats what supposed to be in the top of the master cyl cap.

 

[brianp454]

Hmmm. I wasn't aware of the WMO (thanks gimpy!). I stands to reason that fuel and partially burnt compounds could condense in that line and end up contaminating the brake system.

When I got my truck I saw it was disconnected and thought it was nuts that going through water\mud or just road grit splashing around could easily get into the brake system. That's unacceptable. One of the other things I did was remove all three axle vent caps and clean them in solvent and ensure they were functioning. I plan to run a line from all of the axle vents to the air filter housing so they remain vented, yet somewhat protected from crud. Perhaps the brake vent could be ran to the same or similar spot?

 

[SCSG-G4]

brianp454, add the transmission and transfer case vents while you are at it. As for the brakes, get a remote reservoir kit that mounts behind the driver's seat. Lots easier to check, and it would be even higher than one in the engine compartment.

 

[brianp454]

Good ideas and I agree! Also venting the transmission & xfer case are good ideas. I've been thinking about using 1/4 inch OD rigid wall PE or maybe 3/16 inch ID Prothane flexible wall tubing. I'm thinking the more rigid tubing is better. I'm also looking for T's that I can mount to the frame rail. Any tips appreciated.

I'm planning to do the remote brake reservior as you suggest also. I'll get to it one of these days...

brianp454, add the transmission and transfer case vents while you are at it. As for the brakes, get a remote reservoir kit that mounts behind the driver's seat. Lots easier to check, and it would be even higher than one in the engine compartment.