Master Cylinder Bad?

[Adrok]

JUST re-built this past year with a kit from Mikes, 4th bolt is not a big challenge in the grand scheme.
Replaced with stainless bolts.......so the next owner will scratch their head. lol

Update the thread when you bleed the lines. Let us know how it goes
Cheers

 

[Jeepsinker]

I know it's a NOS master cylinder, but heed my advice here; go ahead and order a rebuild kit for it now..
They're getting to the age now where they're hit or miss when you install them, but at least you have a good clean housing with no corrosion or debris anywhere. A fresh overhaul kit and a few minutes of your time will give you years of trouble free service.

I've had some NOS master cylinders that are just fine, and I've had just as many that either leak or lock up as soon as you put them in service.

- Garrett

 

[SCSG-G4]

Well this is funny. After watching Garrett's video again, I checked if my deuce has the fourth bolt on the brake master cylinder. It does not. Some mechanic decades ago, probably in the military, did not re-attach the fourth bolt. Well, that makes my life a bit easier come Saturday's installation of my new master cylinder.

The fourth bolt is fairly easy IF you have two extensions and a U joint between them. Bolt, socket, first extension, U Joint, second extension, ratchet wrench. Fed them through the hole in the frame and ratchet away! I've done three that way.

 

[cattlerepairman]

Well this is funny. After watching Garrett's video again, I checked if my deuce has the fourth bolt on the brake master cylinder. It does not. Some mechanic decades ago, probably in the military, did not re-attach the fourth bolt. Well, that makes my life a bit easier come Saturday's installation of my new master cylinder.

Too funny! I had the same experience when I changed mine...tried to feel the fourth bolt...couldn't...took gloves off...still nothing...then felt the hole...ahaaaa! I also did not replace it.

 

[LowTech]

Speaking of overhaul kits, what about the gasket that goes under the cap? Is that a make your own if you're not doing a rebuild? Mine is breaking up.

Nevermind, I found them for sale.

 

[cattlerepairman]

Speaking of overhaul kits, what about the gasket that goes under the cap? Is that a make your own if you're not doing a rebuild? Mine is breaking up.

Nevermind, I found them for sale.

I cut one out of a tire inner tube. Works fine.

 

[LowTech]

I would be happy if rubber lasted out here in the desert, unfortunately it has a real short life span so every time I use it as some type of self-made gasket I better be on the lookout for a replacement right away.

I did have to laugh the other day when I was reading on how to bleed the system. This section made me feel like I was back in Britain hanging out w/ the travelers,

 

[LowTech]

Maybe this thread helps:

My Master Cylinder Rebuild with Photos

So here I am again but now with my Master Cylinder rebuild. After my Airpack rebuild the brakes were allot better but I was loosing pressure in the pedal while it was being held down. If you are interested you can see the Airpack rebuild here...

www.steelsoldiers.com

Thank you for that thread link! It explained why I was having trouble finding a breakdown of the MC, `cause they didn't want them getting rebuilt by us lowly individuals.

 

[LowTech]

Well this is funny. After watching Garrett's video again, I checked if my deuce has the fourth bolt on the brake master cylinder. It does not. Some mechanic decades ago, probably in the military, did not re-attach the fourth bolt. Well, that makes my life a bit easier come Saturday's installation of my new master cylinder.

My fourth was missing as well and it seems that both the MC and airpack were fairly new . . . at least when I got it over a decade ago.

 

[GunInstructordotcom]

I spent the better part of today in 103F degrees replacing the master cylinder. Here are a few observations from doing this job.

- Definitely remove the 11/16" head fitting on the rear of the master cylinder where the brake line comes out. It gives the extra space to remove the master cylinder.
- If the old master cylinder has a 3/4" head cap screwed into the side of the rear of the master cylinder, remove it to allow the master cylinder to come out. My new one had the casting, but no hole or cap. I'm guessing this was where the old hydraulic low fluid sensor screwed into?
- I used the old plunger rod attached to the fork. I could not free the threaded rod to place it on the new plunger. I used plenty of force and was worried I would bend the forks if I used more force. The threads seem to be frozen.
- My truck has a brake line quite close to the exact area where you need space to remove the master cylinder, right next to the round hole in the frame. I saw two small threaded holes up higher on the frame and suspect those were fastener holes for an original brake line that did not pass so close to the master cylinder. So every truck can be altered by previous motor pool maintenance, as was my brake line and no fourth mounting bolt.
- Reaching over the top of the air pack and coming from behind the air pack, I was able to remove and install the brake line on the master cylinder with a proper flair wrench. No stripping of the brake line head that way.

In the next few days, I will fill and bleed the system. First I have to install my Big Mike's remote reservoir kit (that I bought back in 2013!).

 

[WillWagner]

Remember to start bleeding with the air pack then go the rt rear and work forward.

 

[GunInstructordotcom]

Remember to start bleeding with the air pack then go the rt rear and work forward.

If I remember correctly, it is air pack, right rear, left rear, right middle, left middle, right front, left front?

 

[WillWagner]

If I remember correctly, it is air pack, right rear, left rear, right middle, left middle, right front, left front?

Yup. Be mindful of the fluid level or you'll start over!

 

[GunInstructordotcom]

Yup. Be mindful of the fluid level or you'll start over!

I have the remote reservoir which makes it a bit easier. Bubbles in the jar, close when bubbles stop. My wife will be applying the pressure. She is good at that.

 

[SCSG-G4]

I have the remote reservoir which makes it a bit easier. Bubbles in the jar, close when bubbles stop. My wife will be applying the pressure. She is good at that.

If you built one of Kenny's pressure bleeders, your wife could be doing more productive things. With a half full 2 gallon sprayer it only takes 2 or 3 pumps to give it enough pressure to bleed the system. Even less mess if you get one of the Duralast One Man Brake Bleeder Kit to capture the fluid coming out.

 

[GunInstructordotcom]

If you built one of Kenny's pressure bleeders, your wife could be doing more productive things. With a half full 2 gallon sprayer it only takes 2 or 3 pumps to give it enough pressure to bleed the system. Even less mess if you get one of the Duralast One Man Brake Bleeder Kit to capture the fluid coming out.

Lori actually likes helping me with vehicle projects. Since her retirement, we have tackled quite a few home and vehicle projects together. It is also psychological support when I get stumped and she offers some solutions. A few times those solutions have been ingenious. She is a civil engineer so she looks at the problems analytically. The Duralast kit does interest me. I suppose it can be washed out and used for DOT 4 vehicles as well?

 

[LowTech]

Since we're both doing this work at the same time I feel like I should just keep posting here instead of starting something new, hope we're all good w/ that

So I did a small amount of honing just to get off some surface stuff, cleaned it out w/ brake cleaner, let it dry, then lubed the cylinder w/ some brake fluid and put the parts back in. Now the problem.
When I pushed the piston in after assembly to make sure it functioned I got limited return. I added a bit of fluid to the main part of the tank so that it would go down behind the piston and still after multiple times using a ratchet handle as the pushrod I still am only getting partial return, it never makes it back to the stop washer.
So now what?

 

[GopherHill]

Check to be sure the tiny hole toward the rear of the master cylinder is not blocked. May have to use a bent wire to check.

 

[WillWagner]

Or the sprinng is weak. Pull it out andd give it a little strecth

 

[LowTech]

The return hole is clear (thats been a main focus of mine) and it doesn't feel like a weak spring, it feels like the piston and/or cup is tight. If I push the piston in it takes quite a bit of effort but then it does dump a bunch of fluid out the back side. The piston then comes back to about 3/4" from the stop washer.
I don't think I could take it out w/o pushing from the other end and I'm not in a hurry to do that since I feel it would, or could, damage the check valve.
It makes me wonder if having them out and exposed in the desert for a week, or maybe the cleaner, caused them to swell or harden some?