M35A2C master cylinder failure?

[oifvet]

Well, guess he meant the one who decided to use THAT master cylinder for THAT application...

Obviously referred "Junior" grew up; realized that his creation wasn't that user-friendly and only a few years later came up with the remote reservoir, in the M35A3...

Oifvet: glad you solved your problem, for now at least.
Since everything looked new, have you considered retrofitting your MC with a remote reservoir? G.

You are correct! The MC is a good one, I'm sure, but Junior redeemed himself with the retro-fitting of the remote reservoir on the A3. I could probably do that another day, but as long as I understand and accept my current MC and reservoir arrangement, I should be o.k. I suppose there is some good to having less lines and fittings, but I cannot help but to think that the current location invites dirt and crud, especially with a plastic twist-to-lock cap.

3dAngus,

That MC will do just fine as long as it is not an Air Force contract (1987-89) M35A2C or an M35A3... the trucks using the dual-circuit system.

 

[oifvet]

One final question on this...

I apparently did not pay attention to how the rubber boot came off of this set-up. The wide end is flapping/loose.

I know the master cylinder bolts on metal-to-metal against the mount, but where does the wide end of the boot tuck in? When I try to slip it back into the opening, it has a kink in it and does not seem to snap into place.

Again, this is on the 1989 USAF M35A2C (same MC as M35A3).

Thanks to anyone with information. I'm sure it's a simple fix and something obvious that I am overlooking.

**************************** EDIT ********************************************************

I figured this one out on my own.

Just loosen the four MC mounting bolts (without removing the bolts or the MC). Push the wide end of the boot back in between the MC and mounting base... (give it a few spins to make sure there is no kinks or binding), then re-tighten the four bolts.

There is a recess for the boot to rest in between the master cylinder and mount, and it fits perfect.

Anyway, that's that.

 

[AMDOOR]

I too am having problems with an M35A3 MC in need of repair. I did a search and found a thread on another website. He had trouble finding a replacement. He rebuilt the MC. He said that it doesn't have cups like other MC's and uses 3 O-rings. He honed the cylinder and used EPDM O-rings that are compatable with the brake fluid. His cost was $.97. I have the link, but not sure that I should post it.

 

[3dAngus]

If its not an ongoing auction, don't post it.
If its a closed auction, post it.
If it's a retailer site, post it.

 

[AMDOOR]

M35A3 Master Cylinder rebuild

This link covers the MC issue and some problems and possible solutions.

http://www.g503.com/forums/viewtopic.php?f=26&t=177512

 

[oifvet]

AMDOOR,

Thanks for the link! You read my mind!

My pedal is s-l-o-w-l-y creeping to the floor with firm, steady pressure. Again, no leaks, drips, drops or anything like that. I bled the system twice until I was getting steady fresh (purple) DOT 5 during the bleed. It really feels like bypassing fluid.

I hate the idea of tearing everything back off again, but what else can I do? As the daylight is getting short, it might be a "next summer" job.

How does that second/inner piston come out? The snap ring allows the removal of one section, but I could not understand how to do a complete disassembly of the MC.

Thanks again for the info above

 

[AMDOOR]

I have the O-rings but haven't had time to pull the master cylinder. I hope to pull it within the next couple of weeks. I'm let you know what I find out.

 

[G-Force]

Amdoor,
where did you get the o-rings. If you have the standard o-ring sizes (- number) please post them.

 

[AMDOOR]

The o-rings that I believe are the right ones are Dash 129 EPDM O-Ring AS568A from McMaster-Carr, part number 9557K163. A pack of 50 for $10.46. I will let you know for sure when I take mine apart. It wouldn't be the first time that I had one size off of what I needed.

I have gotten quite an education in O-Rings while owning military vehicles. I have discovered the meanings of a lot of the numbers in the TM's. They give you the dash numbers and the specifications of the materials. The McMaster-Carr site gives a lot of information and even has a section on military specifications concerning O-Rings. It came in handy when I needed O-Rings and X-Rings for the rear axles of my M35A3.

I have not found any TM's for rebuilding the master cylinder. I will have to check the O-Rings for size when I pull them out.

 

[AMDOOR]

This is a schematic of the master cylinder from the G503 site:

I wish that I had the full schematic.

It looks like the pieces that are circled hold the pistons in place and prevent them from coming out. They must be lifted up along with a pin near the center to allow the pistons to be removed. I assume that the top piece holds the lines to the reservoir and the one way valves are circled.

 

[G-Force]

This is a schematic of the master cylinder from the G503 site:

I wish that I had the full schematic.

It looks like the pieces that are circled hold the pistons in place and prevent them from coming out. They must be lifted up along with a pin near the center to allow the pistons to be removed. I assume that the top piece holds the lines to the reservoir and the one way valves are circled.

Maybe for Christmas Amdoor

 

[oifvet]

This link covers the MC issue and some problems and possible solutions.

G503.com Message Forums • View topic - M35A3 Brake question

The one thing that I do not understand (if the problem I/we are experiencing is internal bypass of some sort), why am I not getting fluid at the master cylinder boot? Or, somewhere like the air-pack?

Even with fluid getting past these internal MC O-rings, pressure is still maintained unless there is some release of fluid outside of the hydraulic system.

At least that is what I am envisioning.

When I had the sloshing master cylinder with the blocked-open check valves, fluid was ejecting out the vent line and into the engine compartment (then down the firewall and into my face). There was still a leak.

My truck still has the brake light switch on both air-packs. I am going to make that mod first before I tear into that MC again. Something about those switches on the fluid side cause me to think there is something going on there.

************************************** EDIT **************************************************

I found the leak!

The brake llight switch on the passenger side air-pack is leaking fluid.

I knew it.

Before I pull the MC off again, I'm going to install the kit for moving the brake light switch, on the second air-pack. I also need to put a plug on the driver's side where the AF left the brake light switch to act as a plug (even though they did the mod, leaving the switch totally defeats the purpose of the fix).

That said, I'll be purchasing more DOT 5 and doing ANOTHER brake-bleed effort.

 

[AMDOOR]

I replaced the o-rings in the master cylinder of my M35A3C, yesterday. The correct o-rings are dash 222 not dash 129. The dash 222 has a larger cross section than the dash 129. Just a note: The valves in the top part of the schematic have small springs under them. Be carful during dissassembly. Upon assembly, the valves want to cock sideways and jam. The solution is to place a probe down through the fluid passage and depress the valve during placement of the top plate. Make sure that the valves are free before torquing the top plate.

 

[peashooter]

I'm glad I finally found this thread! Today I replaced a wheel cylinder (right steer) on my 88 Air force M109A3 with the dual circuits. Bled the brakes and the brake pedal will not move now, its hard as a rock. At first the brakes were locked, I drained all the air and the brakes were still locked, I cracked the bleeders and then the brakes loosened so the wheels would move..... but the brake pedal is still rock hard and wont move. Does this sound like a blocked return line inside the MC?

 

[clinto]

I'm glad I finally found this thread! Today I replaced a wheel cylinder (right steer) on my 88 Air force M109A3 with the dual circuits. Bled the brakes and the brake pedal will not move now, its hard as a rock. At first the brakes were locked, I drained all the air and the brakes were still locked, I cracked the bleeders and then the brakes loosened so the wheels would move..... but the brake pedal is still rock hard and wont move. Does this sound like a blocked return line inside the MC?

How did you bleed it? I have done my '87 the old school way and I'd love to figure out how to use a pressure bleeder on it like my single circuit trucks.

 

[G-Force]

How did you bleed it? I have done my '87 the old school way and I'd love to figure out how to use a pressure bleeder on it like my single circuit trucks.

Clinto,
you need to order the adapters from Motive Products

http://motiveproducts.3dcartstores.com/

i think it's the Chrysler adapter that fits.
There is a thread on here that mentions it. Search is your friend but not mine so look it up......
there is an application guide for what adapter fits.
I went and bought the master cylinder and remote reservoir from TNJ Murray for the A3 and plan on installing it to get the reservoir up on the firewall for easier access.

 

[peashooter]

How did you bleed it? I have done my '87 the old school way and I'd love to figure out how to use a pressure bleeder on it like my single circuit trucks.

Post 31 & 33 talk about how he used a pressure bleeder. I was wondering if we could just hook up 10psi air to the 1/4" reservoir vent line on the firewall to pressurize and power bleed it, you would just have to keep the reservoir full though right.

 

[peashooter]

Okay guys, I need some dual circuit help. I still cant figure out whats going on with my truck.
Yesterday I changed out the right steer wheel brake cylinder because it had some leaking I found behind the seal, other than that everything was working fine. I then bled the brakes per the single circtuit TM process with soldier B.

Problem is after 2-3 pumps of the brake pedal, it gets rock hard and wont move at all. The air can be drained and the wheels are still locked, the only thing I've found that unlocks them is if I crack a bleeder.
Today I re-bled the brakes and the problem persists after 2-3 pumps of the brake pedal. I've got a trip coming up I'm trying to get this ready for and am running out of available time to fix this.
Does this sound like a MC problem or an airpack problem?... or something else?

Any advice is very much appreciated.

couple other questions:
-I cant find any reference to what the full mark would be on the brake fluid resevoir (1/2" from the top?)
-Does the Bleeding proceedure differ any for the dual circuit trucks?. I'm going pass airpack, drv airpack, r.rear, L rear, R intermed., L intermed., R steer, left steer.

 

[caliber1]

Just a shot in the dark here, but check the master cylinder vent. Sounds like it's building pressure.

 

[gringeltaube]

Does this sound like a MC problem ........?
......................

Yes. Specifically, like a primary- (or both) compensating valve(s) NOT ... compensating! With no air, that is the only way that pressure can be built up, from the MC down to the WC; no matter if single or dual circuits.

First, make sure that after pumping the pedal, when fully released, the (primary)piston is returning all the way back to its stop. Then, see if you can feel some play between piston and pushrod, even with the brakes/wheels locked.

To better understand how a typical dual circuit MC works and what does what, see attached brochure, fig.5 and corresponding text, on page 5. (disregard the Hydro-booster part)

(note: first sentence should be: ............ actuators of both the primary and secondary pistons are in contact with their respective compensating valve stems, which project into the cylinder bore.
................)



G.