master cylinder

not sure if this is in the correct spot, but here i go. how hard is it to change a master cylinder on a m35a2? they usually are not difficult on regular vehicles, but never done a deuce. i may be picking one up if its an easy job. but i would have to make a 1/2 day trip to it, replace it and leave that day. would this be possible? thanks.

Disconnect the lines (vent line on the cap and the brake line in the back), remove the protector plate, unscrew the four bolts holding it on the frame, remove. Reverse to put the new one in. Only trick is the lower bolt on the outside holding it to the frame. For that I used a 9/16 deep well socket attached to a six inch extension a universal joint, another six inch extension and finally the ratchet wrench. It all gets snaked in through the hole where the main brake line goes through in the back. Once you have done one, you too will think they built the entire truck after installing the master cylinder. Good luck! Took me about two hours, and I had never done one before, oh, and 3/8 drive stuff fits through the spaces better than 1/2 inch.

I think it could be done in an afternoon, but there are three possible hang ups I can recall:

1. Brake line fittings, if they are are seized to the point you are just stripping them with a wrench, you'll need to cut the lines and remove the fitting with a socket and replace the lines.

2. The MC is held on to its bracket by four bolts, one of which (top-right-facing-the-MC) is a real heart breaker. You'll need to get behind it with a long extension, along the frame rail and through a cross member opening. Sometimes tho, this bolt is not there because of the difficulty of the location in placing it there. Tackle this bolt first if it is present because the MC slipping off the bracket does not help when removing it.

3. Some older MCs have extra fluid port plugs on them in the rear. If the MC has these extra plugs you'll need to remove one to gain enough space to wiggle the MC out. Edit: You'll want to remove this plug while the MC is still bolted to the deuce.

It is possible but you might want to take a tent to pitch!
Replacing the master cylinder on a deuce is a little tedious and then will require possibly bleeding the entire system, then hope the air pack (which is known to leak brake fluid internally) is functional.
It is critical to have the brake systems on these trucks working properly and without a complete brake system inspection it would be very risky to drive.
A better plan might be to have it transported to your location where you could work on it.
Good luck.

If you have a problem with stuck brake line fittings, you can use a crescent wrench and wriggle it on the fitting while you tighten the wrench on the fitting. I got two frozen fittings off this way that I had rounded with a flarenut wrench when replacing brake lines on my duece.

Moved to the Deuce forum

My deuce has a winch and the controls are attached to the master cylinder mounts so my application is a little more complicated. I still have to change it out anyway but keep procrastinating.....

RAYZER said:

It is possible but you might want to take a tent to pitch!
Replacing the master cylinder on a deuce is a little tedious and then will require possibly bleeding the entire system, then hope the air pack (which is known to leak brake fluid internally) is functional.
It is critical to have the brake systems on these trucks working properly and without a complete brake system inspection it would be very risky to drive.
A better plan might be to have it transported to your location where you could work on it.
Good luck.

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You don't need to bleed out the entire system, but Rayzer is right you should just have it towed to your place where you can check out the brake system totally.

rustystud said:

You don't need to bleed out the entire system, but Rayzer is right you should just have it towed to your place where you can check out the brake system totally.

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If you replace the MC, you have to bleed the ENTIRE system-period. (it is actually really easy).

I have never bled out the entire system from replacing a master cylinder. I have not found this in any TM either. You can bench bleed most of it, then finish on the truck. The Air-pac or pacs will finish the bleeding process. No need to waste all that "silicone" brake fluid.

Yep and after you remove the brake line from the master, remove the inverted flair brass fitting that it connects too or the master won't come out. Also agree with Rusty might catch what little air is left at the airpack.

rustystud said:

I have never bled out the entire system from replacing a master cylinder. I have not found this in any TM either. You can bench bleed most of it, then finish on the truck. The Air-pac or pacs will finish the bleeding process. No need to waste all that "silicone" brake fluid.

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The 2320-209-20-3-2 shows how to replace the master cylinder. It also does not mention bench bleeding and at the very end it tells you to bleed the system and refers you to both sections later in the manual for bleeding both the air pack and wheel cylinders. If you use a pressure bleeder you will waste minimal fluid.

Also, attach a clear piece of tubing to the bleeder and catch the bled fluid to reuse.

Anyone remember which thread showed how to make a homemade bleeder?? And is it denatured alcohol you use to flush the system?? I can't find those threads and I've searched for an hour.

John S-B said:

Anyone remember which thread showed how to make a homemade bleeder?? And is it denatured alcohol you use to flush the system?? I can't find those threads and I've searched for an hour.

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http://www.steelsoldiers.com/showthread.php?3229-Deuce-Power-Bleeder-R4x4-Style

Its a sticky in the deuce forum

If you go to Ace hardware there little spray pump up plastic bottle. Just take off the end of the wand that makes it spray. The wand is plastic and will thread right into the master cyl. cap where the vent is. Cheap and works.

As I recall, you also have to position the M/C just right for it to go into the right position. I followed the T.M. including the pics showing the proper orientation.
That being said, I agree with others to take extreme caution to insure the M/C is the only issue. Your break system must be in perfect working order.