Ah, the master cylinder for the rear brakes on our Breakaway developed a small fluid leak which dripped out of the hole in the bottom of the air pressure converter chamber. I looked around the net and found that these Midland "n37116C" cylinders do not have available rebuild kits. Since over the years I have had less than perfect results with rebuilt brake parts anyway, I contacted John at PowerBrakes in FL and bought a new P/N: 0341-MM1 cylinder from them. Also, since the air diaphragm had contacted the leaking fluid at the drain hole area, I thought it would be a good idea to replace it also. When I inspected it it looks perfect, however. PowerBrakes has the diaphragms for $12.50.

I was thinking about using DOT 4 fluid due to its higher temperature rating but thought I would ask if anyone has opinions about whether DOT 3 is sufficient? I will flush both systems and use the new fluid for both. I will probably use ATE fluid.

BTW, NAPA lists this unit for $1,009 and PowerBrakes cost for the cylinder only is $479.

Looks like I'm in market for one of these Air/hydraulic pressure converters. I figured I'd give mine a good look over after reading this post. Well I have the exact same leak you described except mine is on the front master brake cylinder.

Sparten Chassis wants $860 for the replacement 0341-MM1 they show a picture of the part and it is a complete assembly with the diaphragm. Did you just get the master cylinder and the diaphragm seperate?

I've seen brake fluid with DOT 3&4 listed on the same container, So there is no compatibility issue.

Prestone has a DOT 5 silicone based fluid that will not absorb moisture, but it is not compatible with other fluids. Thought about using it for that reason but didn't. I recently had to remove both rear calipers, the one on the passenger side was locking up. The slide rails were rusted together causing the brake to drag. So when I flushed the brakes I could have used the DOT 5 fluid but then read where it's not compatible with all brake systems, so I stuck with the DOT 3.

Tom,

The air chamber is simply a split case device with 4 vent holes in one side. Your fluid is probably dripping out of the lower hole. Anyway, I just bought the new cylinder which was exactly like the old one and a new diaphragm since I thought the fluid leaking out of the cylinder may have compromised the old one. It turned out that the diaphragm was in really good shape and could have been reused.

The air pressure converter chamber is spring loaded to the "off" position by a fairly large spring and you should be careful when you disassemble this unit. There is a clamp around the outside of the split between the two halves of the chamber and if you simply take the two bolts off the spring will fling parts everywhere.

You can probably hold the two halves together but I decided to insert the chamber into the opening of my Stanley WorkMate bench and use it to keep the parts together while I took off the clamp. Then I slowly released the tension by opening the two WorkMate surfaces. It is wide enough to relax most of the spring tension.

You probably know all of this but I'll expound anyway. In addition to the spring there is a travel indicator which sticks through the cover and moves with the diaphragm/plate. It has a round end bent 90 degrees and slips over the rod that drives the cylinder. Pay attention to the configuration of this indicator when you disassemble the chamber in order to make assembly easier.

I am assuming that you are going to do this yourself.

I use DOT 5 brake fluid in my Deuce and a half military truck. The military standardized on DOT 5 because of the water issues with DOT 3&4. DOT 5 costs a ton of $$. You are right about the compatibility of DOT 5 will some brake seals, etc. (I used DOT 3 for this master cylinder job.)

The R & R of the master cylinder is not an easy job. It is heavy and is mounted in a difficult spot especially if you do not have a pit or lift. However, I got mine back together and tested it yesterday and it works great. $479.00 + $12.50 (diaphragm) + S&H so that is a bit less than buying the entire converter unit. I really don't see how the air pressure chamber can go bad unless it rusts out and gets thin. Mine was in great shape. One side is coated with a special coating that provides a smooth surface for the diaphragm to ride against. Since I did not know what I was doing I marked the two halves with chalk prior to taking it apart. You probably do not want to use a punch since the outside of the one half has that special coating as well as the inside.

Do you need the number for PowerBrakes in FL?

A number would be great, I Googled PowerBrakes and came up with a couple different web sites one in FL and one in CA. I sent a e-mail to the one in FL but never got a reply. Could be a different Company.

Thanks for the heads up on the disassembly of the diaphragm, I more than likely would have just released the two covers and said "damn this thing is spring loaded". Makes sense that it is but that would've been an after thought. Sure can't find much info on these units on the internet.

I have good access to both the front and rear brake cylinders, I raised the coach about 6-8" which gives me plenty of room to work underneath.

Thanks!

The number of Poweubrake-Drivetrain is 1-850-433-9729. They are in Pensacola, FL.
Here is the URL for their website: http://www.powerbrake-drivetra...pb-30052c-494cv-rmt/

I found that they do not answer the phone very early and usually had luck calling after 10:00 EDT.

The spring in the air chamber pushes the diaphragm back when the brakes are off, of course. It is not under too much pressure there but there is some residual tension and it is enough to surprise you.

Good luck with the repair job!

Tom,

One more thing--the fittings in the master cylinder are not the usual kind you find in brake systems so be careful with them. The upper one is 1/2"-20 UNF threads with an o-ring to seal at the cylinder opening. The hose fitting on the top is a male 45 degree type compression fitting much like those you see in natural gas systems. The pressure outlet is a more conventional brake line flared fitting with no o-ring required but there is a small copper/brass gasket that would be easy to miss and leave stuck to the old cylinder.

I was going to replace all of them but found that no one in our area had anything like them so I reused the old stuff.

quote:

I found that they do not answer the phone very early and usually had luck calling after 10:00 EDT.

They're on CDT.

Well, it's not a problem. They are indeed on CDT. I am just used to business outfits opening at 8:00 and closing around 5:00 and answering the phone between those times. I guess that is old-fashioned. If they do otherwise, which I don't mind at all, they might list their hours on their websites or say something like "We answer phone inquiries between 12:00 and 3:00."

Anything works if everyone knows the situation and rules and websites are great for letting customers know about them.

Ten-Tec, for instance, says on their website that you have to call the Colorado phone number in order to be issued a RMA then you can receive the shipping addresses for the repair facility which is in another state altogether. It is a PITA routine but works well for them and the customer.