SMI Air Force One on a 2013 Ford Edge issue

I have a 2006 Winnebago Journey 34H DP and tow a 2013 Ford Edge (4 down).  I have a SMI Air Force One system that was installed in 2014. The SMI system appears to work, at least it does make the Edge's brake pedal depress when the Coach's brake is push.

Recently I started to notice a braking issue with the Edge when just driving it, the brake pedal becomes hard to push/hard to stop as if I have lost the power brake booster. When the problem occurs I have to really press the Edge's brake pedal hard to get the car to stop. The problem is intermittent, some times when I apply  the brake the brakes work like normal but sometimes they have the hard pedal feel.

So I am trying to determine if my Ford Edge's brake booster is failing or if something in the SMI system is actually causing the problem. I called Demco (they now own SMI) on Friday and ask them if there was anything with their system that could cause the symptoms I'm experiencing. He mentions the 2 check valves and then explained there was to test if either were leaking by seeing if there was a vacuum on a port when the car engine was running. He explained this 'port'  (brass fitting?) was on the opposite side of the control unit from the side where the 3 vacuum lines went in to it. My control unit does not have the port he described, and since he never ask me how hold my SMI unit was, I assume that there is a newer model than mine that does have this test port.

My concern is that with what seems like no boost, I doubt the SMI unit could pull the brake pedal down hard enough to actually get the car brakes to stop/slow the car. I have a big trip west in a few weeks, so need to resolve this problem.

So has anyone else experienced a hard brake pedal problem that was actually caused  by their SMI Air Force One braking system? Or anyone have any thoughts as to what may be causing my hard brake pedal?

Thanks in advance for any thoughts.

Russ

Russ, there is only 1 vacuum line to the operating unit.  The other two hoses are air pressure lines. One comes from your coach air brakes. The other line goes to the cylinder to pull on the brake pedal.
You can temporarily remove the vaccum from the operating unit and plug it (a golf tee works well) and drive the car to see it brakes better.  You could also just remove the tee and connect the hose from the booster directly to the check valve coming from the engine.
BTW it's pedal not peddle.

ChasA - Thanks for the information. I talked to SMI (Demco) again this morning and explained the age of my unit. Now that he understood the version I have he said the test port is inside the control box. Brian at Demco felt my problem was most likely one or both of the check values, especially since the 'hard pedal' symptom was somewhat intermittent, so I ordered the two check valves and will replace them when they arrive tomorrow.

Shortly after the unit was installed I saw a small cut in the end of the small black rubber protector that goes over the air input on the car and I applied a little silicone over the cut to repair/seal it. Well I learned today that the small cut in that rubber plug is suppose to be there to relieve any pressed build up.  I'll post what the final resolution.

Well at least my mis-spelling of Pedal was consistent  ;D ... I did correct 'all' of them in my OP.

Russ

Update:  I did replace both SMI check-valves and it did not resolve my braking (hard pedal - intermittent). Both the removed check values tested good.  After multiple calls to Demco (SMI) with questions I feel I understand the SMI Air Force One system better and have ruled out it as the cause of my problem. So I did more research relative to braking issues on the 2013 Edge and came across this Ford Bulletin (13N02).

"Problem Description
Bulletin 13N02 - This program extends the coverage of the brake booster to ten years of service or 150,000 miles from the warranty start of the vehicle, whichever occurs first. This is a one time repair program.

In some of the affected vehicles, it is possible for the brake booster to develop a small tear in the diaphragm under certain driving and environmental conditions. If this occurs, the driver may hear a hissing noise while depressing the pedal and may also experience a "spongy" pedal feel without a noticeable effect on braking performance. If the vehicle is not serviced, the tear will eventually expand and the pedal effort required to stop the vehicle will gradually increase. However, in all cases, the fundamental vehicle braking system remains functional."

Much of what I have read on this braking issues with my Edge (Edge Forums) describes the symptoms I have been experiencing. So it appears that Ford has acknowledges that there is a brake booster issue on some Ford Edges and Lincolns where the brake booster can start to fail with symptoms like those I have experienced. Ford did not issue a recall, as the brakes don't fail just the power assist, but they did extend the warranty on the brake booster to 150,000 miles or 10 years.  )

So I fell I have identified my problem, now I just have to get it back to Ford for warranty repair. Unfortunately we leave next week for a 2 1/2 month trip so will have to wait until we return to schedule the repair.  :-\

Russ