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Old 03-22-2012, 03:50 PM   #1
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American Coach Owners Club
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Aux braking system check valve

It's been almost two years since I posted this problem for the first time.

I have a SMI Stay N Play Duo auxiliary braking system installed in our Wrangler. The system's vacuum check valve allows the controller(with vacuum pump) to provide vacuum while towing and prevents it's vacuum from bleeding into the engine manifold when not running. The check valve that comes with the system has failed three times. It appears that the rubber diaphragm inside is swelling and blocking the vacuum in both directions causing no vacuum assist to the Jeep's master cylinder booster. This can be quite exciting driving the Jeep when it fails.

The first two times this happened, SMI replaced the check valves but said they have never had the first failure from anyone else. Our '08 is completely stock and it's hard to believe the braking gods have chosen my Jeep to be the only one 'cursed'. The only thing I can think of that is out of the ordinary is that the controller is mounted inside the pax compartment in the right foot well instead of the engine compartment.

The last time this valve failed was almost a year ago. The reason I waited so long to replace this thing is that I intended a change to synthetic oil instead of the dino hoping that if an oil mist was causing the problem, the syn oil would not have the swelling effect on the valve's diaphragm. Well, that's the scoop.

If anyone's still awake, has anyone's Wrangler with the SMI DUO system installed, have or have had the same problem with the check valve? I have no idea what's causing this. Otherwise, I'm really happy with this system...Thanks, Bob

Jan and Bob

RIP 'Squeaky'
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Old 03-23-2012, 09:04 AM   #2
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Damon Owners Club
Workhorse Chassis Owner
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The only thing I can think of that might cause that kind of problem is HEAT.

You might try getting a valve from US-Gear, should be same part.

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Old 03-24-2012, 08:53 AM   #3
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I'll keep that in mind...hopefully their valve isn't made by the same manufacturer.

While trying to see what was causing the valve to fail, I wrapped the valve in an attempt to insulate it...no help. Never thought about going to another manufacturer... Thanks Bob

BTW, the heat is unbelievable in the Wrangler's engine compartment. That's why I had the controller installed in the pass. compartment to get it out of there.
Jan and Bob

RIP 'Squeaky'
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