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I installed the Jacobs exhaust brake on my '07 5.9 Cummins w/ manual trans, mostly because of engine warrantee considerations. It works OK, but in my opinion, it is not quite strong enough. Although, being too strong is a realistic safety concern, as a friend of mine with a different brand, jack-knifed his rig while hooked up to a flatbed trailer hauling a backhoe on a wet downhill road.
The general consensus at a local, well respected, truck repair/hop-shop facility that specializes in Dodge trucks, is that the Pac-Brake is the way to go.
I had the vacuum pump fail after 4 years on a camping trip, and had to wait a day for the nearest Cummins Repair Facility to get one shipped to them (Hint: Do not go through a Dodge dealership for a Jacobs system or parts, as they will charge a whole lot more than a Cummins Repair Facility). I did the pump replacement myself and it was a piece of cake.
Whether or not a vacuum pump failure will strand you on the side of the road, depends on what type of failure it is. The vacuum pump is separate from the actuating assembly, and is driven by a longer-than-stock serpentine belt.
Pump related failures are the most common problem with the Jacobs.:
If the failure is only diaphragm related in the vacuum pump(not generating a vacuum), then the unit just quits working and you can still drive the rig, just no exhaust brake to slow you down (which is what happened in my case).
If the failure is a bad bearing in the vacuum pump assembly, it depends on the level of failure, whether or not you will be able to continue your trip. If the bearings are just squealing a bit, then you should start looking for a place to get safely off of the road to do repairs. How far you can go before complete bearing or shaft failure is a crap-shoot, push it too far and you may get stranded in a bad situation. In the event of complete failure, you will either burn up, derail, or break the serpentine belt.
Which brings me back to the longer-than-stock belt. I always carry an extra stock length, and an extra longer-than-stock belt. That way, if the pump seizes, I can install the stock belt and be on my merry way (without an exhaust brake), ....or, if the serpentine belt just flat out breaks from being deteriorated, I can put on the longer belt and continue on with a working exhaust brake.
If there is a failure in the butterfly plate assembly (the part that blocks the exhaust flow), if the butterfly gets stuck in the closed position (broken return spring or carbon build-up making it stick closed), most likely you won't be going anywhere until you can move it to the open position.
If the failure is wiring related, and the brake is not engaging, most likely you can keep travelling without an exhaust brake.
In hindsight, if I had to do it all over again, I would most likely get the Pac-Brake.
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