Please Help! Problem with Cummins ISC 350

Hello all...
I am actually writing this for one of my co workers. He has a 1999 Holiday Rambler Imperial, with a Cummins ISC 350. The problem is that the other day, he was applying the exhaust brake, and lost all power. The engine will restart, and drive but the transmission shifts funny. The major problem is that he says the motor has a "knocking" sound from the top. He is going to take off the valve cover to check, but... I was wondering if anyone kno ws if this is a common problem or what? The brake was installed by the previous owner, and he has had the RV for a while. Approx. 50K miles

Thanks in advance,
Please Help! Problem with Cummins ISC 350

The first thing to check is to see if the brake is stuck closed. It could make it sound like a knock. It would also affect power and trans, shifting. If not and you still have a knock top side taking off the cover to look sounds right. Good lick!!!