Engine Braking?
Senior User
Joined: Apr 2012
Posts: 341
Likes: 1
From: Texas
Correct. A Jacobs Brake is a compression release brake. When you release the accelerator on a diesel engine, the vehicle's momentum continues to turn the engine's crankshaft, drawing air into the cylinders as the pistons move down and compressing that air as the pistons move back up. The pressure of the compressed air pushes back against the up-going piston, tending to slow the vehicle. The exhaust valve opens before the piston is pushed back down, giving the distinctive "pop" when releasing the compressed air. Without releasing the compression at the top of the stroke, the piston would be forced down from the pressure and no braking would be achieved.
The VGT braking Ford uses is similar in theory to a Pac Brake which is simply a butterfly valve in the exhaust that creates backpressure in the system without much change in engine noise.
The VGT braking Ford uses is similar in theory to a Pac Brake which is simply a butterfly valve in the exhaust that creates backpressure in the system without much change in engine noise.
Junior User
Joined: Dec 2012
Posts: 54
Likes: 0
RPM hit the nail on the head... These fords don't actually have any added mechanism to provide braking, unlike the large diesels... These just shut off the injectors, and apply some backpressure through the exhaust via closing the turbo vanes. It shifts down, as the higher engine RPM will net you more braking effect. 
Posting Guru
Joined: Oct 2012
Posts: 1,777
Likes: 4
From: Des Moines, IA
Also, for those of you with an SCT tuner there is an option to increase this effect along with an "Aggressive" Tow/Haul mode. I've tried both of them out unloaded and can tell they would definitely benefit the truck when towing heavy.
Cross-Country
Joined: Nov 2009
Posts: 82
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I just got back from a 4000 mile trip with my EX with a 6.0. The whole rig weighed in at 21000lbs....truck and trailer. I ran the SCT +50 hp towing tune with the trans set to harder shifts and the engine brake feature chosen as well. The "package" was flawless!! I'm looking at adding the Pacbrake to keep the brakes fresher for emergency stops
Senior User
Joined: May 2004
Posts: 313
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Since we're discssing engine braking, I thought I would chime in with a recent experience towing:
While towing our 11,000 trailer recently, I noticed that the engine braking held on longer than I would have liked. It did a great job keeping things in range going downhill, but once the grade ended, and my speed began to drop, it remained in low gear and hitting the pedal to keep my speed up just resulted in excessive rpms. Going downhill, it held steady at 55mph, but several times, it dropped down to 40mph before shifting and allowing me to hit the gas again. What signals the braking to end and upshift?
While towing our 11,000 trailer recently, I noticed that the engine braking held on longer than I would have liked. It did a great job keeping things in range going downhill, but once the grade ended, and my speed began to drop, it remained in low gear and hitting the pedal to keep my speed up just resulted in excessive rpms. Going downhill, it held steady at 55mph, but several times, it dropped down to 40mph before shifting and allowing me to hit the gas again. What signals the braking to end and upshift?
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