Do jake brakes damage the engine?

No, it's the compression stroke that absorbs the energy, then releases it thru the exhaust. The vacuum is there whether or not you use the jake. Think of the compression stroke like a spring, as the piston moves up, it takes energy to compress it, and at/near the top of the stroke, the exhaust valve opens and releases that energy before it can return the energy back into the drive train. Sorta like, if you were jumping on a pogo stick, but as you reach the bottom, instead of the thing shooting you back up, the spring in the thing breaks and you stay at the bottom.

 

Same here!

 

That is true, especially the speed shifting cowboys. You know accelerate use jake to drop rpm to grab next gear. Talk about a lot of unnecessary torque and wear.

 

The strong vacuum is only there when the Jake is on. During normal off-throttle operation, it's as you describe, the compression pressure is still in the cylinder, dropping back to manifold pressure as the piston nears BDC. That can be a slight vacuum (roughly whatever your intake restriction gauge shows) , but nothing like the vacuum created by a piston moving down with valves closed after the Jake dumps the pressure.

But the loss of the air spring effect is where most of the retarding power comes from, the vacuum is definitely secondary.

 

@Hammer166 your posts have provided the best explanation of engine braking I've ever seen.

Should be a sticky somehow because the process is one of the driver's most important tools, but maybe the least understood.

 

Thanks. But it's really more info than you need to know how to use it, it's just kinda cool how it does work.

 

I think a lot of my confusion with the subject is that I understand gasoline 4 stroke engines, but never owned or studied Diesel engines until later in life.

Horizontally opposed Subaru motors, and Wankel rotary engines were enough to blow my tiny mind - finding out diesels didn’t have spark plugs and fired upon compression left me with a case of PTSD.

 

Knowledge is power...

 

Wrap your head around these.
Napier Deltic - Wikipedia