Our resident truck drivers please explain this technique (or device) and why is it so damn loud??

Thanks !

it's an exhaust brake, creates a shit ton of back pressure....

Quoted: it's an exhaust brake, creates a shit ton of back pressure....

Close, but no cigar.

en.wikipedia.org/wiki/Jake_brake

google is your friend.  or.essortment.com/jakebraketruck_raio.htm

On a side note, I wish they would hurry up and approve an exhuast brake for my 6.0l.

A true Jacobs Engine Brake modifys the exaust valve timing, keeping it open longer and building lower cylinder pressure, therby slowing the vehicle down.

It is loud because it builds up different pressure in the cylinders as the exhaust valve opens.

Many people refer to any exhaust brake as a "jake break" as a generic term.

An engine brake opens the exhaust valve at the top of the compression stroke, so that when coasting, the compressed air exits the cylinder instead of pushing the piston back down. The brake effect comes from the engine compressing the air and not getting the benefit of the compressed air pushing the piston back down. It is loud because diesel engines are very high compression and the released air is highly compressed.

BTW Withing the trucking industry, drivers are rarely called truckers.

Huh! I thought it was a brake on the drive shaft or on the inside of the engine that applied pressure to a moving surface thus slowing said vehile down

Quoted: An engine brake opens the exhaust valve at the top of the compression stroke, so that when coasting, the compressed air exits the cylinder instead of pushing the piston back down. The brake effect comes from the engine compressing the air and not getting the benefit of the compressed air pushing the piston back down. It is loud because diesel engines are very high compression and the released air is highly compressed. BTW Withing the trucking industry, drivers are rarely called truckers.

Wow.  So much to wade through here...  

Ok, the Wikipedia descripition is correct.  The Jacobs brake was developed for use on trucks in coal country, where heavy loads and steep grades are a recipe for disaster.

I wasn't aware that compressed air "pushes" pistons down in a multi-cylinder recipricating engine

It is loud, because a lot of smaller trucking companies do not properly equip thier trucks with DOT legal exhaust mufflers and many drivers will down shit (thus generating higher RPM's) and then engage the jake.  High RMP's + straight pipes = loud trucks.

In the indstury, we are referred to by many things including: drivers, truckers, steering wheel holders, throttle jockeys, and many more colorful names as well.

Actually they are not as loud as one is lead to believe

the reason some are as loud as they are is because their are some guys out there that will remove the mufflers on a semi in order to get a more throaty sound and when the engine brake is applied then that only amplifies the exaust

I drove truck for 15 years and would never again drive without one, it is a wonderful invention that only adds to the safety of a large vehicle, I never obeyed the "no engine braking" signs on the road simply because they were asking for a person to not use all the safety devices that were afforded to him, it would never hold up in court

Safety first, if you wanted to you could use the engine brake in combination with down shifting to make a complete stop from highway speeds without ever touching the brakes, of course it would take some distance

i know for a fact some asshole truckers do this on purpose, especially at 3am in the morning on a residential street and waking me up. i think 10% of idiot truckers make the other 90% of them look good.

Quoted: i know for a fact some asshole truckers do this on purpose, especially at 3am in the morning on a residential street and waking me up. i think 10% of idiot truckers make the other 90% of them look good.

Those same assholes do that in truck stops where drivers are sleeping

Yes, when coasting, a diesel engine is mostly "freewheeling" because there is no throttle plate.  In a gasoline engine, the throttle plate is mostly closed, making for a high vacuum in the intake manifold.  This high vacuum starves the cylinders of air, making for greater engine braking.

In a diesel engine there is no throttle, meaning the engine is always operating with full manifold pressure.  Even without any fuel injected, the energy used to compress the air is roughly returned on the downstroke, minus friction of the engine and the tiny bit of energy lost to compressive heating which is lost to the metal surfaces.  Think of it as a spring.

The Jacobs Brake bleeds this high pressure air at top dead center, effectively dissipating the energy.  A part of that energy comes out as sound.

Quoted: i know for a fact some asshole truckers do this on purpose, especially at 3am in the morning on a residential street and waking me up. i think 10% of idiot truckers make the other 90% of them look good.

Quoted: Huh! I thought it was a brake on the drive shaft or on the inside of the engine that applied pressure to a moving surface thus slowing said vehile down

On a lot of fire engines there is a brake disk put at the end of the transmission with a caliper mounted to it also.  It is a VERY effective brake.  40k pounds on 2 axles driven by someone without a CDL or enough training makes it a good thing.

ahh so that is what that loud rumbling noise that I sometimes hear trucks make when slowing down...

They work great when you are close to empty... Get to 80,000, and you really dont feel them slow you down too much... I had one fail on me going down the backside of Ashland in Oregon.  

Barrelburner said: BTW Withing the trucking industry, drivers are rarely called truckers.

Sorry Barrelburner.  I should have said "Mother-truckers"  


lawdog