How the 6.7 Exhaust Brake Works-Photos

[sag2]

There were several posts of late discussing how the brake operates. As I hate to see incorrect information information posted I borrowed my neighbors truck and snapped some photos of the turbo and brake assembly. Please don't tell him or he might not let me borrow it again.

 

[sag2]

In the bottom photo I show the exhaust flow. It enters the housing and swirls around until it enters around the gap just where the "d" is in sliding. From there if the slider is in full boost position the exhaust is directed at the turbine wheel and spins the shaft. The slider fins mate with the wing shaped slots in the exhaust housing for support. In the full brake position, the slot around the exhaust housing is blocked completely. In the full boost position the full exhaust stream is allowed to spin the turbine. The ECM controls the position of the slider to keep the boost at the proper level.

 

[sag2]

After spinning the turbine the exhaust exits the center of the housing to the down pipe.

 

[FATCAT]

Wouldn't it have been eaiser if they just had Jacobs make an engine brake for the 6. 7L and put the switches in the cab.

 

[grasmo]

This reminds of powervalves on a high performance 2 stroke engine ... carbon build up was always a problem with some of the early models ... assembly required the use of molybdenum disulfide grease . . the only thing that would hold up to 1100 degrees ... . very cool pictures ... thank you ... I now see how very susceptible this area is to carbon build up.

 

[Bob4x4]

Wouldn't it have been eaiser if they just had Jacobs make an engine brake for the 6. 7L and put the switches in the cab.

No :-laf They had to build the turbo for emmisions anyway why not let it do double duty.



Bob

 

[sag2]

Like Bob said, they needed it to add heat for regeneration so it just makes sense to incorporate it into the turbo.

 

[NBoyd]

Thanks sag2 for the info.

 

[FATCAT]

No :-laf They had to build the turbo for emmisions anyway why not let it do double duty.



Bob

Yeah, but, the FUN factor is removed with only the exhaust brake.

 

[MCummings]

sag2, thank you. Very informative.



Full boost would mean that the turbo is full open, this would be the "biggest housing" size. If the exhaust hoiusing were to stay in that position, the truck would not build boost off the line.



With the brake "full on" that's the smallest exhaust housing size. The ECM varies the "exhaust housing" to regulate the amount of boost depending on many different factors, so to create an "exhaust brake" all the engineers really had to do was write a bunch more computer code, and slide the "exhaust housing" all the way shut. . Nice.



Merrick

 

[jelag]

sag2

Have you ran a truck with a PXRB PacBrake... my new 5500 has about 50-60% of the retarding HP as my F550 or 3500's with the PXRB Brake.

With a loaded truck..... (19,500 lbs) down a 6% grade the exhaust brake will not fully hold the load and we have to use the service brake... . with the 3500's pulling trailers (trailer wt 15,000) we always had control...

Any ideas, the dealer is lost...

also with this load... Longest frame available we have a severe vibration between 40-50 mph on nice highways... acts like a u-joint but unlike a u-joint you can drive through it... . the vibration is not there empty and starts with 3,000 lbs on the bed...

There is severe rear bed sag at weight even with the weight behind the cab in front of the rear wheels... must be 4-5 inches, were thinking drive shaft angles... .

Thanks for your input..... BTW - enjoyed the photo's...

 

[DCreed]

sag2

also with this load... Longest frame available we have a severe vibration between 40-50 mph on nice highways... acts like a u-joint but unlike a u-joint you can drive through it... . the vibration is not there empty and starts with 3,000 lbs on the bed...



There is severe rear bed sag at weight even with the weight behind the cab in front of the rear wheels... must be 4-5 inches, were thinking drive shaft angles... .



Thanks for your input..... BTW - enjoyed the photo's...

check slip joints too.

 

[RWPor]

How does the increased heat from the turbo and DPF etc impact the engine? Have the simease cylinders on the 6. 7L had any bad impact?

 

[sag2]

sag2



Have you ran a truck with a PXRB PacBrake... my new 5500 has about 50-60% of the retarding HP as my F550 or 3500's with the PXRB Brake.



With a loaded truck..... (19,500 lbs) down a 6% grade the exhaust brake will not fully hold the load and we have to use the service brake... . with the 3500's pulling trailers (trailer wt 15,000) we always had control...



Any ideas, the dealer is lost...



also with this load... Longest frame available we have a severe vibration between 40-50 mph on nice highways... acts like a u-joint but unlike a u-joint you can drive through it... . the vibration is not there empty and starts with 3,000 lbs on the bed...



There is severe rear bed sag at weight even with the weight behind the cab in front of the rear wheels... must be 4-5 inches, were thinking drive shaft angles... .



Thanks for your input..... BTW - enjoyed the photo's...

I have never driven a truck with a Pac Brake, but I hear they work better than the Mopar brake on the older trucks. The 6. 7 brake works better than a Mopar brake for 5. 9, but since there is not a spec for retarding force that I know of, not sure how to tell if it is operating correctly when running.

As for the vibration, have your dealer ask the local tech rep if he has access to an MTS 4100 vibration analyzer. It will pinpoint the source of the vibration. If they don't have one perhaps they have an EVA (electronic vibration analyzer) as many of the dealers purchased them a few years back. The MTS 4100 is about $6000. 00 so not many dealers purchased them. Also most GM dealers had the EVA as a required tool. Depending on your dealer and his relationship with other dealers he might be able to borrow one. The only difference between the two is the 4100 does the math for the technician.

 

[PaulBarker]

sag2



Have you ran a truck with a PXRB PacBrake... my new 5500 has about 50-60% of the retarding HP as my F550 or 3500's with the PXRB Brake.



With a loaded truck..... (19,500 lbs) down a 6% grade the exhaust brake will not fully hold the load and we have to use the service brake... . with the 3500's pulling trailers (trailer wt 15,000) we always had control...



Any ideas, the dealer is lost...



also with this load... Longest frame available we have a severe vibration between 40-50 mph on nice highways... acts like a u-joint but unlike a u-joint you can drive through it... . the vibration is not there empty and starts with 3,000 lbs on the bed...



There is severe rear bed sag at weight even with the weight behind the cab in front of the rear wheels... must be 4-5 inches, were thinking drive shaft angles... .



Thanks for your input..... BTW - enjoyed the photo's...

are you sure that one of the tires are not bad. or a rim that is not true. rotate the spare through all of them. alot of work but you could chase this for a long time

 

[jelag]

Paul,

We thought about tires... . but to be honest we followed the truck down the road. . understand that a visual test is not a conclusive test but we saw no tire - wheel bounce like you'd expect with that problem... .

As soon as it gets back from the current trip it goes back to the dealer...

 

[PaulBarker]

If its a tire you may not see anything, like a belt that is separating.

Does the truck ride a bit sideways. is it possible the rear axle becomes out of line under a load.

you would think it would be easy to find such a problem when there is not that much as far as moving parts in the rear.

maybe you have a bad wheel bearing?