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C40109 - Pacbrake PRXB Exhaust Brake Cummins 8.3L ISC 4" Half Marmon

On SALE! C40109 - Pacbrake PRXB Exhaust Brake Cummins 8.3L ISC 4" Half Marmon


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Part # C40109 PacBrake PRXB Exhaust Brake Cummins 8.3L ISC 4" Half Marmon


Pacbrake’s flagship product, the PRXB (pressure regulated exhaust brake), is the unquestioned leader in the supplemental brake industry. The patented PRXB design delivers the strongest braking horsepower, greatest speed reductions and shortest stopping distances possible without the use of service brakes. It maintains optimum retarding performance by maximizing the exhaust backpressure throughout the entire RPM range. Unlike a typical exhaust brake, which requires high RPMs to work properly, the PRXB delivers constant exhaust pressure (braking) as early as 1200 RPM through to the maximum allowable RPM. 

Controlled by a master ON/OFF switch, Pacbrake’s exhaust brakes provide whisper quiet supplemental braking that allows service brakes to be used much less, ultimately saving you money. They have the ability to be left on all the time, making it ideal for in-city driving or for steep, downhill grades. This product pays for itself as less wear on the brake pads means fewer brake jobs.

In order to have consistent and effective braking over the entire RPM range, it is important (and necessary) to maintain constant backpressure. To achieve this, Pacbrake’s patented design has incorporated an additional waste gate on the butterfly valve to regulate the amount of exhaust flow that is being passed through. The flow is controlled by a spring-loaded arm, whose pressure rating and location are key factors in the functionality of the PRXB. Located outside of the housing and away from the heat, the spring is able to maintain its strength and durability for years of proper and precise braking performance.

Backpressure is created by exhaust flow entering the housing, hitting the closed butterfly valve and being forced back out in the direction it came. It is maintained by the pressure-controlled spring that is located on the outside of the exhaust brake housing.

As the engine’s RPM increase, the spring compresses and the arm moves away from the butterfly valve, therefore releasing more exhaust flow through the orifice. As the RPMs decrease, the spring releases and the arm applies pressure back onto the plate, covering the hole, and ultimately releasing a smaller amount of exhaust flow.

There is less than a 10% change in backpressure over the entire RPM range on the PRXB

Features & Benefits: 

  • PRXB Delivers Strongest Braking Horsepower
  • Less Wear & Tear On Service Brakes 
  • Ideal For In-City Driving Or Steep, Downhill Grades 
Updated the Vin straight from insurance website. Looking to add an exhaust brake on my 2001 Damon escaper 3979 with a 350 HP idc Cummins. Did not come with one from factory. ( tyler wilson, 08/22/2023 )
Have you visually confirmed there is no exhaust brake? We checked with Spartan and they are telling us your RV came equipped from the factory with a Jacobs exhaust brake. ( Support )
I have a 2001 Damon Escaper 3979 with a 350 horsepower ISC 8.3 Cummins. Has no exhaust brake from the factory. I want to add one. Do you know what kit or part number I need to order? ( Tyler Wilson, 08/22/2023 )
The VIN you provided is not working for us, can you please check and confirm? ( Support )
The Pacbrake on my '99 American Tradition with a Cummins 8.3L ISC has failed. The exhaust brake serial number is 022625 and I cannot see a part number. It's 4" pipe.
Which replacement Pacbrake part number along with the clamps part number should I order? Do I need anything else?
Thank you!
( Jeff Geier, 07/25/2023 )
If your brake is mounted on a 90 degree elbow, you would want part# C40107 and clamps C10310 & C11350. If it mounts directly to the back of the turbo, you would want part # C40108 and clamps C11355 & C11350. ( Support )
Last year when leaving Florida after a month stay the exhaust brake stuck closed causing the loss of power/boost. By the time I was able to get off the road a lot of heat built up in the engine area. When the heat dispersed the clapper on the exhaust brake closed. I did not use it the rest of the way home. I was able to lube the brake after returning home and it seems to actuate properly now. It does feel that the brake does not slow the coach as well as it used to. Can you offer ideas as to why it does not slow the coach down like it used to? Did the overheating of the brake/engine area cause something to warp or a gasket to become distorted that I can replace instead of the entire exhaust brake. Any help will be appreciated. Thanks ( Thomas Rouillard, 11/12/2022 )
The heat could have damaged the exhaust manifold gasket which would decrease the performance of the exhaust brake. ( Support )
Does this PRXB kit include clamps? Or do I have to purchase it separately? Thanks ( Yilun Yu, 09/19/2022 )
The clamps are sold separately. ( Support )
I have a 2000 Monaco Windsor with Cummins ISC 8.3 engine. My current pacbrake model is C16020 and serial number is 039573. It looks like it is 4 in diameter on the outside, and full marmon to the exhaust and half marmon to the turbo side. I would like to upgrade to a PRXB, please advise the PRXB part number and clamp part number, thanks! ( Yilun Yu, 09/17/2022 )
Your coach will take the PRXB Upgrade part # C40109, C11350 exhaust clamp and C11355 turbo clamp. ( Support )
I currently have a Pacbrake installed. I would like to upgrade to a newer unit. I am not currently at the motorhome, it is a 1999 Monaco Windsor 38' with one slide. I believe the serial number for the Pacbrake is 7044, and the date was 01/31/2005 on the information package.

I don't know the serial number for the Cummins engine. I do have the ISC Ops and Maint. manual and was told by the previous owner that it was a 330 hp engine. It does also have the Banks Ottomind installed, which must be used with the banks power pack.

Would the C40109 be the correct replacement for the Pacbrake that is currently installed?
What is included with this unit? Is it the complete install kit?

Thank you,

Jef Johnson
( Jef Johnson, 08/02/2022 )
Hi Jef, Here is the response I received from PacBrake "That serial number comes up as a C20348. It would be used on a Cummins ISL engine in a Monaco. The PRXB upgrade is part# C40103" So please make sure that you have an ISL and not an ISC. An ISL is an 8.9L and the ISC is an 8.3L. ( Support )
I have a 2004 Holiday Rambler motohome with a Cummins 8.3 engine which has a Pacbrake exhaust brake. The Pacbrake has not been able to slow the coach down like it use to so I took to struck repair shop and so far they road tested it and the electrical aspect of the PACbrake seems ok . The next step they are going to do is go into the mechanical workings of the brake. If it should need replacement what brake would I need to order? The current Pacbrake serial number is 004282. Your advice would be greatly appreciated.

Ron Scherer
( Ron Scherer, 07/24/2022 )

This should take either the C40108 if full marmon turbo face or C40109 if half marmon turbo face.

( Support )
Will the C40109 Pacbrake fit my 1994 Holiday Rambler Imperial motor home? it has an 8.3 L Cummins engine. ( Wayne Ramer, 07/02/2021 )
The C40109 would not be correct as that is for the later model 8.3L ISC and yours is the mechanical fuel C8.3. If the brake is mounted to the backside of the turbo housing, you would likely need C40100 but it is best to get the serial # off the old brake for us to verify. This would be stamped into a metal tag riveted to the cylinder actuator arm.
( Support )
Will the C40109 fit my 2006 Holliday Rambler Ambassador powered by a 8.3 Cummins diesel? Does it include the clamps and or gaskets necessary to complete the replacement. If I have to order them separate can you tell me which ones to order with cost. ( Larry Mahugh, 04/05/2021 )
Your RV will take the part # C40108 brake unit, turbo clamp part # C11355, and exhaust clamp part # C11350. ( Support )
What Pacbrake kit do I need for my 2007 T300 w/ 8.3 ISC Cummins--Allison 6 transmission-- Engine has been uprated to 310 HP
Do I need to change any valve springs?
Can you give me a quote for the parts I need to install a Pacbrake?
( Ed Werkhoven, 06/26/2020 )

Our notes indicate that you would need the following parts: C40107, C11591 and C10218. We do not see anything that would require different valve springs, that was only on the older mechanical C8.3L's.




( Support )
I currently have a jacobs exhaust brake but the actuator had failed, leaks bad and does not activate. All I need is the air actuator not the entire system. Is this something I could get through you? ( Gavin Bitz, 04/12/2020 )
I am not aware of a source for this part. I do not think the PacBrake actuator cylinder would be compatible with the Jacobs exhaust brake either. ( Support )
What all do I need for my 8.3 cummins ISC CM554 it now has a poor exhaust brake.
Will the valve train take the extra force?
I am in Canada.
Thanks for your time. John
( John Stafford, 06/25/2019 )
Yes the PRXB is designed as a direct replacement, the only engines that require modification to the valve train are the older C8.3 mechanical engines. ( Support )
Currently have a PACBrake on my ISC. PACBrake serial 098959. Which I am told is a C20384 PACbrake part number. Can I change out this older product with a new PRXB unit without any changes to the engine or transmission programming? ( Jon Tribbey, 05/19/2016 )


Yes the PRXB brakes are designed to be direct replacement for the original style and do not require any changes to the engine or transmission.

( Support )

Would this brake valve fit the C series 8.3L cummins. Truck is an international acco 2350E

( Gavin, 07/18/2015 )

I always advise to contact PacBrake directly for fitment, their phone number is 800-663-0096.

( Support )

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  • Views: 42181
  • Brand: Pac Brake
  • Product Code: C40109
  • Availability: In Stock
  • $1,297.27
  • $995.00