Attention: TDR Forum Junkies 
Sorry guys it's kind of long but I've made a lot of changes in the last couple of months. Started with a new OFE, PDR Twins, and a Pac Brake PRXB. Next came the RASP and a full Kelderman Air Ride. Now that I've had some time to evaluate each product I thought I would give my impressions. I'll break these up into separate threads to make questions and comments easier to follow.
As parts of the twins upgrade the swap to the new 5" inline PRXB was a no-brainer. The performance after having used the little direct mount Jacobs was however lacking in more ways than one. I knew going in that this was a new design and had very little real world testing on our tiny Cummins behind it.
I started out with the standard air group that is supplied with the 4" brake and added the optional tank (read TINY) that Pac Brake offers. The application time was horribly slow and the braking force was less than spectacular so let the testing and modification begin!
After speaking with TJ (the tech at Pac Brake) I decided to start with a higher pressure air switch on the little Viair 275 that Pac supplies. I finally found an adjustable switch that allowed me to raise my pressure from the preset 85/105 that comes with the supplied pump. Bumping the pressures up to the 115/130 range made a huge difference in the braking force of the PRXB. The application time was still horribly slow however. I also rewired the relay on the compressor to allow it to run when the tank needed air instead of just when the brake was applied. The PRXB's air cylinder is huge compared to the 4" brake and it was wiping the tiny tank out on every application.
The next step was the addition of a much larger air tank from a Freightliner at the local wrecking yard. This helped to keep the compressor from running constantly trying to keep up with the oversized application cylinder. Application was still way to slow for my taste.
During all of this I had the Kelderman Air Ride installed so air supply was no longer an issue. I now had the Viair 400 and added another air tank on the opposing frame rail. We're getting closer.
TJ had sent me a 1/4" solenoid valve for my air horn setup and it was sitting on the bench. Since I no longer need the compressor and relay group mounted on my engine (never liked it sitting there anyway since it looked terrible) I had a brainstorm. I would add a relay like the Jacobs kit switched via the ECM wire and use the 1/4" solenoid valve mounted right where the Jacobs had been removed from.
Got everything done, fired up the truck and hit the switch. BANG! Immediate application finally! Went for a quick test drive and the application time was down to 1 second flat. Just enough time to let the fuel rail clear. Braking performance is awesome all the way down to idle and the warm-up times are much faster than the Jacobs I was so very happy with. I had to add an adjustable valve to the air release side of the Pac to slow the opening down some. With the excellent back pressure offered by the PRXB the "POOF" from the stacks when I turned it off was actually making people jump and stoplights and I was afraid I was going to cause an accident. :-laf With the valve adjusted to slow the opening slightly it's down to a loud "whoosh" similar to air brakes releasing instead of sounding like a 60# air cylinder bursting open.
If you've got twins or a 5" exhaust and need an EB the PRXB is the way to go but plan on giving it a good air supply and a large solenoid valve to flow the needed air. It's a big sucker but it sure works!
Thanks to PDR for the great pricing and TJ at Pac Brake for the tech support! Pictures are up in my gallery of the set-up I ended up with.
Richard
As parts of the twins upgrade the swap to the new 5" inline PRXB was a no-brainer. The performance after having used the little direct mount Jacobs was however lacking in more ways than one. I knew going in that this was a new design and had very little real world testing on our tiny Cummins behind it.
I started out with the standard air group that is supplied with the 4" brake and added the optional tank (read TINY) that Pac Brake offers. The application time was horribly slow and the braking force was less than spectacular so let the testing and modification begin!
After speaking with TJ (the tech at Pac Brake) I decided to start with a higher pressure air switch on the little Viair 275 that Pac supplies. I finally found an adjustable switch that allowed me to raise my pressure from the preset 85/105 that comes with the supplied pump. Bumping the pressures up to the 115/130 range made a huge difference in the braking force of the PRXB. The application time was still horribly slow however. I also rewired the relay on the compressor to allow it to run when the tank needed air instead of just when the brake was applied. The PRXB's air cylinder is huge compared to the 4" brake and it was wiping the tiny tank out on every application.
The next step was the addition of a much larger air tank from a Freightliner at the local wrecking yard. This helped to keep the compressor from running constantly trying to keep up with the oversized application cylinder. Application was still way to slow for my taste.
During all of this I had the Kelderman Air Ride installed so air supply was no longer an issue. I now had the Viair 400 and added another air tank on the opposing frame rail. We're getting closer.
TJ had sent me a 1/4" solenoid valve for my air horn setup and it was sitting on the bench. Since I no longer need the compressor and relay group mounted on my engine (never liked it sitting there anyway since it looked terrible) I had a brainstorm. I would add a relay like the Jacobs kit switched via the ECM wire and use the 1/4" solenoid valve mounted right where the Jacobs had been removed from.
Got everything done, fired up the truck and hit the switch. BANG! Immediate application finally! Went for a quick test drive and the application time was down to 1 second flat. Just enough time to let the fuel rail clear. Braking performance is awesome all the way down to idle and the warm-up times are much faster than the Jacobs I was so very happy with. I had to add an adjustable valve to the air release side of the Pac to slow the opening down some. With the excellent back pressure offered by the PRXB the "POOF" from the stacks when I turned it off was actually making people jump and stoplights and I was afraid I was going to cause an accident. :-laf With the valve adjusted to slow the opening slightly it's down to a loud "whoosh" similar to air brakes releasing instead of sounding like a 60# air cylinder bursting open.
If you've got twins or a 5" exhaust and need an EB the PRXB is the way to go but plan on giving it a good air supply and a large solenoid valve to flow the needed air. It's a big sucker but it sure works!
Thanks to PDR for the great pricing and TJ at Pac Brake for the tech support! Pictures are up in my gallery of the set-up I ended up with.
Richard
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