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Old 07-31-2016, 03:16 PM   #1
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Checking Pacbrake Operation

After my thread about going down steep hills in the Allison forum, I decided to make sure my Pacbrake is operating. I read another thread about removing the cam shaft from the air to make sure its free to close, but I have an issue doing that.



After taking the snap ring, in the center of the picture, off off the shaft, the shaft is too long to drop completely free of the assembly. It hits the top of the body of the Pacbrake. Any ideas?; The area around the cam shaft is wet because I sprayed it with liquid wrench.
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Old 07-31-2016, 04:22 PM   #2
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Ran into same problem with my Pacbrake. Found that there is another snap ring on other end of pin. After removing front snap ring. I pushed pin towards exhaust brake housing. Used a needle nose pliers to remove rear snap ring. Then push pin out from the rear.
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Old 07-31-2016, 04:34 PM   #3
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I take my air hose, remove the air line to the Pac brake, lube it up with Pac Brake lube, then take the air hose put it on the air line fitting and give it enough air to move the Pac Brake rod and the butterfly. I do it several times to make sure it is working right.
Doing this blows the several drops of lube into the cylinder and moves all the pivot points, and I can see if it is operating properly.
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Old 07-31-2016, 07:00 PM   #4
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I got the pin out and I can spin the cam through a full range of motion. From reading several threads on this subject, it looks like that is normal so I guess its working. I can make the arm move using an air compressor so as long as it's getting air when I activate the pacbrake everything is normal. Since the shift panel says 2 and the transmission downshifts it looks like its working. I'm trying to decide if the upgrade is worth the $1100.
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Old 08-05-2016, 08:32 AM   #5
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I finished checking out the Pacbrake this morning. I used the 12 volt battery from my tow dolly breakaway kit and applied voltage to the brake connector. The brake is working fine. The cylinder moves through the full range of its stroke--about 4-5 inches so I'm assuming the brake is fully closing off the exhaust. The only way to really tell is to take it out and look at it. I've read some threads about the brake only moving an inch or so so I was wondering how far it would move in operation.
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Old 08-05-2016, 03:38 PM   #6
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That's a good way to check your Pacbrake. I use a 12 volt DC power supply. I replaced my OEM exhaust brake with a Pacbrake PRXB. It worked OK. But I was noticing that at times it did not seem to be working as well as it should. First thing I did was install a gauge to test back pressure of exhaust brake. Found that after being energized a few times back pressure was about 10 psi less. I then did the same test as you did. After cycling exhaust brake a few times I found that it was not fully opening when the cylinder hit PRXB spring. Next I put a gauge on the cylinder. Found that after cycling exhaust brake a few times pressure dropped below 100 psi. Then cylinder did not have enough pressure to move cylinder full stroke. OEM compressor and pressure switch is set 85 to 105 psi. This did not supply enough air to exhaust brake at times. Also found that OEM compressor had a hard time keeping up with amount of air that is needed to keep exhaust brake working in city driving. Fix was a new compressor and pressure switch that keeps pressure tank between 120 and 150 psi. Also put a pressure regulator set to 105 PSI for supplying air to valve that energizes cylinder. The interesting part of this whole story this is a Pacbrake kit to replace the OEM exhaust brake that came on my Chevy C5500. Pacbrake specifies that a PRXB needs 100 psi to operate properly and fixed orifice type needs at least 80 psi. There instructions say to use stock compressor.
Hope this info helps someone replacing a exhaust brake with a Pacbrake PRXB.
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Old 08-05-2016, 08:26 PM   #7
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Quote:
Originally Posted by ronjhall View Post
That's a good way to check your Pacbrake. I use a 12 volt DC power supply. I replaced my OEM exhaust brake with a Pacbrake PRXB. It worked OK. But I was noticing that at times it did not seem to be working as well as it should. First thing I did was install a gauge to test back pressure of exhaust brake. Found that after being energized a few times back pressure was about 10 psi less. I then did the same test as you did. After cycling exhaust brake a few times I found that it was not fully opening when the cylinder hit PRXB spring. Next I put a gauge on the cylinder. Found that after cycling exhaust brake a few times pressure dropped below 100 psi. Then cylinder did not have enough pressure to move cylinder full stroke. OEM compressor and pressure switch is set 85 to 105 psi. This did not supply enough air to exhaust brake at times. Also found that OEM compressor had a hard time keeping up with amount of air that is needed to keep exhaust brake working in city driving. Fix was a new compressor and pressure switch that keeps pressure tank between 120 and 150 psi. Also put a pressure regulator set to 105 PSI for supplying air to valve that energizes cylinder. The interesting part of this whole story this is a Pacbrake kit to replace the OEM exhaust brake that came on my Chevy C5500. Pacbrake specifies that a PRXB needs 100 psi to operate properly and fixed orifice type needs at least 80 psi. There instructions say to use stock compressor.
Hope this info helps someone replacing a exhaust brake with a Pacbrake PRXB.
That's some good information, I didn't have any idea how much air pressure it'd take to engage the brake. The first time I tried to energize the brake, it only moved about half way, then I'd hear the Pacbrake click, but the cylinder didn't move the brake arm. I started the coach and got the air pressure up to 120 lbs and tried it again and it worked normally.
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