Just six years ago I had a PRXB exhaust brake installed on our C8.3 Cummins. It worked very well for just about five years. During that time I religiously applied the special lubricant provided by the PAC people at least twice a year. This past fall I noticed no change in the sound emanating from the engine while idling, but didn't think much about it. This spring, however, I again heard no change, so I opened up the engine compartment (elevated the bed) and sure enough, the piston did not move when PAC was on or off.
I called the company, described the situation. The reply was "Oh yeah, the butterfly valve is frozen up, probably from corrosion". "You'll probably have to get a new unit". After finding out that a "unit" is the whole brake (last one was $880 not counting installation) system, I am not a happy camper. Six years doesn't seem to me to be very long, especially since the coach sits without engine running for 80% of the time, even when traveling. Yes, I realize that more use is better for components like this, but that is the nature of RVing: one travels to a destination, then enjoys the location.
Has anyone else (has to be the older GV's, before the transmission brake entered the scene in 1993) had experience with the PAC brake, good or bad? Anyone had success in freeing up the valve by soaking in solvent?
Any input would be appreciated.
I am having the same issue. 1990 U280 with dp brake system. Same thing butterfly is stuck. But I think with a litle bit of elbow grease it should work again.
Don, we do not have one but I would think if you took it off surely you can "unfreeze" it. or pour a pile of release oil everywhere (not wd40) and disconnect the air cylinder and try work it back and forth.
JohnH
X2 on JohnH's advice - pull it off and see what's the problem. It's only held in by two big clamps, so not tough to remove.
We have a exhaust brake (not Pac Brake brand) - it's just a simple steel butterfly valve inside a cast iron housing. I haven't had any trouble with ours freezing up - it has a built-in function where every time we start the engine (assuming the coach air pressure is over 60 psi) the brake valve cycles closed and open twice. This is supposed to help prevent the exact problem you have.
Are you sure the air cylinder is working? The Origa air cylinder control valve (similar to a Norgren valve) on ours crapped out, which disabled the brake. I found a identical replacement valve on eBay and got it working again.
Guess that since two members are having this problem and no attention
from PAC anyone thinking about doing business with them need to stop and
think about the companies response. Probably both units did not have too many
miles. This speaks of the quality of the brake???
Carter-
It (butterfly) shouldn't be operable (closed) at an idle, if it was ,it would soot/carbon up and eventually will seize.
And yes they can be freed up, but will take some time soaking in diesel/or other de-carbonizer and elbow grease. the air (or electrical) actuator will need rebuilt/cleaned up as well.
Chuck, I don't know if air cylinder is functioning; I'm just taking the word of the company's tech guy. If I could disconnect the cylinder from the valve, actuate it, I may be able to determine which is the culprit.
The gv I am looking at has the PAC brake disconnected. Hope it can be unstuck. Maybe they should spent 2$ and produced a stainless shaft.
Don,
My D-Celerator brake is made by US Gear (AP Products). Here is a link to the "Preventative Maintenance" tech sheet. It may have some useful tips for restoring your brake to proper function. Also, a few photos of the inside of my brake, the last time I had it apart. On mine, just one nut must be removed to disconnect the air cylinder from the valve lever. Since the brake sits up high in the engine compartment, it is pretty easy to work on by lifting the bed. You can see they are quite simple inside. The "hole" in the side of the pipe upstream of the brake is the bypass port. When the brake reaches the max back pressure setting (30 psi on my engine with stock exhaust springs), a small spring-loaded valve opens in the bypass port, and bleeds off excess back pressure around the brake.
Bushing Service Procedure, D-Celerator Diesel Exhaust Brake (http://www.usgear.cc/dc_bushing.htm)
Yes, there are several places an exhaust brake can fail:
Yes, it can seize mechanically.
It may not have the electric signal from the switch and/or the throttle closed signal-- if Allison 3000, does the gear indicator change to the preselect gear when the exhaust brake is turned on. If so the electric signal in the front is working.
The electric signal may not be reaching the air cylinder on the exhaust brake. You can disconnect the positive wire at the brake and apply 12 VDC positive from any convenient source there in the engine room. Can do this with the engine OFF. Do NOT backfeed the positive wire that goes to the dash, that is why I said disconnect the positive wire.
The shaft on my brake
is stainless steel. I would be surprised if the PAC brake shaft is anything but stainless steel. I think the biggest cause of "problems" with these brakes is simply lack of exercise. The brake should be cycled several times
every time the engine is run.
It's six years old what do you expect/want them to do? Mine is 20 years old and still works like new.
Sounds reasonable, sometimes a little stirring of the pot will bring out the best recipe for success.
Time for some of the acetone trans fluid cocktail or Kroil
Mike,
I'd expect some degree of customer service, do you remember that? They should have
offered to refer the customer to a service facility or shown some degree or empathy.
Carter-
Last summer my son and I took mine apart. The gas cylinder was frozen, and we found a replacement that worked well. We then took the flange section to his shop and he ultrasonically cleaned the section. The valve operates, but no back-pressure is generated. I ordered a blowout valve from PacBrake using the diagram (C-10100) for my system and it came quickly, but the whole mechanism still doesn't operate as specified. I also got the PacBrake lube, and lubed all the parts.
Mine is air-operated with a foot switch on the other side of the steering arm. Activation works, just not what I was hoping for. Was looking at replacements options.
Chuck,
That is quite a route you show traveling with more hills than flat land.
I see where you would need an engine brake. I wonder if anyone on here
knows of a place that rebuilds them?
Safe travels,
Carter-
Hmm, I know ours was replaced in 04 with a "new generation" PRXB , Brett would know. It was lubed in 2014 w/factory spec'd. Ours is on the Allison shifting console at the bottom. Lowered by Brett to give better left-hand access to the retarder rocker switch. Works perfect! b^.^d
Are you just testing it a idle?
The way to test the exhaust brake (can't be done at idle and with engine off only as I outlined above (cut positive wire to air cylinder and supply 12 VDC positive from another source):
On a low-traffic road, use the transmission down arrow/selector to lock the transmission in a gear-- 3rd or 4th work fine-- just depends on what is a good safe speed on that road. Accelerate to higher RPM in that gear. Let off the throttle. Turn on/off/on... the exhaust brake. Because the transmission is in the same gear during the whole test, you should feel additional braking HP with exhaust brake ON.
And, if you have pretty good hearing, you can do the same thing with concrete building on the coach exhaust side. The exhaust sound will be different with the exhaust brake on.
[quote author=mike leary link=msg=266968 date=14913 Ours is on the Allison shifting console at the bottom. Whole unit lowered by Brett to give better left-hand access to the console and retarder rocker switch. Works perfect! b^.^d [/quote]
No, have tried it in low gear, high gear, low RPM and high RPM, hills and regular flats. Nada.
That seems odd. You can see in my photos above how tightly the valve fits when closed. If your valve really is closing completely, I don't see how it could fail to generate
some back pressure.
If I want to check the operation of my brake, I just set the idle at about 1000 rpm, then stand back by the exhaust pipe and feel the exhaust while the DW works the switch. When the brake valve closes, the flow out of the exhaust pipe drops to nothing and the sound changes. When it opens back up, there is a big puff of pent up exhaust pressure, and sound returns to normal.
(The other) Chuck,
You said you replaced the air cylinder. Are you sure the new cylinder has sufficient stroke to move the valve to a completely closed position?
When we bought our 1993GV last July the previous owner said that they never used the Pacbrake. There was no response in braking action when we used it last summer, so I assumed that it was corroded and 'frozen', and in prep for this year's travel season I set out to get it fixed. A mechanic friend led me through checking the components and we found the problem to be electrical rather than mechanical. A dodgy connection and a wire (one of three) not attached to the switch.
The system check steps were (1) disconnect the air hose to cylinder to see if there was air pressure with switch activation (key on, motor off, switch up), (2) using a circuit tester we did continuity and current testing to determine that the solenoid was functioning, (3) begin tracing the wire route between the solenoid and the switch.
The switch/wiring issue led to solving a bit of a wiring mystery. (Being a 1993, our GV has had lots of wiring additions and deletions over the years). I had a disconnected wire end with a slip on connector end, but no apparent place for it to be attached anywhere. When I removed the switch from the dash to check the connections, two out of the three prongs had wires attached and my mystery wire (hanging below the console was the perfect length to be the right one) slid on as if it belonged there. It did. So...the questions then were, Why was it disconnected?, and What purpose did it serve?. Back to the back end wiring. It appears as if at one point there was a switch box (I can still see it but it has no wiring connected to the tabs) that had something to do as a sensor (?) for when the accelerator treadle was released (?) that was a component of the original system. The short 'jumper wire' that replaced the switch and completed the circuit, basically fell apart in my hand when I was checking it and the wires were corroded. Eliminating that bad connection led to proper activation of the Pacbrake when the switch was 'on'. Driving tests to come in a few days to confirm success.
My remaining questions are, what is the real purpose of the disconnected/ by-passed switch in the engine compartment; and, assuming it was original equipment, why was the wiring changed? I will remove it and see if I can find a part number. The Pacbrake Head Office and shop is about 15 minutes drive from where we are now so it should be easy to get a part.
Woody,
It's fun figuring out these electrical puzzles...right? (Keep telling yourself that)
I know your PAC system is different from my US Gear exhaust brake, but hoping there is some similarity that might help you. Does your throttle pedal have any kind of wire attached to it? Mine has a wire connected to the top right corner. If you look closely (photo below), you can just see the tab where the flat "push-on" wire connector is attached. The pedal has some kind of pressure sensor on it, which is part of my exhaust brake installation. If I have the brake turned on and apply any throttle, the brake turns off. If you don't have this wire on your gas pedal, I'm wondering how your brake would "know" when you step on the throttle. Some kind of sensor on the throttle linkage at the engine?
If you are that close to the Pacbrake head office, I would see if they can provide the installation paperwork for your model brake. Might answer a lot of your questions.
I did a run down the road and as Wolfe10 suggested I turned the switch on/off/on while in 3rd and 4th gear at higher revs going downhill. The Pacbrake works - however it seems that it also 'works' going uphill when the switch is on and the same gear/revs combination is at play. Therefore the connections as they now stand are for manual operation only. I am happy to get this far and will sort out the switching/wiring that is needed for the Pacbrake system to 'know' when accelerator is pressed.
I am sneaking up on a full solution and learning several things as I do it. I remain optimistic.
Maybe manually engaging of the exhaust brake would be a simpler solution. Unless you like this sort of challenge. BTW this isn't Woody, a former bluebird owner by chance?
If the same Woody you are referring to, he is still in a Bluebird 2003 LX, full timing, and still in the USAR.
The PAC brake on my 330 Cat appeared to be frozen.. The micro switch in the floor switch had lost contact. Replaced micro switch ..problem solved.....
Update: Replaced the PacBrake mechanism and it all works great. Had replaced it 9 months ago and it works great on downhill and stopping when getting off the highway. Holds the RV steady in 4th gear when going down those long 6% downgrades without brakes. Glad I replaced it.