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Notn2bars · 07-21-2021, 10:24 AM

Fortunately we haven't been in a situation where the pacbrake has been needed. Unfortunately it doesn't work. While at home I discovered the pacbrake was frozen and the valve was stuck. Took everything apart, cleaned and lubed. Worked well on the bench. Reinstalled in the MH. Checked the air valve that operates the pacbrake and it was functioning as it should. While on the road Sunday tried to operate the pacbrake with the foot switch on the floor to the left of the steering column, nothing. My foot was off the throttle, cruise control off, and engine at idle. Any ideas as to what might be the issue? Is there a way to check the operation of the pacbrake while not moving? At a lose as to what to do, and very concerned about not having an operational pacbrake. Your help is greatly valued and appreciated.

Skip426 · 07-21-2021, 10:30 AM

Did you happen to notice if the , transmission down shift program started , on the shift pad , indicating the target gear for downshifting ( 2 or 4 , depending on program )?

wolfe10 · 07-21-2021, 10:31 AM

Assume your test with with your coach above 20 MPH.

If not working and the Pacbrake is free to move, first question is: Is the "turn on exhaust brake signal" reaching the Allison ECU? Said another way, does the Allison shift pad read out go from "6" to whatever the pre-select gear is (often either 2nd or 4th)?

Yes, it can be tested with coach engine off. Cut the positive wire to the Pacbrake air solenoid and apply 12 VDC from any source in the engine room to the air solenoid. It should "snap" shut and then open when the 12 VDC positive is removed.

Have you been lubing your PacBrake? https://pacbrake.com/product/c18037-superlube/

The second picture shows where to lubricate.

Notn2bars · 07-21-2021, 11:35 AM

Skip426 and wolfe10, thank you for taking the time to reply. No I did not notice anything happening on the shift console. Also, may have been going less than 20 mph when I tried it. Will check that out when we hit the road on Friday. The pacbrake works when 12 volts is applied to the valve, that was how I tested it when it was reinstalled. It has been lubed with Permatex Antiseize which is good to 1600 degrees F. It had been completely frozen and was quite a chore to get that portion working again. By the way, what are the steps to read the console to check the transmission fluid? Really want to get all the bugs out before we head out in the fall.

wolfe10 · 07-21-2021, 11:54 AM

If the transmission shift pad does not change from "6" to your pre-select gear when the exhaust brake should come on, the issue is electrical.

First suspect it the throttle position switch. If the switch does not send "throttle closed" signal, the exhaust brake will not and should not come on.

As to checking Allison transmission fluid level, it can only be done after driving a number of miles to get the fluid all the way to operating temperature. As you pull into a lunch stop is a reasonable time.

Park on level surface, engine running transmission in neutral.

Push the up and down arrows on the shift pad at the same time.

That will bring up OL and begin a count down. After the count down you will get either a + or a - and a number of quarts.

Pushing the up and down arrows again (a second time) brings up diagnostic codes. Ignition needs to be on, engine does not need to be running. This will bring up d-1 and any code that is stored. If there is a d-1, push the mode button to bring up d-2. Continue until d-"whatever" comes up followed by - - which means there are no more diagnostic codes. So best answer is that you will get d-1 followed by - -, meaning there are no stored diagnostic codes.

Timaz · 07-21-2021, 12:15 PM

On my coach, (should be the same as yours) when I push the foot switch the trans pad goes from 6 to 2. This shows it will eventually down shift to second gear as the speed allows. As you're coming to a stop at about 10 mph just release the foot switch and use the brakes to finish the stop. I use mine all of the time I need to slow down. I only use the brakes when I need more braking. Hope this helps.

Tim

TRH299 · 07-21-2021, 12:18 PM

How did you free up the butterfly mechanism? Mine has never worked, but trans downshifts when switch is on and foot is off throttle. I tried moving valve by hand, but it is seized. Was hoping I could unstick it some how by tapping with hammer or twisting with pipe wrench or something working through bedroom hatch above and without removing it.

Alpine36 · 07-21-2021, 12:27 PM

Quote:

Originally Posted by TRH299

How did you free up the butterfly mechanism? Mine has never worked, but trans downshifts when switch is on and foot is off throttle. I tried moving valve by hand, but it is seized. Was hoping I could unstick it some how by tapping with hammer or twisting with pipe wrench or something working through bedroom hatch above and without removing it.

As Brett recommended, use this PacBrake lube and follow their instructions.

https://pacbrake.com/product/c18037-superlube/

I've never seen a butterfly stick, but suppose anythings possible.
Usually you can disconnect the slave cylinder air line and lube thru the end of the cylinder port, while manually activating the cylinder by hand, working the lube into and past the piston.
A pair of vise grips and a big screwdriver may be required IF the cylinder isn't easily removeable.

Timaz · 07-21-2021, 12:36 PM

Quote:

Originally Posted by TRH299

How did you free up the butterfly mechanism? Mine has never worked, but trans downshifts when switch is on and foot is off throttle. I tried moving valve by hand, but it is seized. Was hoping I could unstick it some how by tapping with hammer or twisting with pipe wrench or something working through bedroom hatch above and without removing it.

Did you remove the linkage are from the butterfly valve and try to turn the valve? Or is the cylinder ceased?

wolfe10 · 07-21-2021, 12:37 PM

Actually, if the exhaust brake is seized, very unlikely that it can be freed up without removing it, soaking it and working it.

Again, the better answer is to lube it and use it.

TRH299 · 07-21-2021, 12:39 PM

Quote:

Originally Posted by Alpine36

As Brett recommended, use this PacBrake lube and follow their instructions.

https://pacbrake.com/product/c18037-superlube/

I've never seen a butterfly stick, but suppose anythings possible.
Usually you can disconnect the slave cylinder air line and lube thru the end of the cylinder port, while manually activating the cylinder by hand, working the lube into and past the piston.
A pair of vise grips and a big screwdriver may be required IF the cylinder isn't easily removeable.

My air cylinder is not stuck as I could get the cylinder rod to move.... The Pacbrake valve itself is what is stuck open. I tried spraying/soaking with PB Blaster then attempted to move it but I had little leverage and could not get it to budge. I am sure if I removed it I could get it free on the work bench, but it would be nice to get it free while still in place. If I could get it free, then it would make sense to buy or research what the Pacbrake lube is. With it seized up though I don't see the point in squirting anything but penetrating oil where the valve shaft exits the valve body.

Notn2bars · 07-21-2021, 12:41 PM

Wolfe10 great information, this is the info need for the tranny. Searched through all the manuals and couldn't find anything. Thank you so much for the detailed steps, will copy and print. Timaz, good to hear from you, hope your travels are going well. Thanks for taking the time to offer more help. TRH299, ours hadn't been used for at least 3 years by previous owner. MH had been parked at a storage facility. There was no way it could be freed up without taking out and putting it on a bench. Soaked in a bucket of ATF for a day or two, then tapped with hammer and twisted with vise grips. Worked butterfly back and forth until it was all free. Took the assembly as far apart as possible. Cleaned parts and lubed with Permatex Antiseize because of its high operating temp. of 1600 degrees F. Sorry to give you the bad news, but ours wouldn't budge while in the MH. Good luck with your repairs.

TRH299 · 07-21-2021, 12:58 PM

Thanks Notn2bars... Somehow I knew that was going to be the answer.

I was just wishful thinking on the easy way out.

I doubt the PO of my coach had been using it as he lived in the Florida keys with no hills to negotiate. On top of that, it sat unused after the wreck for at least two years before I got it moving under it's own power again and completing the rebuild. Luckily my trip to Oshkosh coming up does not have much in the way of hills.

FWIW, on my '04 the cruise control shuts off when I energize the non functioning Pacbrake and with my foot off the throttle at speed and my transmission downshifts sooner than normal. At low speed actuation however the trans no longer downshifts.

wolfe10 · 07-21-2021, 01:04 PM

Quote:

Originally Posted by TRH299

FWIW, on my '04 the cruise control shuts off when I energize the non functioning Pacbrake and with my foot off the throttle at speed and my transmission downshifts sooner than normal. At low speed actuation however the trans no longer downshifts.

The transmission will not downshift to allow high RPM in the lower gear past the pre-select gear for exhaust brake use.It will revert to normal downshift RPM as you slow down below 4th gear rather than downshift as soon as it will not over-speed the engine in the lower gear.