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Pacbrake malfunctioning and causing damage


Grassy

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I have a low mileage (130K miles) '01 cat 3126b with a pac brake.

 

Earlier this summer, I was driving hilly terrain and I had my pac brake on... I don't usually preferring to turn it on when required... anyway, I lost power going up a hill and then an air line blew. It was a line going from the firewall down through the transmission tunnel. Wasn't quite sure what happened..thought it was that the line was too close to the exhaust and after fixing the line, I had no problems with power. On the way back from the camp site, it happened again and I had a Freightliner tech diagnose the problem as a clogged fuel filter. He fixed the line again and changed the filter and I was on my way.

 

I relocated as many lines away from the exhaust as I could just in case...

 

All was good until last week..same thing happened except as soon as I started losing power, I looked at my pyrometer and the needle was rising very fast.. I cut power and pulled over and shut the engine off. I turned off the pac brake and started the engine again. 2+ hours of driving and no probs. Some plastic was melteded but nothing important.

 

I e-mail pacbrake a couple days ago with what happened and inquired about a rebuild it..I read somewhere that just taking it apart, cleaning and re greasing did work and wondered if there was a rebuild kit available. No word back.

 

Would the pac brake be holding open the exhaust valves causing the exhaust temp to sky rocket ?

 

I am relatively new to diesels and this one has me baffled.

 

Thanks

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Call them, rather than e-mail. They have really good customer support. I didn't read anything that suggests any issues with the exhaust brake, but I might be mis-reading your post. What was the unimportant plastic that melted? Very few things in life are truly unimportant, especially if they're melted.

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Sounds to me like you've got at least a couple unrelated issues going on at the same time.

Clean up the wiring/tubing underneath. Make sure the lines are connected properly, to the correct lines. Add supports as needed to stop the melting.

Determine why the fuel filter was plugged. When was it last changed? Length of time in service, and miles. Is it starting to plug again? What's the fuel look like, in the tanks?

Exhaust brake requires air to activate, so again, make sure you have any melted lines connected properly. A sticking exhaust valve shouldn't cause a spike in EGT, but will definitely cause power loss. When I say EGT spike, it needs some context. It can cause a temp climb, but if you were already off the throttle, when you noticed the gauge climbing, I'd suggest they aren't related. If you were under full steam, then possibly (probably) connected.

I'd suggest running with the brake turned on all the time, and controlling it's activation with your throttle pedal. I also suggest the same thing for engine brakes, but that's a whole other bag of fish.

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Thought so too...that is why I did clean up the wiring..and replaced some of the tubing. Will be wrapping exposed wires / tubes in heat wrap next.

 

My fuel filter clogged (?) at 7K miles. Fuel look clean. Was given the story that the Freightliner dealership was replacing 2 fuel filters for every one oil.. I have asked a lot of semi drivers and they don't agree.

 

Engine temp didn't move. Was hard on the throttle (and on a steep grade) when EGT spikes quickly..as in the pyro needle was moving fast..was not on cruise.

 

Truck works well when pac is turned off. A couple of weeks ago, I left it on for hours when I was on cruise in a relatively flat area.

 

I need to call pacbrake. This is odd.

 

Thanks for the help. I will post when it is solved.

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The most common problem I hear about exhaust brakes is "I rarely use it but when I do try to it is not working right." That is so common because when you don't use your exhaust brake it builds up carbon deposits on the valve and on the bearings which causes it to stick. The cure can be as simple as pulling it apart, knocking off the crud and putting it back together if you get to it before it is fully frozen. The way to prevent that from happening is to use the brake fairly often so that it is exercised and the carbon builds up.

 

Do you have the Allison transmission and are you avoiding the brake because when you use it the transmission downshifts early on activation? That is a simple programming change and you can have the exhaust-brake preselect changed from the usual 2nd gear to either 4th or (my choice) 5th or even disabled completely. That does mean you will need to use the touch pad to downshift and get maximum braking but it will also eliminate all the gear changing you get with 2nd as the preselect.

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  • 2 weeks later...

.

 

Do you have the Allison transmission and are you avoiding the brake because when you use it the transmission downshifts early on activation? That is a simple programming change and you can have the exhaust-brake preselect changed from the usual 2nd gear to either 4th or (my choice) 5th or even disabled completely. That does mean you will need to use the touch pad to downshift and get maximum braking but it will also eliminate all the gear changing you get with 2nd as the preselect.

Great info Stanley. How does one get the trans reprogrammed?

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We usually went to a W.W. Williams Detroit Diesel Allison shop in Arizona, they were pretty laid back and charged 1/2 shop hour for the job. Both times we had things changed the tech was happy to scroll through all the trans settings and explain/change any of them since the preselect change took less time than finding the programming plug under the dash. We ended up setting the transmission to fast-adapt mode and two shifts, that made it reprogram the shift force faster when switching from towing to bobtail, the transmission did need to be warm before it would adapt so you had to remember to do a short drive while it was still warm in the winter.

 

http://www.wwwilliams.com/locations_trans.cfm?p=Allison

 

There are two classes of programming that you can do to the Allison, user facing stuff like preselect and stuff that is done from under the dash and more invasive options like 2nd gear start in economy mode that require cracking the transmission case, we lusted after that change but the $400 or so charge to make it was just too steep for the change. We'd sure look at that if buying new where it is a no-cost option.

 

This may be for an older shift pad than you have but it is good info: http://www.rvtechstop.com/resources/Articles/allsonok.pdf

 

The Allison site - transmission finder page, that will tell you about your specific transmission, last time I dug around they had lots of good info there.

 

http://www.allisontransmission.com/parts-service/my-transmission

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Pacbrake on a small truck may be different. On the Ram I had, the Pacbrake was inline under the floor, not hooked to the turbo directly. I cleaned the butterfly valve spring and arm with brake cleaner and then lubed the piston arm with Pacbrake approved lube. (may have been wd-40). The valve never stuck closed, but after being in south Texas for awhile it was caked with caliche dirt that had hardened and would let the valve operate.

 

As for the EGT spikeing, that means that your exhaust gas temps were rising, meaning that the cylinder temps were getting hot. Usually this means not enough air flow into the engine. Downshifting to a lower gear usually resolves the issue- hifgher RPM means more air into the engine, resulting in cooler temps. NEVER but NEVER shut off a hot diesel, always let it cool first. The oil in the turbo will literaly cook resulting in the bearing being coated with a hard residue. This results in a signifantly shorter turbo life.

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Cannot argue much of what been said...this is all new to me. As per sig, I run an ultrashift. Oddly enough, a very unique on in my area. Freightliner Atlantic has never seen one before.

 

I guess there is some theory/reality happening here. By me getting off the gas ..pulling over..shutting everything down and starting up again, I was able to continue on to my destination w/o having to place another call to Good Sam Roadside Assistance. I have not had good luck with them.

 

I have driven the truck another 6 or 7 hours while pulling the trailer and another 3 bob tailing w/o any repeat of the situation. PacBrake still hasn't returned my e-mail so a call has been in order. I am dealing with an electrical issue with the Eaton (and bad diagnosis) so this issue has been pushed down the list.

 

We are finished rv'ing for the season so other than my normal stuff, I can focus on this. I am guessing that it is lack of use and a tear down is in order.

 

Fun :)

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