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BMC (Bluebird Motor Coach Unique Issues) If you have a unique issue with your BMC coach and it can't be answered in one of the other forums here, then this is where you can list it.....List your BMC Parts here too.

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  #21  
Old 02-09-2010
Lee Davis's Avatar
Lee Davis Lee Davis is offline
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Default Pacbrake issues

I was talking with a guy at Pacbrake (TJ) about some issues and he asked me if my BMC used the bus air compressor or has a separate 12 V compressor for the Pacbrake. I had no clue. Anyone know?

Apparently mine only works down to 4th gear and after that is is not getting the signal to work in the lower gears. (That makes it a little more exciting when going down a mountain in 3rd gear for example . He said he thinks that could be in the Alison software or in the throttle sensor. I had the throttle sensor checked awhile back when I had my injector problems so don't think that's it.

Anyone ever had any Pacbrake work or analysis done and if so, did you find a good place to get work done on that. When Cummins hooked up my throttle after working on the injector pump the Pacbrake didn't work so the guy spent some time figuring out what to do to it. I suggested he get their Pacbrake expert and he said he was it. He admitted he didn't know a lot. So the upshot is that although the Pacbrake guy suggested a Cummins shop that also dealt with Alison transmissions, I'm not sure that will give me much.

Ideas?
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Lee and Jacque Davis - Full Timers

Lee - 423-292-5767 or Jacque 423-262-9569
or lnjdavis@gmail.com Please call or email instead of private messages


1995 BMC 37
300 HP Cummins 6CTA 8.3 Turbocharged Diesel
Boldly Going Nowhere
http://www.bbirdmaps.com/index.cfm #117
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  #22  
Old 02-09-2010
AC7880 AC7880 is offline
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Lee,

Check out the links from this thread:
http://www.wanderlodgeownersgroup.co...light=pacbrake

I'll take a look as well when I get some free time.
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  #23  
Old 02-09-2010
fxdwg fxdwg is offline
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Lee,

Since your bird doesn't have an auxillary compressor (IIRC), then the pac has to be powered through the engine compressor.

Did the pac work before the injector pump work? Something there isn't right, either a wire is dislodged or something. Doing the pump shouldn't have done anything to the pac.

And unfortunately with electronics, just because it tested fine even yesterday doesn't mean it's fine today. It has to be tracked down.
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  #24  
Old 02-09-2010
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Somervillebus Somervillebus is offline
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Lee,

Have you checked to see if the transmission has logged any codes from the selector? Throttle position sensor is certainly a possibility ... you said they checked it. How did they check it?
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  #25  
Old 02-10-2010
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Lee, I also have a question.

When you turn the Pac Brake on does the transmission pad still "preselect" 2nd gear in the left hand window?
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  #26  
Old 02-10-2010
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Lee Davis Lee Davis is offline
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Default Pacbrake

My Pacbrake has worked the same ever since I bought the bus 5 years ago. I thought it was working correctly then and now, but was not satisfied with the braking power below 4th gear. When I am running down the road at about 60 MPH and take my foot off the gas (on the flat) and turn the exhaust switch on coming up to a stop sign or light for example, there is a short delay (it usually slows down to about 50 MPH) and then the transmission indicator goes to 4 - 4 (I assume it is waiting until it won't rev up over 2800 RPM) and it kicks in. That part is fine.

What I don't like is that I don't think it is working below 4th gear. For example If I turn it on at the top of a steep hill in 3rd Gear it doesn't seem to be helping me slow down any as I go down the hill. (TJ at Pacbrake told me to turn it off and on to see if there was any difference so I will do that when I go somewhere next). He said if it is not working below 4th gear there could be a problem with the throttle sensor, or perhaps the Alison software because that's supposed to tell it what to do. He said it should work in the different gears all the way down to 20 MPH at which point it will not. He also mentoned it works a lot better at higher RPMs (which is certainly where I am coming down mountains) because at lower RPMs the butterfly doesn't do a good enough job as i recall I think of restricting the flow? I did notice they have a new PXRB model that works much better at all RPMs and costs about $800 and depending on mating surfaces and Turbo configuration may be real easy to install. However, apparently BMC's have an inline Pacbrake Different from the 1/2 and full Marmon versions for the Cummins 8.3 listed on the Pacbrake website). The new PXRB inline model won't work unless the engine comes equipped with the heavy duty 65 lb exhaust valve spring. I am checking on that now. In any case, TJ said there was no use putting in anything that would work better if my current problem is not fixed first. I would like to make sure my current Pacbrake is working correctly as coming down steep hills now requires more off and on brake use than I like, even at slow speeds (35mph) in third gear for example I get hot brakes occasionally, which is not a good thing. They have never quit working (could at some point) but I'm sure they are wearing faster. I read somewhere you should not have to brake more than two or three times over a mile, but to bring the RPMs down from 2500 (I don't like to get up near the 2800 it says not to go over) to about 2000 where I let off the brakes to let the RPMs start up again, I often have to brake more than 2-3 times per mile.

I have had my Alison transmissionm checked for a variety of other things in the past, and even had to replace the computer under the keypad (very expensive.....don't say anything Woody) and have never had any error codes that had to do with the Pacbrake (I'm not sure there are any). The throttle sensor was looked at when my injector pump work was done and as I recall it was mostly due to the throttle linkage (although I might be wrong about that).

Anyway, TJ said a knowledgeable Alison shop if there really is a problem with the Pacbrake should be able to troubleshoot and fix it. I don't know if that's really true or if it will end up costing me a mint because they might not be familiar with it and end up doing a lot of extraneous stuff while learning (I have had that experience too many times)

So here's my plan.

Try to make sure it really is not kicking in below 4th gear or I just couldn't tell.
If it is working OK, consider a PXRB model that will work better I want more safety on those steep downhills)
If not, find someone who knows something about this kind of thing to check it out (help here would be nice if anyone knows a good shop for this stuff) TJ at Pacbrake suggested a knowlegable Alison place but I guess I better call first to see what they know.

So that's it for now
__________________
Lee and Jacque Davis - Full Timers

Lee - 423-292-5767 or Jacque 423-262-9569
or lnjdavis@gmail.com Please call or email instead of private messages


1995 BMC 37
300 HP Cummins 6CTA 8.3 Turbocharged Diesel
Boldly Going Nowhere
http://www.bbirdmaps.com/index.cfm #117
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  #27  
Old 02-10-2010
AC7880 AC7880 is offline
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I'm not finding much yet. If your replacement Allison ecu was not programmed correctly: http://www.pacbrake.com/PDF/134.PDF

The higher the engine rpm the higher the holding power of the pacbrake due to more exhaust restiction goin on.
Drivers guide: http://www.pacbrake.com/PDF/134.PDF

There is no seperate 12 volt compressor for the PAC on our BMCs.


I'll look for more info.



Quote:
Originally Posted by Lee Davis View Post
My Pacbrake has worked the same ever since I bought the bus 5 years ago. I thought it was working correctly then and now, but was not satisfied with the braking power below 4th gear. When I am running down the road at about 60 MPH and take my foot off the gas (on the flat) and turn the exhaust switch on coming up to a stop sign or light for example, there is a short delay (it usually slows down to about 50 MPH) and then the transmission indicator goes to 4 - 4 (I assume it is waiting until it won't rev up over 2800 RPM) and it kicks in. That part is fine.

What I don't like is that I don't think it is working below 4th gear. For example If I turn it on at the top of a steep hill in 3rd Gear it doesn't seem to be helping me slow down any as I go down the hill. (TJ at Pacbrake told me to turn it off and on to see if there was any difference so I will do that when I go somewhere next). He said if it is not working below 4th gear there could be a problem with the throttle sensor, or perhaps the Alison software because that's supposed to tell it what to do. He said it should work in the different gears all the way down to 20 MPH at which point it will not. He also mentoned it works a lot better at higher RPMs (which is certainly where I am coming down mountains) because at lower RPMs the butterfly doesn't do a good enough job as i recall I think of restricting the flow? I did notice they have a new PXRB model that works much better at all RPMs and costs about $800 and depending on mating surfaces and Turbo configuration may be real easy to install. However, apparently BMC's have an inline Pacbrake Different from the 1/2 and full Marmon versions for the Cummins 8.3 listed on the Pacbrake website). The new PXRB inline model won't work unless the engine comes equipped with the heavy duty 65 lb exhaust valve spring. I am checking on that now. In any case, TJ said there was no use putting in anything that would work better if my current problem is not fixed first. I would like to make sure my current Pacbrake is working correctly as coming down steep hills now requires more off and on brake use than I like, even at slow speeds (35mph) in third gear for example I get hot brakes occasionally, which is not a good thing. They have never quit working (could at some point) but I'm sure they are wearing faster. I read somewhere you should not have to brake more than two or three times over a mile, but to bring the RPMs down from 2500 (I don't like to get up near the 2800 it says not to go over) to about 2000 where I let off the brakes to let the RPMs start up again, I often have to brake more than 2-3 times per mile.

I have had my Alison transmissionm checked for a variety of other things in the past, and even had to replace the computer under the keypad (very expensive.....don't say anything Woody) and have never had any error codes that had to do with the Pacbrake (I'm not sure there are any). The throttle sensor was looked at when my injector pump work was done and as I recall it was mostly due to the throttle linkage (although I might be wrong about that).

Anyway, TJ said a knowledgeable Alison shop if there really is a problem with the Pacbrake should be able to troubleshoot and fix it. I don't know if that's really true or if it will end up costing me a mint because they might not be familiar with it and end up doing a lot of extraneous stuff while learning (I have had that experience too many times)

So here's my plan.

Try to make sure it really is not kicking in below 4th gear or I just couldn't tell.
If it is working OK, consider a PXRB model that will work better I want more safety on those steep downhills)
If not, find someone who knows something about this kind of thing to check it out (help here would be nice if anyone knows a good shop for this stuff) TJ at Pacbrake suggested a knowlegable Alison place but I guess I better call first to see what they know.

So that's it for now
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  #28  
Old 02-11-2010
Lee Davis's Avatar
Lee Davis Lee Davis is offline
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Default Pacbrake PXRBs

Thanks Dan. the Pacbrake guy said that the newer PXRB pacbrakes worked better at lower RPM's because it adjusted to that as I recall by how much it closed and there were different size holes in the butterfly valve or whatever. It did sound like a major improvement.

But first I need to find out if mine is working correctly and if not, how to fix that.
__________________
Lee and Jacque Davis - Full Timers

Lee - 423-292-5767 or Jacque 423-262-9569
or lnjdavis@gmail.com Please call or email instead of private messages


1995 BMC 37
300 HP Cummins 6CTA 8.3 Turbocharged Diesel
Boldly Going Nowhere
http://www.bbirdmaps.com/index.cfm #117
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  #29  
Old 02-11-2010
thudpilot1 thudpilot1 is offline
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Posts: 332
Default

Lee,
Had my exhaust brake replaced a couple years back cuz it was sticking in on position.
My experience learning the proper descent since downhiller 1 was a loose nut on the steering wheel which I have since adjusted. The brochure with the installed brake had some good info - - like the downshift to keep rpm up - - - which I do religiously - - no specifics on my rpm but I believe less than 2500. Over xmas, we descended a 6 mile 6 degree hill and ran a comfortable 45 mph - - -Have had lots of experience throughout rockies over last few years and no longer seat the big stuff downhill.

I do remember when a rookie smokin the brakes descending into Moran, Wyoming from the east. That was not fun and definitely had a very loose nut on the wheel.

See ya in March.

ed nowokunski
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  #30  
Old 02-11-2010
Lee Davis's Avatar
Lee Davis Lee Davis is offline
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Default Pacbrake

Ed, did you get one of the new PXRB Pacbrakes? Don Baker got a new one for his BMC awhile back and I'm not sure what he got but he did say it worked down through all the gears.

Do you remember the model number of your new one or maybe it's on the paperwork? Who did that for you?
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Lee and Jacque Davis - Full Timers

Lee - 423-292-5767 or Jacque 423-262-9569
or lnjdavis@gmail.com Please call or email instead of private messages


1995 BMC 37
300 HP Cummins 6CTA 8.3 Turbocharged Diesel
Boldly Going Nowhere
http://www.bbirdmaps.com/index.cfm #117
Reply With Quote
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