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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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  #1  
Old 03-28-2009
AC7880 AC7880 is offline
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Thumbs up Pacbrake Information and Issues (Combined Threads)

Lube guide:
http://pacbrake.com/PDF/L5300.PDF

Info:
http://www.pacbrake.com/PDF/

Parts:
http://www.pacbrake.com/index.php?page=parts-cummins

http://www.pacbrake.com/index.php?page=pac-cummins
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  #2  
Old 07-27-2009
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bwinter1946 bwinter1946 is offline
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Default PAC Brake Newbie Questions

I just got back from my first big trip (2100 Miles) with the BMC. I had a variety of roads with numerous hills and down grades of 7% plus. Coach ran and drove great. I love that Cummins and Allison combo.

Now the really newbie questions.

There were times when my PAC brake really held back on the down grades and it was great. Control and effectiveness were really handy. Now there was a time when even down to second gear the PAC brake was not enough on a 7% plus down grade. I understand there are limits to what it can do. My question is fairly basic. How can I tell if the brake is really on? There is no indication light. There are no sound differences that I can hear, unlike a Jake Brake. No pressue guage to read. The trans does preselect 2nd gear on the touch pad every time, but how can I tell if the actuator has really closed? Sometimes I could not really feel much hold back. I did check and lube the actuator and all moved freely. Is it possible there could be an intermittant relay?

I have a feeling it may have been working but it met its match on those big grades.

Thanks for any thoughts.
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Brad Winter
Madera, California
1997, 37' BMC
1999, Jeep Cherokee, Toad
1970, VW Baja Bug, Alternate Toad
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  #3  
Old 07-27-2009
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If I'm running in 6th gear with pac on, and let off the throttle, it will auto downshift to 4th (unless too fast for 4th - it self protects and won't downshift until you service brake it slower). No sound, just a downshift and gentle exhaust brake slowing.

Today I came down a grade of 6 miles of 6% westbound over Stevens Pass Hiway 2 in WA. I used the service foot brakes intermittently. I brake down to around 1800-2,000 rpm, let off the service brakes and "coast" with the pac brake - starting with 4th where safe for speed, curves, traffic, shoulder width, etc. The pac can't hold the coach back and builds speed. Around 2500 - 2700 RPM I brake back down again with service brakes to around 2000 rpm, repeating cycles regularly. I don't ride the brake down the hill, though I see some cars, pickups, and some rv's do that - their brakes must be smoking by the bottom.

When I get into curves and narrower roads still on the 6%, I select 3rd on the keypad (2nd if really bad hill/road). Again, the trans won't downshilft unless you brake down to a safe rpm for it to do so. Again in 3rd, it takes intermittent use of the service brake, in cycles coasting with pac from lower rpm to higher, brake down, repeat cycle.

The Cummins 8.3 has rpm limits of 2500 under load (pulling), and 2800 rpm unloaded (coasting). I never see the 2500 under load, but see it all the time in mountain downgrades unloaded. I had my valves adjusted before fulltiming which makes me at least feel better running it up unloaded to between 2500 to 2700 rpm. I painted the gauge yellow around the rim from 2500 to 2800 rpm, red from 2800 up so I can see at a glance when approaching safe engine rpm limits.

Even using the pac in this way, and "trying" to cool the service brakes with only intermittent use I can occasionally smell the service brakes. When this happens, I brake once more, and downshift a gear for more holdback. The old saying is go down a hill in the same gear you climb a hill. If I think the brakes are getting too warm on a real long downgrade, I look for a pull out and take a break for myself and the coach.

I also have a brake system on the toad, so it should be be taking care of it's own weight whenever I use the service brake, but under pac braking, that weight is still pushing me down the hill.



Quote:
Originally Posted by bwinter1946 View Post
I just got back from my first big trip (2100 Miles) with the BMC. I had a variety of roads with numerous hills and down grades of 7% plus. Coach ran and drove great. I love that Cummins and Allison combo.

Now the really newbie questions.

There were times when my PAC brake really held back on the down grades and it was great. Control and effectiveness were really handy. Now there was a time when even down to second gear the PAC brake was not enough on a 7% plus down grade. I understand there are limits to what it can do. My question is fairly basic. How can I tell if the brake is really on? There is no indication light. There are no sound differences that I can hear, unlike a Jake Brake. No pressue guage to read. The trans does preselect 2nd gear on the touch pad every time, but how can I tell if the actuator has really closed? Sometimes I could not really feel much hold back. I did check and lube the actuator and all moved freely. Is it possible there could be an intermittant relay?

I have a feeling it may have been working but it met its match on those big grades.

Thanks for any thoughts.
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  #4  
Old 07-28-2009
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bwinter1946 bwinter1946 is offline
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Thanks for the reply Dan.

That is precisely the technique I use. In addition, my coach behaves the same as yours.

Your information and experience give me confidence that my technique is fine and I am on the right track.

I also put range operation colors on my tachometer.

My engine normally slows building RPM at about 2,200 RPM on power. In addition, an alarm sounds if I allow RPM to get to 2800 while coasting on the PAC brake. I try to hit the brakes no later than 2,700 RPM and brake down to below 2,400 RPM.

I have found that I am most confortable going down steep long hills one gear lower than I went up it. I use less brakes and I am more confident that I won't get my brakes to hot.

I have found 4th and 5th gear very effective to maintain power and vehicle speed in normal twisty mountain roads.

My engine valves were adjusted 26,000 miles ago and I believe the interval is 24,000 first valve adjustment and then every 48,000 miles there after.

Thank you very much for your timely and informative, detailed, response. You once again have proven the value of this forum as I had no other way of learning about this BMC.
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Brad Winter
Madera, California
1997, 37' BMC
1999, Jeep Cherokee, Toad
1970, VW Baja Bug, Alternate Toad

Last edited by bwinter1946; 07-28-2009 at 10:28 AM.
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  #5  
Old 07-28-2009
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Lee Davis Lee Davis is offline
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Default Pac Brake

My approach is pretty much the same except that I try to start intermittent braking every time it hits 2500 RPM (I try not to get close to 2800) I've never had my valves adjusted (may need that at 70K miles). A trucker said to get on the brakes pretty hard to bring down the RPM, do not try to "ease it back" with lighter braking. Supposedly I heard you should not need to do that more than every 1/4 - 1/2 mile or so down a hill, but occasionally I have had to do it more.

I have East and West Coast Mountain grade books (recommended) and when I get to those steep grades I like to start at the top of the grade in the gear I think I will need. (usually 4th or sometimes 3rd on the steep curvy ones) I don't like downshifting a lot when it gets steeper, so I like to know what I am facing ahead of time if possible (hence the books) . On interstates I don't worry about the slow speed. Often I am over in the right lane at 30-35 MPH with the flashers on like the trucks. I am maybe overly cautious occasionally, but in my opinion that's a good thing.

So far I have only found one grade going down a secondary road in Branson, MO to a campground where I needed 2nd gear. (They later told me I had come in the wrong way). And one hill in a State Park where I went in the wrong place (campground was in a different location) where I went up and down a long hill in 1st gear. That sucker was really steep.

Only smelled the brakes one time on an ill advised short cut between Gettysburg and Antietam at the bottom of a very long windy hill on a two lane road with signs saying nothing over 40 feet. ( I figured if I didn't count the toad I was OK). Worst case scenario... there was a stop sign at the bottom of the hill and I really had to stand on the brakes then and wasn't sure if I would stop...but I did.

I sure like those grades with nice long straight run outs at the bottom.


Going up hill, I find my engine seems happier at about 2000-2200 RPM and doesn't lug so I try to keep it there in whatever gear that takes, shifting manually. Again, often I am in the right lane on steep grades at 30 MPH with the trucks. Since trying that, I have had no overheating problems. Once when I was new and thought it would downshift on it's own at the right points (not) the RPMs got too low and I had to pull over and let it cool down.

I typically run about 55-60 on the flats and small hills (what's the hurry and I get about 9 MPG at that). Going down some of those Interstate grades with long run outs I let it get up to about 75 MPH at the end (now that I have "H" load range tires I feel much better about that).

Anyway, that's my style now and I'm open to other suggestions.
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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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  #6  
Old 07-28-2009
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Thanks Lee.

It sounds like we use about the same technique with the same success. That is reassuring to a newbie like me.

I often manually downshift as the trans usually waits to long or lets RPM drop to much for me. I also prefer 2,000 RPM while climbing.

Last Saturday, while climbing a long steep grade at 2,000 RPM in 4th, on a 95 degree day, my engine and trans temps went up to 190 degrees. Wow, I could not do that in my SOB gas coach. The engine would have been much warmer than that!! These coaches are well engineered and built in my opinion.

Lee, I see you upgraded to load range "H" tires like the 1997 BMCs have. Did you change tire size? I am curious as I think Dan is running 295-80-22.5 as opposed to the original 275-80-22.5 that I have.

I would recommend a valve adjustment for your engine if it has not been done. I could not find any record of a valve adjustment on my engine until I called the Cummins Service Center that the dealer said they used. It was still in the computer. I had to give them the engine serial number and they were able to look it up. (I did not know the PO name) I think I was quoted $300 for the job before I was able to determine it was previously done.

Thanks again,
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1997, 37' BMC
1999, Jeep Cherokee, Toad
1970, VW Baja Bug, Alternate Toad
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Old 07-28-2009
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Previous owner changed tire size Aug 2004, and put less than 50 miles on them before I bought the coach. I have 12,000 miles on them running 110 lb front, 100 rear.

Tires are: Goodyear G397 LHS (Long Haul Steer) for big rigs (not rv specific). Size is 295-75-22.5, H rated. They are dead on with the odometer and speedometer as verified by gps. Orig size was 275-80-22.5.

I'm not sure what size I will use when I change tires, but they will be H rted again.
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Old 07-28-2009
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Dan

Do you know if the 295-75-22.5 is perhaps a little more common than the 275-80-22.5 size is? My current tires are one year old and are good for a while but I was thinking if they used the 295s on big rigs they might be easier to get by the side of the road. (Just info for a future 6 years(?) purchase)
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1997, 37' BMC
1999, Jeep Cherokee, Toad
1970, VW Baja Bug, Alternate Toad
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  #9  
Old 07-28-2009
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Default BMC Tires

I'm not sure which is more common - but I'm thinking along the same lines as you. Whichever of the 295-75 or 275-80 is more common, I am likely to go with that size. Easier replacement on the road is important to me.


Quote:
Originally Posted by bwinter1946 View Post
Dan

Do you know if the 295-75-22.5 is perhaps a little more common than the 275-80-22.5 size is? My current tires are one year old and are good for a while but I was thinking if they used the 295s on big rigs they might be easier to get by the side of the road. (Just info for a future 6 years(?) purchase)
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Old 08-12-2009
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Dan,

Today while I was refueling my BMC, I checked the tire size on an OTR truck in the next bay. It had 295-75-22.5 size tires. I'll keep looking as I would be interested in that size if it is more common than our 275-80-22.5 size. Especially since you are running that size without issue.

Also did you weigh your coach to decide on 110 PSI front and 100 PSI rear?
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