Stranded in Flagstaff

[flloyd]

After more than a week of preparation in the baking hot summer of Phoenix, we finally hit the road today, Friday July 10 at around 1pm. We are heading north with a final destination of Glacier National Park, Montana.

The route takes us north along I-17 with a climb of about 5500 feet along the way. Robin and I are still green and we're getting used to what falls over in the cabinets as we drive, and shamboo bottles that decide to empty themselves as we ascend in altitude.

Going uphill was pretty steady with speeds dropping to 35 mph in spots, but there didn't seem to be a lack of power, just a lot of weight. We have the 470HP version of the Series-60 engine and the 6-speed B500R Allison World transmission. For the first 3/4 of our drive up the hill to Flagstaff (a total of about 140 miles), the coach performed well and downshifted/upshifted smoothly. After passing Munds Park, however, which is at about 6000 feet, I noticed the tach pegged at about 2100 rpm. A quick glance at the Allison keypad showed that it was in fourth gear. Forth was appropriate for the climb, but then it stayed in fourth, no matter what I tried. The selector was in Drive and the indicator said 6-4. Yep, stuck in fourth gear.

I had seen this before on our trip out from California when we picked up the coach. It happened in the morning as we entered the Phoenix valley. I pulled over and took a look around but saw nothing out of the ordinary. After spending some time on the phone with Steve from California Coach (my new best buddy), neither of us could really figure out what was going on. When I started up and took off again, it shifted normally and went past 4th, into 5th and finally 6th. All seemed well.

Well, today, the same thing has happened again. it was after about 1 and a half hours of heavy hill climbing that it decided that fourth was the top gear. I pulled off the road an an exit and came to a full stop. Taking off again the shifts from 1 through 4 were normal, but again, it would not go into either 5th or 6th gear. I drove the last 30 miles in fourth gear at about 50 mph with the engine at about 2000 rpm.

As we approached Flagstaff, we heard a clicking sound and I finally noticed that a red AC light was coming on beneath the OTR Air switch. The light came on, then off, several times. What does this light mean? It looks like an AC compressor symbol. I switched off the OTR and waited a while, then turned it back on. It still works. Hmmm.

Also, while driving around the town of Flagstaff I noticed a couple of other anomalies. First, whenever I brake, the battery imbalance light (yellow) comes on. It stays on for a few moments and then goes out again. I have a brand new set of engine batteries and the dash voltmeter reads 26 V. nearly all the time. Maybe it's related to engine RPM, but, the light goes out at idle, standing still.

It's Friday evening and I'm very concerned about the transmission. It was shifting poorly around Flagstaff and again, after a short rest in a parking lot, all 6 gears returned to service. There is nothing unusual on the transmission temperature gauge which reads between 180 and 230 and most of the time around 200. Another thing that I've noticed, especially when we're stuck in 4th is that the transmission retarder doesn't provide very much braking, if any.

While stopped in a parking lot at fast idle, I checked the trans fluid dipstick and it showed over-full, with a few bubbles. Later, at Steve's suggestion, I checked the level from the keypad. At first I got an OL-59 reading which, it turns out, means speed to high. So, I took the engine off of fast idle and after a few moments the display read OL-OK which is "oil level okay". There is another diagnostic code that we haven't figured out, however, and that's "d1 63 40".

Flagstaff has no bus service but they do have a couple of truck repair shops. They are puzzled regarding the Allison B500R model, but since it looks like a 4000 series they said they would have a look - on Monday. Steve and I decided that perhaps the best thing to do would be to drop the transmission pan, change the oil and filters, and see if anything changes. I can only hope at this point. The bad news is that I'm stuck in Flagstaff for two days, but the good news is that it's a good 20 to 30 degrees cooler here and the Cruise Air's work flawlessly. We're in the Black Bart campground which although not very fancy, it does have 50 Amp service and pull throughs.

So, here I sit, waiting to find out whether I'm a candidate for a new tranny, or if I might just get lucky with an oil and filter change. Let's hope that when the pan comes off on Monday that it's not terribly full of crud. If it is, I'll probably just have them put in the fresh oil, button it up, and head back down the hill to Phoenix where there is actual Allison service available. Oh yes, and the coach just turned 100,000 today.

[Jon Wehrenberg]

Fred,

Our conversions are 4 serial numbers apart. I am pretty sure your ills may be tracking mine. I am far from a transmission expert, but I can tell you that my original transmission was of a series Allison built that had poor transmission clutch materials. Those materials were not durable and after a while there was excessive clutch wear on the 5-6 clutches. The dealer told me in some cases the wear is so pronounced the material which is shed gets spread througout the trannie and generally plugs things up.

I hope you are not dealing with those issues because the cheapest and easiest fix is a factory re-man.

Having said that dropping the pan and filters and changing fluid may in that case help temporarily. You really need to get to an Allison dealer because they have the ability to connect your transmission computer to Allison's factory via the internet and run a full diagnostic. When they do that you will see graphically how much wear your clutches have and can make an informed decision about your next step.

The AC light on the OTR will come on whenever the system experiences problems and on my coaches I have had it happen twice with similar issues. In the passenger side AC compartment to the top right is a white box that houses the relays (solenoids) that control power to the condenser and evaporator fans. If either fan fails to run the system light will come on. The reason I am focusing on those solenoids is because it sounds from your description like one failed to make good contact and you got the light, but after resuming the operation of the system it functioned properly. Those solenoids have been availble at NAPA stores and also at WW Grainger. They are 24 volt coils. If you can check their function to see if you can get one to fail. They are relatively cheap so you may wish to just replace them. When a problem is intermittent you are just guessing so until you have a total failure of the system that is my best guess.

To have only 26 volts seems wrong. If you have a multi-tester try checking at the batteries to see what the real voltage is. Admittedly at idle it will be a lower voltage than when you step up the RPMs, but that seems low. If your AC is functioning when you see that voltage at low idle then it might be normal due to the current draw of the OTR fans.

[aggies09]

This is just a thought and those of you with more expertise can jump in to clarify, but I had a similar problem a couple of years ago and my problem was internal to the transmission but was related to several sensors. I had them replace all sensors since you have to drop the transmission to get to them and I haven't had any problem since. Good luck.

[garyde]

Hi Fred. Maybe there is a relationship between the trans retarder and the 4th gear issue. Did you shift manually into 4th gear or was it automatic? Did you try turning off the trans retarder.

[flloyd]

Thanks for all your replies. Nothing to do now but wait for Monday Morning. We'll get a flush/oil change and pan inspection and decide from there.

[rfoster]

FWIW I had a 97 Liberty with retarded tranny a while back, it developed a shift problem - took it to a local Allison dealer, he attached his laptop and told me that he needed to replace the speed sensor. 69 bucks and another 50 to put it on - I was a happy camper again. I later had the oil changed to Syntrend to help keep the temps down - fixed it.

Hopefully yours with turn out that well.

[BrianE]

Fred, Last October I delivered your coach to California Coach after picking it up in VA. Had no issues until a few miles east of Oklahoma City. Was decending a moderate hill with assistance from the retarder and got an uncommanded shift to 4th which caused a slight overspeed estimated around 2200 RPM. At that point the tranny would not shift past 4th gear so I left the freeway at the next off ramp and called Prevost Action Service (PASS) 1-800-463-7738. The service adviser told me to wait for an hour and that the tranny should reset and all would be well. He also suggested I visit the nearest Allison service center and that the retarder temp sensor was probably the culprit. He was right (at that time) on both counts. I continued to Oklahoma City with the tranny shifting normally, had the sensor replaced and had no more issues. Due to the fact that the sensor was bad the Allison mechanic did not drop the transmission pan at that time. The fluid did not appear to be overheated or dirty and the computer parameters and codes were normal. Hope this history helps get you back on the road.

Additionally, occasional cycling of the battery balance light is normal and indicates that your equalizer(s) are doing their job. If for any reason you have shut off the 12v switch in the right hand engine bay or if an equalizer CB trips, the balance light will stay illuminated. Best of luck.

[parksincpp]

Fred, sorry to hear your having such a hard time with everything. At least your stuck in a place that's a whole lot cooler the PHX. Have you ever checked out the Lowell observitory? I've never been but was thinking about stopping by next time we go thru Flag. Is Black Bart the only choice to stay in Flag? Here's wishing you good luck tommorow on your service.

[flloyd]

After reading Brian's post and going over pages of Prevost maintenance manuals it became clear that the failure to shift was intentional on the part of the Allison control unit. There are a few conditions that cause it to avoid 5th and 6th gears, and one of those is temperature exceeding 260 degrees F.

Not wanting to stay in Flagstaff until Monday, I elected instead to drive to Las Vegas where there is factory Allison service available for the B500R. The trip to Vegas was quite pleasant and shifting was normal for the entire route, including crossing the Hoover Dam. Had the cruise control set on 65 most of the time. The amount of speed this beast can pickup on a downhill stretch is astonishing and it's now clear that I need a retarder that's available all the time, that can hold the coach to 65 or less on a 6% grade. Maybe I'm dreaming...

I had to use the retarder on several occasions and each time I kept a watchful eye on the trans temp gauge, keeping it below the 230 mark at all times. After reading in the manual that there was a specific 260 degree threshold, I found it somewhat curious that the trans temp gauge had graduations at 200, 230, and 320 degrees - clearly a non-linear presentation. This means that if the needle ever passes 230 that it's entering into "logarithmic range" (just kidding), or in other words, very hot. I didn't let the needle get much past the midpoint between 200 and 230, even though there were times I really wanted more retardation. I stabbed the service brakes instead, which is recommended over riding them. The retarder really digs in when you hit the brakes, in three increments according to brake pressure, as I recall. This makes for a very rough downshift at lower speeds and when driving around town at in-town speeds, it seems better not to retard so that downshifts are smoother.

So, tomorrow I'll be pulling into W.W. Williams to find out what they can do for me. At a minimum I think I'll have them do a full diagnostic, change the oil and filters, and perhaps upgrade to synthetic oil. Depending on the results of these tests, I'll either hit the road and hopefully make it to Glacier National Park by this weekend, or, bust.

Our spirits are still high and we're growing accustomed to our new living quarters aboard the bus. It's very nice, overall. We're in the Oasis Las Vegas RV Park and it's got everything we need. Oh, and the rear CruiseAir konked out with HI PS again, two times. These things are simply not reliable when the temp is over 100.

[ajducote]

Fred,

Sounds like you are getting pretty good at trouble shooting. Sometimes it just takes time to sit down and think it through. Do you have a Jake Brake and a transmission retarder or just the trans retarder? If you have the Jake Brake did you try using that? I have found that ging down hill the Jake Brake has done a great job. I occasionally have to manually downshift to 5th to hold my speed with an occasional stab on the foot brake. As you have discovered, the retarder really heats up the trans fluid, and that is not a good thing.

Hope you get good news at Allison.