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RPM Surging
Recently, at less than full throttle going up hill, the RPMs surge about 100-200. You can feel it as well. Switching the transmission to PERF seems to help, although it will surge in that mode as well. Fluid levels are normal. Our bus is a 1999 chassis, H3, Detroit series 60, Allison World Transmission. Surging occurs with Cruise Control on or off. No codes on transmission or faults on dash. Any ideas what is causing this? Using synthetic transmission fluid (switched about 4 yrs ago). We drive our bus 7-10k per yr and it was recently serviced (10k) at TEC in Coburg, OR. We have a minor seep at the transmission output yoke seal. We had this replaced previously by Prevost about 4 yrs ago.
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14 Replies
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Surging would indicate a fuel supply issue. Could be air in fuel, water in fuel or a plugged fuel filter.
2000 Featherlite H3-45
2024 Jeep Grand Cherokee
Leesburg, FL -
Thank you for the reply. I do not notice the surging in PERF mode at full throttle going up hill. And I do not notice it around town. Just at freeway speeds, particularly with PERF not selected, at less than full throttle.
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Replace the fuel filters, that’s the easiest to start with.
Chuck
P.S. Make sure you don’t ingest air into the system when changing filters!
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Hello All,
It turns out our problem is in the transmission. We have 178,000 miles on the coach. We ended up taking the coach to Freightliner NW in Coburg, OR. They see our coaches and have trained Allison Transmission techs. They discovered the torque converter was not staying locked up under load. They recommended replacing the transmission. We decided rather than replacing the transmission with a rebuilt unit, we would see if our transmission could be repaired. During the tear down they discovered a damaged bearing race that spewed some metal into the rest of the transmission. They are rebuilding our transmission now. The people at Freightliner have been very helpful and have kept us informed on the progress of our repair/rebuild. We hope it will be completed next week.
Joe Wilhelmi
1998 Country Coach
Dixon,IL -
Thanks for the update! Always interesting to know the end of the story.
These transmissions are supposed to be good for 500k miles. Yours retired early. Any heavy towing in the past? Were filters and fluid changed? Of course, impossible to know when you buy used and there is no maintenance log.
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Even with the best of care and maintenance, stuff just happens. I’m awfully surprised it happened to Tad and Lisa as it usually happens to me!
I’m “told” the Allison World transmission is bullet-proof. But like I said in my opening comment “stuff just happens”.
Tad and Lisa keep us posted on the outcome. Does the shop in Oregon see this often with the Allison World transmission? Mountain driving have an impact? (I’m suspecting not). All the PC members who have a coach with that transmission are anxiously waiting to hear the rebuild cost.
I’d like to think Tom and Jon will waive your PC dues for a year or two given your misfortune … especially if you share all the details.
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While the Allison transmissions are highly regarded, the Knoxville Detroit Allison dealer has expressed an opinion that the previous generation 5 speed is more robust and capable of absorbing more abuse. It has been used in vehicles used in severe service such as heavy off road equipment and emergency vehicles.
The 6 speed world transmission is a good one, but earlier models were prone to excessive wear of the clutch plates.
The 6 speed can be connected to the Allison computers and get a complete diagnosis, including measurements of clutch wear and other issues.
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Long story short, we had to have our tranny pulled (at Prevost’s expense) and while it was out I had them inspect it. They said it was OK but showing signs of wear. They said they could put in a rebuilt tranny for $4000 (parts only as the labor was already built in). I still think I made a mistake but I still have the original tranny!
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Tad,
Did your bus have a transmission retarder or jake brake. The second owner (whom I spoke with) of our bus had transmission rebuilt at 150K miles on it. Bus has 260K on it now. When at TEC their Prevost technicians warned us that the transmission retarder raises the fluid temps when in use …..so watch trans temps carefully when using.
The second owner own a trucking firm and used bus in his business. He pull a 1/2 ton pickup truck all through the Southwest and Rockies. When we bought our bus in Colburg, OR we had Freightliner and TEC go thru it because my only requirement was for it to roll down the road. They are good folks.
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Jon you mention earlier world trans had tendency to exhibit problems.
What is the cut off for the early models? If you have a time frame or some criteria would be great to have to evaluate my unit.
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I have no idea of the dates other than the Knoxville dealer the problems with some early 6 speeds was premature clutch wear.
The dealer can hook up to the transmission and via the internet Allison can actually measure clutch wear among other diagnostics.
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Hello All-
Some transmission pictures attached.
To answer some of your questions. We are out west and do some mountain driving but we have only owned the coach 5 years during which time we put about 27,000 miles on it. I think we are the 4th or 5th owners. We bought it with 150,000 miles on it. When we bought the coach, we had an extensive service performed at Prevost in Richmond, BC. We switched our transmission fluid at that time to synthetic Transynd.
We tow a Honda CRV. I’m not sure what previous owners may have towed.
The coach has a two stage Jake brake instead of a retarder so hopefully no heat issues.
The overhaul took about 3 weeks and was in the vicinity of $13,000. Some parts were difficult to source so that’s why it took so long. Freightliner Coburg, Oregon did a great job of getting parts for us. We are glad to be back on the road!
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Tad:
What failed or wore out?
Could the shop determine what the problem was by hooking the computer to it? Or did they need to tear it apart to find out.
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Hi Dick-
The shop connected a computer and test drove the bus. They found the torque converter was not staying engaged (hence the surging when under load like climbing a hill or getting on the freeway) when it should due to low pressure. We had a choice at that point to either replace our transmission with an overhauled unit or repair/overhaul our transmission. We decided to overhaul our transmission thinking maybe once the tech started the tear down we might find the problem early and save some money. Also, the service advisor noted it was beneficial to overhaul our transmission rather than installing an overhauled unit since we would not know the history of a random overhauled unit. During the overhaul they found a bearing race damaged which sent metal through the transmission.
In the end, it was a wash because of the parts and the labor to remove and install the transmission. But we do have our original transmission.
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