Transmission Overheating

Apologies in advance for the rambling nature of this report, but such is my demeanor after spending a day babying my sick coach.

Well, things took a turn for the worse today when after a short, hour and a half drive from West Yellowstone, MT, north on US 191 to Bozeman, everything went very well. The road was mostly flat and the speed was under 60 most of the way. Then, upon arriving in Bozeman, I got the "DO NOT SHIFT" light and had to stop and restart the coach to move it. I limped into a parking lot and along the way my SilverLeaf systems monitor indicated a transmission temp of 281 degrees. The trans temp gauge on the dash, however, showed normal, less than 200.

I checked the fluid and the level seems too high, also, there are bubbles on the stick. According to Allison, high fluid levels can cause aeration of the fluid, and overheating problems. Hmmm. I've never added a drop since it was last changed, 20,000 miles back.

The fluid is TranSyn and was changed a year ago last July when I posted in this same forum when the tranny got stuck in 4th gear, due to my overuse of the retarder on a few long downhills going into Flagstaff. Well, I've since driven about 20,000 miles and always baby the retarder and watch the Trans Temp gauge like a hawk. Never a problem until l10 days ago got a bit too hot on another long downhill in Montana and it went into 4th -only mode again, but only for a short while until the things cooled.

There has been additional odd behavior. Two weeks ago when I was pulling out of a spot where we had been sitting for 10 days, the drivetrain made a loud gear THUNK when I first put into gear. It was alarming but everything seemed normal and it didn't happen again, until this morning when again the coach at for 7 days. This morning, when the coach first started to move, another loud gear THUNK. As before, the coach ran and drove fine, that is until we reached our first stop, in Bozeman.

While maneuvering into a parking spot in Bozeman, another loud thunk as I was pulling away from a stop light.

After a 90 minute shutdown in Bozeman, the temps had fallen to 140 or so (according to the SilverLeaf) and so we took off. In about 15 miles, it had already reached 245 so we pulled off at a rest stop and while coasting into a parking space, we got DO NOT SHIFT again. We're headed for Billings now, 150 miles away, to the nearest Allison shop.

Since the first rest stop, we've been driving about 20 to 40 miles at a stretch, watching the temperature, and limping our way to Billings at 45 to 55 mph. The speed doesn't seem to have much of an effect in the temperature rise, but climbing hills does cause it to go up quickly. I turned off the retarder before we left Bozeman and haven't used except for one time, just to see what happened. Well, it had next to no effect. I would guess that this was because the hot oil has nearly zero viscosity left. Throughout all of this, the dash temperature gauge still shows normal readings. The engine temperature has been steady as a rock, hovering around 195.

We're about 50 miles out now. Most of the passes are behind us. The last pass spiked the temperature to 302 degrees, but oddly, the ECU didn't shut down the tranny and we pulled into a truck stop with no apparent problems or odd noises, shift hesitations, nothing. Everything seems fine except for the digital temperature. One final note, the transmission cools best with the engine sitting parked in idle.

We're hoping to make it to Billings this afternoon, in one or two more hops. We'll be spending the night in the Allison parking lot and the service guy has already informed me that there is no guarantee that he'll get to us tomorrow. So, it's looking like a little unscheduled vacation in Billings is in store for us.....

By the way, I can accept that the tranny is blown, but what I'm most eager not to experience is a towing. I'll be pretty happy just to make it this last 50 miles.

-fred

Update. Me made it to Billings and are sitting at the Allison shop. Had one last DO NOT SHIFT event upon exiting the freeway.

What does the shifter display say your oil level is at? I know you said you checked the dipstick, but I think that the keypad display is supposed to be even more accurate. I know mine is very accurate.

Not to be a smart ass or anything, but have you had regular grease jobs? The clunk could be in the driveshaft slip shaft, or even possibly even a u-joint failing. Both of these can give a clunk when starting out or shifting...but they would not make the transmission run hot.

If the transmission oil is getting that hot your not getting adequate cooling. seems like it could be a sensor problem since your transmission temp is not reading correctly.

Mark, according to my younger sister nothing could ever overheat in Duluth. Have you turned on your A/C yet.

Sounds like the torque converter isn't locking up, or is jumping in and out of lockup.

Your transmission is displaying all of the warning signs of imminent failure. Being in an Allison authorized shops parking lot was a wise move on your part.
A rebuilt transmission with a good warranty will run you between 7,500 to 9,000. The installation time is usually 2 full shop days. Be sure that the shop inspects and flushes your transmission cooler prior to the installation of the new tranny and reprograms your new transmission after the installation.

Good luck to you.

Fred,

About thre years ago I opted for a new (factory rebuilt) transmission. It exhibited harsh 3/4 and 4/3 shifts and the Allison computer showed excessive clutch wear. Since our coaches are of the same vintage what i was told may be of interest.

According to the dealer Allison had a run of transmissions whose clutch materials exhibited excessively fast wear and our coaches are in that time frame. The result was often large amounts of clutch material deposited throughout the transmission. Since the cost to replace clutches and do whatever service was necessary to complete the repairs was not much cheaper than just R&R I opted to go with one that had all the upgrades and latest software. I am not a transmission expert and even if I was it wouldn't matter in your case because you are now with the experts who can correct whatever the problem is.

I was at Prevost nashville several weeks ago and talked with an entertainer driver about his bus. he had 760,00 miles on the engine but was on the 3rd transmission WE must have million mile buses except on the transmission.

Working with the Allison tech now. We went for a test drive and quickly had 3 DNS events. He confirmed that the oil level was 5 quarts high.
He drained the excess oil and is now sending the data diagnostics to Allison. The oil smells a bit burned, a bad sign. It's TranSyn and it looks like coffee now. It had the color of vegetable oil when new. Granted, they didn't drain the torque converter when it was changed it so at least a gallon of the old red oil was still in there.. The tranny was last serviced by the Allison dealer in Las Vegas just a year ago with TranSyn and filters. I haven't added a drop since and so it's hard to argue that they don't share a big deal of the blame for this. Overfilling leads to aeration (foaming), which leads to heat and all sorts of problems.

Granted, I should have paid closer attention to the level myself but my only defense is that I relied on the experts to do it right.

It is starting to look like I'll be here for a week since there are no B500R's on the shelf here in Billings.