Transmission Overheating

[Danss]

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.

[flloyd]

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.

[Jon Wehrenberg]

This is after the fact and kind of like Monday Morning quarterbacking, but I have learned that nobody cares as much about our coaches as we do. So the cynic in me mistrusts everyone who works on my coach (very rare) to the point I double check their work.

For those who have not yet been burned by poor service (I was literally burned, but that's another story) it never hurts to check and verify. For our transmissions there are two ways we have of monitoring them. The first is to observe the transmission temperature gauge. I constantly monitor it and under all conditions except when the retarder is in use it almost perfectly tracks the engine coolant temperature. When the retarder is in use it will climb (rapidly) but I limit it to 230 degrees. I suspect Fred saw higher transmission temps than normal and in his defense if you talk to techs or Allison experts they know a retarder will heat up the fluid so they are very quick to say to not worry about temps because the transmission itself will limit the temps as required. What they fail to recognize is that their comments are taken to heart and are not qualified as not being applicable to over filling because nobody thinks of that.

The second tool owners have at their disposal is the Allison fluid level check. With the transmission up to temperature press both arrows and the transmission (at idle and in neutral) will measure the fluid content and display the results. This is a great thing to do while waiting with the engine idling waiting for the turbo to cool down after a run. (You all do understand that before shutting down it is good practice to idle for a couple of minutes to cool down the turbocharger, right?)

Had this check been done as soon as the service on Fred's transmission been done the technician would have known of the overfull condition, and had Fred done this somewhat regularly he also would have been alerted. Using the transmission fluid level check is preferable to pulling and reading the dip stick, but don't forget that is a good way to double check.

It is unfortunate this happened and I hope the Allison dealer in Las Vegas can be held responsible for the cost of the repairs.

[flloyd]

Thanks Jon,

I would like to add that the temperature shown on the dash is apparently the Retarder Temperature whereas the 300 degree spike I was seeing was the Sump temperature. Each has a separate sensor and the sump reading comes only over the DDEC bus.

[jack14r]

I have the Silverleaf display and in my case the Detroit information center and the Silverleaf display are always the same,i guess that they changed something along the way,I hope that you have good luck Fred in repairing or replacing the transmission.