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.

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.

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.

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.

Quote:

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Originally Posted by BoaterAl

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

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Yep! We have actually had a warm summer for a change. Even some over 90 degree days with high humidity. I thought it was hot at Prevost TN when I was there, but when I got home it was the same or warmer for a few days.

Well, after more troubleshooting and a phone call to Allison, we ordered a reman and now have to wait several days for it. It will be at least a 7 day delay when its all over. Quoted price is $13k, parts and labor.

Quote:

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Originally Posted by flloyd

Well, after more troubleshooting and a phone call to Allison, we ordered a reman and now have to wait several days for it. It will be at least a 7 day delay when its all over. Quoted price is $13k, parts and labor.

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That is too bad. Any idea if you will get any consideration from the dealer who last did the service on it?

OUCH.....Sorry to hear about that getting your attention for $13 large. One thing about the Allison rebuilds all units are dyno tested before going in your bus.

What kind of warranty comes with it ?

We keep a couple of spares in our shop. A B500 & B500R. Nobody stocks these, unless they're a bus company.
We haven't had the best luck with the Allison Remans. We had a couple of seal issues while they were under warrenty.
We have had excellent service and delivery from a company in Illinois. Authorized Transmission Remanufacturing. www.atreman.com
Their warrenty is the best in the business (3 years vs Allisons 2 yrs), also their warrenty extends to labor if the transmission fails.
Shipping is free. A B500R was priced at 7,500.00 to your location. But that was eariler this year.

Great information Kevin.

When my transmission was replaced it had the latest Allison software. As I recall it took about 2 hours for the DD and Allison software to be updated so they would work together. I do not know if that is always required, but my '96 DDEC had to communicate with an '08 transmission before everything would work as required.

Fred,
How did your transmission experience end? (or has it)...

Not that it would be significant in Fred's situation but I thought we were told at the seminar in OK City that Transynd could take 300 degrees without creating issues. Did i get that wrong?

Jim mentioned that you can check the oil level from the Allison pad. For those of you unfamiliar with this function it's a good idea to perform this after each day of driving.
Depress both arrow buttons with the transmission in N (neutral) at normal idle speed.
Here's some codes for everyone..........
OL,OK - oil level is OK
OL,LO,01 - oil level is low 1 quart - 02 is 2 quarts,etc.
OL,HI,01 - oil level is high 1 quart - 02 would be high 2 quarts, etc.
0X - settling time too short
50 - Engine rpm too low
59 - Engine rpm too high
65- Neutral must be selected
70 - Sump fluid temp too low
79 - Sump fluid temp too high
89 - output shaft rotation
95 - sensor failure

Here's an example of what you might see if you tried this without warming up your trans oil first - OL,70

Patrick,

300 degrees is the temperature at which the Allison computer starts to remove the retarder function. I can find no technical information regarding temperature limits or safe operating range for the fluids in our transmissions. If it is out there I have not found it, and our gauges do not have markings to indicate the normal operating range or red line.

But Allison provides a huge clue about the effect of heat on the transmission fluid. In their maintenance schedule a retarder equipped vehicle has its fluid change interval cut in half. With the retarder off my transmission fluid temps measured at the outlet just prior to the intercooler track engine coolant temperature reasonably well. The temps will never get beyond about 210 (hard to read because the gauge is poorly marked). With the retarder on I can see the needle head towards the high temperature range very fast so it is not hard to imagine that the fluids are being subjected to much higher temps than normal. Personally I limit my temps to 230, not for any scientific reason other than my plane had an oil temperature limit of 240 (red line) regardless of whether I used conventional opil or synthetics. I chose to personally limit the temp because as stated above there is no real guidance on our gauges or the Allison technical data, other than their reduced maintenance interval.

Limiting my temps to 230 requires some effort and anticipation. If I know I am approaching a steep downhill slope I gear down and reduce speed. Out west where long downhill runs of 6 to 8% are not that unusual I try to be just below 55 at the crest and in 4th gear (which on my coach 55 is the 4th gear upper limit) and the retarder in the second position. If the speed creeps up I go into the 3rd position, if I slow too much I go back to the first position. By doing that I can descend at no more than 55 MPH and my tranmssion temp gauge stays at 230 (clearly marked) or below.

Braking with the retarder on, even with the control in the "0" position will drive up the temps because the retarder is employed proportionately with braking force. Again, like hills I anticipate the need to brake and can limit temps by taking longer to slow or stop. When I have to brake suddenly I ignore the temps because safety is more important.

My coach is equipped with an amber trans fluid temp warning light which, I believe, is supposed to come on @285F at the retarder output. I've seen it a few times. I try to limit my trans-synd temps to 250F @ retarder output which usually involves no more than level 3 in 5th or level 4 in 4th for any extended downhill run but I usually gross about 65-70,000#. I use the brakes to keep rpm's under 2000. My last trans-synd change at about 25,000 miles use came out pretty good; I could go a little longer. Obviously, this is severe use. I'm on the original trans @150,000 miles.

P.S. Even if you're not breaking down your fluid, plastic, rubber, and certain other parts of the trans will wear faster with elevated temps.

Here's an issue that I ran across over the past weekend. The bracket that holds the accumulator for my retarder equipped transmission broke again. As provided on my coach (1999 chassis) this is a 1/4" plate. It had broken before and was welded as a repair. The local DD/Allison shop says that there is a tremendous amount of torque generated through this valve when the retarder is actuated, the plate flexes causing failure. I have it off again and will be fabricating a replacement from 1/2" stock.


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Orren, my $.02 on this. I personally would go with a new original part or one just like it, the reason being the chain break always goes to the weakest link. You presently have an escape valve of sorts and I would rather have it brake than the casting it is bolted to.

As I am sure you know mechanical failures will just move down the line to the next point that will fail.

The area of the components appears from the photo to be quite rusted and corroded, maybe due to road salt or storage in a damp environment, be that as it may, I would clean everything up as well as possible and use a new plate and high grade fasteners all torqued to specs. Also note the elongated bolt hole next to the failure point, this suggests to me that the assembly was loose and moving. This would in itself lead me to think that improper fastening and not the bracket/plate thickness/strength was at fault, but then again, who knows ....happens and your there and I am here.
As an aside the welded plate probably was doomed to failure from the start and should have been only regarded as a temporary repair, just say'n, please take no offense.
Hope it all works out!

JIM

I am curious, how did you find out about the failure?

Was it suspected by some indication in handling, or was it found in routine inspection??

JIM

I'm going to look at that on my bus. I have the same situation but have not seen a failure of the bracket, but then again I may have missed it.

It looks to me that the bracket as mounted is being stressed since the two broken halves are not lined up. Consider a bracket repair that uses the original attach points, but is attached to the accumulator as the accumulator now sits with no forces on it. The stress combined with what is likely a full range of vibrations is the probable cause of the failure.

Quote:

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Originally Posted by JIM CHALOUPKA

Orren, my $.02 on this. I personally would go with a new original part or one just like it, the reason being the chain break always goes to the weakest link. You presently have an escape valve of sorts and I would rather have it brake than the casting it is bolted to.

As I am sure you know mechanical failures will just move down the line to the next point that will fail.

The area of the components appears from the photo to be quite rusted and corroded, maybe due to road salt or storage in a damp environment, be that as it may, I would clean everything up as well as possible and use a new plate and high grade fasteners all torqued to specs. Also note the elongated bolt hole next to the failure point, this suggests to me that the assembly was loose and moving. This would in itself lead me to think that improper fastening and not the bracket/plate thickness/strength was at fault, but then again, who knows ....happens and your there and I am here.
As an aside the welded plate probably was doomed to failure from the start and should have been only regarded as a temporary repair, just say'n, please take no offense.
Hope it all works out!

JIM

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Excellent analysis Jim. Do you think Stress Corrosion Cracking could be the cause? Looks like a salty environment. It looks like Prevost designed the bracket to flex and absorb energy. Toughness is key. Unless this is a widespread problem, I'd do what Jim suggested. Replace it with a new part. Make sure it's nicely painted with new hardware torqued to spec. Just my 2 cents. :)

Good catch Orren, guess what?, Mine is also broken, found it today after church.
Had my suit and tie on so I didn't get to do any work, just wiggled it a little and it fell down a couple inches. The break is in the same as yours, without the weld of course.
All the bolts are still torqued tight and I have no corrosion or rust. So goes my theory up in smoke. I will treat it as a perishable item needing to be checked regularly and replaced at some interval yet to be determined.

I use my retarder a lot and never noticed any deficiency with the broken part (looks to have been broken for some time as the break does not look fresh) (how do I know you might ask, well I just know when a crack is fresh :rolleyes:)

JIM :D

Jim,

When I spoke with the service manager at the local DD/Allison shop he indicated that their repair was to weld the crack/break and then gusset the mounting plate when equipment was in their shop for this repair. Since you've looked at yours, you know that in the way that Prevost mounts this valve that welding a gusset on the back of the plate is not an option. My mounting bolts were also tight and the second break was just below the mounting bolts on the transmission - the plate actually looked like it was torn in half. I'd be curious as to the amount of stress being placed on the hydraulic hoses while that 15-20 pound valve is just dangling there being actuated by the retarder. For my repair I went with a 3/8" plate and increased the width of the tapered section from teh transmission mount as it goes down to the accumulator mounting position.
I'll post a photo when I get a chance.

Evidently this is not a common repair with Prevo parts anyway. I ordered one and it is coming out of Canada, $68.43. Could have made my own with more time, but I am preparing to get on the road soon time does not allow for fabrication.

I do know what you mean about the gusset, looks like there is barely room for an open end wrench!

I think there are a lot more broken out there than owners know about :eek:

Thanks again for the warning.

JIM :D

Has the transmission issue been resolved yet? Inquiring minds want to know....<g>!

Sorry for the delay in getting the details back, it's been a busy season.

The transmission was replaced in Billings at Interstate Power Systems, an authorized Allison dealer. They used a reman from Weller which come painted red as a trademark. The exchange price was about $7500. I also needed a U-joint, which they also replaced, and refilled with TranSyn fluid.

The retarder accumulator bracket wasn't broken, but now that I look at the picture I can see that it has had some strain. We'll see.

After the change, we took it out for a test drive while attached to the Allison diagnostic computer and everything looked fine. The shifting
was a bit rough at first, but got better as the control computer learned the bus. Downshifts into 4th, when slowing down, continue to
be somewhat rough and the mechanic said that I might have to replace the control unit to fix that. Other than that, it runs smooth
as silk and the retarder works better than ever.

I constantly monitor the sump temperature now using the Silverleaf box and it stays around 210 most of the time. We've since put
over 1000 miles on it and all seems fine, again except for some rough downshifts when slowing from highway speeds.

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Fred,

I assume you are using the arrow buttons to periodically check fluid levels?

When you pull into a level space after driving and things are up to temperature that is a good time to check. If the transmission is too warm or cool it will tell you, but if you have been driving a while it should be in range.

Last month I had to add one quart even though I have no signs of leaking. I surmise when last filled with Transynd and it read OK it was near the bottom of the range, and after about 3.5 years this last reading finally showed it down one quart. Trying to be that precise with the dip stick is almost impossible.

The shifting should smooth out because it takes a certain number of shift cycles before it has "learned" to match your driving habits.

Glad you got fixed up Fred, the cost was less that what I had expected to hear from you. Hopefully the hard shift will get better as time goes on.

:D:D:D:D............

Any suggestions for a code 2511?