Allison is getting HOT! What to do?

[TC]

I have a 2001 Duramax/Allison with 187,000 miles. It is completely stock with no power chips or other modifications. The use has been approximately 25% towing with most loads being 10 to 12,000 pounds and a couple of occasions of more than 30,000.

The transmission has never given any indications of slipping or noises, but it recently started getting hot. I have changed both the internal and external filters and fluid a couple of times. Now it tends to get hot after about an hour of highway driving even without a load. When the warning light goes on it goes into a mode like tow-haul where the engine braking and higher shift speeds take effect. I verified that it is getting hot with an external thermometer that showed a 215 degree reading on the case just in front of the pan. That was after it had already cooled down for 20 minutes or so. Meanwhile the engine oil pan temperature was only 138 degrees and the ambient temperature was about 50 degrees.

The "Dead Allison" thread from December looks kind of similar in the comment that a converter failure can cause the overheating. In talking with a local transmission mechanic he recommends both replacing the converter as well as going through the transmission.

I would like to avoid working on the inside of the transmission if possible due to a lot of expense. Besides, from the comments on this forum, it sounds like the Allison is pretty bullet proof up to 300,000 or so miles. Can I get by with only replacing the converter?

What should I do next? We are going to check the codes first to see if it is giving indications of internal failure, but other than that I am clueless. Thanks for the help.

[Mark Rinker]

You can get by replacing just the converter, IF the tranny fluid hasn't been scorched and contaminated the tranny...if its burnt or stinky, you'd better consider a complete replacement. If you are catching it early enough...well...its a gamble. Do you feel lucky? :)

Also, if you aren't setting transmission related codes yet, that would indicate no problem with Allison clutch slippage...yet. The torque converter can slip without codes. Sounds like your limp is fluid temp related...pay close attention to the codes, they will give you clues as to what is happening, and determine what you can 'get by' with.

Personally, I am very glad to have replaced both torque converter and transmission, eliminating all variables, and reducing the exposure of doing the labor twice...

Based on my recent experience and the abundance of low-mile Allisons out there with a wrecked truck attached to them... I would recommend shopping a used Allison 1000 with matching torque converter out of a low(er) mile salvaged truck. The labor and parts of going through your tranny will be more expensive. The only way I would go that route is if you were building up the tranny with aftermarket parts to handle MORE POWER, which doesn't sound like your thing...

Good luck!

[TC]

Here is an update on my HOT Allison problem.

I finally located a reputable local guy who has done a number of Allison rebuilds. He checked the codes with his Snap On reader and confirmed that the converter is going out. His recommendation was that the transmission should be rebuilt at the same time due to the high temperatures and debris likely coming from the bad converter. Reasoning is that the rubber parts in the transmission are beginning to turn hard due to the 300 degree treatment and it would be a matter of time before problems, etc, etc. I heard the same song and dance from at least 3 transmission guys.

So, I bit the bullet and put it in the shop for a converter and rebuild. Cost will be $3,500. I also ordered the transfer case fix-it plate from Kennedy Diesel so it should be here on Monday or Tuesday in time to be installed along with the transmission.

[Mark Rinker]

Questions:

What codes did they encounter to lead them to the diagnosis of the torque converter failing?
What brand of torque converter will they be replacing yours with? New OEM Allison replacement? Aftermarket rebuild?
What is the warranty on the converter?
What hard parts are they replacing in your transmission as part of the rebuild?
What warranty, if any, do you get with this approach?I am asking the hard questions - because I don't know how they can quote you a fixed price of $3500 before the transmission is apart. Total cost of $3500 for a converter and rebuild sounds LOW. Converter alone would be $1200-1500. Hardparts for a complete Allison 1000 rebuild with clutches ... ?

What aren't they replacing to keep cost at that point? Internal filter should be replaced - entire transmission cooler and lines must be thoroughly flushed, my shop left my truck on their flush machine for 8hrs and cleaned the 10micron screen filter every two hours, getting all the clutch material out of the tranny cooler.

If this important step is omitted, you can put residue right back into a clean transmission/torque converter...

[TC]

I was looking over his shoulder when he read the codes. One of them was P0741 but I can't remember the other. It was related to the converter also.

He said he was using Allison parts, but since they are not the official Allison sanctioned dealer they don't have to charge list prices. I will have to find out who rebuilt the converter they are using.

The replacement converter is supposed to be a heavier duty rating than the original stock. Also they will be installing a "shift kit" which increases the oil flow to the clutches and will enable me to pull heavier loads without worry about burning things out. Apparently the earlier Allisons needed more oil flow and this was corrected in the later models.

As far as prices go, I did stop at a Chevy dealer for a talk. They looked up converter prices at between $650 and $800 and said there were a number of different ones. I didn't price a rebuilt transmission job because I figured it would be too high. The local Allison shop only works on bigger trucks and wouldn't take mine in. They are the ones that recommended the guy I chose for the work. The $3,500 price was based on their experience in rebuilding a number of similar units. He said most of the trucks they are seeing have around the same mileage as my 187,000 except for the UPS trucks that see really hard use every day. And he had build one 40,000 mile truck that tows a 30,000 pound trailer and backhoe around every day.

Also in plowing around on the internet I located an outfit in Florida that would ship me a rebuilt Allison with converter for just over $2,000. They claim to have an 18 month warranty. Of course I chose to deal locally so I can look they guy in the eye and have potential issues taken care of.

I will update more on this when I get the truck back. That is a good point about the flush so I will be sure they do that step.

[Mark Rinker]

Sounds like I was way off on the cost of the converter. Maybe I was thinking of the aftermarket billet jobs.

Good luck with your rebuild approach. Sounds like it was well thought out.