Author Topic: Transmission over-temp issue  (Read 3895 times)

Brian Chavet

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Transmission over-temp issue
« on: September 27, 2020, 08:27:12 PM »
2000 Marquis Jasper - the analog gauge in the dash is pegged to the max reading and always has been. Two RV repair shops said it could be very expensive to troubleshoot and repair (not sure if I believe this or not, any suggestions would be most helpful). So I rely on my digital reading on the Silverleaf panel. On 9/22 this reading went to around 275 degrees (the engine temp reads around 180) and coach went into "limp" mode. Also the transmission clunks VERY badly downshifting into 2nd and 1st gears when the temp "displays" above 260 or so. The transmission fluid looks like it was just changed and is clear and red, but it has been ~15,000 miles, so ass-u-m-ing the fluid is fine. The transmission temp tracks with the engine temp and appears to be about 90 degrees too high. Took it to a repair shop and they determined the internal sensor of the Allison 4000 series transmission was bad (~7.5 K ohms). So dropped the lower unit of the transmission and replaced the sensor (~20 K ohms). I did not actually see these readings and it is possible the shop "fabricated" this info to justify the hours spent so far, they won't let me in their shop area. Not making accusations but throwing it in as a data point..... The digital readout is still the same, ~275 degrees with engine temp normal and transmission case temp reads 155 degrees. Back to square one. Can't really understand why the new sensor didn't change the reading for starters. The mechanic working on it suggests it is a wiring issue and at $275/hour that is a scary proposition - any other shop was quoting me an appointment date of around 10/20 and we were supposed to be leaving for a five week vacation on 9/23. The wiring inside the transmission ohm'ed out fine. So that leaves the entire circuit from there to the front panel of the coach. Anybody have any suggestions? Is there a schematic for this wiring available? Could it be the ECM (Cat C12) or the TCM and if so is there a schematic for these? Any help would be most appreciated! I've searched the forum for a similar posting with no success. Thanks in advance!!
« Last Edit: September 27, 2020, 09:29:29 PM by Brian Chavet »

Mike Shumack

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Re: Transmission over-temp issue
« Reply #1 on: September 27, 2020, 09:31:14 PM »
If you let the Coach sit over night so everything is cool will the trans temp then read ambient air temp (i.e. 80 or whatever the outside air temp is)?
If the temp was then reading high (say 160+) that would indicate high resistance in the wiring or a bad sensor (which was just replaced).
But the fact that the transmission is not operating correctly and clunks, suggests to me this is more serious than a bad sensor or wiring.

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Re: Transmission over-temp issue
« Reply #2 on: September 27, 2020, 09:36:19 PM »
Brian,
PMed you the steps to reach Coach Assist. Since the coach went into limp mode when tranny temp showed hot and shifts badly, sounds like tranny is getting too hot. Don't quote me but I seem to remember that Allison considers anything over 260 HOT. Tranny should normally run within about 20 degrees of engine temp. your dash guages are "for entertainment only". rely on the Silverleaf. On my 00 Marquis I had tranny trouble that we traced to bad wiring connections at the tranny.
IMHO, run, don't walk from that shop. $275/hour is robbery, especially if they don't know what they are doing (other than emptying your wallet). They should be able to tell you what the actual tranny fluid temp is when running w/o relying on the Silverleaf. if they can't I'd tell them they obviouly put in a faulty sensor and demand my money back.
Steve
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Brian Chavet

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Re: Transmission over-temp issue
« Reply #3 on: September 27, 2020, 10:25:27 PM »
I have satisfied myself that the reading is faulty. When the temp displays 275 the tranny case temp reads 155 and would be MUCH higher if the actual fluid temp was 275. And the ambient condition reading on the Silverleaf is way high, as you suggest.

I have experienced the clunking whiile downshifting before, especially when using the air brake, and is very intermittent.

I'm leaning toward a wiring issue. I'm going to call authorized Allison service centers tomorrow to see if I can get some immediate help, even if it costs a premium. Anything is better than $275/hr!!! And I'm not too concerned about driving it in this condition, even if it puts me on the back roads to get there. The closest one is about 40 miles away. Not sure if/when it will go back into limp mode.

And I can get more info on the hard downshifting from a service center once I can get it in.

Thanks for the input!

P.S. I call dash gauges an idiot light with an indicator...

Mike Shumack

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Re: Transmission over-temp issue
« Reply #4 on: September 27, 2020, 11:55:06 PM »
it may be worth just replacing the temp sensor. For around $100 its still cheaper than paying the shop for an hour of time.
You can replace the temp sensor from the outside (no need to remove pan) - from what I've read.

I did a little Google search and the job looks pretty easy (although I have not done this myself). I will also ask about this on the irv2 forum since they have a transmission section - and see if this is as easy as it looks.




Fred Brooks

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Re: Transmission over-temp issue
« Reply #5 on: September 28, 2020, 12:32:26 AM »
   Brian,
  As mike suggested, what is the silverleaf reading for the trans when you start it early in the morning. My trans runs about 10 degrees within my engine temp at all times. You may inspect the trans cooler at the bottom inner location of the radiator. See if there is any issue with collapsed or kinked hoses to and from the cooler. Sorry about your issue with the shop that does not respect you. I would ask the owner for your money back. Let us know, Fred 
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Eric Maclean

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Re: Transmission over-temp issue
« Reply #6 on: September 28, 2020, 02:15:14 AM »
Mike
I believe the temp sensor on the 4000 series is part of the trans internal harness and measures sump temperature this is why the mechanic had to drop the trans pan / valve body to access the temp sensor.the temp sensor you are referring to is only for the optional retarter.
The hard shifts are a result of the TCM reaction to too high a temp ( leading me to believe there is likely a code in the TCM)
Not all TCM codes set the check trans light  it might be worth checking for codes (DTCs) at the shift counsel and following the troubleshooting for the codes that appear.
Brian
At this point my advice would be to go to the 3000/4000 troubleshooting guide in the coach assist section of the forum and scroll down to DTC PO711 which will help you verify the sensor readings by pining out the harness at the transmission.
The mechanic may be right as the PCM is reading volt drop across the sensor circuit if there is a wiring problem ( corrosion/ high resistance) the TCM will be interpreting that as higher than actual temp remember there is likely 40 feet of harness between the trans and the TCM.
The troubleshooting guide gives the pin numbers and discription of the circuit operation to help diagnostics.
The fact that the ambient reading is high and moves linear with temp rise would tell you the sensor is working and either the Resistance of the sensor is not correct ( bad sensor) or there is a resistance elsewhere in the circuit.
But to diag properly the first thing that should be checked is the 5volt ref voltage to the sensor as the TCM reads volt drop if the ref voltage is low at or before the sensor the voltage return to the TCM will also be low.
At any rate the only way forward is to pin out the system as described in the troubleshooting guide.
Hope this helps
Eric
« Last Edit: September 28, 2020, 03:03:34 PM by Eric Maclean »
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Eric Maclean

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Re: Transmission over-temp issue
« Reply #7 on: September 28, 2020, 03:15:11 PM »
Brian
It appears you are looking for a high resistance in the wiring and with that said the obvious places to look would be at the connections is the plugs to the trans and to the TCM seeing as the plug has been apart to drop the transmission lower and made no difference I would check the plug at the TCM located in the area under the shift counsel.
Your looking for corrosion or poor fitting pins.
You may even want to run a new wire from trans plug to TCM plug to effectively by pass the high resistance this would give you a definitive diagnosis. Use the wiring diagram in the troubleshooting manual to determine the right pin numbers .
Feel free to give me a call at (613) 374-3194
Hope this helps
Eric
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2009 Chevy HHR
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Demco Air Force one tow brake.

Brian Chavet

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Re: Transmission over-temp issue
« Reply #8 on: September 28, 2020, 09:53:32 PM »
Hi all,

Dropped the coach off at Stewart and Stevenson in Denver this morning. The service manager there said this is a very common problem and it is caused from low voltage to the TCM (likely because of too much voltage drop due to high resistance elsewhere in the circuit). The control panel display was giving me the "Cat's Eye" by the time I got it down there and he said that is exactly what that symbol is telling me. I asked him if they had all the diag tools talked about in the troubleshooting manual and he just laughed. His guys have seen so many of these they rarely even need to use them. Should have gone there first, I'd be in Montana by now fishing on the Bitterroot! I did get my outrageous bill down from $1,845 to $845 at the first shop. Still a lot of $$ for nothing. I have a very bad back and cannot work on this myself, but I really do appreciate all the advice. The Allison Troubleshooting Guide in the help section is a little daunting, 861 pages of information, and most likely would be pretty challenging without the diagnostic tools mentioned there.

I will update when the job is completed!

Eric Maclean

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Re: Transmission over-temp issue
« Reply #9 on: September 29, 2020, 01:41:56 AM »
Brian
Great to hear you got it to a competent shop.
The troubleshooting can be done with nothing but a good multi meter the special tooling is nice to have but not essential.
but the nature of these coaches mean working in places a bad back won't let you go.
It sounds like the service manager has a good handle on the problem and will have you up and running quickly.
Good news.
Keep us posted
Eric
1997 Patriot Yorktown
3126-B
2009 Chevy HHR
Roadmaster falcon tow bar
Demco Air Force one tow brake.

Joel Ashley

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Re: Transmission over-temp issue
« Reply #10 on: September 29, 2020, 12:21:04 PM »
Ah, yes... the Bitterroot. 
May the Brown and great weather be with you there, Brian.

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Brian Chavet

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Re: Transmission over-temp issue
« Reply #11 on: October 02, 2020, 07:33:55 PM »
OK, time to update ... what would you say the worst possible scenario could be? If you guessed replace the transmission you're right. The fluid was contaminated with engine coolant. How is that possible? Take a look at the attachment. This cooler failed internally and mixed the fluids. How it works and where it is located are unknown to me as the coach is 50 miles away at Stewart & Stevenson's Allison repair center in Commerce City, CO and all my manuals are in it. Also take a look at the other attachment which is a Service Information Letter from Allison. This memo states that contamination from water or glycol >0.2% is detrimental to the reliability and durability of the internal components and should not be used. In my case the wiring was affected therefore sending erroneous signals (fluid temp 275 degrees). All the internal components detailed in the SIL are beyond salvaging. Now the fix ... rebuild the transmission as outlined in the SIL or buy a rebuilt Allison Certified replacement? Cheaper (that's a laugh) to swap with a rebuilt unit. Looking at about $10,500 for the unit with about a $4,000 core credit. And in the Allison SIL doc is a quote from Beaver for the cooling unit at $957. If I get away with $8,000 I will consider it very lucky (ha!).

Mike at Beaver Parts pulled some strings yesterday and said the supplier can build one in 1-2 days, miracle! These are not off-the-shelf units so each one is built from scratch. They will not drop ship to S&S so Beaver is going to overnight to Commerce City. The transmission is coming out of Minnesota ground freight and should be there mid-week, another miracle in my book. Then time to put back together and test puts the coach back in my hands 10/9 BEST case.

What to take away from all this ... the transmission fluid looked absolutely clean when I looked at it at the first repair shop and the fluid was not tested there. So, if your coach is an older unit, next time you check the transmission fluid HAVE IT TESTED FOR CONTAMINATES! 0.2% is a very small amount. What is that old adage ... an ounce of something is worth something else that won't cost you thousands of dollars? I learned an expensive lesson here. Maybe this has been discussed here before, I didn't look. But if you know someone that is in my boat you may want to share this tale.

I'll update again once this is behind me.

Save travels!

Brian Chavet

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Re: Transmission over-temp issue
« Reply #12 on: October 02, 2020, 07:46:34 PM »
Here is the photo...

David T. Richelderfer

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Roy Warren Co-Admin

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Re: Transmission over-temp issue
« Reply #14 on: October 03, 2020, 12:03:49 AM »
Tim Bentley had this happen to him.  Contact him and he can tell you all about it.
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