M35A3 Transmission Temp

[Terra1936]

Just joined the M35A3 Club. Today was my first run and I let the truck idle for two hours an noticed the transmission temp gauge creeped to 225 (at idle) and when i took it for a short spin it climbed to 275. I checked the fill and was at the top mark on dipstick. Bad Gauge or am I missing something? The truck has not been operated much the last three years. I did operate all gears on my test and high and low and the engine temp was fine.

 

[snowtrac nome]

The trans temp should mimic the engine temp as its the engine coolant that cools the transmission . It really shouldn't get much more than that unless you let it idle long periods of time in gear where there is a lot of torque converter slippage.

 

[rustystud]

Just joined the M35A3 Club. Today was my first run and I let the truck idle for two hours an noticed the transmission temp gauge creeped to 225 (at idle) and when i took it for a short spin it climbed to 275. I checked the fill and was at the top mark on dipstick. Bad Gauge or am I missing something? The truck has not been operated much the last three years. I did operate all gears on my test and high and low and the engine temp was fine.

I would suspect a bad gauge. Your temp should be around 160 to 180 at idle and when pulling hard you should see around 180 to 220 tops.

 

[Terra1936]

any idea how to verify the temp? Before I change gauge? Is there a thermometer or? I can't find anything on the web? I have not looked yet but is there a sending unit?

 

[Terra1936]

I did have it idle in neutral for two hours and the engine temp was around 190?

 

[Ajax MD]

Buy an IR temperature gun and shoot the transmission and the cooling hoses to see if they match what the gauge is telling you.

 

[sue]

“Probably” bad gage, mine did the same thing.
reached under the truck when the gage said 250
touched the pan and could have not been over
140-150.

 

[tobyS]

Like Sue said, get your hand on a line or the pan. You won't keep it there long at 190.
Smell your tranny fluid. Does it smell burned? Do you have a nice solid reverse?

My tranny ready to go in.

And the "Coastal Warfare Unit" mark on my truck...AjaxMD....I'm holding out to have one made with the teeth and more aggressive look.

 

[Ajax MD]

Like Sue said, get your hand on a line or the pan. You won't keep it there long at 190.
Smell your tranny fluid. Does it smell burned? Do you have a nice solid reverse?

My tranny ready to go in.

And the "Coastal Warfare Unit" mark on my truck...AjaxMD....I'm holding out to have one made with the teeth and more aggressive look.

Toby- NO WAY!!!!! Awesome, brother! You're a brother X2! Submarines and the MIUW! Ha, I wish you lived closer. We'd have a **** of a time.

 

[Mquirin]

Resurfacing this post. I've got a similar scenario with my A3. All fluids appear clean and at the correct level (I flushed and refilled everything when I purchased it). It seemed to drive correctly, but after running for a short period of time, the transmission temp quickly hits 275+ with some simple driving (hauling zero load). I took an infared thermometor and the Allison Trans pan registers at around 165 degrees. Similar temps when I measure temp at lines headed to and from coolant reservoir and radiators/coolers. The water temp hold right around 185 degrees.

Bad gage? Issues with gears?? Anything else I should check? I just finished 2, 1 hour highway trips and seemed to drive well around 50mph (seemed to be about as fast as it wanted to go).

 

[HDN]

Sounds like either a bad gauge or bad electrical connections to the gauge. Your temperatures are probably fine based on your IR thermometer readings.

Like others in this topic, left idling in neutral for awhile will build up temperature. I left it idling in neutral for two hours and then drove it away, only for the cooling fan to engage 50 feet down the driveway. The trucks seem to like cool air while driving. I'm guessing this is pretty common with diesel trucks in general.

 

[glcaines]

On my M35A3, the trans temp barely leaves the 100 deg mark, even when idling for a long period. I live in the mountains and when I'm pulling a very heavy load in the truck and trailer in the summer with the temp in the 90s, the trans temp will increase to around 180 - 190, but it never goes higher. One difference is that I changed my trans fluid to Dexron 3 when I first got the truck. Dexron 3 made a tremendous positive difference in the way the transmission shifts, etc. over the motor oil.

 

[HDN]

On my M35A3, the trans temp barely leaves the 100 deg mark, even when idling for a long period. I live in the mountains and when I'm pulling a very heavy load in the truck and trailer in the summer with the temp in the 90s, the trans temp will increase to around 180 - 190, but it never goes higher. One difference is that I changed my trans fluid to Dexron 3 when I first got the truck. Dexron 3 made a tremendous positive difference in the way the transmission shifts, etc. over the motor oil.

I'm still running 15W-40 in mine, so that temperature difference makes sense.

 

[tobyS]

Smell your oil. Does it smell burnt?

There is nothing, like clutches with pressure, that I know of to make heat at idle.....unless it's really in gear.

The government made a real screw up puttion a locking torque converter on the 545....calling it a 1545. It's part of the reason the 4th/r clutch pack fails. Flow does go to the torque converter while at idle.

Heat is usually a sign that the clutches are giving up, because of the old seal. The 2 we have built had melted aluminum and friction lining in the oil.

Hope you knew about a potential fourth seal-clutch problem....they fail and have given the A3 a bad reputation. Do you know the history of your tranny?

 

[Mquirin]

On my M35A3, the trans temp barely leaves the 100 deg mark, even when idling for a long period. I live in the mountains and when I'm pulling a very heavy load in the truck and trailer in the summer with the temp in the 90s, the trans temp will increase to around 180 - 190, but it never goes higher. One difference is that I changed my trans fluid to Dexron 3 when I first got the truck. Dexron 3 made a tremendous positive difference in the way the transmission shifts, etc. over the motor oil.

Thanks for the reply. I'm running Dex3 in mine as well.

 

[Mquirin]

Smell your oil. Does it smell burnt?

There is nothing, like clutches with pressure, that I know of to make heat at idle.....unless it's really in gear.

The government made a real screw up puttion a locking torque converter on the 545....calling it a 1545. It's part of the reason the 4th/r clutch pack fails. Flow does go to the torque converter while at idle.

Heat is usually a sign that the clutches are giving up, because of the old seal. The 2 we have built had melted aluminum and friction lining in the oil.

Hope you knew about a potential fourth seal-clutch problem....they fail and have given the A3 a bad reputation. Do you know the history of your tranny?

I don't know the history of my tranny, but appears to be stock with the truck. Oil doesn't smell burnt. It's Dex3 and I added it about 2 years ago (truck had Dex3 in it when I bought it). Would a failing 4th seal clutch problem create that heat and would that mean the 4th gear isn't engaging? If it was failing and heating that much, would the temp at the tranny pan (measuring with a point and shoot thermometor) match what the gage was showing, or would it not be related?

 

[frank8003]

Why not put a REAL temperature gauge where you can see it in the cab?

any idea how to verify the temp? Before I change gauge? Is there a thermometer or? I can't find anything on the web? I have not looked yet but is there a sending unit?

It, that information is in the TM

 

[tobyS]

The seal used on the fourth clutch pack by the OEM fails. The locking tc shifts from 3to 4 with it locked, putting more stress on it. Over time the seal holds less and less pressure on the clutch pack, causing it to slip. As it slips, it heats up. It gets hot enough to melt aluminum and turn the steel plates blue.

I used the OEM aluminum piston and clutches when I rebuilt mine, but have found the truck pull people have stronger clutch plates and a steel Vulcanized piston that is much better at holding pressure and has 2 more clutch plates. These are the "direct" clutch for the 4l80 and they should fit right in..

No Allison rebuilder will stand behind one with motor oil because motor oil will not prevent clutches from absorbing water.....atf does. Water...even small amount kills clutch facings.

 

[Mquirin]

The seal used on the fourth clutch pack by the OEM fails. The locking tc shifts from 3to 4 with it locked, putting more stress on it. Over time the seal holds less and less pressure on the clutch pack, causing it to slip. As it slips, it heats up. It gets hot enough to melt aluminum and turn the steel plates blue.

I used the OEM aluminum piston and clutches when I rebuilt mine, but have found the truck pull people have stronger clutch plates and a steel Vulcanized piston that is much better at holding pressure and has 2 more clutch plates. These are the "direct" clutch for the 4l80 and they should fit right in..

No Allison rebuilder will stand behind one with motor oil because motor oil will not prevent clutches from absorbing water.....atf does. Water...even small amount kills clutch facings.

Thanks Toby, great insight. Based on what you said above, if the 4th clutch was failing, would I also have issues with reverse? My reverse is strong, and I keep going back to a bad gauge since the infared thermometor has my trans pan at 165 when the gauge is showing 300. That said, maybe it's best to take to a transmission shop to let them put their eyes on it.

 

[Mquirin]

Why not put a REAL temperature gauge where you can see it in the cab?

It, that information is in the TM

Thank you Frank. Are you saying bypass the temp sending unit and just run a mechanical temp gauge?