T/C Lock Question

[RedRamer]

Just pulled my trailer for 2nd time with in-line trany temp guage and have a question.

When pulling with the O/D lockout switch "on" third gear TC locks in.

When pulling with the O/D lockout switch "off" (normal position), third gear does not seem to go into a TC clutch lock situation.

Is this normal operation?

The reason I think the TC does not lock up in third with normal switch position, is because when pulling through towns my temp can go high, to over 290 up long grades through towns. When I lockout the OD, to "on", which I do now when I get into small towns, the temp never goes over about 180-190 and I can feel the torque much better in third gear. The other reason is because when going through normal 4 gear shifts, going through third gear, the tack follows normal engine speed without any change like you normally see when 4th locks up.

thanks

 

[Dieselnerd]

Normal operation. TC only locks in third gear with OD off.

 

[WyoJim]

Dieselnerd is correct!!!

Goober, Thats the way mine works too, just like yours.

You have made some observations that most drivers of automatics don't seem able to grasp.

It seems very few drivers will let their truck teach them what it wants and drive accordingly.

 

[RedRamer]

Thanks guys.

Now I know how it works and can work with it. transmission temp guage is best investment I made in a while.

So in order to lockup in 3rd or 4th, all one has to do is hit the o/d button.

My next questions have to do with temps in 3rd, while driving through small towns.

The fan never comes on, so when in towns, the transmission cooler doesn't get enough air through it. I wonder if there's a fan that can be put in front of the cooler as there seems to be a few inches of space there. I hate to see the temp go into high 200's.

Second... I read a chart somehwere that said if transmission oil hits those high temps it basically wears out faster and should be changed.

When I hit hi 270-290 temps, for small runs of about no more than 5 minutes, is this burning the oil? And also I read somewhere there is better transmission oil than the stuff transmission centres put in. What's better oil to use?

thanks again.

 

[Dieselnerd]

Goober, those seem to be pretty high temperatures. You ought to check your cooler to make sure it isn't clogged with bugs. Mine never goes over 200 even in heavy stop and go traffic. The only time it actually exceeds 200 for a short time is while parking the trailer and going back and forth. I would say that normal temps while locked up are around 150, towing or not. Stop and go it runs around 175 even in the 90 degree weather we have had lately. I do take my temps at the hot line going out of the transmission. It's possible you are not getting full fluid flow to your cooler, maybe a stuck check valve or debris in the lines or cooler. I have never seen mine go that high.

 

[John_P]

goober:



When the transmission temperature gets up near 300 degrees

you are in the "danger zone. " The TDR had a chart on the

longevity of the transmission versus transmission temps.

I have looked for it but can't find it. Maybe one of the other

members will post it for you.



As far as transmission fluid, I have used the Amsoil ATF and

found that it will lower my temperatures when towing but

only slightly. A good auxiliary transmission cooler will keep

the temps down permanently while you are towing or in

heavy traffic. Bill Kondolay at DTT can get one of these for

you.



Hope this has helped you.



----------

John_P

 

[RedRamer]

Mind you getting 275-290 only happended a couple of times, but I can imagine the temp when I get on a 2+ mile grade.

Dieselnerd, I'll get the flow checked as that would explain high temps at slow speeds.

As far as a new cooler john_p, is that a replacement cooler or another add on?

denis

 

[Extreme1]

High temps like that happened to me too.

Try pulling the shifter into 2. What was happening with mine was that I didn't have the kick down cable to the trans set right and it was cruising along in 3rd in town and should have been in 2nd. According to Bill K. (on another post), with the throttle all the way open, the kick down lever (at the trans) should only have about 1/8" travel left.

 

[SlyBones]

I never see more than 200, stop and go, unloaded.



Stop and go, in town with the TT attached gets me 230. Usually takes stop light to stop light where the transmission cant even get to 3rd locked up. Mostly 1st and 2nd. And some amount of it.



I can also see 230 if I have to pull a hill, with the TC unlocked. Like the one on the way to I-5 from the house. Have to pull at 30mph, usually in second. Heats it right up.



Always cools down once the load, hill is removed and/or the TC locks up. These are the two conditions where I can see the high temps. I agree with over 300 bad things are happening.



Yes this does degrade the fluid. Thats why the manual says 12K intervals ( or something like that ) in the heavy duty service schedule. Prolly extreme or casual towing and those that never see over 200. Heavy towing and lots of 200+ temps you had better see regular fluid change intervals.

 

[John_P]

Goober:



Sorry for the delay on your question about the aux.

transmission cooler.



Those trans coolers are IN ADDITION to what you

already have. The one Dodge sells is mounted right

behind the drivers side under the bed and it is LARGE

and very efficient. A friend of mine has one to tow his

5'er with the auto and he NEVER gets temps above

about 180-190!



Hope this helps! Sorry for the delay.



---------

John_P

 

[RedRamer]

Thanks. That will make 3 of e'm

But I'm sure if that transmission keeps cool, she'll last a long time.

I meausred a sending unit, same as I have on, and guess what, the fitting the hydraulic guys made up with the "t", well it has to stick into the flow through part somewhat from what I figure.

To plumb up that third cooler, I would think the line comes from the front cooler to the third one, then to the transmission.

Seems to me the water tank cooler is only there to prevent the high temps from hitting the front cooler.

 

[JohnE]

goober;



Does the engine temperature guage stay low during the high trany temps periods? Maybe a Horton fan clutch will help in the crunch times.



I think you got it straight on the O/D "on" versus "off"? If you have O/D " th TC will lock in third and stay there. If you push the button while running loaded you will see higher RPM as the TC unlocks. After it shifts into OD and then finally goes back to TC lockup will the engne RPMs drop back to cruise mode.



I feel the heat exchange between the coolant and trany fluid is "in" versus "out". In other words, it warms the trany fluid to help it stay above minimum operating temperature. It is not big enough to do much else.



John

 

[RedRamer]

Thanks.

I think you're right about the water cooler. Mostly for winter use I guess.

The Cummins temp never goes above 80c. Keeps cool no matter what.

Mechanic is on holidays for a week, so when he gets back, we check restriction and sending unit. If that's not it, i'll plumb a another cooler in behind the front one and might add a fan to it also, as I know I'll get high temps expecially in cities like Toronto with its stop and go highway traffic for long period of times.

 

[Extreme1]

Check the check valve for debris too. It is located at (or in) the inlet to the water cooler.