Transmission temps

[sgriffing]

Attacked a "Major" hill Yesterday (Goat path with blacktop).

Truck pulled that car hauler up no problem.

Boost was good, EGT's stayed below 1100 and transmission wasn't bad.

Backing it into the driveway is another story.

The transmission temp hit 140* the long way around.

Why is it I can pull 20,000 GCVW up a grade (that kills my gasser without a load) but backing up with the slightest resistance cooks the transmission?

What is the max safe transmission temp for an extended pull?

Can anyone recommend a good transmission shop in Atlanta?

Or should I just run down to Suncoast?



Let's hear it.



Thanks!

 

[formula]

I'd assume your temp sender is in the pan. You should really have the sender in the hot line between the trans and the heat exchanger. Reason being is that the oil will be hottest when it exits the convertor. The oil in the pan has already been through the cooling system. By the time you heat the oil in the pan too hot, you've most likely got other problems.



Sean

 

[sgriffing]

ASSumptions

Why would you assume that?

My gauge sending unit is in the same line as the factory sending unit.

I also have a 25,000 GVW Aux cooler with fan under the bed.

Like I said, It does fine pulling forward, it's backing up that has me really concerned.

 

[Philip]

When a auto trans is placed into reverse. All trans pressures are doubled from its normal operating spec's for forward motion. The transmission is made for forward motion. To have a reverse means to turn it against its designed operation. In forward the trans pressures are in the 70 to 150 psi operating range. In reverse it starts at 225 and goes up depending on the amount of throttle thrown at it.



So heat build up can happen if your in reverse to long with some throttle thrown at it. Just make your reverse moves as little as possible and allow a cool down time before you shut the engine down.



The pressures are also why it is hard to back up a gasser when it is cold with out it dieing. This is common for most all auto's on the market. Reverse =double pressure to move the vehicle= double the heat produced.

 

[formula]

Re: ASSumptions

Originally posted by sgriffing

Why would you assume that?

My gauge sending unit is in the same line as the factory sending unit.

I also have a 25,000 GVW Aux cooler with fan under the bed.

Like I said, It does fine pulling forward, it's backing up that has me really concerned.

Sorry 'bout that. Your aux cooler explains the relatively low temps. I didn't see that you had one.



Philip, what is the cause of the higher pressures when the trans is in reverse gear? Also, for what reason are the pressures higher?



Sean

 

[sgriffing]

No apology necessary. I don't have it in my sig yet.

Has anyone else noticed this tempurature rise while backing?

Could someone PLEASE recomend a good transmission shop (Or list member) in the Atlanta area??

 

[Philip]

what is the cause of the higher pressures when the trans is in reverse gear?

The tran is designed to have the least resistence going forward. The design people decided that reverse is not used enough to be a concern. So to get reverse and not cause any friction lose in forward. It was cheaper to just apply more pressure to the reverse circuits to overcome any slipping that might occur. At normal forward apply pressure a trans will slip in reverse.



Higher temps in reverse can be normal if you stay in reverse for an extended amount of time. Higher pressures mean higher temps.



Another thing to remember is in reverse you do not have any air flow threw the coolers like you would running down the road at 60mph. That is another reason for a temp spike. Just allow for a proper cool down or go for a drive after backing a heavy trailer.

 

[formula]

 

[jbolt]

At 140* I would have assumed the same as Formula. My trannys not up to normal temps at 140. The normal factory temp is 175. I usually see temps from 165 to 185 daily driving and have had it up to 220 pulling heavy. The fan on my cooler under the bed does not even kick in until 200 or so. I could be wrong but I'd guess if you think its hot at 140 your not getting a true reading.



Jay

 

[sgriffing]

Originally posted by sgriffing

The transmission temp hit 140* the long way around .

As in "Went past all the other numbers and started over again". :--)

>300*

Hit the low peg on the high side.

"It was freakin' HOT"



It normally runs 160-180 unloaded (Higher if I'm having fun).

Runs in the low to mid 200's loaded.

If it gets to the high side of the gauge while going up a hill, I back out of it.

 

[formula]

OOOO MAMA



How's that fluid look and smell? What gear and speed do you usually pull with?



Sean

 

[sgriffing]

Originally posted by formula

OOOO MAMA



How's that fluid look and smell? What gear and speed do you usually pull with?



Sean

I'm afraid to pull the dipstick.

I usually pull in third gear. Ocasionally, if I'm empty and the weather is cool, I'll put it in O/D on long flat runs. The other day, I started in first, let it shift into second and then back into first towards the top where it really got steep. The transmission never got above 270*. The backing up is what killed it. It was a short distance so I'm sure it's not too bad, but still... . it makes me wonder what kind of life this transmission had before I got it. Granted it wasn't turned up then but it didn't have the extra cooler or a temp gauge either.

 

[cwienenga]

transmission temp

I know that in the manual,the od sensor is there to kick the od out at 270 deg so they must figure that is getting near the limit.

mine doesn't take to much to get in the 240 range pulling, and I shift out of od anytime I see a hill of any consequence coming up.



cliff

 

[jbolt]

"the long way around" :-laf I get it now. YIKES!



Looks like backing up a trailer is hard on our trannies.



DTT discussion



Check your fluid!



Jay

 

[Philip]

Went past all the other numbers and started over again

I understood what you were talking about. The top side temps on a 727 when I took the rebuild class on it a couple of decades ago was stated as 300. Anything above that change the oil ASAP if it smelled burnt. So pull the sitck and see what it smells like.

Looks like backing up a trailer is hard on our trannies

If your backing a heavy loaded trailer and just putzing around. Yes you can do damage to a trans.



To sum it up better. When you are in reverse just think of you doing a full converter stall test on the trans. Dodge says 5 seconds max to avoid trans damage. Being in reverse is close to this test in real life. At twice the pressure also.