Off-road transmission temperature (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

SJWantsADiesel

GOLD Star
SILVER Star
Joined
Jul 30, 2014
Threads
24
Messages
184
Location
San Francisco, CA
My ‘97 has 260k miles on it. Running 5.29” gears in the diff.

I had the transmission oil changed less than 10k miles ago and have a temperature gauge installed with the sensor in the pan. What I struggle with is keeping the temperature manageable off-road especially on dirt roads where speeds is between 15-30mph.

If I run in 4-lo, it tops out at 25mph with RPM at about 3k and I guess there is no OD in 4-lo. Eventually the temperatures start to climb.

4-Hi isn’t a good option either obviously. Shifting down to 2nd or L doesn’t work well either since I can’t lock the torque converter.

Wondering if pretty much everyone ends up installing an aftermarket torque converter lockup unit or my tranny needs a rebuild? I have noticed that once the pan temperature crosses 150F, the tranny starts to behave very odd. A few times when I have come on the freeway after hours of trail time, the tranny seems to get stuck in OD and if I step on the gas hard then it shifts down momentarily but shifts up quick and won’t stay locked to pull the truck. Usually end up with see saw effect, at which point I quietly move to the slow lane and lick my wounds.

Is this normal for the A343F or should I look to get my tranny rebuilt?
 
Why would you run 4L on a dirt road? I get when you’re slinging mud or traversing an obstacle. Please tell us more.
 
Why would you run 4L on a dirt road? I get when you’re slinging mud or traversing an obstacle. Please tell us more.
Yes, obstacles and last week, I was in Mojave where trails are sandy.

I think I read somewhere that the you can remove a detente ball from the t-case and shift between Hi/Lo without stopping?

Edit: I should add that I have the CDL mod so I don’t have to worry about center automatically locking when shifting between Hi/Lo.
 
Last edited:
Is your trans cooling system complete and properly plumed? How hot does the trans actually get?

From the info you have thus far supplied, something is wrong with you trans or cooling system or both. 150f is within the ideal fluid temp range and shouldn’t trigger funky trans operation.

I haven’t read or heard about removing any detent balls from the the transfer case. What does shifting the transfer case on the fly have to do with the subject of this thread?
 
... I guess there is no OD in 4-lo ....
There can be. @Tools R Us (RIP) disconnected one of the electrical connectors on the t'case (can't remember which one, and can't look right now, either), and that'll give OD in 4Lo. Coming from a Chevy 700R4 I'd been worried about transmission temps in our 80/LX, but was told by @Tools R Us that 80 transmissions do not overheat. And so far they haven't.
 
There can be. @Tools R Us (RIP) disconnected one of the electrical connectors on the t'case (can't remember which one, and can't look right now, either), and that'll give OD in 4Lo. Coming from a Chevy 700R4 I'd been worried about transmission temps in our 80/LX, but was told by @Tools R Us that 80 transmissions do not overheat. And so far they haven't.
I realize the trans in question here is an A343 but I’ll add that my 93 and previous 94 A442f will shift into OD while in low range with no modifications. I agree that these transmissions run cool, cooler than any auto I’ve experienced.
 
What size tires?

With 5.29 diff ratios, I can't see running at low speeds in HI being a huge problem, but I have no direct experience with 5.29s or auto.

If the trail is good enough to be running at 15-30 mph, you should be able to run in HI
 
What size tires?

With 5.29 diff ratios, I can't see running at low speeds in HI being a huge problem, but I have no direct experience with 5.29s or auto.

If the trail is good enough to be running at 15-30 mph, you should be able to run in HI
35” tires. Running in Hi poses two issues - going downhill and trans temps climb faster in Hi than Lo. I don’t know if it’s supposed to be that way but just reporting what I see.

In Lo, it is hard to go above 20-25mph, the engine revs to 3k+ rpm. This Mojave trip, the gauge eventually climbed to over 160F after running trails for a few hours.

Keep in mind that the temps I am reporting are in the pan so inside the tranny, the oil has to be much hotter. Cruising on the freeway, depending on air temperature, the gauge shows anywhere between 90 to 105F.

I suspect something is not ok with the TC because one time, climbing up in the Sierras during a really cold winter stormy night, the tranny seemed to lock itself and wouldn’t shift down. The gauge was stuck at 80F, made me think it broke.

Sorry, the Hi/Lo shift question is whole another issue. Please ignore that.
 
Your trans is definitely doing some odd things performance wise but 160f in the pan is a good representation of the core temp of the trans. When an unlocked converter is working hard and shearing the fluid aggressively temps off the converter can be quite hot but that would be indicated on your temp gauge even though fluid off the convert flows directly to the cooler. The temps you have reported here will have no adverse affect on the transmission one way or another.

Having said that, my older A442f has a hard time eclipsing 150f. I have seen 170f while crawling slow rocks with AC on in 90f ambient temps. Shut the AC off and the trans temp gauge dropped like a rock to 140-150f.

Is you cooling system plumbed properly per the FSM?
 
The torque converter will not lock up below 48mph:
1683407404792.png

The A/T oil cooler is two stage cooling system: the first stage uses the radiator to "precool" the A/T oil; the second stage is an ambient air heat exchanger. If there is insufficient airflow, the cooler will not function to reject additional heat.

Having said all that, 150°F is the "normal" A/T oil operating temperature. If your operating temperatures rise above 180°F, the oil begins to thin and the friction discs will have a hard time sticking to the plates. However, if this does happen, you will see a sudden engine RPM rise with no associated speed increase. If you don't see this, there is nothing wrong with your transmission - that is, nothing that would require rebuilding, which typically involves replacing the steels and friction discs (along with other wear items: bearings, seals, etc.).

IIRC, if the A/T oil temperature rises above 210°F, you'll get a code. And maybe limp mode to go along with it.

Your pavement driving experience after trail driving sounds like it's related to the external mechanical components; maybe the transmission cable (from the throttle body) connection to the transmission. I'd look there before I pulled a transmission. Or paid someone else to do it.
 
Anza Borrego and Mojave are common areas for me, and never had trans issues.

4Lo+D is good if you don't want to lug the motor. There are a lot of grades and elev changes that 4Hi just ends up lugging the motor.
You can do 2nd start so you don't have that slap out of 1st in 4Lo on more level terrain.
Also, 3k rpms is nothing. You're not going to hurt the motor by reving it- you kinda have to if you're in 4Lo and want to get anywhere.

We only have 4 speeds so you're never really in the correct powerband. Use the gas pedal accordingly. :)

You should see the Venezuelans drive the 80s through - 4Lo and send it. LOL
not great gas mileage but you get good control and stay in the power.
 
Anza Borrego and Mojave are common areas for me, and never had trans issues.

4Lo+D is good if you don't want to lug the motor. There are a lot of grades and elev changes that 4Hi just ends up lugging the motor.
You can do 2nd start so you don't have that slap out of 1st in 4Lo on more level terrain.
Also, 3k rpms is nothing. You're not going to hurt the motor by reving it- you kinda have to if you're in 4Lo and want to get anywhere.

We only have 4 speeds so you're never really in the correct powerband. Use the gas pedal accordingly. :)

You should see the Venezuelans drive the 80s through - 4Lo and send it. LOL
not great gas mileage but you get good control and stay in the power.
Hah! Thanks for that tip ;)

I was reading another thread (can't find it now) about OD in Lo and some people seem to say that it eventually shifts to OD above 3500rpm, some said it never does.
 
The torque converter will not lock up below 48mph:
View attachment 3316277
The A/T oil cooler is two stage cooling system: the first stage uses the radiator to "precool" the A/T oil; the second stage is an ambient air heat exchanger. If there is insufficient airflow, the cooler will not function to reject additional heat.

Having said all that, 150°F is the "normal" A/T oil operating temperature. If your operating temperatures rise above 180°F, the oil begins to thin and the friction discs will have a hard time sticking to the plates. However, if this does happen, you will see a sudden engine RPM rise with no associated speed increase. If you don't see this, there is nothing wrong with your transmission - that is, nothing that would require rebuilding, which typically involves replacing the steels and friction discs (along with other wear items: bearings, seals, etc.).

IIRC, if the A/T oil temperature rises above 210°F, you'll get a code. And maybe limp mode to go along with it.

Your pavement driving experience after trail driving sounds like it's related to the external mechanical components; maybe the transmission cable (from the throttle body) connection to the transmission. I'd look there before I pulled a transmission. Or paid someone else to do it.
Thanks. I guess the only odd behavior I see is on pavement - it will seem to get stuck in OD and won't downshift on a grade. Then it will suddenly downshift for a few seconds, send the revs up but again shift up before the truck has a chance to gain any speed or momentum. I realize these are 4-speed boxes so not much of a selection in terms of gears :D
I will have the cable looked at.
 

Users who are viewing this thread

Back
Top Bottom