Trans shifting while loaded

I was wondering about all the guys towing heavy, and how they are shifting their transmissions? I just climbed Sonora Pass over CA Hwy 108 with roughly 3k pounds of cargo. I turned OD off, and ran it mostly in 3rd. During the heavier climbs I would manually shift down into 2nd. At the 25% grade I pulled into 1st. Does this seam normal? I am trying to figure out if my trans or converter is slipping, or if this is normal. I will be pulling my trailer over passes in the 6%-8% range and trying to calculate my shifting. Thanks.

 

On anything I have climbed I take it out of overdrive and have not had to go any further. Mine has a DTT and provides TC lockup in second over 18mph if need be which does happen in slow traffic. If your trans is stock it can heat up pretty good if your in 1st or 2nd since the TC is not locked. Do you have a trans. temp gauge ?, mainly from the output of the trans to tell you how hard it is working.

 

I believe my trans is a stock replacement trans. It was changed before I bought the truck. It appears to have no upgrades when I looked around inside. I do have a Derale 15960 and Isspro gauges. How do you control 2nd gear lockup? I wasn't concerned too much about going into 1st gear, because climbing a 25% grade isn't common. But wondered how my trans was compared to others.

 

With a [slide in] camper and a trailer I'm around 13,000#. There's a lot of mountains in BC so I'm always picking the gear. On steeper roads I keep the RPM in the 2,500 - 3,000 range and I do end up in first from time to time. The TC will only lockup in 4th or 3rd with the OD off.

 

DTT installed an external Microswitch on the trans and valve body modifications. I believe some have installed a switch in the cab to control lockup also. Maybe wired into the PCM ?. I really cannot remember all the details as it was a very long time ago.

 

That is exactly the kind of real world I am looking for. Thank you.

 

Thanks. I am debating on hooking up a mystery switch for 2nd gear lockup. I do know that I will need to also mod the valve body. Just not sure if I want to go that route.

 

that is one of the steepest road in the US. Sound like you are doing great, that road is a challenge without a load.

 

The 2nd lockup works great for me when hitting road construction but like I said, I have to get up to 18mph before it kicks in and starts lowering the trans temp which doesn't always happen. Then it's spin the roulette wheel between N and D.

 

Thanks. I was wondering if everything seems ok. My trans was heating up in the past. I made some adjustments to my trans cooling and am hoping for the best.

 

I had just learned about the N and D swapping when in stop and go. I have started doing this also. I am no stranger to towing heavy. I got my commercial license at 18 years old, I am 43 now. This is my first Cummins. In the past I have towed with Chevy square bodies. 1 was a 454/TH400/4:10's and the other was a pumped 383/TH400/4:56's. I never had heating problems with the TH400's. Maybe that was due to the lower gearing? I just recently started driving this trans like I probably should've been.

 

When I have been towing with this truck in the past, I have just turned on the electric fan on my Derale, popped off the OD, and put the hammer down. That caused my trans to heat up alot. I quit driving like I was 16, and started driving like I wanted to save the trans. It seems much better. I am just trying to figure out if I am too late, or if others have to pay attention like this too.

 

If you do not have one a trans temp gauge is invaluable. I guess the line that I bought from the dealer a long time ago is still available with the bung for temp probe from the aftermarket, maybe dealer also. There was a recent thread here that was listing it but I cannot remember the name of the thread. The gauge is good/bad. Good that you know what's happening, Bad because you may get worried that it is.

 

I have Isspro Trans/Boost/Fuel. I am only needing Pyro. I don't get worried too much. Since I started paying attention, my trans might get to 200°F max. My sensor is located in the return line after the coolers. I also have the Derale 15960 located after the sensor. So my trans may get hot inside the pan, but if the temp sensor doesn't go over 200 and I still have 1 more cooler, then I don't worry. I wish I could see how cold the Derale brings it down further. I am looking into adding a second sensor after the Derale, then wiring it up so that I can switch back and forth with the 1 gauge.

 

If your at 200* AFTER the coolers, your transmission’s getting too hot.

 

So if my trans is getting too

My trans feels good when driving. I haven't removed the check valve because I didn't have the fitting in my hydraulic stuff. I can also watch the rpms drop 200-300 during lockup. And my truck start moving the trailer right away. This thing has me stumped then. Maybe remove the check valve and monitor temps, then proceed from there? My trans will ride at 130°F-160°F just driving the country roads home from work. Does that sound excessive?

 

Your temp sensor needs to be in the line from the transmission to the cooler. That’s the only real way to know what’s going on.

 

Whats the difference then between the discharge line and the pan?

 

If I had to surmise, I'd say that with the temp sensor in the discharge line, you only know that the heat exchanger is working well; you *don't* know how hot the lube is coming out of the trans. That is, if the air is cold enough, it's pulling most of the heat out of the lube. But you still need to know how hot the trans is getting.*That* temp will give you a better idea how long the trans and lube will last.

IIRC, few valve bodies (prolly a few performance VBs) will lock up (the torque converter clutch) in 2nd gear; fewer (prolly only racing VBs) will lock up in 1st.

 

The line out of the transmission to the cooler gives you true transmission temp and reacts instantly.

The line after the cooler will tell you what the cooler lowered it to. If this is what you’re watching, you have to try to figure out what it was before it went into the cooler.

Pan temp is going to be lower than the line temp and will react much slower. If all you’re watching is pan temp, it could be burnt up before your gauge tells you it’s too hot.