Auto trans service question. Trans temp also

[NSperduto]

Is there a write up, video, diy, etc of changing all the trans fluid in our trucks and changing the sensor and selonoid. 　

I have a mag pan with a trans temp gauge and the temp sensor in the pan. Last week while towing a small enclosed trailer for my boy scout troop, the trans temp gauge went up to 250 degrees. It was odd, it had never gone anywhere near that temperature. It also was not hot outside, nor was it a long drive. Maybe 15 miles. Do our trucks have a light on the dash at all? I thought they did and would have thought if it was actually that hot, it would have come on.　

The trans was not slipping and was shifting normal.So I'm not sure if there is a trans problem or if it's the temp sensor. 　

Either way it was time for a trans service, 　

The trans sometimes has a delayed final down shift coming to a traffic light, it's been that way for awhile. So I was going to drop the pan, change the filter and the governor pressure selonoid and sensor. I already had them. 　

After that I will go for a test drive with and without the trailer and see what happens. I'm also wondering if there is a way to test the temp sender that I have in the pan. 　

I know dropping the pan gets out some fluid. Is there a way to get the rest of the fluid out. It's either I find a way to get the rest of the fluid out or I fill it and drive for a bit and then empty the pan (I think the mag pan has a drain plug) and refill it again and do that a few times to get as much new fluid as possible into the trans.　


I actually forget how much fluid the mag pan holds...Last time my trans was serviced a friend of mine did it for me. I needed new trans lines and a cooler from rusting lines..　

 

[DaveHess]

What I did last time was pulled the rear most transmission cooling (transmission cooler return line) off the transmission, hooked a short hose to it, and used a 6 gallon drain pan. I started the truck in neutral and as soon as the fluid quite running out, I shut the truck off immediately. Then pulled the drain plug followed by dropping the pan. I do not recall how long this took or how much of the pan was filled. I changed the filter, put everything back together, filled the transmission with fresh fluid, warmed the truck up, ran her through the gears and checked the fluid level repeatedly until it was between add and safe (closer to safe). Be careful not to overfill. The solenoid and transducer are really quite easy to replace. Be gentle with the electrical connectors. Mine does have the Transmission Temperature light on the dash but the only time I see it is on "key on". If I remember correctly, the sensor for that light is in the valve body and will light the dash light at somewhere around 275F. I am sure Cerb will jump on here at sometime and set you up with better information.

 

[cerberusiam]

I think the light on the dash comes on at 260 degrees as the transducer measures it. The transducer gets flaky with age so that really doesn't mean anything, they may show hot when it isn't and not when it is.

At 24o measure at the transducer the trans should starting shifting harder and locking up sooner, on an 04 that is debatable as that TCM was not very smart. If you saw no other symptoms I would guess the probe\gauge has issues.

I usually drain the pan, change the filter then starting pumping out the cooler return line until I have gone thru 18-20 quarts of fluid to make sure it gets exchanged. A machine would be cleaner but cost more for the same results, depends on what you want to do. Some say just top it off but mixing worn out fluid with new fluid tends to defeat the purpose of doing a change, it is only as good as the worst fluid in it.

 

[NSperduto]

I think the light on the dash comes on at 260 degrees as the transducer measures it. The transducer gets flaky with age so that really doesn't mean anything, they may show hot when it isn't and not when it is.

At 24o measure at the transducer the trans should starting shifting harder and locking up sooner, on an 04 that is debatable as that TCM was not very smart. If you saw no other symptoms I would guess the probe\gauge has issues.

I usually drain the pan, change the filter then starting pumping out the cooler return line until I have gone thru 18-20 quarts of fluid to make sure it gets exchanged. A machine would be cleaner but cost more for the same results, depends on what you want to do. Some say just top it off but mixing worn out fluid with new fluid tends to defeat the purpose of doing a change, it is only as good as the worst fluid in it.

Well right now the lift in my garage is being hogged up by a 63 Cadillac that I'm doing a full brake job, master, booster, timing chain, waterpump, etc...that will be apart in there for awhile. I spoke to a friend about 1.5 hours from my house who owns a transmission shop. I had already bought the sensor and selonoid. He told me to drop the truck off and he'll flush it and change out the filter and put in my new parts and check a couple other things he was rattling off. I figure I'd rather be safe than sorry. I do 99.75 percent of my own work but I'll farm this one out. Especially once I figured out it would be close to $200 in just new fluid...If all looks well to him, I'll get a new gauge.

 

[Motorhead]

Isn't there a check valve in the trans oil cooler line that can stick closed and keep the trans from cooling?

 

[cerberusiam]

There is a check ball in the cooler output line that is there to stop drain back of the TC. It can't stick because of the flow direction but it does collect trans and does reduce flow. There is also a thermostat in the front cooler that will bypass the main cooler and cause it to heat. Neither really means anything if it is the gauge\probe that is bad.


If it over heats the TCM will try to protect things and it will be obvious something is wrong.