2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

[Big Bubba]

Hello everyone,
I have a question about my transmission on my 2000 year, C3500, 2-wheel drive, Chevrolet Crew Cab Dually, with 7.4 liter engine. Anyway, I have an issue with my transmission when it gets up to normal operating temperature then it wants to shift harder and seems like it doesn't want to go into overdrive and the RPM's are a little higher. Anyway, when I first drive it for the first time of the day and it is not up to operating temperature the transmission shifts like a brand new one and shifts smooth as glass and goes into over drive just fine. Now, I just got this truck about a month ago, maybe three weeks ago, and I have done nothing with the transmission, like changing out the fluid and filter on it. I have like yesterday did a compete tune-up on her putting brand new distributor cap, rotor, spark plugs and new spark plug wires and changed out the oil and filter for the engine. I have NOT changed out the transmission oil and filter. I am praying that the transmision is not going out on her but I tell you when I first drive it in the morning she works Great!!! but it is when I drive it down the interstate it starts to do the hard shifting thing and seems it does not want to go into over drive after it has been drove for a bit and warmed up to normal operating temperature. Now, I did have a loss of antifreeze, due to a bad gasket inside the radiator cap and a slightly leaking bypass hose coming off the top of the water pump and going to the intake manifold but I have since fixed that and seems the fluid is not getting lost it is staying the same level as I topped it off, the radiator that is. What do you think might be wrong with my transmission? I also have a OBD-2 scanner and there is zero or no codes present or come up just a "0" reading with no codes at all. Thank you for your help.

 

[TilliamWe]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

That is weird. If there is a time they shouldn't go into OD, it's when they are cold.

 

[Big Bubba]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

Will replacing both shift solenoids fix my issue? Does heat cause them to fail when the transmission temperature/pressure goes up?

 

[stackz]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

how many miles on it? sounds like the bands are worn in it and once the trans fluid comes up to temp, the bands start slipping due to the added clearance in them and the warm fluid (thinner) fluid.

 

[calvinator]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

I've had a lot of these trucks over the years. Always seems to be a sensor that tells the computer wrong info and then you get weird shifts.

Research the Throttle Position Sensor, Vehicle Speed Sensors, and the shift solenoids for your model truck. Also borrow/buy an OBDII diagnostic device to see if your computer has some errors codes. The sensors are cheap and easy to replace -- lots of youtube vids too.

 

[jtmarten]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

Change the fluid and filter. My K2500 Suburban had issues losing OD a few years ago after having the intake gasket replaced. The tech replaced the 180* t-stat with a 195*. Towing the then new Welly Nova II from Detroit back to Colorado a few days later, I'd lose OD after about 15min drive time. Put another 180* in it after we got back and all was well again.
Fresh fluid and filter really improved the shifting when I changed it a few months ago.

 

[Ibl0wstuffup]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

What trans is in it? Maybe the bands need to be adjusted.

 

[babbot]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

Sounds more major than just a check of how much fluid you have but would be an easy check. Check the manual or the dipstick. It may tell you the level you are checking is when it is hot. Usually after 20 minutes driving. The level will change once warmed up.

 

[Big Bubba]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

Jtmartin,
So changing the thermostat fixed your Overdrive issue with your K2500 Suburban? Was the 195 degree stat causing your transmission fluid to get too hot and that caused the Overdrive to fall off so you went back to 3rd gear and your RPM's went up as well. Well mine does about what yours was doing after about 15 minutes of Freeway/interstate driving. Mine will automatically downshift from Overdrive to the gear below it I believe it is 3rd gear and will cause the RPM's to increase as well. I also noticed after it does this that it will shift kind of funny like quick slightly harsh shifts. I guess my tranny must be getting too Hot!!! Im guess causing my issues after driving it a while. The first run of the day it shifts and drives just fine around town but it only happens when I go about 15 minutes done the interstate doing about 70 mph for about 15 minutes. I will take your advice and change my thermostat out because I am thinking mine is partially stuck open because it will fluctuate alot it seems on the temperature gauge on the dash. Hopefully that will cure my issue as well and I will do the old fashion transmission fluid and filter change by dropping the pan on mine as well. Keeping my fingers crossed that it works for me.

 

[Big Bubba]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

IblOwstuffup,
I believe my transmission, I think, is the GM's 4L80E. Thank you for your help.

 

[Big Bubba]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

Yeap, I did some more thinking and I have a local AAMCO that I will call and have them do a check, hopefully a free check, to see if I do actually have a problem on my truck's transmission. If they do a "Free" transmission computer diagnostic that should tell me or them what is really going on. I don't want to throw money into parts I do not need and just purchase the part/parts that are causing the issue. AAMCO is where I will go and see what they say.

 

[TilliamWe]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

Alright Bubba, now that you have given more info, I can lend you some personal experience. But I don't know if it will help.

Heat is bad for GM transmissions. And running a 4sp OD in 4th gear without the torque converter locked up will KILL them. Now, we had a thermostat that was TOO low that caused our 1990 4sp transaxle to not lock up soon enough, all the time. Then, after 4 years, it wouldn't stay in OD, just as you describe. It would unlock the converter in 4th gear, not shift down to 3rd. If yours is doing that, DON'T LET IT, anymore. You will BURN it up. Ours needed to be replaced, and when it came back, it had a different thermostat in it. The proper one.

 

[jtmarten]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

Jtmartin,
So changing the thermostat fixed your Overdrive issue with your K2500 Suburban? Was the 195 degree stat causing your transmission fluid to get too hot and that caused the Overdrive to fall off so you went back to 3rd gear and your RPM's went up as well. Well mine does about what yours was doing after about 15 minutes of Freeway/interstate driving. Mine will automatically downshift from Overdrive to the gear below it I believe it is 3rd gear and will cause the RPM's to increase as well. I also noticed after it does this that it will shift kind of funny like quick slightly harsh shifts. I guess my tranny must be getting too Hot!!! Im guess causing my issues after driving it a while. The first run of the day it shifts and drives just fine around town but it only happens when I go about 15 minutes done the interstate doing about 70 mph for about 15 minutes. I will take your advice and change my thermostat out because I am thinking mine is partially stuck open because it will fluctuate alot it seems on the temperature gauge on the dash. Hopefully that will cure my issue as well and I will do the old fashion transmission fluid and filter change by dropping the pan on mine as well. Keeping my fingers crossed that it works for me.

Mine only did it after we picked up the boat and started towing. And it was fine after replacing the 195* with a 180* t-stat. I don't think the issue was really the t-stat, but I'm guessing the fluid was in need of a change and was just too broken down to handle the heat properly. I'd start with a fluid/filter change and see if that helps.

 

[Big Bubba]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

JTMarten,
Thank you for the response. You and the others have been very helpful with my truck. Yeap, what I have decided to do, after reading yours and the others post in this forum, that I will do a complete radiator flush because the fluid inside the radiator right now looks like dog poop, literally, and when I do that I will swap out the thermostat while I am in there doing the complete radiator flush. I also will do the transmission fluid and filter change. Now with the transmission fluid and filter change did you change out all the transmission fluid or just the 6 quarts that was inside your transmission pan and then swapped the transmission filter as well and bolted the transmission pan back up and filled the transmission fluid back up. Thanks again, Bob

 

[stackz]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

old transmission fluid will contaminate new fluid.

the redneck way to flush a trans is to drop the pan, put in a new filter, and then unhooked both of the radiator cooling lines. run some hose from each line (couple feet) and put one hose into a discharge container, and one hose into a new container of fluid (you'll need a couple). crank the vehicle up and let it suck the fluid from the new container through the system while pumping out all fluid into the discharge to fully flush the system.

this is basically what shops do but they have a machine that forces the fluid through the system to completely flush out old fluid...which is also why it costs like $75~100 due to the amount of fluid the flush goes through.

 

[jtmarten]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

Now with the transmission fluid and filter change did you change out all the transmission fluid or just the 6 quarts that was inside your transmission pan and then swapped the transmission filter as well and bolted the transmission pan back up and filled the transmission fluid back up. Thanks again, Bob

I just drained fluid, dropped the pan, replaced the filter, buttoned her back up and refilled. Your fluid sounds like its in bad shape, so I'd either do the method stackz recommended, or you could drain the pan, refill and run it for a few minutes, then drop the pan, etc. That'll get most of the fluid changed. On my BMW's I do 3-4 drain/fills before dropping the pan to change the filter.

 

[TilliamWe]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

...

this is basically what shops do but they have a machine that forces the fluid through the system to completely flush out old fluid...which is also why it costs like $75~100 due to the amount of fluid the flush goes through.

Actually stackz the flush done at shops that don't want to ruin anything is done EXACTLY as you describe. With a fancy, wheeled unit that holds the new fluid and has a "bypass" that when it runs low, the fluid circulates. They do NOT force the fluid through the trans, they let the transmission's pump pump it through, just like it normally does. They charge so much because people don't know how easy it is to do it themselves.

 

[TilliamWe]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

Bubba, it's going to take a while to flush all that DexCrap out of your radiator and heater core. So be prepared to use LOTS of water. And take your time.

 

[Big Bubba]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

TilliamWe,
Yeap, I agree the Dexcrap, will take a while to get out. What I have done is watched some Youtube videos and what I am going to do is drain the dogpop, LOl, looking crap out of the truck's radiator first then add plain water and let it get up to temp, cool down and then drain, fill up again, let get up to temp, cool down and drain. I will do this until the fluid that runs out the radiator drain is pretty darn clear. Then once it is clear, I am going to purchase, probably, two bottles of Prestone, radiator clean, and let it run in the truck for about a week since I do not run or drive my truck that much. Do you think using the Prestone, radiator cleaner, for about a week be too much o the radiator or will it be fine. I really want to clean that nasty looking radiator fluid out of the radiator. That could be causing, not to sure, my transmission fluid to, maybe, heat up too much maybe causing my issues with losing overdrive and slightly harsh shifting, due to a partially clogged/stopped up radiator that is dire need to be cleaned. Also, I will be doing my transmission fluid change and filter as well.

 

[Big Bubba]

Re: 2000 year, C3500 Chevrolet Dually with 7.4 liter engine, Transmission question?

TilliamWe,
Yeap, I agree, that the extremely dirty Dexcrap, LOL, will take a while to get out. What I will do is drain the radiator, fill with water, drive the truck, get it up to temp, drain again and do the same over and over until the radiator/coolant fluid drains clear. Then once that is done, I will purchase two bottles of Prestone, radiator cleaner, and fill that up with the Prestone and top off with water and let it run for about a week in my truck and then drain again. I don't drive my truck that much at all since it is my/will be my tow vehicle for my fifth wheel camper. Will that work for my truck and will not harm my radiator system? Also, another question, can I put in any extended antifreeze in my system?