Doctor Diesel
Newbie
Answer: ATF
This is out of the 4L80 in the K2500 Farm Truck with a new life. This fluid had a life of dirt and heavy pulling. Before I changed it out I sent an oil sample to CAT and let’s say it wasn’t good. The only thing going for it was “normal” amounts of friction material so I know the clutches are TOO worn. Lots of water, pretty dirty, viscosity almost didn’t exist.
Before I changed the fluid, I dumped a container of Sea Foam Hydraulic Cleaner into it and ran it for well over 500 miles. Before changing the fluid, the transmission had harsh shifting, converter shudder and was sapping engine power. After the cleaner had time to work fluid change started.
I disconnected the external cooler return hose and hooked it to a suction unit and got about 1.5 gallons out before it sputtered. Reconnected the hose, started the truck and shifted through the gears. Trans still shifted. Repeated the process until the trans wouldn’t shift and I couldn’t pull fluid out. I then directed the suction hose to the bucket and started the truck. I added new ATF and out came another two quarts of nasty. I added fresh fluid until that was what was being dumped out. Reconnected it all and filled with that sexy Mobil 1 you see. This is the latest and greatest and is the type specifically engineered by Mobil for GM to rectify those Colorado trans issues.
Test drive and WOW! That trans shifts like it’s new from the factory. No harshness putting it in gear, shifts are smooth as silk and I gained 1-2 MPG in fuel efficiency. Trans also runs about 5-7 degrees cooler. Converter shudder is still there (What do you expect at 25 years and almost 180,000) but it has gone down considerably. I did not change the filter due to the line pressures being damn near factory after the change. I assumed they would get there with the new fluid. The trans is scheduled for a rebuild next year but this seriously needed to be done regardless. The truck well pulls it max capacity and sometimes then some and in the South it’s easy to cook a trans. For 45 minutes of work, teaching the apprentice how to do it without a fancy machine and the improved trans performance, it was worth the $145 in fluid.
This is out of the 4L80 in the K2500 Farm Truck with a new life. This fluid had a life of dirt and heavy pulling. Before I changed it out I sent an oil sample to CAT and let’s say it wasn’t good. The only thing going for it was “normal” amounts of friction material so I know the clutches are TOO worn. Lots of water, pretty dirty, viscosity almost didn’t exist.
Before I changed the fluid, I dumped a container of Sea Foam Hydraulic Cleaner into it and ran it for well over 500 miles. Before changing the fluid, the transmission had harsh shifting, converter shudder and was sapping engine power. After the cleaner had time to work fluid change started.
I disconnected the external cooler return hose and hooked it to a suction unit and got about 1.5 gallons out before it sputtered. Reconnected the hose, started the truck and shifted through the gears. Trans still shifted. Repeated the process until the trans wouldn’t shift and I couldn’t pull fluid out. I then directed the suction hose to the bucket and started the truck. I added new ATF and out came another two quarts of nasty. I added fresh fluid until that was what was being dumped out. Reconnected it all and filled with that sexy Mobil 1 you see. This is the latest and greatest and is the type specifically engineered by Mobil for GM to rectify those Colorado trans issues.
Test drive and WOW! That trans shifts like it’s new from the factory. No harshness putting it in gear, shifts are smooth as silk and I gained 1-2 MPG in fuel efficiency. Trans also runs about 5-7 degrees cooler. Converter shudder is still there (What do you expect at 25 years and almost 180,000) but it has gone down considerably. I did not change the filter due to the line pressures being damn near factory after the change. I assumed they would get there with the new fluid. The trans is scheduled for a rebuild next year but this seriously needed to be done regardless. The truck well pulls it max capacity and sometimes then some and in the South it’s easy to cook a trans. For 45 minutes of work, teaching the apprentice how to do it without a fancy machine and the improved trans performance, it was worth the $145 in fluid.