2001 Silverado 1500 transmission issues?

Mallery O'Hara · May 30, 2020

Hey guys,

After many many hours of forum reading and trying to find a answer for a problem like mine I've finally given up and decided to just ask.

I've got a 2001 Silverado 1500 LS 2wd with the 5.3L. We were driving down a back road the other day and to simply say that it was muddy would be a huge understatement. Had I not know better I wouldn't have believed it was an actual road and not a trail. The mud was so deep that it reached clay in spots and we basically snowplowed mud with the front bumper. After making it back to the highway we went to go accelerate only to be bounced around wildly and were unable to go much faster than 80km/h due to a random and sudden lack of 3rd gear and overdrive. Limped the truck home and did a transmission fluid and filter change the next day. Fluid was filthier than heck, dark dark brown in color sort of like Cola. After that now the truck sometimes finds 3rd but 4th is nowhere to be found and once you get over about 70km/h it shakes so hard it feels like the worst washboard despite doing our best to get all the mud out of the wheels. Reverse still works fine. Looked under the truck and there does appear to be a bent crossmember but the frame still looks fine and straight.

Some backstory; Never had any transmission problems before this or signs of slipping. The tires on the truck are oversized, from a stock 245/75r16 to running 275/70r17. At present there are no rear brakes, had a bolt on the caliper come off one day and long story short ended up disconnecting them and pinching off the lines for the back brakes. We also have kids who like to play driving and occasionally jerk on the shifter, one day our toddler somehow manged to get the truck out of drive without hitting the brake and it started rolling, it didn't go very far before I stopped it but nevertheless was certainly surprising.

So my question is; what could be causing this to happen? Is the transmission completely gone and if so why no warning signs? Could it be the 3/4 clutch pack, the shift cable, transmission mounts or something else? Any input would be appreciated!

davester · May 30, 2020

A bent crossmember? That can cause all sorts of problems, including also bending the frame, altering driveshaft angles. And if a crossmember got bent, driveshaft also could have been hit, transmission shift input could have been damaged, also the transmission wiring plug.

sefiroxx · May 30, 2020

Wow, lots of "tranny abuse", may have to call the tranny rescue team.

Bent cross member - tranny and differential may not be aligned, bent, etc

Dirty fluid - probably blew out the clutch pack in the mud.

Messed up rear - might have a bent axle, out of balance tire/wheel.

Did you find anything in the pan when you dropped it to change the filter?

You might shredded the wire harness where it connects to the side of the tranny.