04 3.4 Carrier bearing/rear end

Have a very bad shudder when downshifting while in overdrive. Whole truck shudders and doesn’t downshift. Can feel it towards middle of truck and rear end. I’m thinking either carrier bearing or rear end slipping. Is there anyway to troubleshoot either instead of throwing parts at it? No unusual noises, and carrier bearing doesn’t have any slop in the driveshaft.

 

If the trans does not downshift, the CSB and rear end will have nothing to do with that.

 

Transmission fluid level? And color? Sounds like the trans is slipping, nothing to do with the driveshaft or rear differential. There is nothing to slip in those anyway, unless that 190hp v6 is spinning the rear tires in OD lol

 

Recently did timing belt job and pulled radiator, lost some trans fluid in process so drained the pan and refilled. Old fluid was black.

 

issue existed prior to the TB or after?

 

Black is…not good. Recommend a few drain and fills, as one only gets 3-4 qts changed out of 11 total iirc.
How is the level? Checked fully warmed up, run through all gears, etc.

 

Yes issue was there before timing belt job. Im thinking maybe a misfire, but it’s not throwing any codes, I did valve covers when I did the timing belt and 2 of the boots on coil packs were corroded. It will shift and goes up in rpm and starts shuddering fairly violently. I would think if trans is slipping it wouldn’t get into gear and just rev rpm until it caught. I was also thinking maybe torque converter before researching, but from what I’ve read you can throttle out of torque converter failing to lockup, and the shudder from TC isn’t as violent. I’m guessing coil packs are getting weak and not generating enough spark causing misfire.

 

Level is good and you’re able to go through all gears, drove it past weekend after finishing timing belt up. Even able to go 70mph down the highway, shifts smooth no hard or hesitant shifts. Just when you get down on the throttle and make it downshift it will shudder until you get off the throttle.

 

A misfired will 98% of the time, generate a 300 and or cylinder specific code. If it’s severe enough, the knock sensor can also get trigger. There’s a bunch of avenues that protects the engine such as a flashing check engine light.

TBH, I would drive and get the engine/transmission hot and check the fluid. Almost sounds like low fluid symptom.

 

Level is good, could it be something in the driveshaft, ex. U-joint, carrier bearing?

 

I have no idea what is actually happening at this point.
Still highly suspect transmission fluid level. I suppose torque converter could be a culprit, or hell maybe you’re missing a bunch of teeth on the ring gear.

 

Yeah I could’ve worded it better when I said it doesn’t downshift, it shifts and goes to around 3k rpm but shudders until you let off the throttle and doesn’t throttle out. When I was saying it shifts smooth is under regular driving, as long as I don’t get down on the gas hard, drove on highway other day and was doing 70-75mph.

 

When you coast and off the throttle, does it whine or howl?

Chock both front tires, jack up the rear axle until the tire is ~2-3” off the ground. Be safe and support the axle with jack stands. Then put the car in drive and try to mimic the issue. Will be good to have someone standing by without going underneath to listen. Try to record it as well.

 

Haven’t noticed any weird noises, I was going to try tomorrow and see if it does the same thing in park or neutral. I’m not sure if I’d be the same as going down the road but if it does it then, then I know it’s not driveline issue. But yeah that’s a good idea I’ll try it both ways, but would have to see/hear something to know where to start doing it that way.