I've been going through all the shudders, shimmies, shakes, and whines on Stinky - and I had them all resolved... until a new one cropped up recently. While in the throes of looking for an intermittent miss, that problem up and disappeared on its own... my economy even returned to normal. Then... this showed up:

There is a shudder as I drive - but the vibration is side-to-side, not forward and backward. I can feel it in the steering wheel and my beverage shakes pretty good in the cup holder, but the seat doesn't transfer a lot of the vibration.

New road tires (not ATs), new rear-end guts, balanced and trued driveline, new front bearings, and front end alignment checks good. Transmission fluid full, but not very cherry-looking (doesn't stink). I had the transmission serviced (fluid and filter) about 6000 miles ago.

The shudder is there on the flat, going uphill, going downhill, decelerating and mildly accelerating... but it's difficult to tell if it's still there when I hit the throttle hard.

I check my brakes (inside and out) with a thermometer after a drive, and there are no unusual readings - about 120-140 degrees in the front and back, depending on the weather and the amount of braking I did.

I check all bearings and U-joints with the thermometer, and there are no readings I haven't seen before the shudder began.

The transmission is running about 140-160 degrees (weather dependent), and the transfer case has shown 140 degrees every time I checked it. No torque converter slip readings above normal (jumps around with Torque Pro, but peaks at 10).

The differential is riding about 150 degrees (10 degrees higher than the "old" normal), but everything in the transfer case has about 900 miles on it (fluid changed after proper break-in and 500 miles of driving).

I get up to speed and put the truck in neutral - all vibration gone... it's silky.

I climb steep hills on my drive (8 percent grades) with 40 MPH limits, and the shudder is subdued until Torque Converter Lock Up, then the shudder is stronger and stays strong. There are other subtle things I can feel during this test, but I'll leave those out... I don't want to turn onto Merry Path lane.

I take it out of Overdrive, shudder still there - but it's hard to tell if it changes frequency.

I swerve side to side and I take corners at varying G-forces - no change to shudder.

Did I overlook any tests?

Flex plate?

Torque converter?

If it is my transmission, I wouldn't blame it one bit. That tranny has taken some severe beatings in my learning years, and only now is it getting the proper treatment with the truck hardware and tuning - plus my driving style.

 

Check the rear driveshaft ujoints and the center support bearing carefully. Can be tight just a little and cause this.

From there, I'd look at the tranny based on you saying it is worse once locked up. Maybe just converter, or solenoid. But that is a whole new world of tests to verify. Not sure of your tool availability to pressure check and so on...

 

When you check the u-joints, make sure there's no movement of the bearing caps in the rear pinion yoke and the straps are tight. We just had one of those replaced yesterday because the bearing cap straps allowed movement and the u-joint basically hammered the pinion yoke and wore it oval shaped. The vibration it caused was pretty bad.

 

That's actually more common then you'd think. Usually a result of improper torque of the caps. Also, these are old used trucks at this point, some natural wear too.

 

I do believe it was due to improper torque. The bolts on one strap were loose when I checked it, as in not even touching the strap.

 

Make sure those ladder bars haven't loosened up, brackets etc.

 

Rich just throwing this out there. How about your steering stabilizer shocks.

 

Rich, based on the description:
The truck coasts without vibration. This rules out wheel bearings, rear differential, steering and steering dampener, ball joints etc.
The problem occurs when you put it in drive and moving and gets worse when the T/C locks. I agree with your idea that the flex plate or torque converter is the problem. The clutch could be starting to come apart.

Could some bolts on the flex plate be loose?
Could you have cracked the flex plate?
Bad hub on the torque converter?
Bad input bearing to the transmission? Planetary gear etc. problem? If there is no leakage out of the torque converter bottom cover, that probably rules out a bad input shaft bearing. The seal leaking there is usually the first indication of a bad bearing.
Transfer case problems-something coming apart in there due to improper torque? You probably checked the output shaft of the transfer case.
Finally-would it be worthwhile to remove the driveline to check that center support, even though you checked those u-joints? Sometimes a loaded drive shaft acts differently than an unloaded one (while coasting).
For some reason, I keep thinking torque converter.
Larry

 

U-joint straps are tight and caps are against the stops - I checked them after it was suggested. I tinkered with a carrier bearing shim... until my tests started hinting at the hardware North of the drive line. The carrier bearing is shiny new, and I'll be taking that shim back out... to see what that does. My stabilizers had the bushings/bolts replaced within the last year. There is so little of the old truck remaining from the frame down, that I'm running out of things outside the transmission to point at. There are no leaks anywhere on the truck, and all my fluids are staying on their marks.

 

So driving down the road at say 50, and you are in lock up. If you then quickly tap the brake pedal just to come out of lock up, does the shudder change?

 

What kind of carrier bearing did you install, Rich?

 

I have to get down to 35 MPH to fall out of lock-up, I think you're thinking of the 4-3 shift.

Neapco - same as OEM.

 

No, a tap of the brakes will take it out of lock up.

 

Wrong. Not with his programming strategy.

 

Will the "Stock-ish" tune behave like that? I don't ever remember the coast clutch kicking in so high... I thought 40 was the top limit.