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Discussion Starter #1
Hey all,

I have been plagued with a vibration for some time now. I originally attributed it to the driveshaft and imperfect u-joint angles due to my lift, but I recently had the driveshaft balanced (including all new u-joints and carrier bearing) and the vibration persists. I have also tried varying the u-joint angles and the amount of shimming on the carrier bearing and nothing seems to change the vibration. I am thinking that it is transmission/torque converter related since I only get the vibration in 3rd or 4th gear. I get the vibration in any speed above roughly 40 mph, but it is more pronounced at some speeds. I don't think it is tire balance since the steering wheel is rock solid and does not vibrate at all. The vibration feels almost like a washboard when initially shifting into overdrive, but becomes a slower pulsing type vibration as speed is increased.

The vibration seems to start on torque converter lockup, but is very noticeable when the transmission shifts into 4th gear. I occasionally feel a momentary slowdown as if something is placing additional load on the engine (it feels like taking a big wind gust head on). Pushing the "O/D Off" button on the shifter makes the vibration go away (this would also coincide with the torque converter unlocking when the transmission downshifts) but I have not done this at speeds above 60 mph since I don't want to send the engine RPM through the roof.

The transmission is the original one the truck came with and has about 151,000 miles on it. Fluid was changed earlier this year and looked perfectly fine for its age. Nothing other than normal wear products in the pan. The transmission has had a relatively easy life (occasional towing) and has only been close to overheating once (in the yellow on the dash gauge) during a tough mountain pull (remedied with a larger cooler). The only transmission-related work that has ever been done is a warranty replacement of 2 flexplates and the original torque converter about 13 years ago.

I'm leaning toward the torque converter on this one as I don't think there is anything internal to the transmission that would cause the same issue. I'm hoping that I don't need to buy a new transmission.

Any thoughts? Thanks in advance.
 

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It is possible. Generally with the electronically controlled transmissions slippage during any upshift including the torque converter clutch can be detected by the PCM/TCM as equipped if the engagement time exceeds the programmed limit for the shift to occur. once that limit is exceeded a code is set. If you have a scan tool capable of reading parameters it is also possible to monitor and record what the transmission is doing at the time the vibration occurs. That will help point you in the right direction. If the vibration is momentary I might agree with you. If the vibration is semi-continuous the source may be a little more difficult to pinpoint. Your truck has a 4R100 transmission which I do not have a lot of experience with but the principals apply. I still would not rule out engine performance concerns as well. It is difficult to comment on this without driving the truck for myself.
 

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I don't think it is tire balance since the steering wheel is rock solid and does not vibrate at all. The vibration feels almost like a washboard when initially shifting into overdrive, but becomes a slower pulsing type vibration as speed is increased.
At at steady speed with the converter locked hold the accelerator steady and gently tap the brake pedal just enough to unlock the torque converter. In a couple seconds it will relock, does that make the washboard feel again?

The vibration seems to start on torque converter lockup, but is very noticeable when the transmission shifts into 4th gear. I occasionally feel a momentary slowdown as if something is placing additional load on the engine (it feels like taking a big wind gust head on). Pushing the "O/D Off" button on the shifter makes the vibration go away (this would also coincide with the torque converter unlocking when the transmission downshifts) but I have not done this at speeds above 60 mph since I don't want to send the engine RPM through the roof.
It is impossible to overspeed the engine by pressing the OD OFF button. The computer won't allow the shift to happen if it would overspeed the engine.

Fluid was changed earlier this year and looked perfectly fine for its age.
What ATF was used when it was changed? How much fluid was changed?
 
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Discussion Starter #4
At at steady speed with the converter locked hold the accelerator steady and gently tap the brake pedal just enough to unlock the torque converter. In a couple seconds it will relock, does that make the washboard feel again?


It is impossible to overspeed the engine by pressing the OD OFF button. The computer won't allow the shift to happen if it would overspeed the engine.


What ATF was used when it was changed? How much fluid was changed?
I'll give that a try the next time I take it for a drive.
I figured that the PCM would not allow the engine to overspeed - guess it's just something in my head that I don't like to downshift at higher speeds (not that 60 mph is all that high).

I changed the fluid using the procedure that is recommended here - drain the pan, refill with the same amount drained, remove the specified cooler line, run the engine until air bubbles are seen, etc. I have an aftermarket deep pan, so however many quarts all that is - something like 20-24. I used Castrol Mercon V.
 

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Went for a drive and it seemed like tapping the brake would not unlock the torque converter. No difference in engine RPM or the vibration - I tried it at several speeds. The vibration is most noticeable as soon as the transmission shifts into overdrive, and the vibration seems the worst (highest frequency shuddering) at about 50 mph. Above 50 mph, the vibration is more like a steady pulsing. Forcing the transmission to downshift with the "O/D off" button lessens the vibration, but it is still there. I have a mirror on the back window so I can see my son's car seat, and that mirror shakes like crazy in tune with the vibration.

Is there anything in the transmission internals that could cause this? I keep coming back to the transmission since the vibration seems linked to transmission shifts. I could remove the rear driveshaft and drive the truck using the front axle to see if that changes anything. I also have AutoEnginuity - is there anything I can monitor on the transmission that would be useful?
 
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