[Smittyd55]

I have a 99 GMC Suburban, 350, 2WD, 1500 with a 4L60E auotmatic transmission. I'm having trouble with a pretty serious vibration. The vibration starts around 40 MPH and will end around 67. It doesn't appear to be RPM related. I've had the tires checked to make sure it's not that. I've had the drive shaft checked as well. The vibration is only noticable when the vehicle is cruising. If I'm speeding up or slowing down it's not apparent. I can get the vibration to go away if I keep my foot steady on the gas, when the vibration starts, then lightly press on the brake. The vibration stops immediately and the rpm gage jumps up 100 to 200 rpm. Can this be the torques converter?

Thanks for your help.
David

[paul poirier]

The vibration is most likely TCC shudder. The clutch on the torque converter is slipping causing a chattering (pulsating ) in the driveline. There are TSB,s Technical service bulletin for that complaint as well as GM Poweretrain bulletins .Usually a repaired valve body and a new PWM (Pulse Width Modulated ) Torque converter clutch solenoid will cure this. If It has been doing this for a while then the torque converter will have to be replaced. The clutch material will be Glazed and/ or worn.

[55mole]

Smittyd55 , I have the same suburban with the exception I have 4wd . I know you checked the drive shaft , but did you check the u-joints & yolks ? 55 mole

[Crosley]

TransGo has a small kit with a replacement valve for the valve body that will repair the excessive slippage of the converter clutch if that is the problem.

The valve body must be removed to install this kit .

There are two solenoids working with this PWM system for the converter. Replacing these two would be an easier repair than removing the v-body to see if the vibration goes away. The TCC solenoid and the PWM solenoid work together to pulse the converter clutch on for a smoother apply.

I am surprised the 'service soon' light is not on. Usually a P1870 code is set with converter slippage outside of parameters.

Since the converter clutch is a carbon fiber material and engineered to slip, I would think the converter is OK at this time. We repair several v-bodies a month with the TransGo kit.

When the tranny pan is pulled , I would break open the filter to inspect the filter media for debris.