TQ Lock Up / Diff Noise / Lugging question
 

Car is a 1998 Z28 with 9" rear 3.70 gears, Circle D 3600 Converter, Built 4L60E (700hp). Now the question is what MPH/RPM is anyone with similar specs having there converter lock up at? I am getting a rattle noise from rear diff at 40-43mph and about 1600-1700 rpm, sounds like a stick shift when you grab a gear and lug the drivetrain down. The noise goes away if you give it any extra pedal or slow down or speed up, makes no noise at 45 and up. Talked to a bunch of people and we narrowed it down to the drivetrain is lugging down at this RPM/MPH and was advised to raise lock up to 50-55 mph and remove PWM and have 100% lock up at that speed. Anyone ever run into this before? I am having tuner raise lock up and remove PWM, just wondering if this was a halfway common problem.

Can definitely happen, especially with a big cam. Probably hitting resonance of something at that load and rpm and yes it's like lugging the clutch. I usually lock up around 45.

Yes that is a common problem.

I have mine so it will not lock in 1st, 2nd or 3rd. The converter will only lock in 4th above 55 mph.

When you feel the lugging keep your foot on the gas at that steady speed and lightly press the brake without slowing the car down. This will unlock your converter and your lugging should go away.

Yes it goes away when i do that. Having tuner try 45 mph first then go to 50 if needed. Thanks for the replies, just verifying if this was a problem.