Getting a thunk after moderate throttle and letting off - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 11-16-2004, 06:39 PM   #1
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Default Getting a thunk after moderate throttle and letting off

I never get this thunk any other time. If I get on the gas, let'* say 2/3 or better throttle and when I let off the gas I get a muffled thunk that is coming from the general area forward of the driver'* foot.

Engine mount?

Shock?

Any suggestions?
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Old 11-16-2004, 06:50 PM   #2
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You sure it isnt the pedal thunking or like the cable maybe?
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Old 11-16-2004, 08:02 PM   #3
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Do you let the pedal snap back when you get off the throttle....Does kinda sound like maybe a CV shatft going.......I knpow my LF shaft is shot and I hear kinda tha same noise sometimes.
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Old 11-16-2004, 08:25 PM   #4
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Much bigger thump than a pedal. I can almost feel it thru the floorboard. I guess it could be a CV shaft. I'll keep an eye (or ear) on it and see if it gets worse.
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Old 11-16-2004, 08:27 PM   #5
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Check the CV boots and underside of LF area for grease, rips or cracks.
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Old 11-16-2004, 08:52 PM   #6
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I'll go with motor mount. Easy to diagnose. Have a TRUSTED friend get in the car. Set the parking brake, and chock the tires. Start the car, and put it in D. With the left foot firmly on the brake, have him/her rev the car to 3000 rpm'* in gear, then drop the throttle quickly.

Watch the motor while they do this.
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Old 11-16-2004, 09:09 PM   #7
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I have the exact same problem. It will do it when the car is put in reverse or park, or park to drive, and when you are on the throttle and then leave off as described. It is not my engine mounts. They are all good. I believe that it is the gears trying to align when the car is put into reverse or drive. But my dad and i are stumped as to the letting off the throttle and the trans clunking
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Old 11-17-2004, 08:59 AM   #8
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Quote:
Originally Posted by 1993 SLE
I have the exact same problem. It will do it when the car is put in reverse or park, or park to drive, and when you are on the throttle and then leave off as described. It is not my engine mounts. They are all good. I believe that it is the gears trying to align when the car is put into reverse or drive. But my dad and i are stumped as to the letting off the throttle and the trans clunking
My 93 used to do the same thing. Never bothered fixing it, but it was the transmission mount on the firewall side on the passenger side.
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Old 11-17-2004, 11:09 AM   #9
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Default thunk

Use the process of elimination mount per mount also check exhaust flange and pipe clearances.
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Old 11-17-2004, 12:52 PM   #10
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Thanks, guys. I am going to make sure it'* not suspension by doing the brake/gas torque thing in the driveway. I'll then try to narrow it down. I want to find this guy now before it bites me bigger later. I'm in the 120'* now and want to get to 200K miles w/o major repairs.
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