Clunking Upon Letting off and on gas - Pontiac G8 Forum: G8 Forums - G8Board.com
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post #1 of 14 (permalink) Old 06-12-2019, 10:20 AM Thread Starter
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Clunking Upon Letting off and on gas

I am trying to pinpoint a problem with my g8 when I let on and off the gas usuaully above 30mph I will feel a clunk which feels like its in the rear end. I have the bmr street bushings. I also do expierince a loud pop when in 4th or 3rd and low a low speed and gas it. Im assuming the bmr bushings have worn? but if i take the ass off the ground and spin the wheels back and fourth i can feel some amount of play before the driveshaft spins and somewhat hear a clunking sound. So maybe its the diff? I have the geforce one peice driveshaft aswell. any tips and advice would be nice!

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post #2 of 14 (permalink) Old 06-12-2019, 01:32 PM
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That is the differential. A little bit of slippage; usually during transient throttle situations when you let off and press the gas pedal lightly.

The rubber bushings absorbed more of the noise, but anything from poly and stiffer will transmit more of the noise through the chassis.

While I haven't heard your noise, I'm fairly confident that this is what you are hearing.

'09 PSM G8 GT - OPG Intake, DOD-Delete w/ Stage 1C 218/229 .600 Lift 117.5LSA, Kooks 1 7/8 Mids, Solo Axle-Back w/ X-Pipe, SuperPro Bushings (Front and Rear). BMR Sway Bars (Red)
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post #3 of 14 (permalink) Old 06-12-2019, 01:35 PM Thread Starter
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When I first did the bushings I noticed no noise or clunks, it was only until i took my car on the tail of the dragon it really started to clunk, I beat the **** out of my car, but it took it like a champ besides the clunking. I'm thinking the diff is bad or the bushings wore..

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post #4 of 14 (permalink) Old 06-12-2019, 01:37 PM Thread Starter
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It sounds like a clunk, kinda like a hammer going back and forth on a table

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post #5 of 14 (permalink) Old 06-12-2019, 05:57 PM
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Well, sounds like it's not that clunk, then. You gotta get under the car and have a look. (OR pay someone else to do it).

'09 PSM G8 GT - OPG Intake, DOD-Delete w/ Stage 1C 218/229 .600 Lift 117.5LSA, Kooks 1 7/8 Mids, Solo Axle-Back w/ X-Pipe, SuperPro Bushings (Front and Rear). BMR Sway Bars (Red)
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post #6 of 14 (permalink) Old 06-13-2019, 10:18 AM Thread Starter
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Nothing looks loose. My guess is that the diff or the bushings went bad.. Im gonna take the diff out when i reweld my exhaust with cutouts and ill take a look. until then if anyone else has advice.. thanks

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post #7 of 14 (permalink) Old 06-13-2019, 10:43 AM
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Does replacing the differential bushings with SuperPro bushings really make the ride harsher?

I don't mind replacing the OEM rubber with another rubber bushing. The problem is that the OEM rubber bushings need to be pressed out (or burned) and pressed in. The SuperPro bushings, while a somewhat softer Polyurethane, are of the three piece variety.

SPF2869K: https://superpro.com.au/find/superpr...999501035/vid-

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post #8 of 14 (permalink) Old 06-13-2019, 01:45 PM
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GXP25, I would say very little if any. The only thing I noticed after the cradle and differential bushings were replaced with those Superpros was mostly noise related. I'd hear the differential clunk a bit more than I did before.

The front cradle bushings came out with the press I made with a threaded stud and some washers & sockets. A correctly sized steel pipe works well as a receiver for the bushing.

The rear ones are taller and the rubber piece tore out, but the plastic remained. I carefully scored the plastic with a hack saw (enough to score but not cut through), and I was able to tap them out. One of them had to be scored in two places to create enough flex to make tapping out a breeze.

In order to get the saw in there, I took the blade off, turned the blade backwards (saw teeth toward handle), and then placed it inside before reinstalling the blad and it was easy.

Mind you, I had the subframe out of the car when I did it.

The differential bushings are harder to get out with the differential still in the frame.

'09 PSM G8 GT - OPG Intake, DOD-Delete w/ Stage 1C 218/229 .600 Lift 117.5LSA, Kooks 1 7/8 Mids, Solo Axle-Back w/ X-Pipe, SuperPro Bushings (Front and Rear). BMR Sway Bars (Red)
Power: 400HP/392TQ


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post #9 of 14 (permalink) Old 06-18-2019, 11:26 AM
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Quick and dirty check I did to isolate the diff as the source of my clunk was try to spin the driveshaft with the parking brake set. In neutral there was about 1/2in of play and a nice thunk, in gear it didn't move or make a sound. It's been a while since I was under an auto with a driveshaft but I imagine it would work the same... I'm having an RPM built Camaro 3.70 put in on Monday.
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post #10 of 14 (permalink) Old 06-18-2019, 02:21 PM
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Just in case: have you checked the rubber flex coupling between the transmission and driveshaft?
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post #11 of 14 (permalink) Old 06-18-2019, 11:04 PM
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I have that same noise and I pulled the exhaust and checked the center driveshaft bearing and it was fine. So I'm wondering if it is the convertor or diff itself. I have the Camaro 3.27. Let us know what you end up finding out after the diff replacement.

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post #12 of 14 (permalink) Old 06-19-2019, 03:34 PM Thread Starter
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I have a geforce one peice drive shaft with solid couplers. Like I said the clunking was not noticable after these mods. They got worse over time. I'm going to get a 3.27 Camaro diff from cle power and performance. Im hoping it's not the conveter as I have a cam and a tune, what the weird thing is when I'm going to take a sharp turn going at a slight decent the rear end seems like its clunking alot. So I'm just hoping it's the diff.. dont feel like pulling the trans at the moment.

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post #13 of 14 (permalink) Old 06-25-2019, 08:17 PM
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i had the same issue and dealership replace the part within a year i am now having the same problem again
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post #14 of 14 (permalink) Old 06-25-2019, 09:45 PM Thread Starter
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What was the part they had replaced?

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