Jolt / Clunk in drivetrain - M6

2023 Views 13 Replies 8 Participants Last post by ThunderOne, Mar 2, 2022

Got Bearings?

Discussion Starter · Feb 20, 2022 (Edited)

I've got a "jolt" in the drivetrain as soon as I let out the clutch. I feel it most in 1st and 2nd gear when I let out the clutch normally. If I ease it out slowly, I won't feel it. It sounds like it's coming from the rear and the best way I can describe it is as if someone is giving me a 3mph "love tap" on my rear bumper. It doesn't sound like metal to metal clunk... if that makes sense. Car has about 117,000 miles and clutch replaced at 90k miles with stock.

Engine Mounts - Inspected yesterday and no fluid leaking. Looks to be intact
Transmission Mounts - Inspected yesterday and looks fine. Replaced the rubber isolators about 2 months ago. 1 of the 2 isolators was broken. No change on replacement.
Diff Bushings - Inspected yesterday, looks fine. Tried to move the diff by hand to induce movement but seemed sturdy and solidly attached.... or I'm a weakling
Driveshaft - Inspected yesterday, looks fine.

I'm at a loss here. I'm thinking it could be the diff bushings since it could induce some movement with some power. CS has replacement bushings but not sure how easy this is to replace or if they are even in stock.

09-15 Cadillac CTS-V Differential Bushing Set

Put the power to the ground and reduce wheel hop with our polyurethane differential bushings for the 09-15 Cadillac CTS-V.

creative-steel.com

Any thoughts on additional items to check? Cradle bushings? Axles/half shafts?

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Teh V

· #2 · Feb 20, 2022

I had a similar feeling and majority of it went away with new mounts (ALM) but still something there.

Have a feeling it's rear end/driveshaft related.

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random84

· #3 · Feb 20, 2022 (Edited)

Put the car in neutral and try to turn the driveshaft (or both rear wheels at the same time for more leverage) . Could just be gear slop in the differential or joints - pretty common really.

Worn bushings will contribute to driveline deflection and the amount of "clunk" you get. I'd only worry if it sounds appreciably worse than before.

If you're on the factory differential, the various bearings could be going out, increasing clearances in the gears and the noise you hear.

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RocketSled

· #4 · Feb 20, 2022

Get in there with a pry bar and lean on shit. Trying to move things with your hands is only good for finding stuff that's on the brink of falling apart already. The forces you can produce with your hands are trivial compared to what the motor generates even at idle. You're simply not in the same league unless you're colored green and all Hulked out when you try. Not being able to move things by hand IMO doesn't say squat about whether or not you've got a problem in the area you're looking.

I learned this lesson way back in the early 1980s with my 74 Datsun 260Z. Driving down the highway, the rear of the car would move sideways a little as I got on/off the gas. Jacked it up my my driveway and tugged on everything I could think of tugging on and it was all tighter than a virgin's ass. Took it to a local mechanic and explained what I'd done, he just laughed and put the car in the air and jammed a pry bar between the frame and lower control arm and with one tug and it was clear the bushings for the arm were totally shot. Even knowing that, I could not get things to move enough by hand to diagnose. From then on, any time I thought something might be loose I'd get a pry bar or a piece of 2x4 or whatever jammed between the components I thought might be moving and yank.

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Got Bearings?

Discussion Starter · #5 · Feb 20, 2022

Thanks for ideas. Def gonna use a pry bar and look for things.

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Karch

· #6 · Feb 20, 2022

Got Bearings? said:
Thanks for ideas. Def gonna use a pry bar and look for things.

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I can bring the bourbon, for moral support.

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Got Bearings?

Discussion Starter · #7 · Feb 20, 2022

Karch said:
I can bring the bourbon, for moral support.

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Not working tomorrow. Feel free to come by

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random84

· #8 · Feb 21, 2022

Awww. I'm missing out on the bonding. And bourbon. I think I miss the bourbon more.

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random84

· #9 · Feb 21, 2022

Zoom call for the bonding? I can BMOB.

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Got Bearings?

Discussion Starter · #10 · Feb 21, 2022

random84 said:
Zoom call for the bonding? I can BMOB.

I can arrange that

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specialp

· #11 · Feb 22, 2022

For me it was the clutch. The stock clutch is a dual mass flywheel that buffers the clutch when you let it in. over time this gets play in it and clunks

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Got Bearings?

Discussion Starter · #12 · Feb 22, 2022

specialp said:
For me it was the clutch. I forgot the term for it but we have a 2 piece flywheel that buffers the clutch when you let it in. over time this gets play in it and clunks

Dual mass flywheel?

Yeah, i suspect that as well

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Eighthtry

· #13 · Feb 24, 2022

I have had that problem on two or three different cars. Not on my V. Old mechanic told me my drive shaft was loading up in front due to lack of lubrication. In other words, the shaft and the spline need to slip to make up for drive train movement. My problem was exactly as you described. I removed the driveshafts, lubed up with quality synthletic grease, and presto-o change-o the problem was resolved. I would look at that first before you begin your journey in the weeds.

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ThunderOne

· #14 · Mar 2, 2022

I have this issue and have an AT. It sounds like it's coming from the rear, at slow speeds and applying load to the engine from a no-load condition. I found one post mentioning aligning the rear end fixed it. I keep thinking it is slop in the driveshaft or diff. Unfortunately the driveshaft is built very weirdly and is not serviceable at all so a full replacement is the only potential fix. I am not sure how I would diagnose sloppy diff bearings.

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