spqr

I hear a clunk coming from the back of the car when I accelerate from a stop, accelerate after braking, and when I brake after accelerating with the car still in gear. I'm not able to reproduce the sound with the car out of gear.

I tried pushing down on the back of the car to load and unload the shocks and springs but it didn't make the noise. I tried taking off the handbrake, putting the car in gear (while off), and pushing it and it did make the noise.

I tried putting the car on stands and the LCAs, shocks, and sway bar all seem securely bolted. I haven't been able to check the UCA yet, so it could be that. I tried rotating the tires and heard a soft tap when I changed directions, so I wasn't sure if the noise was just some slop in the rear gears or the driveshaft u-joint. Has anyone experienced anything like this?

thanks,
spqr

galens47

I've experienced this. It feels like slop in the drive line to me. Taken a driver mod and it is mostly mitigated.

Cheers,

G

ace72ace

Sounds like your 2 piece drive shaft saying 'hi'.

cdynaco

Wrong. The 2 piece has no roll in. Look elsewhere for driveline lash.

cdynaco

Is this your first experience with a Traction-Lok diff SRA? The clutch packs are not noise free.

Cobrakev

Yep it's the mid bearing in the driveshaft. Mine has made that sound from the start. A one piece driveshaft will fix that clunk.

Ltngdrvr

It's driveline slack, be smoother on and off the throttle and brakes and you won't get the noise.

cdynaco

Prove it. Both points. You and others spread that rumor.

The OP didn't say whether its a manual or an auto. If its a manual then he needs to learn to be better with the clutch.

cdynaco

FYI - From an S197 Ford engineer on the Bullitt project that used to post here:

>>Clunk is driven by total driveline lash, dominated by the gear sets and clutch tuning/capability. The 3.73 amplifies this a bit compared to the 3.31 and 3.55 axles. The 2-piece driveshaft is not the cause of the clunk noise. The Bullitt will have higher levels of clunk compared to the base GT. The base GT throttle response is a bit softer than the Bullitt's. The increased throttle response makes the clunk a bit easier to get. It is a trade-off - improved performance feel vs clunk.

>> I don't recalling "dis" ing anyones products. It's up to you to believe what you want. Whatever criteria you have for something being superior or inferior may not match mine or others. I've met Gary Patterson- he's a nice guy.... I'm just here to answer questions and try to be of help.

The post mentions high speed and 160 mph - The Mustang (as it leaves AAI) is speed limited well below that for a reason. Like I said before, I do not know specifics about the dynotech piece, what it does or does not do.
I do know about the 2-piece in the factory car. It is a fairly robust piece. Vibration is not an issue unless the center bearing shims are not installed properly, the shaft has a balance issue or the pinion angle is off. These would be quality issues (that I'm not aware of having in production), not design. The 2-pc has no roll in whether or not you have a random vibration. U-joint angles, run-out (flange or shaft), balance and system modal (resonance) response govern vibration.

>> The 2-piece driveshaft is required to meet internal engineering requirements for safe operation at max vehicle speed. Basically, itis designed to provide a driveline system resonance well above what the speed limiter will allow you to operate at. If you put your driveline into resonance, bad things may happen! I've seen what it does to a car and it isn't pretty.

The driveshaft CV joints are required components on this type of driveshaft when combined with a live axle. If the rear suspension were IRS, simple flex couplings would be used (look at the new Camaro, Challenger, etc...) and would make for a lighter driveshaft.

The driveshaft also has an internal torsional damper (ITD) which is soley there to attenuate axle whine. If package allowed, the ITD would be mounted on the exterior of the driveshaft as a much lighter ring design. Since the equivalent inertia is required out of the smaller diameter part when installed inside the driveshaft, the mass has to increase. So, you get a heavier ITD vs a lightweight ETD.

A single piece steel or aluminum 1-piece would have to be larger in diameter than the current package allows. Basically, you would have contact with the fuel tank at full rear suspension jounce. 1-piece carbon fiber was explored at one time...

Hope this helps.

>> I would not assume an aftermarket piece "solves" a problem. Yes, you can stuff a massive driveshaft into the tunnel but it will not meet standard vehicle engineering requirements. Our requirements take many factors into account, with the biggest one being your personal safety under a wide variety of operating conditions. Our parts are engineered to work in one big system. Aftermarket parts are generally not engineered. By this, I mean that they are designed to fit properly (usually) and improve one or two attributes specific to your application.

For example, if you want a lighter weight driveshaft that gives you less rotating inertia, you can buy this aluminum 1-pc driveshaft. But, that's all you get - lighter weight. Not proven durability, safety (how does the driveshaft react in arear impact?, clearance to other parts like the fuel tank?), NVH, ride (driveshaft plunge force actually affects your ride quality), etc...

But that's the great part about it being your car. You get to decide what you want your Mustang to be. Just be cautious and think about how these parts may affect the rest of your driving experience, safety and wallet if it breaks or breaks something else in the car.

I've been in your shoes (which is why I became an engineer and worked my way onto the Mustang team!) and know exactly where you are coming from, though. I don't know specifics about the d/s you are referring to but I'm just giving you some things to think about and consider.

Thanks for buying a Bullitt!

GT50GO

FYI, I have a DSS aluminum drive shaft, 3.73 gears, SC, etc... and still have the clunk. It's not an "all the time thing" but I do hear it occasionally.

VidPro

I hear it and I had in on my 2000 GT from day one.

FordService

Hello spqr,

You should speak with the service manager at your Ford Dealer. He is in the best position to ensure a proper diagnosis, and will be able to provide available options and/or coverage for any work needed.

You can schedule an appointment online here. Let me know the outcome.

Deysha

spqr

@ace72ace: v6, so isn't it techincally a 1 piece shaft? Does the slip count as a joint?

@cydnaco Manual & first traction-lok car. I'm not saying I couldn't improve my clutchwork, but I don't understand the relevance. The clunk appears to be independent of the clutch as I noted in my post. I can successfully reproduce the issue by changing between acceleration and deceleration in gear (or vice versa); no clutch needed to get noise.

for those saying it's driveline slack, is this something I need to worry about?

cdynaco

A) Why are you driving like that? You're trashing your gearsets needlessly.

I can get drive train noise out of any RWD if I simply pedal on pedal off. Even my FWD though the noise isn't as loud because of no hollow driveshaft.

If you are in traffic trying to avoid disengaging the clutch, then ease the throttle better as you back off. And when you have to let off the throttle to brake, disengage the clutch a bit earlier so as not to get noise.

B) Assuming its not something major like suspension dragging the ground all gearsets have slack to take up - whether its the trans or the diff.

ace72ace

It's nothing to worry about, it's just annoying. My guess would be the dealer would say it's within 'acceptable tolerance', up to you if you want to bring it in...

I have a one piece DSS alum shaft and can also sometimes hear noises from the drivetrain, but the noise is at least 75% less than the original shaft.

spqr

The clunk occurs primarily during every accleration if there was previouly any deceleration in gear (with or without brakes, for a brief or extended period). It is not necessary for it to be aggressive in either direction to get a loud clunk.

I've never heard that deceleration in gear will trash your gears. Is there a source you can link to to explain why it's bad?

spqr

It is annoying, haha! The noise probably isn't helped by the UCA's poly bushings; more nvh comes through.

cdynaco

I didn't say that. Maybe I'm misunderstanding how you are driving. But it sounds like you're just thumping the accelerator on and off with no finesse, no feathering of the throttle, while in traffic. Like you said, you could learn to get better with a clutch. Well remember your throttle foot works with in conjunction with your clutch foot.
If you're just letting the accelerator fly back without disengaging the clutch so as to get a clunk when the drivetrain reverses, you are putting needless harsh wear on the gearsets vs normal wear. Think about it. Same goes if you're not using a bit of finesse to 'take up slack' in the drive train when you accelerate before you accelerate hard.
No I don't have an internet source for you to check up. I have a brain and been around machinery enough as well as rebuilding a toploader a few times. Every time you clunk it needlessly you are putting harsh wear on the gearsets vs normal wear. Take care of your machine and it takes care of you. My '83 F150 4X has 254k with the same transmission, transfer case, and front & rear diffs, and believe me its been worked hard over the years. But never thrashed with no concern for the driveline...
Google your heart away. lol

dusman59

I believe the GT500 uses a one piece carbon fiber DS. So why the two piece in the GT? I did eliminate 90% of the clunck with the one piece. I however picked up more NVH , some is from the poly bushings in the UCA. I could shift without the clunk before the install but sooner or later the clunk would happen if my timing was not right on with the clutch and throttle.

spqr

I think you misunderstood. I didn't specify the harshness of my driving style, but I thought that being able to get the clunk by simply pushing the car with my body was indicative of how little force it took. I guess we both made some assumptions.

I have been easing off the accelerator and coasting or dabbing the brakes. A very light acceleration afterwards will result in a loud clunk. It's all under circumstances that should be well within normal operation (unless any decel in gear is considered outside normal operation.)

Hopefully that's more clear. Thanks for the help.