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HELP! driveline rattle

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pufferfish

Supporting Vendor
1,094
66
Maryland
i have always had drivetrain noise. mostly gear whine after the steeda 3rd link, but some other faint clunking and whatnot. i installed an aluminum driveshaft and immediately noticed an issue. between the point of accellerating and decellerating, the drivetrain consistantly develops a horrible rattling sound you can feel. i don't have a vibration under load (tested to 160mph at VIR). i double-checked my driveline angles. to me, it sounded like excessive gear backlash causing the gears to bang from the front of the teeth to the back of the teeth. i steer clear of gears, so i took it to JPC. their first impression on the ride-along was exhaust hitting. it was all checked and nothing. they agreed the next logical source of the noise was the gearset. i decided to have the gearset replaced with a different ratio and add a torsen diff. going from 3.73 to 3.55 did quiet down the whine, but did nothing to kill the rattle. they changed out the driveshaft with 2 different aluminum pieces and checked my driveline angles, which were good, and the rattling persisted.they put a stock 2-piece in and the rattle is gone. i called dynotech (the mfg of my driveshaft) to ask if they had ever heard of this issue. nope. JPC installs many driveshafts and never saw this issue. the next thought was the transmission. i took it overto the ford dealer and had their shop foreman take a ride. i think he fully expected it to be normal NVH for a modified car, but quickly changed his tune when he heard it. he believes i should be looking at the trailing arms for a bushing that walked and allows the arm to touch another piece of metal. i disagree, but will look at it anyhow.

it makes the noise at highway speeds when i let off the throttle. once the engine starts braking, it goes away. if i push the clutch in at highway speeds, it rattles tremendously until i re-engage the clutch in gear. the likelyhood of a chassis metel to metal contact rattle only occurring under these conditions is really unlikely and i would still rattle with a 2-piece shaft in there.

since its not the rear gears/bearings or the driveshaft, the only place left for a drivetrain rattle is the trans, right?

i have scoured the internet and can't find another example of this issue, but figured i would post here to see if anyone else has heard of such an issue or has a suggestion to check as the possible culprit.
 
Ugh I hate those. I have on in my GT500 that you hear under relatively low speed bumps and we've looked and looked and can't find the damn thing.

Is it loud clunking like something heavy...driveline/suspension or is it higher pitched/lighter like heat shield exhaust etc.?

After my driveshaft install (DSS) I had a rattle and vibration under load. I assumed it was the driveshaft but when we got it on the lift realized one of the headers was hitting the frame. Moved it over and it went away. Have you installed LT headers? There's not a lot of clearance up there and I've heard of others hitting the steering shaft.
 
Where do you hear the sound coming? It's usually not a good indicator since it can resonate from anywhere, but I'm curious.
Also, when you feel it, is it in the seat or the steering wheel?

Is the vibration/rattle harmonic with your speed/gear? For example if you're going 50mph in 5th gear and shift to 4th gear (while maintaining 50mph), does the rattle speed up, get louder?
Does the rattle speed up when your mph increases regardless of gear?
 

pufferfish

Supporting Vendor
1,094
66
Maryland
i have a video of the noise on my phone. i will try to post it to youtube and link it here.

the noise is sort of speed related. under the right circumstances, it will happen at 40, but consistantly above 60. it seems to just need enough speed to make the rattle happen. it doesn't matter what gear i am in, but with the loud exhaust, it is easiest to hear in 5th or 6th. the higher the speed, the more violent sounding it gets. i would say the frequency also changes.

inside the car, it definitely sounds like its coming from the rear. this was confirmed by justin at JPC and the ford tech, when they both looked into the back seat when the noise happened. under the car(on a lift with the back wheels up), it actually soulds more like its coming from the middle of the driveshaft. there are no marks to indicate anything is contacting the shaft. there is also plenty of clearance between all of the exhaust comonents and no signs of rubbing or hitting. since it goes away without doing anything but change the shaft to the stocker, a chassis or exhaust interference is unlikely.
 

pufferfish

Supporting Vendor
1,094
66
Maryland
phone video sound was too muted. i took another video with my in car camera:
[youtube]http://www.youtube.com/watch?v=P2NVK-UkkxQ&feature=youtu.be[/youtube]
 

pufferfish

Supporting Vendor
1,094
66
Maryland
can't imagine 3 random 1 piece driveshafts needing a rebalance. if so, i'm the unluckiest person alive!
 
check for play or wear in the bushing for the output shaft in the trans and check the flange on the ouput shaft, make sure it isn't loose.
 

jneary

Performance Fords
323
0
Norcal
You should go through and check the tightness of every bolt including the transmission mount. I had a noise in my 1995 GT that I just couldn't figure out. It was a clunk that would occur over bumps and when going in and out of gears. Turned out to be the transmission mount nuts were loose.

My bet is on something that you either took off to get the drive shaft replaced and didn't tighten back down or a happen stance with a mounting point that simply is amplified by the new drive shaft. Aluminum drive shafts will have a different resonance than the heavy two piece and it probably amplifying the noise.

Check all of your mounts for tightness....

John
 

pufferfish

Supporting Vendor
1,094
66
Maryland
i will take a look at mounts and whatnot. the only bolts turned other than the driveshaft were the 4 header collector bolts to lower the x-pipe. oh, and the 3rd link turnbuckle to adjust the pinion angle. i checked to make sure that was tight yesterday.
 
I got a wicket rattle at low rpms after removing the restrictor plates. I loosened and moved the side pipes a bit and it went away. Other than that, I have always had a drivtrain clunk when transitioning between accel/decel, even on my GT. BUT I notice the clunk much less after putting on my Nurburgrings for some reason. I would definitely check the exhaust if you hear a rattle. Even though my side pipes (the flat section) looked plenty far away from the chassis, the vibration of the motor moved them around quite a bit.
 
Maybe you can run it on a dyno (low speeds) and stick your head underneath to better identify where its coming from.

I think it has to be drivetrain related if you are "feeling" a vibration vs. a rattle you only hear. Which I had for the longest time and only just the other day fixed. Was driving me nuts.
I thought I had fixed the sidepipes good and never revisited it as the source, then put some rubber washers over the passenger side pipe mount just for kicks since I had the car jacked, and poof. Noise is gone.
 

pufferfish

Supporting Vendor
1,094
66
Maryland
JPC had it up on a lift while running it and tried to find the source. it appears to be from the driveshaft...the middle to be exact. i am tempted to pull the DS and paint it with plasti-dip to see if that will help reduce the noise. the more i drive it, the more it seems like a backlash death-rattle. backlash is necessary for proper gear wear and its not excessive (as verified by a new gearset properly set up). there is also no indication that the transmission is at fault. its like there's just a perfectly wrong harmonic between the trans backlash and the rear backlash and the tight 1-piece DS between them is a perfect mechanical connection. the stock 2-piece is just so sloppy that the trans harmonic never gets to the rear to make their rattling byproduct.

also, i did check the trans output and its tight. you can hear the backlash in the trans, but again, backlash is normal and desirable.

i am reminded of a friend of mine that is creating his own super 7 with a ZX12 crotch rocket engine mated to a miata manual trans. he disassembled the engines built-in transmission case, so he could direct drive it to a standard automotive dry clutch inside the miata bellhousing. the crankshaft has a step down gearset before it gets to the stock wet clutch basket. there was no way to eliminate this single gear reduction because of how the crank case design. the larger second gear is actually a sandwich of 2 gears. a broad face one and a narrow one with a sprung hub between them. their combined width equals the face width of the crank gear, so they both mesh with it. he eliminated the thinner second gear and the sprung hub and grafted his shaft to the clutch basket to drive the automotive clutch. well he got it done and running and had a rattle in neutral and off gas. turns out this sprung 2 gear arrangement put the gears on opposite faces of the crank gear teeth, so there was no effective backlash. they did this because there is natural harmonic of the reciprocating motion of the pistons and rods to the rotational cranskaft output. without the second gear on the opposite side of the gear teeth, the gear backlash would cause the larger gear to rattle. he added this sprung hub and secondary gear and the rattle went away.

im not suggesting i need to create this secanario to fix my issue. cars have been very successful with trans gear backlash, rear gear backlash and a 1-piece driveshaft since the dawn of cars. what i am suggesting is there may be a funky harmonic frequency from the transmission that causes the ring and pinion to rattle violently when not loaded.
 
You make a good point. Not all gears are manufactured equal. Maybe theres just too much backlash from your 3.55's? Who made them? Are there other manufacturers?
 

pufferfish

Supporting Vendor
1,094
66
Maryland
the gears are ford racing. not sure who makes them for ford? but, the likleyhood that the factory 3.73's and a ford racing 3.55 set exhibiting the exact same backlash rattle, would be incredibly rare. and if it were the ford brand causing it, there would be more search data to draw from. this seems to be like one of those uber-rare diseases that are named after the person inflicted with it. so, once diagnosed and fixed, we can name it the Pufferfish Death Rattle (or PDR Syndrome, for short).
 
pufferfish said:
the gears are ford racing. not sure who makes them for ford? but, the likleyhood that the factory 3.73's and a ford racing 3.55 set exhibiting the exact same backlash rattle, would be incredibly rare. and if it were the ford brand causing it, there would be more search data to draw from. this seems to be like one of those uber-rare diseases that are named after the person inflicted with it. so, once diagnosed and fixed, we can name it the Pufferfish Death Rattle (or PDR Syndrome, for short).

What did you end up with for backlash? What kind of pattern did you get after the gear set was installed? More heel, more toe or a neutral pattern ?
How much Pinion preload?

Are you running the stock trans mount?
 

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