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driveline clunk

Getting a slight clunk in my '13 Boss from either the rear end or the drive shaft when tipping back into the gas after decelerating in 6th gear. Usually happens 60 to 70 MPH. Feels like a u joint or differential issue. I have the Torsen. Anyone else experience this?
 
I haven't experienced a clunk like this but its time to use your warranty and have your dealer look at it.
 

pufferfish

Supporting Vendor
1,094
66
Maryland
i have always had a clunk. i figured it was the sloppy driveshaft. i replaced it with a 1-piece and the real culprit showed itself. the gears have WAY too much backlash. the OE driveshaft was covering up a serious issue. that excessive backlash was going to prematurely kill my gears and possibly more from the drivetrain shock. i don't do gears, so i had JPC (local drag mustang shop) check it out and they confirmed the issue and said they have seen many cases of this since the availability of the factory 3.73 option.

so, if your backlash is out of spec as mine is, its a new gearset. once the gears have broken in, they cannot be re-shimmed. it will destroy the gears even faster. as much as we all want to save money, i will never take a vehicle to a dealer for a gear change. they never seem to get it right. they swap parts and gears are anything but a "plug-and-play" job. go to an expert in rearend gear changes, pay the money and get it done right the first time.
 

Justin

Save the dawn for your dishes!!!
I had the clunk with the factory Driveshaft once I went with a DSS one piece I dont have it anymore. Seems to be common in all the mustangs with the two piece DS. I had the same clunk in my 06 and it too went away with a one piece DS.
 
Many owners have had this issue with the GT, also. My 2011 did with stock gearing, and my Boss does with the Torsen. I just assumed it was normal since drivetrains can't be perfect for our price point and will have some backlash. I don't know of anyone breaking their diff yet, but what pufferfish said is making me nervous. I was going to change the fluid, but now I am thinking I will hold off until we get some more info on this since Ford might try to use that against me. But I already have a new 1-peice drive shaft and engine mounts, so maybe I am already screwed if this really is a problem?

Anyone here racing with their Torsen, having the "clunk", 1-peice DS, AND having premature wear issues? I bet they will be the first to notice.
 
I've had a wicked clunk since day one with the 13. My 11 had it as well, its more noticeable with an Adj. UCA. I'll be putting a DSS on once I have the time.
 
pufferfish said:
i have always had a clunk. i figured it was the sloppy driveshaft. i replaced it with a 1-piece and the real culprit showed itself. the gears have WAY too much backlash. the OE driveshaft was covering up a serious issue. that excessive backlash was going to prematurely kill my gears and possibly more from the drivetrain shock. i don't do gears, so i had JPC (local drag mustang shop) check it out and they confirmed the issue and said they have seen many cases of this since the availability of the factory 3.73 option.

so, if your backlash is out of spec as mine is, its a new gearset. once the gears have broken in, they cannot be re-shimmed. it will destroy the gears even faster. as much as we all want to save money, i will never take a vehicle to a dealer for a gear change. they never seem to get it right. they swap parts and gears are anything but a "plug-and-play" job. go to an expert in rearend gear changes, pay the money and get it done right the first time.

A lot of people think they know how to setup a rear diff. Truth be told, the number of people that can is very small. It is an exact science to get it right and have it noise free.
 

pufferfish

Supporting Vendor
1,094
66
Maryland
NewBossowner said:
A lot of people think they know how to setup a rear diff. Truth be told, the number of people that can is very small. It is an exact science to get it right and have it noise free.
its worse than that. to get noise free, you need to hand-select gears. the manufacturing process results in inconsistant meshing from one set to another. i believe it has to do with how worn the tooling is when they are being cut. the owner of JPC told me they have actually swapped gear sets because of whine and with the exact same shims and backlash and they got different levels of whine out of different gear sets from the same manufacturer. its obviously not cost effective to do this, so you get what you get for the parts and they don't guarantee noise free, just that the backlash will be properly set.
 

Glenn

Still plays with cars...
12
0
Omaha
pufferfish said:
its worse than that. to get noise free, you need to hand-select gears. the manufacturing process results in inconsistant meshing from one set to another. i believe it has to do with how worn the tooling is when they are being cut. the owner of JPC told me they have actually swapped gear sets because of whine and with the exact same shims and backlash and they got different levels of whine out of different gear sets from the same manufacturer. its obviously not cost effective to do this, so you get what you get for the parts and they don't guarantee noise free, just that the backlash will be properly set.
Got the clunk here too and only 350 miles. I've learned to minimize it with clutch/throttle compensation, but it's there. Definitely excessive ring and pinion backlash - I had the same problem with an '06 GTO after I had an "expert" install a set of 3.91s. What a nightmare, after two more attempts to get it right (including another set of very expensive gears/bearings and a TrueTrac), I gave up and got rid of it. I didn't expect this again after coming back to the Ford family. In addition to the slack while in motion, if I'm sitting at a light in neutral and then shift into first, I sometimes get a very light "thunk" from the rear end as it goes into gear - same thing the Goat did after the gears got all hosed up. Now I'm not sure exactly what to do, I absolutely love this car, so it'll get fixed one way or another. I agree completely with pufferfish - most mechanics don't know s**t from Shinola when it comes to properly setting up a rear end....
 
88
0
Yes I also have the clunk at low rpms in 6th. Firgured it was normal. I'm not going to worry about it.
 
Some amount of clunking during accel/decel in sixth gear at low rpms is to be expected and not necessarily a backlash issue.
 
Hi all,

Well, at 875 miles, I am getting some of this driveline clunk. I am completely stock, and did not have any intention of changing the stock suspension. I also do not have any gear whine. My noise actually sounds like the entire rear axle assembly is rocking front to back under on-off throttle conditions. It almost feels like the entire rear end assembly is just a bit loose.

Would a stiffer adjustable PH bar such as the BMR help eliminate this? Or perhaps one of the spherical/adjustable upper control arm and matching mounts? It's not unbearable, but it is a bit irritating. I can only imagine what it will be like when I get the track key software installed, which I understand offers a bit more jerky on-off throttle.

Anyway, I have absolutely no tracking intentions, I just want the rear end to stop being so 'jerky.' Any advice would be greatly appreciated.

Thanks,

JJ
 

unrealford

Mustang owner since 84
521
0
Mines been that way since new, nothing that concerns me. I kind of expect it with a manual transmission.
 
VTBoss302 said:
Some slack in the drivetrain is TBE...

Hi....

I did expect some of the driveline slack, it's just that my last few American V-8, manual trans cars never had this level of it. I realize that those were leaf sprung live axles, and as such, would not have as much 'movement' potential, however, it does seem a bit excessive on this Boss.

I am certainly willing to add a more solid upper control arm/mount and change out the softer rubber mounted PH bar to a heavier adjustable PH bar. I just would like to know if those changes will really help stop the movement I am feeling. I can only expect it to get 'looser' as the rubber bushing age. I don't even mind a bit more noise/vibration, and would even consider heim jointed PH bar if it will really help. Has anyone completed these changes and if so, what results did you have?

Thanks,

JJ
 
Not to muddy the water but my '12 Boss has no driveline clunk under power or deceleration but it does make a clunk sometimes (sounds like its from the driveshaft or aft) when I am at a stop and am shifting from neutral to first.
 
jjgi5150 said:
Hi....

I did expect some of the driveline slack, it's just that my last few American V-8, manual trans cars never had this level of it. I realize that those were leaf sprung live axles, and as such, would not have as much 'movement' potential, however, it does seem a bit excessive on this Boss.

I am certainly willing to add a more solid upper control arm/mount and change out the softer rubber mounted PH bar to a heavier adjustable PH bar. I just would like to know if those changes will really help stop the movement I am feeling. I can only expect it to get 'looser' as the rubber bushing age. I don't even mind a bit more noise/vibration, and would even consider heim jointed PH bar if it will really help. Has anyone completed these changes and if so, what results did you have?

Thanks,

JJ

PHB, brace, and lower LCA's have not fixed this for me so I doubt a PHB would fix your issue. Possibly a stiffer UCA could reduce it, but if it's gear lash or the u-joints on the driveshaft I would think none of these things would fix it.
 
Brandon302 said:
PHB, brace, and lower LCA's have not fixed this for me so I doubt a PHB would fix your issue. Possibly a stiffer UCA could reduce it, but if it's gear lash or the u-joints on the driveshaft I would think none of these things would fix it.

Thanks for the response...

I will check out the gear lash and the u-joints as a first cause. But, after reading just about every Mustang forum there is, the constant recurring theme is that the UCA seems to be too softly bushed, which causes a lot of wheel hop and traction loss issues. I guess I may just be too sensitive to the issue because my last V-8 muscle cars did not ever experience these issues. However, they did not handle quite as well as this Boss does, either! Perhaps a new technology trade off...

I may just go for a good, stronger UCA assembly and try that out...if there is no issue with the gears or u-joints. A good set-up is only about $200.00 and a lot of my time and labor to install it! I think I also want to install a beefier, adjustable PH bar anyway, just in case I decide to install slightly lower rear springs.


Take care,

JJ
 
jjgi5150 said:
Thanks for the response...

I will check out the gear lash and the u-joints as a first cause. But, after reading just about every Mustang forum there is, the constant recurring theme is that the UCA seems to be too softly bushed, which causes a lot of wheel hop and traction loss issues. I guess I may just be too sensitive to the issue because my last V-8 muscle cars did not ever experience these issues. However, they did not handle quite as well as this Boss does, either! Perhaps a new technology trade off...

I may just go for a good, stronger UCA assembly and try that out...if there is no issue with the gears or u-joints. A good set-up is only about $200.00 and a lot of my time and labor to install it! I think I also want to install a beefier, adjustable PH bar anyway, just in case I decide to install slightly lower rear springs.


Take care,

JJ

I thought we had been talking about the clunk, I don't think that has anything to do with the rear-end hopping. And I would spend a little more then 200 on just an adjustable arm if you're in there, might as well do the bracket as well which would be a little closer to 350-400.
 
592
167
A new UCA will actually add more noises in my experience. My new Steeda non-adjustable UCA with the Steeda adjustable bracket is much quieter than the Whiteline I had in for a brief while (don't even get me started on the Whiteline UCA debacle!). But there is still more noise than stock, sometimes a sort of squawking on shifts and a little more differential noise but neither is very bad in my opinion and nothing like as bad as the Whiteline.

In saying that, the new UCA made a very profound improvement in the 'tightness' of the rear end of the car. I have P springs, Steeda billet LCAs, Whiteline relo brackets, J&M adjustable panhard, and a Drake panhard bar brace. I think that that UCA has probably made the single biggest difference in terms of keeping the rear end settled under acceleration and through corners. All of those modifications combined have really helped tremendously.
 

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