By on November 3, 2014

u joint. Shutterstock user Tossapol

Mark writes:

Sajeev–

Here’s a weird one to test your skills of remote diagnosis. Fire up your Magic 8 Ball for this one.

Car: 2012 Mustang V6, manual gearbox, performance package (currently running some crappy General AS Max-03 tires), 33,000 miles. I’m the only owner; special ordered to get it just the way I want. Mods limited to a Shaftmasters one piece drive shaft (scared into it by a few YouTube videos), a Draw-Tite receiver hitch to pull my one bike motorcycle trailer, and an 87 octane tune uploaded via SCT (on your recommendation). The car will go into a nearby Ford dealer for a look at this issue under warranty this coming Friday, but based on the “quality” of some of the work I’ve had done over the years, I thought it would help to give the techs some clues.

Problem: For the past few days, I’ve heard irregular “bangs” or “clunks” from under the car.

The noise is heard, not felt, and I’m unable to pinpoint the corner of the car from where the noise emanates. It doesn’t seem to be speed related: the noise can happen at a walking pace on up to about 40 mph, and the frequency doesn’t vary with speed; the noises can be 2 seconds apart or 30 seconds apart. I think the noise continues at higher speed, it’s just drowned out by wind/road noise. Some bumps set off the noise, some don’t…can’t seem to figure out any common threads on the bump-noise relationship. The one thing I have noticed: no noise if the brakes are applied. Even a very light drag of the brakes silences any noise.

My Own Research: I’ve had the car jacked up in the garage and I don’t see any obvious issues. The exhaust system seems to be well secured, as do the anti-roll bars. No obvious hanging parts. The brake pads have plenty of meat. No leaks from the shocks/struts. The receiver hitch is not loose.

This car has had a few chassis issues: a new steering box around 15k and a new rear anti-roll bar around 30k. I blame the poor condition of roads here in Illinois for those failures, along with the lack of give from the low profile 40-series tires.

Some digging in Mustang forums failed to uncover a smoking gun.

Bonus Question: When these crappy Generals give up the ghost, do you see a major problem with switching to 45-series tires in an effort to gain a little more bump compliance?

Thanks, Sajeev!

Sajeev answers:

I’ll answer the easier (bonus) question first: sure, no problem and it might help a little. But wanting bump compliance from 19″ wheels on a car is like expecting an honest answer from a politician.  Both are laughable: try minus sizing via 17″ wheels from an older S197 (as they get dumped on craigslist for dirt cheap) over the performance package’s upgraded front stoppers.  If not, maybe 18″.  If not, give up be awesome and get a Grand Marquis as a second car.

That was easy.  Now, I suspect your first question shall have no solution when a mechanic starts prying/wiggling suspension things to test for play.

I commend you on the modifications, but…there’s always a but. My gut thinks the new U joints on that new (and necessary) upgraded driveshaft are the problem. Can you (gently, with millimeters of throttle input) load/unload the drive line while the tires are losing/gaining traction?  Like maybe on a bumpy/slick road at highway speeds. If the thud/clunk comes back, it’s the U joints.

If not? Maybe it’s a shock/strut mount. Or maybe a sway bar mount, but the speeds you mentioned make me think U joints Über Alles.

[Image: Shutterstock user Tossapol]

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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32 Comments on “Piston Slap: UR U Joints Be Bangin’ Dat Stang?...”


  • avatar
    petezeiss

    Well, it certainly isn’t that Reynolds Wrap.

  • avatar
    zbnutcase

    And somebody too stupid to know u-joint noise should not be allowed to own a motor vehicle…sheesh

    • 0 avatar
      MPAVictoria

      Well if that is the rule my wife, mom, both sisters, pretty much every close female friend I have ever had and most of the male ones are going to have to start taking the bus. Seems like it might be a pretty dumb rule. Most people just want to drive their car not play mechanic.

    • 0 avatar
      tresmonos

      Somebody who knows u-joint noise so well should be taken off the road and put directly in the nursing home.

      CV-joints have been the norm since the mid 80’s, grandpa/grandma. SHEESH

  • avatar
    kosmo

    Put the OEM drive shaft back on and see if the noise disappears.

    The dealer is almost certainly going to glance underneath, and tell you the aftermarket driveshaft is the problem, anyway, so keep digging yourself.

    • 0 avatar
      olddavid

      Is upgrading the driveline prima facie evidence of extreme driving? Is that sufficient to void any associated warranty claim? While I cannot imagine anyone being so bold as to expect the factory to warrant someone else’s product, if the differential were to be SOL, would the altered driveline be enough to disallow any claim? I think kosmo has the right idea – if you still have the original. Not an easy diagnosis, but it would put the boots to any doubt, and allow you to continue driving it while going through any claim with the manufacturer. Lose/win/win?

  • avatar
    PonchoIndian

    Have a rear pinion walking up the ring gear on my 2nd Gen F-body. Makes random bangs and clunks that can be heard but can’t feel anything.

    As someone else already said. Put the stock driveshaft in. If the noise goes away then you’ve found the problem. If not, leave it in for the dealer visit. Ford may not legally be able to void the warranty on the rear end (if it indeed is the problem), but I’m sure they’ll at least try to with the aftermarket drive shaft. Why go through the headache of dealing with that if you can avoid it.

    • 0 avatar
      rpol35

      This is a really good point, Ford will definitely walk away from this one due to the driveshaft replacement – swap it back and see if that solves the problem, if it doesn’t Ford will be more inclined to provide service.

      Oddly, I had a ’92 Mustang LX with a 5.0 litre engine and a T-5 manual transmission. The drive train made lots of clunks that could never be pinpointed. The dealer checked the ring gear to pinion clearance and said it was in spec but it clunked and clanged like a car with 300,000 miles instead of the less than 30,000 that it had. I never got to the bottom of it and dumped the car for a whole host of reasons/problems. One issue with your situation, it’s peculiar that it stops when the brakes are applied……

  • avatar
    bumpy ii

    Suspension bushing(s).

  • avatar
    Andrew foote

    When did they replace the tires? I ask because I had the exact same thing over the summer with my Miata. Seriously- Check your lug nuts. I went all over the car trying to figure it out-Drive shaft, axle, everything.It Turned out that the Tire place hadn’t properly torqued the lug nuts on my driver rear wheel. I was about to check the brake calipers/brake pads and when I went to remove the wheel I could literally turn the lugs with my fingers! I had just driven 50 miles on the highway about 15 minutes before this. I could have been killed.

    • 0 avatar
      st1100boy

      Andrew– Lug nuts were the first thing I checked, with a torque wrench.

      In high school I had a Plymouth Turismo that started making weird noises. Sure enough, all four nuts on one of the front wheels were little more than finger tight. My fault as I had just did a tire rotation in the garage and didn’t finish the job right. Lesson learned.

      • 0 avatar
        olddavid

        I’m glad you have entered the conversation, as I am very curious about how you proceed. This – and all noise problems – is difficult to pinpoint because it is sometimes so hard to duplicate the circumstances. Bushings, u-joints, ring gear (all of the third member), tires, lugs, etc., are all good places to look. Please keep us updated as to the cause and cure.

  • avatar
    greaseyknight

    Usually noises and vibrations from the driveshaft are speed dependent. Based on the fact that apply the brakes will stop the noise. I’m leaning towards something wrong with the rear brakes. Possibly something wrong with the anti-rattle clips, or something like that.

  • avatar
    cronus

    First off the only choice to downsize the wheels is 18″, the 17″ wheels don’t fit over the brakes. That’s the reason I ordered mine without the performance package, I wanted the 17’s for snow tires, and 18’s for summer. There’s a big difference in ride quality between the 17’s and 18’s, I would think the 19’s would be brutal.

    The noise could be a number of things from bad bushings to a loose bolt or the u-joints mentioned. The only way to find it is to get the car up in the air and start shaking parts to find what’s loose. If you can’t find it with the cars weight on the suspension sometimes it helps to unload the suspension and try again.

  • avatar
    carguy67

    Motor mount(s)?

  • avatar
    rpn453

    255/45R19 has narrower tread and therefore recommends a narrower rim than the 255/40R19, so watch out for that. Some only recommend up to an 8.5″ rim but most go to 9.5″ so you’d be okay there with your 9″ wheel unless you want some curb protection. You might not gain as much ride comfort as you’d expect by stretching a narrower tire onto your wheels though. Depending on what you’re going for you might prefer a 275/40R19 if your fenders can handle the extra width. It certainly looks like it can handle a lot more tire in the pics that google provides me. The 275/40R19 are a little shorter than the 255/45R19 but pretty close, and having wide tires on narrower rims is good for compliance and grip on bad roads. I’m also a fan of the mean look that provides. To me, the stock size looks dainty. 265/40R19 may be the ideal size but there aren’t many tire options and the ones available are surprisingly expensive. 275/40R19 actually provides more options than the 255s, at around the same price.

    As others have mentioned, I’d want the stock driveshaft in there before taking it in. But before removing it, I’d be under there twisting it and yanking on it as much as possible to see if I could find any play.

    • 0 avatar
      Fordson

      Not sure how much narrower a 255/45-19 will be than a 255/40-19, since the 255 indicates the tread width in millimeters, but…

      I was going to guess a loose caliper on the OP’s car, since one of those will bang around kinda randomly and the noise will go away upon brake application.

      • 0 avatar
        Scoutdude

        255 represents the section width, that is the widest part of the tire when inflated on the preferred width rim. There is a often a slight difference in tread width as you go through each step in profile.

  • avatar
    st1100boy

    I’m Mark with the Mustang. Shortly after sending Sajeev the email, I could no longer stand the noise and took the car to the local Ford dealer.

    Turns out it was nothing in the driveline, or even the suspension. It was a brake issue. The friction material on one of the front brake pads pulled away from the backing material. Sort of makes sense now that the noise went away whenever the brakes were applied–the friction material couldn’t rattle around when being squeezed.

    I guess the stock pads just got overheated/overworked between a trackday and a few hard braking incidents from high speeds. A set of Hawk pads will be on my shopping list if I do another trackday. The fix, consisting of a set of front pads and turned rotors, was reasonably cheap. I like that. What I didn’t like was breaking my “brake streak”: I had never put a set of pads on a car, and that includes two cars with over 150k miles.

    • 0 avatar
      raresleeper

      Wow. Two cars, over 150k, no brake pad replacement?

      You must have holes in the floor and very strong soles on the bottoms of your shoes. Fred Flintstone style braking.

      EDIT: I stand corrected re: shoes with good soles. Freddie didn’t have shoes.

      • 0 avatar
        st1100boy

        The first car to pass 150k w/o needing new pads was a ’92 Mercury Topaz, 2.3 5MT. Didn’t really need brakes as it was too slow to get much speed going in the first place. Between it’s lack of speed and light weight, Fred Flintstone tactics might work OK w/ that car.

        The second was a ’98 Pontiac Grand Prix. Not a fast car, but the 3800 could get that barge going pretty well, eventually. Not sure how the brakes held up so well on that one, other than a highway-heavy proportion of those miles.

        • 0 avatar
          raresleeper

          Ahhh… Tempo/Topaz.

          The 2.3L was a dog, but at least Ford was nice enough to offer a 5MT as opposed to a 4MT.

          The slushbox-equipped versions were slower than dirt. Those cars were notorious for chewing up and spitting out alternators.

          The Vulcan V6’s were turds, too. I’d still love to have a V6, AWD 5MT Tempo just to beat on. Why?? I dunno… just cause, I suppose. (Not even sure if the V6 5MT came with AWD, or if AWD versions were only offered with the four banger…?)

          So I can see never putting brakes on it. Yup.

          Now your Grand Prix? Not putting brakes on that heavy bastard is impressive.

          The 3800 was okay. I can already hear them valves just a slappin’ away with that familiar tone coming out of those loose, hanging, square tipped “dual” exhaust. :)

          Endearing.

          • 0 avatar
            Scoutdude

            AWD versions were only on the AT equipped cars since the transfer case replaced the transmission pan and then drove the rear output off of the ring gear, opposite the side it was driven. So no MT and AWD in a Tempaz and no real way to make it happen.

            AWD was dropped before the Vulcan came to the option list but since the HSC and Vulcan share the same bellhousing pattern you might be able to stick a Vulcan in an AWD car.

          • 0 avatar
            Scoutdude

            Well it looks like the first comment got ate, so I’ll try again. There was no MT equipped 4WD/AWD Tempaz. The transfer case replaced the pan on the AT and drove the rear output off of the ring gear. So no real way to convert one either.

            Now the Vulcan and HSC share the bellhousing pattern so in theory you could stick a Vulcan in an 4WD/AWD Tempaz. But if you are going to go to all that trouble might as well stick a SHO engine instead since they were based on the Vulcan and share the same bellhousing pattern. There is or at least was one SHO equipped Tempaz though it was a 5sp FWD car. Google SHO Tempo and/or Topaz.

    • 0 avatar
      rpn453

      Well, you can still say you’ve never worn out a set of pads!

  • avatar
    st1100boy

    By the way, the dealer said nothing about the aftermarket driveshaft. The only thing they asked me was what I was towing. Apparently they thought I may have smoked the brakes while towing a heavy load.

  • avatar
    raresleeper

    Hey, Sajeev!!

    Why you no answer Honda Submissions?

    I call bias on your part, Sir. Lol

  • avatar
    danio3834

    Random noise from underneath on accel on a vehicle with driveline mods? Your Ford dealer won’t be looking at much as far as warranty is concerned…

    • 0 avatar
      st1100boy

      I took a calculated risk that it wasn’t a driveline noise because it didn’t happen only on acceleration and didn’t seem to be speed related. Definitely I would have put the stock driveshaft back on if I thought it was something that could bite me. Call it confidence or just being foolhardy, I didn’t even put the stock tune back in the ECU.

  • avatar
    FormerFF

    Check the swaybar links. I had a Focus, at about 80,000 miles these wore out and did nothing but clunk.

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