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Thread: Curious Vibration While Coasting

  1. #1
    No mean-spiritedness here. IPreferDIY's Avatar
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    Default Curious Vibration While Coasting

    My 2000 MGM developed a curious vibration after an unintended "neutral drop" in a parking lot. I messed up my initial reverse from a parking spot just as someone else came along. After seeing this person was going to wait for me rather than go a different route, I went to put it in Drive to move forward, but the gear didn't engage. (I'm guessing the steering column could use new bushings.) I was feeling pressured from the other person waiting (it was one of those days), and as it happened, I ended up putting it into Reverse while the RPMs were up, though not too much. I heard a "bang" just before the left rear wheel spun (because it was wet; no trac lok).

    I didn't notice anything the first time I went on the highway just after that. But while on a long trip during the wee hours with the cruise control on, I could feel a curious vibration in what I presume was the rear end while the car was coasting. The only thing that came to mind is some kind of damage to the reverse side of the diff gears, since driving forward under power is still smooth. The same problem was still there without cruise control on. I don't notice anything with city driving or reversing.

    Is there some kind of obvious part or interface that might have got jostled or something? The only other thing I can think of is knocking off enough rust from the driveshaft to unbalance it, but that wouldn't seem to explain why the problem only shows up while coasting on the highway.

    2000 Grand Marquis LS HPP, a hand-me-down in 2008 with 128,000 km; 175,000 km as of July 2014
    mods: air filter box "tuba" (in place of the "trumpet"), headlight relay harness, J-mod (around 186,350 km), 70mm throttle body, NKL4 PCM (from a 2000 CVPI, nothing great there apart from highway cruising), KYB Gas-A-Just shocks (after >202,000 km on originals)

  2. #2
    drink a beer, grow a beard, cut it, grind it, weld it back His Royal Ghostliness's Avatar
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    At 175k miles you're kinda due for inspections and likely rebuild - I've seen 8.8 axles with less miles that have their carriers slide sideways under load cause bearings wore out. A pattern check on the gears will tell you if the coast side is meshing looser/tighter than the drive side, but even so it should not cause a vibration - humming maybe, but no vibrations. Also typically the U-joints are a whole lot easier to damage with shock loads than gears are. I say start by dropping the driveshaft and checking the U-joints for play and/or stiffness. Go from there.
    The ones who accomplish true greatness, are the foolish who keep pressing onward.
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  3. #3
    GMN Regular DerekTheGreat's Avatar
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    I support the message of checking the U-joints, simple things first. Ashley's TC had a weird vibration above certain speeds and that's what it turned out to be.
    1985 LTD Crown Victoria - SOLD
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  4. #4
    I'm an air-conditioned gypsy gadget73's Avatar
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    yeah, U joints would also be my first guess. Not uncommon for them to get goofy and act up only loaded in one direction.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  5. #5
    No mean-spiritedness here. IPreferDIY's Avatar
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    I donít know much about U-joints yet, but itís nice to know it might be something relatively simple. From what Iíve read about diff internals, thatís really not something Iíd ever want to mess around with. (Itís still under 122,000 miles btw. ) I wonít be doing much driving over the winter (especially while worried about my timing chain tensioner stuff), so at least I can put it off until the spring. Many thanks for your input!!

    2000 Grand Marquis LS HPP, a hand-me-down in 2008 with 128,000 km; 175,000 km as of July 2014
    mods: air filter box "tuba" (in place of the "trumpet"), headlight relay harness, J-mod (around 186,350 km), 70mm throttle body, NKL4 PCM (from a 2000 CVPI, nothing great there apart from highway cruising), KYB Gas-A-Just shocks (after >202,000 km on originals)

  6. #6
    I'm an air-conditioned gypsy gadget73's Avatar
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    Pulling the axles for inspection is actually really simple. Outer bearings and seals are also easy. Those are really the only parts that typically wear. Where you get into fussy stuff is when you remove the carrier and change the gearing.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  7. #7
    drink a beer, grow a beard, cut it, grind it, weld it back His Royal Ghostliness's Avatar
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    Wouldn't even mess with the axle guts at this point, mileage is low enough (I saw the 175k but missed the KM behind that) to where there shouldn't be any issues inside yet. Stick with the U-joints for now, four 12-point 12-mm bolts hold the shaft to the axle - remove these and the driveshaft will easily slide out of the transmission tail-housing (may wanna have the car nose down ass up for this so fluid flows towards the front and doesn't leak out the rear hole when you pull the shaft out). Then you can wiggle the U-joints by hand, you should be able to feel which one is seizing up (feels very notchy/bumpy) or wearing out (feels very loose, even flops around with the sound of cow bell in more extreme cases), what you want is tight but smooth motion that doesn't require a lot of force. Replace as needed.
    The ones who accomplish true greatness, are the foolish who keep pressing onward.
    The ones who accomplish nothing, are the wise who know when to quit.

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    No mean-spiritedness here. IPreferDIY's Avatar
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    I'll be planning on changing both just to be done with it. With any luck, I'll be able to get an aluminum driveshaft to avoid rust issues in the future. Apparently I would only need to swap in my slip yoke on the front end and get the Fabtech spacer for the back end.

    2000 Grand Marquis LS HPP, a hand-me-down in 2008 with 128,000 km; 175,000 km as of July 2014
    mods: air filter box "tuba" (in place of the "trumpet"), headlight relay harness, J-mod (around 186,350 km), 70mm throttle body, NKL4 PCM (from a 2000 CVPI, nothing great there apart from highway cruising), KYB Gas-A-Just shocks (after >202,000 km on originals)

  9. #9
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    U-joints!

  10. #10
    No mean-spiritedness here. IPreferDIY's Avatar
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    It looks like the problem has largely resolved itself all on its own, though replacing the U-joints (preferably while swapping in an aluminum driveshaft) is still on my list of eventualities.

    2000 Grand Marquis LS HPP, a hand-me-down in 2008 with 128,000 km; 175,000 km as of July 2014
    mods: air filter box "tuba" (in place of the "trumpet"), headlight relay harness, J-mod (around 186,350 km), 70mm throttle body, NKL4 PCM (from a 2000 CVPI, nothing great there apart from highway cruising), KYB Gas-A-Just shocks (after >202,000 km on originals)

  11. #11
    drink a beer, grow a beard, cut it, grind it, weld it back His Royal Ghostliness's Avatar
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    I actually strongly dislike such self-resolving problems - mostly cause then I don't know if whatever was causing them has truly gone away for good, or is just lurking in there gathering strength and waiting for the right moment to come back with a vengeance. Therefore I suggest you still pull the shaft and inspect the joints, or you may be risking doing a transmission output shaft bushing and/or pinion seal well before you're ready for the aluminum shaft upgrade.
    The ones who accomplish true greatness, are the foolish who keep pressing onward.
    The ones who accomplish nothing, are the wise who know when to quit.

  12. #12
    I post a lot... knucklehead0202's Avatar
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    Quote Originally Posted by His Royal Ghostliness View Post
    I actually strongly dislike such self-resolving problems - mostly cause then I don't know if whatever was causing them has truly gone away for good, or is just lurking in there gathering strength and waiting for the right moment to come back with a vengeance. Therefore I suggest you still pull the shaft and inspect the joints, or you may be risking doing a transmission output shaft bushing and/or pinion seal well before you're ready for the aluminum shaft upgrade.
    This, totally. Shit that "fixes" itself has come back to kick me in the balls more times than not. Had some valvetrain noise in my HO that went away then killed my oil pressure when all the needle bearings from one of the roller lifters lodges themselves in various parts of the engine. Not cool.

  13. #13
    Wagon Addicted Tiggie's Avatar
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    Meh lost first year in the 88 for two weeks. Then it came back. That was 45k miles ago. Sometimes self healing is good.
    1988 Crown Vic Wagon - daily
    1990 Country Squire - weekend cruiser, former lawn ornament
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  14. #14
    drink a beer, grow a beard, cut it, grind it, weld it back His Royal Ghostliness's Avatar
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    Junk in the valve body is one thing. Loose/binding U-joints are completely different, especially once you get them spinning above 2000 RPMs. Heck I just replaced a pair of U-joints that run $50 a piece, and those shafts turn at quarter of the main driveline speed. High-speed rotational vibrations are not to be taken lightly, lots of shit can get damaged by it, not cheap to fix shit either.
    The ones who accomplish true greatness, are the foolish who keep pressing onward.
    The ones who accomplish nothing, are the wise who know when to quit.

  15. #15
    No mean-spiritedness here. IPreferDIY's Avatar
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    Yeah, good point. I was planning on crawling under my car for other stuff on Friday, so that would be the ideal time to check them. Are there special lube considerations for the slip yoke and seal? With non-automotive basic seals I've worked with in the past, I was told to put grease between the two lips. I know for the harmonic balancer seal, you're supposed to lube it when installing, but is it self-lubing after that? The one I got has a patterned surface on the inner lip, which I'm guessing is to allow oil to get in. For the slip yoke, I read something recently about some kind of special grease for the splines, but would that only be for an initial installation?

    2000 Grand Marquis LS HPP, a hand-me-down in 2008 with 128,000 km; 175,000 km as of July 2014
    mods: air filter box "tuba" (in place of the "trumpet"), headlight relay harness, J-mod (around 186,350 km), 70mm throttle body, NKL4 PCM (from a 2000 CVPI, nothing great there apart from highway cruising), KYB Gas-A-Just shocks (after >202,000 km on originals)

  16. #16
    drink a beer, grow a beard, cut it, grind it, weld it back His Royal Ghostliness's Avatar
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    Slip yoke splines need no grease, they will flood with transmission fluid quickly enough after you fire up the engine.

    Yes do use some grease on the seal between the two lips, really doesn't matter what kind it is as it's there just to make things slippery and all grease dissolves into transmission fluid eventually anyways.
    The ones who accomplish true greatness, are the foolish who keep pressing onward.
    The ones who accomplish nothing, are the wise who know when to quit.

  17. #17
    I'm an air-conditioned gypsy gadget73's Avatar
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    Just don't go nuts with the grease. You only need enough there to keep it slippery until a bit of trans oil works its way in there to keep it moving.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  18. #18
    No mean-spiritedness here. IPreferDIY's Avatar
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    I pulled the driveshaft last Friday and the U-joints seemed fine enough. They all had a full range of smooth movement with no hint of binding etc. There was at least one axis on one U-joint that had noticeably freer movement than others (I didn't keep track, but I'm pretty sure it was on the front end), but there wasn't any slop in it. My drive afterwards felt pretty much the same as after the problem largely corrected itself. By "largely" I mean I think I can detect a very brief and small amount of the curious vibration during transitions between powered and coasting movement, but I might be imagining things.

    Just before the problem largely corrected itself, my car had been sitting for many days, and the battery had been disconnected for some of those days (as a result of going to check my plugs and change boots before deciding to put it off until I do the tensioner stuff). I canít imagine that thereís a computer aspect to the curious vibration, but Iím far from being an expert.

    FWIW, I donít know how the pry bar on the diff end of the driveshaft trick is supposed to work, but what I ended up doing is putting two pry bars back to back so they served as each otherís fulcrum and then squeezed them together. It worked like a charm.

    2000 Grand Marquis LS HPP, a hand-me-down in 2008 with 128,000 km; 175,000 km as of July 2014
    mods: air filter box "tuba" (in place of the "trumpet"), headlight relay harness, J-mod (around 186,350 km), 70mm throttle body, NKL4 PCM (from a 2000 CVPI, nothing great there apart from highway cruising), KYB Gas-A-Just shocks (after >202,000 km on originals)

  19. #19
    drink a beer, grow a beard, cut it, grind it, weld it back His Royal Ghostliness's Avatar
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    Quote Originally Posted by IPreferDIY View Post
    FWIW, I don’t know how the pry bar on the diff end of the driveshaft trick is supposed to work, but what I ended up doing is putting two pry bars back to back so they served as each other’s fulcrum and then squeezed them together. It worked like a charm.
    WTF are you talking about? Xplain yoself pleez!
    The ones who accomplish true greatness, are the foolish who keep pressing onward.
    The ones who accomplish nothing, are the wise who know when to quit.

  20. #20
    No mean-spiritedness here. IPreferDIY's Avatar
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    I just picked a random photo from the internet (apparently from another type of car, ignore the arrows) to show the square slot (seen at the bottom) where people say to use a pry bar:

    Click image for larger version. 

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    I used two pry bars:

    Click image for larger version. 

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    Last edited by IPreferDIY; 11-21-2016 at 09:18 PM.

    2000 Grand Marquis LS HPP, a hand-me-down in 2008 with 128,000 km; 175,000 km as of July 2014
    mods: air filter box "tuba" (in place of the "trumpet"), headlight relay harness, J-mod (around 186,350 km), 70mm throttle body, NKL4 PCM (from a 2000 CVPI, nothing great there apart from highway cruising), KYB Gas-A-Just shocks (after >202,000 km on originals)

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