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Thread: Rear end vibration....pinion bearing?

  1. #1
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    Default Rear end vibration....pinion bearing?

    Ok here comes the story. I'm getting a vibration from the rear end on my T-bird over 70 mph. It's been going on for a year or two but I had chalked it up to bad u joints and a out of balance drive shaft. The vibration feels like I'm driving over rumble strips on the pavement and vibrates the floor, seats, dash and steering wheel. How do I know it's not a front suspension issue? Well 1. The whole front end is less than a year old and 2. if I jack up the rear of the car and drive it to over 70 mph the sucker vibrates

    So since I know for sure that the rear is causing the vibration let me tell you what I've done to figure out that it's the rear end:

    1. I know it's not a wheel balance issue. The car vibrated with the old 8 holes as well as the Snowflakes it has now. Plus when I remove the rear wheels and just thread the lug nuts on to keep the drums on and drive it over 70 mph it still vibrates.

    2. I had the u-joints re-placed, the drive shaft balanced, and the tail shaft bushing in the trans re-placed this year. No difference in vibration.

    So I've spun the rear wheels and drive shaft by hand (with the trans in neutral) and everything seems to move freely with no noise. The axle bearings don't make any funny noises. Plus AFAIK the axle bearings won't cause a vibration. I doubt that it is a bent axle shaft because I would get some sort of vibration below 70 mph if it was. Also watching the wheels spin there is no wobble as far as I can see.

    I'm starting to suspect the pinion bearing or gears. The pinion has no up and down movement as far as I can tell (I move the whole rear end when I wiggle it ) but I can rock the drive shaft back and forth till it clunks slightly and starts to turn the rear. Also if I turn the rear wheels by hand the wheel I'm turning will start to move before the one opposite will. So any ideas?

    Also I just remembered that yes the engine is not the cause. I can rev it to 6000 rpm in park and it's smooth as glass. I'm pretty sure it's not a drive shaft issue either as it's speed sensative NOT RPM sensative. It will vibarte at 70 mph+ in both 3rd and OD.
    Last edited by thunderjet302; 07-11-2009 at 01:10 PM.
    '88 Thunderbird LX: 306, Edelbrock Performer heads, Comp 266HR cam, Edelbrock Performer RPM intake, Edelbrock 70mm TB, 76mm C&L MAF, 30lb injectors, 2.5" exhaust, AOD with 2800 PI converter, 8.8 with 3.73 gears, 31 spline Traction-Lok, 31 spline Moser axles, 04 Cobra front arms, Maximum Motorsports extreme duty rear arms, subframes.
    '11 Focus, '12 Mustang 3.7, '17 Accord EX-L V6

  2. #2
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    THAT is the issue I'm having !!!! Exactly.I also replaced the axle bearings and seals,same problem persists.
    '88 Sport--T-5,HURST shifter,Trick Flow R intake,Ed Curtis cam,Trick Flow heads,Scorpion rockers,75mm Accufab t-body,3G,mini starter,Taurus fan,BBK long tube headers,O/R H-Pipe, Flowamaster Super 44's, deep and deeper Cobra R wheels, Mass Air and 24's,8.8 with 3.73's,140 mph speedo,Mach 1 chin spoiler,SN-95 springs,CHE control arms,aluminum drive shaft and a lot more..

  3. #3
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    So we are both screwed

    I'm going to take the car to the guy who put the 3.73s in 6 years ago and see if he can figure it out. I bet it's the pinion bearing. I mean what the hell else could cause it?
    '88 Thunderbird LX: 306, Edelbrock Performer heads, Comp 266HR cam, Edelbrock Performer RPM intake, Edelbrock 70mm TB, 76mm C&L MAF, 30lb injectors, 2.5" exhaust, AOD with 2800 PI converter, 8.8 with 3.73 gears, 31 spline Traction-Lok, 31 spline Moser axles, 04 Cobra front arms, Maximum Motorsports extreme duty rear arms, subframes.
    '11 Focus, '12 Mustang 3.7, '17 Accord EX-L V6

  4. #4
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    My thoughts exactly.I also went through everything you spoke of.Baanced the driveshaft,new wheels and tires,balanced.new axle bearings,swapped the tranny,swapped the harmonic balancer,new clutch and flywheel,new tranny mount.It sucks.
    '88 Sport--T-5,HURST shifter,Trick Flow R intake,Ed Curtis cam,Trick Flow heads,Scorpion rockers,75mm Accufab t-body,3G,mini starter,Taurus fan,BBK long tube headers,O/R H-Pipe, Flowamaster Super 44's, deep and deeper Cobra R wheels, Mass Air and 24's,8.8 with 3.73's,140 mph speedo,Mach 1 chin spoiler,SN-95 springs,CHE control arms,aluminum drive shaft and a lot more..

  5. #5
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    Quote Originally Posted by thunderjet302 View Post
    I'm pretty sure it's not a drive shaft issue either as it's speed sensative NOT RPM sensative. It will vibarte at 70 mph+ in both 3rd and OD.
    An out of balance driveshaft issue WILL be speed sensitive not RPM sensitive. Regardless of engine speed, driveshaft speed continually increases with vehicle speed.

    I also, am experiencing a similar problem...although, mine doesn't sound nearly as bad as yours. When I swapped the 2.73 7.5 out for my 3.73 8.8, it continued to happen right around 70mph...I think I may just have had some wheel weights come off.

    Good luck,
    Don
    Project 3G: Grandpa Grocery Getter-'85 Crown Vic LTD 2-door, 351W with heavily ported/polished GT40 heads, heavily ported/polished Typhoon Power Plus upper & lower intake, Comp Cams 265DEH retarded 1*, FAST EZ-EFI, HD T5, 8.8" 3.73 trac lock with extra clutches, 3G alt. swap, '99 CVPI front brakes, '09 CVPI rear disc brakes, '00 CVPI booster&m/c + wilwood adj prop valve.

    Parted & Gone-'88 T-bird Sport, 351W swap, ported GT40 heads

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    True but the vibration always occurs above 70 mph, either in 3rd or 4th gear. The thing is the drive shaft is spinning much faster at 70 mph in 3rd than 4th. However the rear wheels/rear end are turning about the same speed in either 3rd or 4th gear at 70 mph, making me think it's a rear end issue. As I said I know it's not the wheels as it will still vibrate with the wheels off at 70 mph.
    '88 Thunderbird LX: 306, Edelbrock Performer heads, Comp 266HR cam, Edelbrock Performer RPM intake, Edelbrock 70mm TB, 76mm C&L MAF, 30lb injectors, 2.5" exhaust, AOD with 2800 PI converter, 8.8 with 3.73 gears, 31 spline Traction-Lok, 31 spline Moser axles, 04 Cobra front arms, Maximum Motorsports extreme duty rear arms, subframes.
    '11 Focus, '12 Mustang 3.7, '17 Accord EX-L V6

  7. #7
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    Quote Originally Posted by thunderjet302 View Post
    ...The thing is the drive shaft is spinning much faster at 70 mph in 3rd than 4th. However the rear wheels/rear end are turning about the same speed in either 3rd or 4th gear at 70 mph...
    The difference in 3rd and 4th gear is input shaft speed...not output shaft speed or driveshaft speed. If the driveshaft were spinning much faster in 3rd than 4th, then vehicle speed would be higher. Driveshaft, pinion, differential, axle and wheel speed are all directly related to vehicle speed, not RPM. That's why a bad u-joint (just like a hub bearing) will get worse the faster you go, regardless of engine RPM.

    Example, wheel speed is 70mph (gear selection is irrelevant), axles are turning the same speed, differential is turning the same speed. Assuming a 3.73 gear ratio, the pinion gear is turning 3.73 times faster than the differential/axles. The pinion gear has a flange on it which the driveshaft is bolted to. Do you see how engine speed does nothing to affect driveshaft speed while maintaining a constant vehicle speed? There is nothing between the tires and the driveshaft to allow it to increase or decrease speed independently of the vehicle speed.

    Good luck,
    Don
    Project 3G: Grandpa Grocery Getter-'85 Crown Vic LTD 2-door, 351W with heavily ported/polished GT40 heads, heavily ported/polished Typhoon Power Plus upper & lower intake, Comp Cams 265DEH retarded 1*, FAST EZ-EFI, HD T5, 8.8" 3.73 trac lock with extra clutches, 3G alt. swap, '99 CVPI front brakes, '09 CVPI rear disc brakes, '00 CVPI booster&m/c + wilwood adj prop valve.

    Parted & Gone-'88 T-bird Sport, 351W swap, ported GT40 heads

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    Ok after reading what I wrote I worded it all wrong. What I meant to say is that in 3rd or 4th (or any gear) the driveshaft and pinion are turning faster than the axles. Being that the drive shaft is balanced (it was balanced up to 4500 rpms) I'm fairly sure that the vibration has to be a rear end problem, speciffically the pinion bearing. The only thing in the rear that can cause a vibration like I'm feeling is the pinion bearing, unless the gear set is screwed, which I highly doubt.

    I'm taking the car over to the guy who did the rear end a week from today. He's going to look it over and if everything checks out I'm back to the drive shaft. If it's the shaft fugg it I'm getting another one and having the new one balanced.
    '88 Thunderbird LX: 306, Edelbrock Performer heads, Comp 266HR cam, Edelbrock Performer RPM intake, Edelbrock 70mm TB, 76mm C&L MAF, 30lb injectors, 2.5" exhaust, AOD with 2800 PI converter, 8.8 with 3.73 gears, 31 spline Traction-Lok, 31 spline Moser axles, 04 Cobra front arms, Maximum Motorsports extreme duty rear arms, subframes.
    '11 Focus, '12 Mustang 3.7, '17 Accord EX-L V6

  9. #9
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    Let me know what you find out.
    '88 Sport--T-5,HURST shifter,Trick Flow R intake,Ed Curtis cam,Trick Flow heads,Scorpion rockers,75mm Accufab t-body,3G,mini starter,Taurus fan,BBK long tube headers,O/R H-Pipe, Flowamaster Super 44's, deep and deeper Cobra R wheels, Mass Air and 24's,8.8 with 3.73's,140 mph speedo,Mach 1 chin spoiler,SN-95 springs,CHE control arms,aluminum drive shaft and a lot more..

  10. #10
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    Error in communication...lol. Personally, I wouldn't think it would be a pinion bearing...That thing should make a lot of noise if it's loose enough to do that...and if the gear set isn't just right, it'll whine...usually there are some warning sounds that the rear will make before something gets loose enough to do that.

    Best of luck, hope you get it figured out!

    -Don
    Project 3G: Grandpa Grocery Getter-'85 Crown Vic LTD 2-door, 351W with heavily ported/polished GT40 heads, heavily ported/polished Typhoon Power Plus upper & lower intake, Comp Cams 265DEH retarded 1*, FAST EZ-EFI, HD T5, 8.8" 3.73 trac lock with extra clutches, 3G alt. swap, '99 CVPI front brakes, '09 CVPI rear disc brakes, '00 CVPI booster&m/c + wilwood adj prop valve.

    Parted & Gone-'88 T-bird Sport, 351W swap, ported GT40 heads

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