Knocking In The Rear End!

Discussion in 'SN95 4.6L Mustang Tech' started by purpstang, Aug 14, 2014.

  1. purpstang

    purpstang New Member

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    Hi guys, i actually have two issue first.. if i let the clutch out to hard or jerk the car hard it sounds like a loud knock coming from the rear end.. anyone ever have the same problem and know what this could be? Also my stang was sitting for a good 6-7 months and ran completely fine before besides the knock..when i went to crank her over she didnt start i assumed it was the battery and i was right the battery was completely dead so i jumped it to try n charge the battery but after 15 mins or so she just shut off. And all the gages were reading correct nothing seemed wrong.. does anyone have any insight on what this could be??
     
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  2. 1987stangman

    1987stangman Member

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    As far as the car shutting off is concerned your going to have to check out the cars charging system. Start with the simple things first like the battery cable and terminal connectors. They can corrode quickly if the car sat for an extended period. If that checks out then get the battery checked and make sure it is good. If it is your going to need to make sure the alternator is doing its job by using a DVOM at idle or by having it checked as well. I would pull it out and take it to your local auto parts jobber. If a faulty battery,alternator, or other charging system issues exists our Mustangs will not run and you will get the symptoms you have described.

    As for the rear end. Since it sat up for a while make sure no fluid escaped from the differential. Prob not but it's a good idea to check it. You didn't say what year your car is or how many miles but over the years there are people that have had issues with the factory diff going bad and needed to be rebuilt.

    This should get you started. Let us know what you find.
     
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  3. purpstang

    purpstang New Member

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    Is a 96 gt with about 135000 on the body n newer motor wit h about 75-80k on it the rear was swapped with the 4.10 gears im not sure about the diffeer.. i know the abs sensors need to be changed but i dont think thats whats making the noise. It almost sounds like the exhaust is hittin the axel but i looked underneathe everything looked ok
     
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  4. StarbuckSapien

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    I might be worth checking to see if there is any play in the u-joint or the yoke for the axle. Car's not old enough for that, but a u-joint coming apart can make your day interesting. You didn't give much explanation for the knock. The Car Talk guys would tell you to make the noise. Is it regular? Does the frequency/volume increase with speed?
     
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  5. purpstang

    purpstang New Member

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    The frequency is only when the car jerks hard from the gear to the next..same volume of the knock everytime n the pitch is not super low but is by no means high on a scale of 1-10 1 being high 10 being low pitch its about a 6.5 ish ...it almost sounds like the exhaust hits the axle but i checked it n the exhause is nice n tight.. im goin to check the u joints tomorrow.. i doubt thats the problem but you never know..
     
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  6. StarbuckSapien

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    I think the u-joint might sound more like hitting metal with a hammer. But it would coincide nicely with changing gears. It might be worth checking for a broken spring, while you're down there. Or possibly worn out spring isolators. I'm just guessing based on the sound you described, though.
     
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  7. purpstang

    purpstang New Member

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    Im leaning more towards the u-joints or maybe the spring isolator.. buti just replaced the shocks and springs all around so im sure they had to do the isolators also.. maybe not ill check them out..
     
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  8. StarbuckSapien

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    If you just put in springs I'd be very surprised if they didn't come with new isolators, so I'd say that's unlikely. It's possible the installer didn't button something up properly (I've done that before) but you probably would have noticed that right after the install.
     
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  9. purpstang

    purpstang New Member

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    I literally got them done and drove it for maybe 5 days and then it sat from the middle of september til now.. so maybe i havent noticed if they didnt button it up correctly .. but they r usually good with it so im gonna check it out anyway n the u joints.. are u joints expensive to replace?
     
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  10. StarbuckSapien

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    It's been a very long time since I was involved in a u-joint replacement and it wasn't for a Mustang. As I remember it was helpful having 2 sets of hands because of needle bearings that tended to fall apart (and all over the ground). American Muscle carries one for $50 (as of right now) and they classify replacement difficulty as "hard". I don't know how much someone would charge to do it for you, but a reviewer on AM said $63 for their pro install. Anyway - that all may not be much use if there is no play in the thing when you get under the car.
     
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