Vibration off start? - Vintage Mustang Forums
 
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post #1 of 11 (permalink) Old 11-11-2012, 12:36 PM Thread Starter
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Vibration off start?

so im still rebuilding my 69 mach 1 351w. i replaced the u joints last week. when i start out going forward or reverse i get a load bagging sound. i was thinking it was comming from the drive shaft so thats why i replaced the ujoints. is there anything else it could be? im running out of ideas. anything will help thanks!
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post #2 of 11 (permalink) Old 11-11-2012, 02:14 PM
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a loud banging sound you mean??

auto or standard?

I would start by jack it up from the pumpkin, put it safely on jack stands on a cement floor with the exhaust pointed toward the door. Block the front wheels, put in neutral and spin the rear wheels by hand. If that seems fine in both directions start it up, put it in gear and slowly let off the brake. It could be a hung up rear brake shoe or ebrake cable would be my first guess if it's been sitting.


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post #3 of 11 (permalink) Old 11-11-2012, 03:27 PM
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Driver's side motor mount. Get a helper, open the hood. Lightly power brake and watch the engine lift up...
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post #4 of 11 (permalink) Old 11-13-2012, 12:00 PM Thread Starter
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So i jacked the car up yesterday and turn the car on. When i put the car in first and reverse it made the same bagging sound. so i took the tires and drums off and started the car again. no banging. its a standard. im gonna put the tires back on today and see if it still makes the same sound. maybe the drum was just hung up. its been sitting for the last 30 years
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post #5 of 11 (permalink) Old 11-13-2012, 02:31 PM
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Is there oil or grease on the brake linings? There shouldn't be, if there is try to clean them with some kind of brake cleaner. Keep us posted.
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post #6 of 11 (permalink) Old 11-15-2012, 01:23 PM Thread Starter
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when i put the car on the ground and put it in gear, bang bang bang same noise. a guy at work was saying to jack it back up and put ur hand on the rear end with someone inside the car and see if you can feel the bang coming from the rear end? could it just be low fluid or just oil fluid. but once i start moving something bangs aroudn untill you get past like 4-5 mph the noise goes away. also if you rev it up higher than normal when starting out it helps with the nosie.
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post #7 of 11 (permalink) Old 11-15-2012, 07:01 PM
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If you have toasted rear springs and the *** end is sitting on the ground, the torque windup on the rear end will lift up the front of the housing and bang the pinion snubber against the floor. It will sound like someone is thumping with a rubber mallet and it increases with the speed.



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post #8 of 11 (permalink) Old 11-15-2012, 07:42 PM
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What bartl says is surely possible... it even did it in the air until you took the wheels and drums off. Assuming everything looked good in there the simple weight off the wheels was enough for it to do it again... So it is pretty bad. While you could Cut a 2x4 and jam it above the snubber...see if the noise is gone this wont pinpoint the exact problem. likely your springs are wasted but also there Could be no bushings left in the front eyes of the rear springs, the centering pins could be completely gone or you could have loose or broken ubolts as well. All of this needs to be looked at.


...FRH

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post #9 of 11 (permalink) Old 11-16-2012, 12:27 PM Thread Starter
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I replaced the u joints a few weeks ago and same thing. So you guys are saying the shocks are bad and when the driveshaft spins its hitting on the floor pan? illl have to have someone hit the gas while i look under there and hopefully see something going on.
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post #10 of 11 (permalink) Old 11-19-2012, 10:31 PM Thread Starter
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it seems to be louder when i put the car in reverse and start to move back. it sounds like someone is banging on the bottom of the car. i noticed the shocks in the back are midis, i wonder if i can get a lifetime warranty out of them
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post #11 of 11 (permalink) Old 11-20-2012, 01:34 AM
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Check your transmission mount to make sure it's not broken and exhaust all the way back to make sure it's not hitting anywhere.


Mildly built 302, 4 speed, 3.40 gears. 6 pt. cage.
Narrow rear. Pro-Stars-15X7'' & 15X10'' on rear.
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