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LT1-LT4 Modifications
1993-97 Gen II Small Block V8

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Old 01-23-2010, 07:45 PM   #1
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Default loud banging sound under the car??

When ever i get on the gas fairly hard in a low gear like from a stop or something there is a lound banging sound underneath the car. It also feels like what ever is making the sound is hitting the floor. I cant pinpoint where the sound is exactly but it sounds like on the drivers side. It really only does it when the car squats. If im already cruising and i put it to the floor it doesnt do it...any ideas?

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poly trans mount
pacesetter longtubes, catted y, magnaflow catback
all stock suspension except for a solid panhard bar. (not sure of brand)
K&N intake, which i want to get rid of
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Old 01-23-2010, 07:47 PM   #2
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My guess would be the tranny mount. Comes loose and the tranny hits the tunnel. Does the stick come up when you gun it at low speeds? If so the mount is the problem.
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Old 01-23-2010, 07:51 PM   #3
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the trans dipstick? doesnt it have a lock on it so it cant come off of the tube?

but no i do not believe it comes out of the filler tube at all.
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Old 01-23-2010, 07:53 PM   #4
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My guess, but I could be wrong, is a broken motor mount. letting the motor raise up and causing the exhaust to hit the floor. if you can hold on the brake and put a load on the motor in gear alittle, you can see if the motor raises up more then normal... just a guess.
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Old 01-23-2010, 07:53 PM   #5
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A buddy of mine had a 97 TA that done the same thing, i want to say he found out that the drive shaft was hitting under there some how.
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Old 01-23-2010, 07:55 PM   #6
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Sorry man I mean the shifter. However where you are an auto it won't move anyway. I think you will just have to take it out and make sure it is ok. One of the bolts may have come loose or it might have some other issue. I have never used a poly mount, but when my mount went bad once it caused the tranny to hit the tunnel. My mount actually ripped in half. I suppose you could look and see if there are signs of contact in the tunnel. BlackGTO might be right too. Think is if it moves that much you will leak fluid too as it will damage the little rubber seal where the driveline goes in. (whatever that is called?)
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Last edited by Breathing Fire; 01-23-2010 at 07:57 PM.. Reason: more info
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Old 01-23-2010, 07:57 PM   #7
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Quote:
Originally Posted by Quick_Z View Post
A buddy of mine had a 97 TA that done the same thing, i want to say he found out that the drive shaft was hitting under there some how.
that is what i was thinking since i first noticed it. but what would cause a driveshaft to move like that? u joint?
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Old 01-23-2010, 07:59 PM   #8
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Quote:
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Sorry man I mean the shifter. However where you are an auto it won't move anyway. I think you will just have to take it out and make sure it is ok. One of the bolts may have come loose or it might have some other issue. I have never used a poly mount, but when my mount went bad once it caused the tranny to hit the tunnel. My mount actually ripped in half. I suppose you could look and see if there are signs of contact in the tunnel. BlackGTO might be right too. Think is if it moves that much you will leak fluid too as it will damage the little rubber seal where the driveline goes in. (whatever that is called?)
That is possible as well. but i thought that the poly mount was the repair for the stock rubber mount that is notorious for tearing??
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Old 01-23-2010, 07:59 PM   #9
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Make sure you didn't break the torque arm where it mounts up to the rear... A lot of times that will cause your pinion angle to change aggressively under accel and decel (especially breaking) causing your driveshaft u-joint ears to bind up against the pinion u-joint ears. I almost guarantee you that is your problem!
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Old 01-23-2010, 07:59 PM   #10
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Quote:
Originally Posted by 06blackGTO View Post
My guess, but I could be wrong, is a broken motor mount. letting the motor raise up and causing the exhaust to hit the floor. if you can hold on the brake and put a load on the motor in gear alittle, you can see if the motor raises up more then normal... just a guess.
Thats a good idea i should go out and stall it up and see if it does it.

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Make sure you didn't break the torque arm where it mounts up to the rear... A lot of times that will cause your pinion angle to change aggressively under accel and decel (especially breaking) causing your driveshaft u-joint ears to bind up against the pinion u-joint ears. I almost guarantee you that is your problem!
Very possible!! Ill look into that!!
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Old 01-23-2010, 08:02 PM   #11
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Also have someone look at the tranny and driveshaft if you can swing it and see what is moving. Something is giving more than it should.
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Old 01-23-2010, 08:08 PM   #12
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I want to lean twoards something with the driveshaft. Even when im cruising on the highway it seems to have a slight drivetrain vibration. I almost want to throw in an ls1 driveshaft and see if it smooths out. (i have an ls1 driveshaft laying around that came out of a 6spd car. I read that it should work). Either way i gotta figure it out soon because it seems pretty violent and i dont need to break anything major right now being its my daily.
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Old 01-23-2010, 08:16 PM   #13
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Quote:
Originally Posted by twokss View Post
that is what i was thinking since i first noticed it. but what would cause a driveshaft to move like that? u joint?
The only thing we could think of is the rear end was twisting upward under acceleration, he still had all factor suspension and figured the LCA bushings were shot among other things, might can put it on some jack stands, and look above the drive shaft where the trans tunnel runs and see if it has been rubbing anywhere.
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Old 01-23-2010, 08:26 PM   #14
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Long tube headers, by any chance? A soft motor mount insert (failing/failed) will let the left side collector telegraph on the floorpan 3-5 times as torque is applied under acceleration from a stop. Happened to me. I thought the trans mount was busted after all my upgrades. It was fine but I replaced it anyway since the Energy Suspension mount is like $22.00. Also did the torque arm bushing at the same time (also ES). The actual problem was the left side motor mount and I couldn't see the failure until I got the insert out of the clamshell (pair of Prothanes for those). Pacesetter LTs like mine are really close to the floor already for clearance. I guess most LTs are going to be close. Slip fit are less likely since there's no flange. My exhaust guy is a huge fan of putting tricorner flanges on everything. Only thing I wish had been different, but it's all happy now anyway with the new MM inserts.
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Old 01-23-2010, 08:39 PM   #15
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yea it has pacesetter longtubes. i have off from work monday so im sure most of my day will be under the car checking over everthing that was suggested above
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Old 01-23-2010, 08:39 PM   #16
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Its a transmission mount, look for the polished mark on the trans tunnel from the driveshaft.
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Old 01-23-2010, 08:41 PM   #17
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Quote:
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Its a transmission mount, look for the polished mark on the trans tunnel from the driveshaft.
will do
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Old 01-23-2010, 08:44 PM   #18
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torque ARM>>>>>>>>>>>>>>>>>>>>>>>>>>>
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Old 01-23-2010, 08:52 PM   #19
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Scratches on the floorpan just above the left side collector will be a dead giveaway if that's it.
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Old 01-23-2010, 08:59 PM   #20
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i lost a torque arm bolt where it mounts to the transmission and did the exact same thing you are describing.
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Old 01-23-2010, 08:59 PM
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banging, car, care, diff, drive, engine, exhaust, hammering, load, loud, ls1, lt1, mount, rear, sound, stop, transmission


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