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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?
mods:
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
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.
__________________ 99 NBM TransAm M6.
Typhoon 85/85, SLP Lid, SLP 85mm MAF, SLP 25% underdrive, $80 shorty's, MAC ORY, SLP LM2.
UMI 2pt Weld-in SFC's. UMI upper and lower CM adjustable A-Arms. UMI Panhard relocation. UMI adjustable Panhard bar. UMI adjustable CM rear trailing arms. UMI 35mm front bar and 22mm rear bar. Srano's on SLP Bilstein shocks.
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.
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?)
__________________ 99 NBM TransAm M6.
Typhoon 85/85, SLP Lid, SLP 85mm MAF, SLP 25% underdrive, $80 shorty's, MAC ORY, SLP LM2.
UMI 2pt Weld-in SFC's. UMI upper and lower CM adjustable A-Arms. UMI Panhard relocation. UMI adjustable Panhard bar. UMI adjustable CM rear trailing arms. UMI 35mm front bar and 22mm rear bar. Srano's on SLP Bilstein shocks.
Last edited by Breathing Fire; 01-23-2010 at 07:57 PM..
Reason: more info
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??
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!
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.
Quote:
Originally Posted by badss_02
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!
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.
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.
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.
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
loud banging sound under the car?? 
