Loud banging noise underneath car

[grandpa_spec_F6]

God this is getting old... I've had the car on the road a week (I know i've been slack with the how-to guide for the IRS, busy with uni etc) and now this loud HORRID banging noise is coming from underneath the car.

I thought it might be the handbrake which hasn't been adjusted yet but even with the handbrake on its still there.

Pulled the wheels off and checked all the screws were still holding true which they were. Tyre pressure seems fine etc, the car drives fine (which weirds me out considering how awful the noise is) and it seems to happen more so when going downhill without much power going to the accelerator.

I know its a hard ask when no one can hear the sounds but its this intermittent banging sound, like gears arnt meshing properly or there isnt enough oil somewhere, any idea?

[CAT600]

First up is to check the exhaust system, a broken mount can do exactly what you describe

The next thing to check is driveline/halfshaft fidelity. You had the wheel bearings apart lately ya? I suggest this as you have described an overrun situation down the hill and the backlash may be making the sound worse.

After that it might be time to back it on a dyno and have a look under while the car is running up.

Daniel

[Mr Hardware]

oh man grandpa_spec, the old ghia-saurus just isn't behaving itself is it.

[frd906]

if its auto, check the back of the gear box and make sure the rear main seal hasnt gone, becuase if it has its the shaft witch is hitting the side of the extension housing causing the loud noise in side the housing and flapping around, did the same with with mine,

[grandpa_spec_F6]

Originally Posted by CAT600

The next thing to check is driveline/halfshaft fidelity. You had the wheel bearings apart lately ya? I suggest this as you have described an overrun situation down the hill and the backlash may be making the sound worse.

Daniel

I might take it to a mechanic as I have no clue how to check any of that, the exhaust seems solid as a rock, it barely moves. I've got a dyno place down the road but I don't know if they are any good.

[51OAU]

sounds like my problem aswell, mine does it only under load, ive removed my whole diff and had it sent away to be pulled apart, hoping to find something. If there is nothing wrong with the diff im gonna be spewing cause its gonna cost me a load of money.

[grandpa_spec_F6]

Well i've taken it to the mechanics who is going to go over the car with a fine tooth comb, im seeing him tomorrow afternoon so hopefully the results will be good

I relayed all the info from on here to him and he seemed to agree that they could most likely the cause so once again, thanks guys! your knowledge astounds me.

I've got him to do a transmission service, fit the slotted rotors i've got (im lazy), adjust handbrake and obviously, find out what that awful knocking sound is.... shall get back to you all with the results!

[GK]

Originally Posted by grandpa_spec_au

Well i've taken it to the mechanics who is going to go over the car with a fine tooth comb, im seeing him tomorrow afternoon so hopefully the results will be good

I relayed all the info from on here to him and he seemed to agree that they could most likely the cause so once again, thanks guys! your knowledge astounds me.

I've got him to do a transmission service, fit the slotted rotors i've got (im lazy), adjust handbrake and obviously, find out what that awful knocking sound is.... shall get back to you all with the results!

Hope it works out okay, and relatively cheap also!

GK

[grandpa_spec_F6]

Ok well he's just phoned me... feeling like a bit of a fool :

I'd only tightened up one of the caliper bolts properly apparently and the other one had come loose and fallen off! So my caliper was hanging there knocking about against the rotor. I checked every other bloody bolt down there except the caliper ones that that would explain the noise.

While its up on the hoist i've got him to do a transmission service including new filter etc, put the rotors on, service the calipers i.e. graphite them up so they dont stick, and adjust the handbrake, so all up including labor for everything he's put it square at $400

Very relieved it wasn't the transmission that had gone I have to say!

Thanks for all your help again people

[klawsterfobik]

I was going to suggest Road Side Collectors, or possibly a neighbours cat.

Glad to hear that you've found the problem no worries.

[GK]

Glad you got it all sorted.

GK

[grandpa_spec_F6]

Well hopefully once tax is back i'll look into a set of rims and lower her a bit, as much as I love her its no fun cornering an ocean liner :(

Once again thanks for all the help guys!