A nice BANG under load...

[usafdarkhorse]

I've owned my 76 Z now for about a month and haven't driven it since about the 2nd day I've owned it due to fixing some issues that will make it a good daily driver.

However, while it's in the fix-it stage, I would like to get a question answered.

As I was driving it home ( and subsequently around the neighborhood once I got it home), I noticed a nice metallic BANG anytime I put a decent load on the car ( not full throttle...not even really quarter throttle).

I tried to see if I could replicate this by putting it into third gear and gently coercing the throttle to see at what point this BANG occurs. If I'm really gentle, it won't do it at all. When it does BANG, it's only one and it happens as soon as the load is applied. It sounds like I've got something loose up there that's whacking the bottom when the car hunches down to accelerate.

I found an exhaust hanger had broken, so I fixed it, but I haven't driven the car since fixing it.

It feels like somebody is hitting my car with a sledge hammer. I don't think it's suspension, but then again I'm a little new.

Any ideas?

[hd240z]

Check your differential mounts. If the front one is bad, the differential will jump up under load and hit the floor. The rear mounting bolts can also cause noises if they are loose.

Good Luck

[76Datsun280z]

Are you sure it's not a backfire?

[usafdarkhorse]

positive it's not a backfire, though I will check the differential mounts. It sounds very metallic.

[usafdarkhorse]

One thing I haven't thought about is if it does this only while moving or while both moving and static. So maybe I can put a little load on the car while it's sitting still and replicate it. Can I check it this way? Would the differential still jump in static?

[m4xwellmurd3r]

maybe an engine mount is bad? if one of those breaks, i'm sure you'd get a nice loud bang.

I know my diff needs new mounts. If i drop the clutch into gear i get a nice thunk from the diff shifting.

I know if you put a static load on it in gear, it SHOULD still shift. you won't get the bang, but you'll be able to see parts moving and such. It would be good to have a friend help ya with that. pop the hood open, put a GOOD set of wheel chucks in front of the wheels, and start loading it up to see if anything starts moving where it shouldn't.