I was wondering if anyone could give me some kind of input on this. It seems almost whenever i back up (i say almost cause its not every time) theres this horribly loud grinding but its really low pitched.

I can't really feel it and its done this since i've had the car, I'm not sure if its brakes, suspension, or possibly diff although i'm kind of ruling that out because its sounds so open not like muffled at all.

Any way if anyone would have any suggestion that would be much appreciated.

 

i had a similar issue
turned out i got some grease on my rear rotors and didn't clean it off

when it rained it'd rust up, only made the noise when i reversed.

few seconds later went away.

take rims off spray the rotors with brake cleaner and see if it happens still.

 

If it's coming from your transmission, the noise is normal. The reverse gears are straight cut gears that whine and are louder than your forward helical cut gears. If it's extremely pitched enough to sound very odd and strange(annoying), then it's probably something else.

 

i'll def try the brake cleaner thing, cheap enough, and it does seem to happen more when its wet. Yarou, i'm not sure if it would be the trans cause it sounds more rear than that and its kind of sporatic.

 

same thing happens with me, but it also does it in first gear
It's like a grinding noise and trying to pop out of gear
Guess my transmission is messed up, SR20 here i come.

question:
Is the GReddy td06-20g turbo larger then the stock turbo on an s13 sr20?

 

your brake pads could also be rubbing if the retainer clips and damaged or missing. if this is the case there should be signs of uneven wear. pick up some disk quiet i think it's called while you're getting the brake cleaner.

 

yeah i should probably just replace the brakes anyway. Haha, when i first got the car i braked very quickly from about 90 to like 45, you know to test things out and since then have had some shimmy at higher speed braking, so knew rotors and pads are in the near future. hopefully that will fix things.

 

Could be:

Transmission - will no necessarily sound muffled
Differential - Under reverse load it pushes the bearing and the entire until in the oppsite direction which if worn or not clearanced correctly could cause a metal on metal grind. Saw this happen once with a slightly incorrectly shimmed diff
Bad carrier bearing or driveshaft - again, under reverse load, everything moves together differently and could be worn in a way that the reverse causes a grind
Brakes - Worn, rusty, or foreign object could make noise, but the noise would change as you touch the brake pedal

A way to test this would be to put the back of the car on jack stands securely. Have someone outside the car, but clear of it listening. Apply the parking brake about half way or until it has some grab on the brakes, but not enough to stop the wheels. Put it in reverse and get the wheels turning. Adjust the parking brake as required to put more or less load on it.

 

my parking brake doesn't work at all could that be whats making the noise whatever is broken is also making the noise?

 

The parking brake on a stock caliper 240 is basic...just squeezes the caliper, so if it breaks, it has no parts the touch anything moving. So no, that could not be it.

If the sound is pretty consistent in reverse, you may be able to do that test without the parking brake

 

mine did the same. when i swap my open diff for my vlsd yesterday, i had to take off the old diff cover so the new one can go on and when i took it off the diff looked like it had a chain saw takin to it. but my noise wasn't as low as your discribing mine was noticable almost everytime i backed up.

i know this may seem like a pain in the *** but you might want to check the diff.

 

yeah i could do that sometime, i was planning on welding the diff anyway so if it is the diff i can replace it with the one from my 90

 

back when my diff bearings were bad it used to clunk and grind while reversing. mabey you should look into that?

 

Hey, new to club240 threads. my 93 240sx fastback makes a grinding sound from the rear too. It's only Sometimes though. i could be in reverse, or in 1st with clutch in rolling backwards or in neutral rolling backward. doesn't matter any backward motion. but its only once in a while. i checked to make sure nothing was rubbing can't see any visual damage. Going to check the back brakes today. I herd it could be a wheel baring too.