Terrible Scrape/Shuffle Noise

tk · Postby tk » Tue Dec 20, 2016 10:34 pm

So today I picked up my first MX5, a 1990 NA with 380,000 km on the odo. It was cheap, thankfully.

Engine pulled hard, gears felt sweet and all that.

Driving it home, all good. Doing 100 km/h on the freeway. Decide to try coasting since this car's got no power steering so what's the harm? I switch the engine off. I think I put it in neutral first, of course. I think. Anyway, all fine, I coast for a bit downhill. Start car back up (with starter motor), shift back into gear. Start noticing this weird scrapey & shuffly noise when the car's in gear, especially when coming off the throttle. Engine sounds fine when revved in neutral and the sound definitely sounds like it's coming from the transmission.

Did I somehow wreck the clutch or cause the flywheel to unbolt itself or something? Noise is worse in 4th but there in all gears. Especially weird grindy noises when coming off throttle in fourth at say, 40km/h or so. Have searched and there's threads about shielding coming loose or stuff but I really am worried it's a transmission thing. Video below.
https://www.youtube.com/watch?v=DzmBBWNTRr0
Any help greatly appreciated.

smy0003 · Postby **smy0003** » Wed Dec 21, 2016 6:13 am

Why would you turn the engine off while driving on a public road? The ECU cuts fuel when off throttle in overrun.

My guess is the diff, na6 diffs are as weak as American coffee.

Almost every NA/NB has some mechical 'grinding' noise when coming off the throttle. There's no sound deadening to hide the sounds of the parts (box and diff) working so it may just be normal noise.

EDIT: watched the video, that's beyond normal levels of noise.
Sent from my LG-H815

tk · Postby tk » Wed Dec 21, 2016 7:31 am

Yeah it was dumb.

Don't reckon it's difficult just cause the sound is coming from the transmission tunnel area towards the front, not the rear.

Gonna take it to a mechanic I reckon. I normally do all my own work but I just spent 3 weeks working on my other ride and I'm a bit done.

jordan.k · Postby **jordan.k** » Wed Dec 21, 2016 7:34 am

Im going to say it's the diff,

My na6 had this noise for a while until the diff exploded and I upgraded to an nb diff.

Made the exact same metal on metal grinding on deceleration, sounded like its coming from the gearbox but it was the diff.

tk · Postby tk » Wed Dec 21, 2016 9:18 am

jordan.k wrote:Im going to say it's the diff,

My na6 had this noise for a while until the diff exploded and I upgraded to an nb diff.

Made the exact same metal on metal grinding on deceleration, sounded like its coming from the gearbox but it was the diff.

I see. I'd heard people on other forums saying similar things, that due to the hole in the transmission tunnel, it sounds like the gearbox but it's actually the diff. Time to start parts hunting I guess.

mattyredlocks · Postby **mattyredlocks** » Thu Dec 22, 2016 3:50 pm

Just drive it till it stops, then it'll be really easy to work it out.

Seriously though, probably the diff. They make a bit of noise when they're nearly dead. Buy an NB one (and half shafts!), do a skid, pop the old one, put the new one in.

Then do another skid, but this time it won't pop.

tk · Postby tk » Fri Dec 23, 2016 10:21 pm

mattyredlocks wrote:Just drive it till it stops, then it'll be really easy to work it out.

Hahaha. I like this method of troubleshooting. Though I am worried that if I keep driving it I'll damage more parts than I can afford to replace.

I do wanna upgrade to a 1.8 LSD at some point down the road anyway. Might have to start saving pennies a little faster.