- My model of MX-5 is: 2007 NC Sport
- I’m based near: Guildford/ Farnham
- I’m looking for technical help or recommendations on: NC
Evening everyone
Looking for some help on some noises my NC has started making today.
Engine sounds like it’s rattling to me but I’m not sure if it’s something like a knock or if it’s just classic fuel injector noise. Read a lot about the tensioner and idler pulleys starting to fail which can cause a slight ticking noise. Will check that out this weekend but until then can you take a look at the videos?
Last thing is when I’m actually driving I can hear some sort of grinding from the rear. At first I thought it might just be road noise as I hear the drains can get stuck open. But now I’m thinking it’s the diff or driveshafts. Don’t think it’s the transmission.
Seems to only happen when slowing down no braking just foot off the accelerator. Uploaded another video. Apologies it’s not the best quality but I think you should be able to hear what I can hear.
Any help would be really appreciated.
Hi, hope I can be of some help.
The first video I hear nothing but a smooth, quiet engine. Wish mine was that quiet! I can hear the rhythmic injector tick (slight fast metallic pingy noises - normal) but nothing else, at least on my phone speaker. My car had all its pulleys failing basically - it would randomly and very loudly rattle and ping away at idle, sometimes only when moving the wheel or revving slightly.
2nd video is more interesting - I have had this exact same noise. It should be when accelerating or decelerating, maybe most in low gears? It’s likely the PPF alignment.
If you don’t know, the PPF (power plant frame) is an aluminium girder-looking bar that rigidly joins the gearbox and differential. The entire drivetrain is connected and suspended from just engine and diff mounts.
However, if your gearbox has ever been off (clutch change?), most independent garages won’t know you’ve got to put the PPF back and align the height of the gearbox relative to the chassis braces before tightening up the nuts. It’s roughly 31mm above the X-brace if I remember correctly, numbers are quite easy to find.
I’ve had the same PPF grindy noise since I had my car (140,000 miles then, changed my clutch at 150k) and nothing I do will get rid of it. My car appeared to have an original clutch even, and I still had this noise (although quiet). I wonder if having it misaligned causes permanent wear on some internal gearbox bearings or something and a refresh/rebuild of GB/diff is needed. Maybe it’s just old and worn mounts? I hope so, for my case at least.
If you’ve got a jack, axle stands and torque wrench have a read on PPF alignment, shouldn’t take you an hour unless you’ve not been under a car much, rather simple procedure.
Bit long-winded but hopefully someone can benefit.
Good luck with your issue.
There is a known problem with the NC differential in earlier year models:
The most common issue with the MK3 Mazda MX-5 (NC) rear differential is a loud whining noise, often described as a “whine” or “grumbling”. This is usually caused by wear and tear on the worm gearwheels within the differential. A differential oil change can sometimes help, but in many cases, replacing the differential is the best solution, according to Haynes manuals.
Elaboration:
Many MK3 MX-5 owners report a loud, persistent whining noise coming from the rear of the car, especially when accelerating or under load.
The problem is often traced to worn-out worm gearwheels inside the differential, which are responsible for distributing power to the wheels.
While a differential oil change might temporarily alleviate the noise in some cases, it’s often not a long-term solution, according to MX-5 Owners Club Forum.
- Differential Replacement:
The most reliable fix for a whining rear differential is to replace the entire unit with a new one.
In addition to the whining noise, other symptoms of a failing differential can include vibrations, grinding or clicking noises, difficulty steering, oil leaks, and excessive tire wear.
Adding to this ^ apparently Mazda managed to leave some lapping compound on the gears inside the diff, and sent them out to be sold like that. Rather funny mistake, but usually if a diff oil change doesn’t solve (and it was caused by this issue) then the gears are already worn.
Diff oil is quite easy to change but you need some huge sockets (24mm if I remember) so short of buying another LSD (5-speed one is crazy money now as people like me want to swap them into 6-speed cars) this is a cheap/easy way to start.
Thank you so much for taking the time to write all of this out, it is really appreciated!
Good to know the engine sounds okay, I got this car coming from a 1.4 polo and as it’s my dream car anything that sounds a bit off instantly gets me worrying. Good to know it’s all sounding normal though.
It’s exactly as you’re describing it, 1st to 3rd gear up to about 40mph, mainly deceleration but also when accelerating especially if I really put my foot down. I can’t say I’ve heard of the PPF until now so that’s really useful thank you.
I got the car in January and it did have a new clutch put in before I got it, how long ago I can’t quite remember. So I’m assuming it’s like you’ve said they used an independent and just didn’t align it properly when rebuilding. I’ve got a jack, a pair of stands and some hand tools and torque wrenches. I’m fairly mechanical so I’ll take a stab at it myself this weekend. Doesn’t look too difficult to do but I said the same when replacing my coolant hoses…
Will probably also change the diff oil while I’m under there anyway too. At least I know it’s done then!
Thank you again for the really detailed reply it’s much appreciated. I’ll come back with an update once I’ve given it a go!
No worries at all - I’m new to the whole forum thing, glad I can help someone!
I’d just recommend watching a couple videos and finding the Mazda service manual for the torque and height specs. All MX-5 generations use the same method more or less, but the specs are different.
Think the nuts are all 21mm, same as wheels.
If the gearbox oil hasn’t been done recently I’d try that too - though the 5-speed is apparently less picky and sensitive.
Good luck, please update if you manage to fix the noise! I was able to reduce it sometimes, but I’m planning to get the car up fully off the ground and try and load it with the handbrake to see if I can hear the noise (and where it comes from… I still haven’t seen one explanation for what the noise actually is) and mess with the PPF angle while the car is running to find the quietest position.
That, or I’ll start replacing everything until it goes away!
