MX-5 OC Forum

Hello folks!

Mate of mine has 1.8 on a 54 plate, mk 2.5? It has develped a noise coming from the rear when off throtle, applying the throtle makes the noise go away. I'm thinking driveshaft or diff. Anyone come across this before? 

 Sounds like the diff.

M-m

Mazda-mender:

 Sounds like the diff.

M-m

 Thanks for that  That will cheer him up no end.

 I was just about to post about exactly the same problem when I saw this post! 

The noise has been gradually getting worse over the last few months, happens as the OP said only when off the throttle - applying throttle or depressing the clutch stops it. Seems to be coming from somewhere under the gearstick, so I was guessing it could be clutch/gearbox/drivetrain. However I honestly am not sure exactly what the differential is or does, but a quick google search shows lots of thread on various forums about noise from this when engine braking. It's part of the drivetrain, right?

Anyone got any idea how big a job this is to replace? Also, is it something I should deal with immediately i.e. could it be causing cumulative wear and damage to other parts of the drivetrain? Certainly doesn't sound like it's doing anything any good...

 Just spoke to a friend who's an ex-mechanic, he reckons this is unlikely to be the differential if it's happening in a straight line - not that he was certain, but just wondering if anyone's got any further thoughts on this noise? I'm pretty sure this is exactly the same problem as the OP describes, hence why I'm sort of hijacking this thread (sorry!) - someone let me know if I should start a seperate thread here though, I know what forum rules can be like..

Does this noise also happen in high gear- low speed.

Say 5th or 6th gear at 25/30mph and put your foot hard down. It will eventually even out once you build up speed.

Autolink have diagnosed mine as the gearbox, most likely the input shaft which could have been caused by wrongly installing the gearbox ( I've noticed it shortly after having my clutch replaced )

Apparently, it is where you simply 'pull the two faces together' by using the bolts, where as there should be no gap between the engine and gearbox housing when reinstalling.

This causes the input shaft to wear where it is not seated correctly.

We had the car up on the ramp and went though the gears, standing underneath when the car was but though its high gears at the equivalent revs/speed you could clearly hear that the gearbox sounded like a spanner was in there somewhere, this noise obviously resonates down the propshaft and makes it appear like its coming from the diff when moving.

Believe me, I've chased this for over a year, I'm leaving it as my 6 speed is very expensive to replace, if it blows up, which is highly unlikely, then I will change it!

 Hi, Diffs "sing" or "whine" and vary their tune with load. It's a constant noise changing with road speed and load and happens in a straight line and corners. UJs and CVs have a "cyclical" sound, "whirr whirr" or "click click" you can hear something is running rough and off true, and may also cause vibration and clicking particularly from CVs in slow tight turns, go somewhere quiet with the hood down and have a listen if suspected.

GmoLargey, yours may well be the gearbox but anyone who's stood near a car on a ramp doing road speeds will tell you the noise is horrendous from everywhere. Autolink may well be right about the box but I doubt the reason why. The box and engine are dowled. If they're together then they're in line. If they were put together roughly the clutch plate may be bent and the spigot bearing may have been damaged but you'd hear and experience these as drag and noise when disengaging. 

Hi,

Diffs on the Mk 2.5s 1.8, which incidently is what I have, can cause problems. Lots of threads on here about them so I'll not go into too much depth. The Diff which seems to cause the most problems is the Fuji super LSD which has been known to fail much more than you'd expect. If your mate changes his diff oil ask him to look carefully at the old oil that came out, he's looking for some flat bits of metal about the size of you finger nail. Please do have a look at the other threads about this problem as they are very informative. Hope your mates diff is alright.

shoestring:

Hi,

Diffs on the Mk 2.5s 1.8, which incidently is what I have, can cause problems. Lots of threads on here about them so I'll not go into too much depth. The Diff which seems to cause the most problems is the Fuji super LSD which has been known to fail much more than you'd expect. If your mate changes his diff oil ask him to look carefully at the old oil that came out, he's looking for some flat bits of metal about the size of you finger nail. Please do have a look at the other threads about this problem as they are very informative. Hope your mates diff is alright.

Ah yes, seconded, if a tab has gone through the crownwheel and pinion it could have chipped it and be making a thunk thunk noise on the over run. I suppose we should ask what sort of noise he's got.

Did you change your diff oil Stuart (shoestring)?

Rich M:

Did you change your diff oil Stuart (shoestring)?

Not yet, I've no noise to alarm me but I want to check just to make sure, I seem to be very good at preparing a jobs/mods to do sheet but a bit slow to get the jobs done. First off I'll have to clear/tidy the garage as it full of junk (my good lady thinks it's there just to put stuff in she doesn't want in the house & my son has it full of his weights and exercise stuff), can't work very well on the drive as it's on quite a slope and when you eventually get a dry day I want to be out with the top down. Thats it this weekend I'm going for it (unless she gets me to do something else) got to keep her sweet as the mods I want cost dosh, I've told her a supercharger will cost £3000 so as to make the jobs I want to do sound less expensive

Rich M:

 Hi, Diffs "sing" or "whine" and vary their tune with load. It's a constant noise changing with road speed and load and happens in a straight line and corners. UJs and CVs have a "cyclical" sound, "whirr whirr" or "click click" you can hear something is running rough and off true, and may also cause vibration and clicking particularly from CVs in slow tight turns, go somewhere quiet with the hood down and have a listen if suspected.

GmoLargey, yours may well be the gearbox but anyone who's stood near a car on a ramp doing road speeds will tell you the noise is horrendous from everywhere. Autolink may well be right about the box but I doubt the reason why. The box and engine are dowled. If they're together then they're in line. If they were put together roughly the clutch plate may be bent and the spigot bearing may have been damaged but you'd hear and experience these as drag and noise when disengaging. 

I've seen many people put gearboxes and engines together incorrectly as Autolink have described. It's so easy to do.. and if you've not done many before you'd probably think that's what you should do..

There are two sets of splines on a input shaft - you can line the first set up and not the second very easily. Then bolt it up damaging the second set.... If you don't line the input shaft up properly you can still put it together with the dowls lined up... the dowl locates the box casing to the engine not the input shaft..... As for the "noise" on the ramp at road speeds, why road speeds? And certainly not my experience and I've seen plenty...  :-).  

Input shaft or diff and if you've checked the diff oil and it's clean then the gearbox input shaft is next....

MrChrome:

I've seen many people put gearboxes and engines together incorrectly as Autolink have described. It's so easy to do.. and if you've not done many before you'd probably think that's what you should do..

Hi MrChrome, Yes many people do a similar thing, they hang the box on a bolt loosely to help locate it then wiggle it till it goes home under light force. The dowels then make the axial alignment exact. If it had been forced together with the bolts, with no regard to aligning the splines or spigot, it would have either found its way home ok or damaged the plate or spigot bearing as I said.

MrChrome:

There are two sets of splines on a input shaft - you can line the first set up and not the second very easily. Then bolt it up damaging the second set.... If you don't line the input shaft up properly you can still put it together with the dowls lined up... the dowl locates the box casing to the engine not the input shaft.....

Yes almost right, there are just one set of splines on the input shaft but there are 2 steps to engaging it all together; they mate with the clutch plate splines first, then the input shaft needs to be coaxed into the spigot bearing, I've done it many times.

You can't get the box and engine together without them being in line (down the crank axis). When they're together, if they have been forced to get there without first aligning the splines then spigot, the plate may have been bent or the spigot bearing may have been damaged. Neither will be the cause of this noise though, as it occurs under drive and the input shaft and engine are locked together under drive, rotating at the same speed, so the plate and spigot bearing are not (effectively) being used. Yes it could be the first motion shaft bearing.

MrChrome:

As for the "noise" on the ramp at road speeds, why road speeds? And certainly not my experience and I've seen plenty...  :-).  

Input shaft or diff and if you've checked the diff oil and it's clean then the gearbox input shaft is next....

That's what the poster said, "We had the car up on the ramp and went though the gears, standing underneath when the car was but though its high gears at the equivalent revs/speed"

shoestring:

Rich M:

Did you change your diff oil Stuart (shoestring)?

 

Not yet, I've no noise to alarm me but I want to check just to make sure, I seem to be very good at preparing a jobs/mods to do sheet but a bit slow to get the jobs done. First off I'll have to clear/tidy the garage as it full of junk (my good lady thinks it's there just to put stuff in she doesn't want in the house & my son has it full of his weights and exercise stuff), can't work very well on the drive as it's on quite a slope and when you eventually get a dry day I want to be out with the top down. Thats it this weekend I'm going for it (unless she gets me to do something else) got to keep her sweet as the mods I want cost dosh, I've told her a supercharger will cost £3000 so as to make the jobs I want to do sound less expensive

Ah, price conditioning, like your style  hope you get it done. I can get the car in the garage, it lives there for the worst few months when I've shifted a few bikes etc, but it's not really wide enough to work on easily. Nicer outside on a warm day, sun on my back, roll on Spring!

There was no load on the wheels once its in the air, you could put it in any gear and 'pull away' and it still made a really horrible noise, once it drops the revs you can also hear the same noise.

This gets worse the longer you drive for/ hotter the car/gearbox oil gets.

As for the 'let off noise'  it feels as if the drive train has slack in it when lifting off, again I have no idea what it is and can only go by others recommendations.

My car has the torsen 2 diff, which if completely fine, I noticed the noise maybe a week after having the car back from the clutch fitters.

Surely if the disc was put in at such an angle to bend it, the noise would be noticeable strait away?

As you can imagine, I would rather it not be the gearbox, but seeing as the labour cost would be the same, it really leaves me with only one viable option- to replace the box.