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Ok basic run down of what's happened.

Fitted new exhaust and extractors on saturday last week. Started to here what sounded like an exhaust leak from the cat. Let it go as I will be going to an exhaust place soon to get a new cat.

Last thursday dropped the car off at the mechanics. Getting a few things done:
Lightened flywheel
Twin plate clutch (both came together in a kit from 949racing)
Braided clutch line
Slave cylinder
Gearbox oil
Rear main seal
And ask them to check the cat.

Well figured it would be a half day job, dropped it off at 8.30, but didn't get the call to pick it up till 6.30. When I recieved the call, they also asked me if there was a noise coming from the gearbox, to which I said that there could be, but i thought it was the cat. Anyway went down there an picked up the car. Oh an the cat was loose which they had tightened back up. They told me that the reason it had taken so long was because the spigot bearing was too small and had to be enlarged a couple thou. Didn't say anything was just happy to get my car back.

Not even 2 minutes into the drive back home, I heard that gearbox noise they were talking about! It's extremely loud, and only really happens above 2-2500rpm when decellerating. On acceleration there is no problem. I went back the next day and they said it could have been the gearbox oil is too thin, so Monday morning went back and got that changed. (Now I should mention that I don't know when the last time the gearbox oil was changed as that would have been the previous owner that had it done. I did see the gearbox oil a few weeks back when I fitted the short shifter in, and it was grey. I took the gear stick out on the Saturday before it went back in for another oil change, and it was blackish. Haven't checked it since, but it will soon.) So took it for a drive and went straight back in to the mechanic and told him that, that sound was not there before it came in to him and it's still there. He said it's nothing to do with them, as they only changed the oil. Should also add that there is a knocking sound coming from the clutch when idling and a rubbing sound when the clutch is pressed in, figured you get that with a twin plate clutch, but not this loud. I also asked the mechanic about this, to which he said it's the trust bearing, but that came in new with the kit.

So I've been looking at buying a new gearbox, but today I realised that when I'm decellerating and it's making that noise, that there is no vibration in the gear stick. Now I think it's the clutch, and that they opened (enlarged the spigot) too much and that would be the cause too all the issues I have now.

I still have the old clutch and flywheel and they are still in good condition. I figure that if I put that back in and there is no noise that I would be proven right with my theory of where this noise is coming from, but I can't do it myself and can't afford to pay to get it done to find out it is the gearbox, as that would be money to go to it.

Any ideas on what it could be? Or any ways to try and figure out what it could be or to narrow down the list out what it could be?

I am willing to let people take it for a spin or take them for a spin and tell me what they think it is. I will try to come down to garage cafe tomorrow night, if I finish work early enough, if you need to hear the problem for yourself.

Sorry for the long post, but I figured if I said everything about it it may answer some questions and lead to more answers

Evan

I experience the same problem and from further reading/research in the past, so do many other MX5 owners. They have all reported the problem occurs after they change the clutch or remove & refit the gearbox. Many have falsely diagnosed the problem as a gearbox bearing, diff or even the resonation of exhaust heat shields, until they troubleshoot by trying to rectify those things only to find the same noise still occurs.

I take it the noise is a grinding noise on declaration, usually more prominent in higher gears or when decelerating from usually 3k RPM+. When you engage the clutch the noise stops?

If so, I have yet to do this myself, but others from experience have resolved the problem regarding the decelerating grinding noise by re-aligning the PPF (power plant frame) to within factory spec.

I am on my phone at the moment, but I will post up a scan soon showing you the measurements for proper alignment.


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Hopefully this resolves your issue (steps 9-12).

Make sure you report back with whether it does/doesn't.

If the PPF trick fails then it could also be exhaust resonating, probably when in contact with something. When it's up for the PPF check have a really good look for any points where the exhaust could be rubbing against the power train or the body work. Also can be loose heat shields on the manifolds or exhaust. When decelerating the engine twists clockwise a few degrees on its mounts so think about where the exhaust might move to then.

I have fitted one oe 949's Twin plate clutch/flywheel combo
AND I can tell you that Gearbox noise goes thru the roof with this setup
Its all to do with rotating mass and the fact that there are no damper springs on the clutch plates

my car was quite till i did this mod

This is the price of a modded car

MrRevhead wrote:I take it the noise is a grinding noise on declaration, usually more prominent in higher gears or when decelerating from usually 3k RPM+. When you engage the clutch the noise stops?

When I engage the clutch the noise stops.

MrRevhead wrote:If so, I have yet to do this myself, but others from experience have resolved the problem regarding the decelerating grinding noise by re-aligning the PPF (power plant frame) to within factory spec.

I'll definitely give this a go. So it could be mis-aligned when the gearbox was put back in? Also it is hard to tell from the picture, A in section 11 is the measurement of which 2 points?

manga_blue wrote:If the PPF trick fails then it could also be exhaust resonating, probably when in contact with something. When it's up for the PPF check have a really good look for any points where the exhaust could be rubbing against the power train or the body work. Also can be loose heat shields on the manifolds or exhaust. When decelerating the engine twists clockwise a few degrees on its mounts so think about where the exhaust might move to then.

I will be checking this all out as well. Now just need to get lucky with the hoist to be empty this weekend at work

Russellb it's nice to know that I'm not the only one with this clutch. When you say loud, how loud?

Thank you guys!!! May have saved me a heap! And I will let you know if this was the problem.
BTW any thing else is also welcome for me to try

Evan

StockNA wrote:I'll definitely give this a go. So it could be mis-aligned when the gearbox was put back in? Also it is hard to tell from the picture, A in section 11 is the measurement of which 2 points?

If you run a straight edge across where the green line is marked in the picture below, "A" is the distance between the straight edge and the PPF.

It is also recommended to do it when the vehicle is parallel to the ground (not jacked at one end).




Looking forward to hearing the outcome.

Just remember the oil in the turret is not the main gearbox oil. Having just put a torsen in I had the PPF out . I looked at the diagram in the workshop manual and could not for the life of me figure out how you "'reposition the
PPF at the gearbox". I just bolted it up as I couldnt see how there was any vertical adjustment even after your great pic MrRevhead.

trader wrote:could not for the life of me figure out how you "'reposition the
PPF at the gearbox". I just bolted it up as I couldnt see how there was any vertical adjustment even after your great pic MrRevhead.

i have read that some people use a jack on the gb/ppf to help adjust the position to be "within spec" by measuring with vernier calipers before tightening the bolts on the PPF.

I'm going to hop under my car again and measure - if its out I will try and adjust - still cant see how those two bolts (that attach PPF to gearbox and visible in your pic) can affect the horizontal angles although they certainly can affect the lateral movement.

Ok guys, had it up on the hoist, was out of alignment, have now re-aligned the PPF to within specs only to still have the same problem. Now I have found 2 vids on youtube with a guy that has the same problem.




Now apparently he has been told that it could be his diff. He agrees. Hasn't been any word on if that was it or not yet, but he has a viscous LSD and I have an open diff. Could this still be the same problem?

Evan

what a nightmare. You sure have stuck your neck out for a lot of grief and burning money. The workshop that did the job has to rectify it- thats what warranties are all about and other items do not just fail because they have done a number of things. All the business about machining etc is very worrying. If you are not a mechanic - I will take that as a no- you should be taking the car back and asking for it to be fixed. It might be possible to ask another mechanic to check it but you wil find that they will not want to offer an opinion if you mention that business X has done some work on it. Incidentally it' s rubbish that there is magically something wrong with the diff and same for oil etc- just bulldust. Maybe take a friend down with you as a witness to what they say and do not take it on as something that you have to fix.

If you start fiddling around and doing things they might blame you for that- ie they did a job and it should be right even if they have to do it again. If there is still a problem you might have to reverse some of the things that have been done. I had an installation on a clutch which was done wrong and it was rectifed without any problems- its not your job to fix their fault.

Stock NA, that may well be a diff noise but from my personal experience it is that is not the viscous diff noise which is not as abrasive and gets worse over time. Cant tell you what it is but seems like it must be something to do with the recent work.
Reading this post reminded me to check out my PPf measurement. Just did and its on 55 mm. bugger so I'm about to crawl under and adjust.

I tried to re adjust my PPf but to no no way I could move it up to 60 mm gap. Having the factory manual (for an NA) I checked it out (it doesn't have step 11 and 12 in it so it is obviously only adjustable on the NB). Strange because they both look the same!

trader wrote:I tried to re adjust my PPf but to no no way I could move it up to 60 mm gap. Having the factory manual (for an NA) I checked it out (it doesn't have step 11 and 12 in it so it is obviously only adjustable on the NB). Strange because they both look the same!

Apparently Mazda revised the factory manual in 94 to include those points from what I have read.

Did you measure from the bottom of the PPF or the bolts on the PPF to the gearbox? Further research says to take the measurement from the bolts and it should be within 60-72 MM (2mm more tolerance compared to the other scan).



Were you experiencing the deceleration noise as well trader? If so, has it decreased with adjustment?