Have you aligned the PPF/gearbox to the correct distance from the chassis?

Loosen off the 3 big bolts that hold the gearbox to the PPF, Jack up the gearbox so it sits 65mm (I think the factory manual specifies between 55 and 65mm), between floorpan and bottom of frame where the gearbox bolts to it, then re-tighten the bolts. You will find the gearknob will sit slightly higher than before.

Cured my gearbox lash noise on the overrun...

 

Stock 1.6? Check the shielding on the Cat. It rattles if its loose and you decel. Sounds stupid but a lot of ppl found out that that was the problem.

 

How long have you had the problem for? Do you still beat on your car?

 

Can we be more specific on where to measure from to? Where on the floor pan and where on the trans?

 

all I know is, since replacing my trans and clutch last weekend, I have zero draintrain noise like this anymore. It's win.

 

the floor's pretty flat and it's not an exact measurement, there is a range given you're not measuring from the chassis rails, just use a bit that's near to the gearbox.

I don't really know how to be more specific on the gearbox part?!?

Where the PPF bolts to the gearbox.

 

The floor of the car right?

Is it possible that the diff could also be out of alignment? And is there a spec for doing that as well?

 

No.


Turns out we broke the 2nd diff in a mile and that was the noise. Now it has a 1.8 diff, well see how long this one lasts.

 

Hmm...I just put this damn thing in and its already making noise

 

You sure...? Never heard of this before, and can't see where that would cause any noise. I can't imagine you could get any more than maybe 3/4''-1'' of total play out of the PPF in that area around the bolts, and I don't see how that would affect anything. Maybe the angle of the output to the drive shaft, but that little bit shouldn't cause any kind of noise.

Sorry for beating an old post.

 

Definitely confirmed. I raised up the tranny a little bit, and my driveline noise just got about 10 times quieter. ****!

 

I wonder why? I can't picture in my head what changes to make this happen. Maybe this would alleviate my horrible transmission noises, though I'm quite sure it's simply worn out. I know my PPF was forced into place with a crow bar, then bolted up as it sat with the trans and engine weight pushing it down. Maybe I should crack them loose and jack it up a bit and tighten them back up.

 

The only thing I can think of is the output shaft/pinion bearings taking too much lateral load or the pinion being pushed in some odd way, or some crazy nonsense like that that you would never think of.

 

Yeah, it would have to be something there, since the other end is snug against the block. Maybe this weekend I can get around to it.

 

Went on a long drive and really got everything warmed up. Wanted to make sure I wasn't imagining a quieter drivetrain. Still way less drivetrain noise.

 

I think it's prop alignment, the straighter is exits the gearbox the better.

It is in the Mazda service manual afaik. Though I know of some aftermarket MX5 specialists in the UK who swear such a thing doesn't exist and even that there isn't any play in the gearbox/PPF alignment.

Fair enough if they aren't aware of the procedure, but to blindly refuse it's even possible is rather obtuse.

 

Oh it's on page K-130 in the manual Braineack kindly hosted on here


https://www.miataturbo.net/showthread.php?t=48633

 

Well damn. I thought I had it fixed. I jacked up the car and secured it, then I loosened up the 3 PPF bolts and put a jack under the tailshaft housing and jacked it up about an inch from where it previously was. Bolted it all back down and I'll be damned if the noise wasn't 90% gone (though replaced with a slightly unsettling sound. Almost sounded like the engine sound changed under load, a deeper roar). It would idle silently and even when the a/c would kick on, it was silent. When the a/c kicks on, it used to go into violent rattle noise mode like the trans was about to start dropping parts under the car. Drove it a bit, still no sound, GREAT! Let it sit for a few hours, get back in it and drive and the damn noise comes back completely. I doubt the bolts slipped since I put a bunch of *** on them. Maybe my trans is just that worn out. I can go from on throttle to off throttle in gear and hear and feel the slack in all gears, worst being 4th. I'm just driving it till it blows, then find either a lower mileage 5 speed or a 6 speed if I'm lucky enough.

So this jack up the PPF thing does work, but only temporarily in my car, not sure why yet. Might check it out again next weekend. Just got hot and I'm not leaving the house again for the rest of the day.

 

Hmm, I've realized my gear rattle comes back too, but not in a few hours, more like a few days. Mine is also really bad in 4th, not as bad in other gears.

 

Make sure the wiring along the PPF is ziptied. The wiring was causing loud rattles on my 1.6. There is even a TSB about it: http://www.miata.net/garage/tsb/sb011_98.html