PPF Flex / Prop knocking
 

Hi Guys,

I am trying to get rid of an annoying issue with my NA 1.8 Turbo.

When I reverse, even at idle RPM's, I get a vibration from the PPF which I think hits the prop, it seems to be from the gearbox end.

I have changed engine mounts, MazdaSpeed, Direnza and some Poly ones. The mazdaspeeds were dead, the direnzas were seriously harsh but stopped it the most and the poly ones are a nice balance but the vibration is there, slightly. The diff mounts are I.L Motorsport ones, pretty solid, rubber.

The car is a turbo, lightweight flywheel and grabby clutch, i've change the flywheel and clutch from a competition clutch stage 3, same thing.

It's nothing to do with the cars power, its engaging the clutch at idle, i think the grabby clutch may cause the movement somewhere along the line. Once clutch fully engaged (foot off the pedal) it's fine but during that bite point, the vibration is felt through the car, kinda makes the car hop, clatter and just a bit annoying.

I am thinking to experiment with an engine torque damper, just as an extra anchor point for the engine to see if that firms it up, beyond this, I just don't know how to stop it. Do PPF's get weak and begin to flex as they age with hard use?

I did snap my diff carrier arm, I think it was due to this vibration as it got really bad with my worn mazdaspeed mounts. I've seen replaced and had that strengthened.

You can see the cars spec and history here;

https://www.mx5nutz.com/threads/94-e...133236/page-27

Any advice to stop this would be amazing, I want to reverse onto my drive way without vibration!

Youtubes,

This is before i changed the mounts. There is no contact between prop and PPF, i can get my fingers in between all areas, UJ's dont appear to have play. PPF has been aligned about 10 times over, torqued up, washers are in and present. ahhhhh




Thanks,
Mark

Is the bushing that goes around one of the PPF-to-diff bolts still present?

Any idea whether any diff work was done immediately prior to the noise/vibration starting? Regardless, working on from your propshaft/UJ investigations, I'd take up afm's point and would be looking at the PPF/diff mounting area, making sure all the torques are healthy and all the little do-hickies in that area are present and correctly installed. I'd even look at the axle UJs too, but I can be pretty ---- sometimes.

A PPF crack/failure should be pretty obvious, but it would be worth checking with a strong light.

I assume there are no shiny bits showing up, where contact is occurring?

If all that doesn't show up something wrong, maybe you need to open the diff?

This seems to me like the normal vibration you get in a high mileage NA/NB with a light flywheel and grabby clutch. The ring and pinon have more lash than when new. Light flywheel reduces damping. Grabby clutch excites the mass (makes things vibrate). I don't think there is much
you can do about it without going back to a stock flywheel and less grabby clutch. If you ever swap differentials and have the lash reset, the clunking could be reduced or eliminated.

Sounds like a Miata. If Emilio says it’s fixible with less lash, I’d look into it. More of an annoyance than a concern.

I should say that the bulk of that slop in a high mileage NA/NB is in the transmission usually. Old halfshafts can also contribute some slop.

Thank you guys,

Just to answer your questions, bolt bushing is in place. I have undo and re-torqued bolts on too many occasions, the noise that you can hear in the clips, is 1000% from the gearbox end of the prop..

The PPF appears in perfect condition, no cracks and no signs of being contacted by the prop or anything.

No work has been done on the diff itself, I removed it after I cracked the casing arm off, undid the casing and have now fitted a strengthened casing to it, Lash was never played.

This is my 3rd gearbox, mileage is unknown. It is my 2nd Torsen Type 1. I could not say when it started but I think it was a gradual thing which has got worst, certainly helped when I recently fitted some solid engine mounts but the vibration is still there. I can slowly engage the clutch, no throttle and it will just vibrate through the car. It did this with my previous OEM flywheel with competition clutch, I had hoped the new flywheel/clutch would resolve but clearly not.

After recently fitting the new diff casing/flywhweel/clutch, there was no shaving from the old drained oil.


I can live with it but it is damn annoying and embarrassing at times.

I will see if I can replace the UJ's in the prop if this is a done thing, probably worth while doing as my car has covered 100k miles now.

Next time the diff is down, I will investigate the lash!

One thing I will add, when I let off, i do get a loud lash/rattle sound between 2.6- 3krpm.. It's really loud. So I guess the lash sound may be indicator to the vibration issue? It does sound like it is coming from the gearbox but it is hard to say without being under there when it is happening.. It did this before the recent new parts. I am using redline fluids now too, no change to sound.

With the car in gear and no throttle being applied, while rolling, the car will begin to jump around 2-2.5k rpm, regardless of what gear or speed. It just becomes jerky as the revs drop. Sometbing it never used to do.

next symptom, if you lightly engage the clutch, it almost feels like you are driving over small perfectly spaced dimples in the road. There is no feedback through the clutch pedal but you feel it through the car.

something is definitely not right!

thanks!

Did you ever figure this out? I'm having the exact same thing happening. Seemed to start right after a clutch and flywheel job.

I haven't yet.

I am convinced, in my case, that it is my gearbox. It rattles like hell and I think something has broken on the output shaft which is resulting in play being pushed down the driveshaft.

These cars do seem to go a bit weird after you change the clutch, when I first fitted my stage 3 clutch, I had a vibration but it was minor and I put it down to an aggressive clutch. If your issue appeared immediately after the clutch job, I will imagine it is just the common vibration we all face after doing a swap or you kept the original flywheel which may be warped? it's damn annoying either way and there seems to be little to no resolution for it when checking online!

Good luck!

Well darn. I was hoping you'd have th silver bullet to fix my issues.

I installed the FM Happy Meal Stg 1, so all new components throughout. Maybe it is a reduction in damping from the lighter flywheel? It has always had kind of a ring when you shift a gear.
I've since also installed a turbo and have a pretty harsh vibration around the 3k mark, so next up is a set of new motor mounts I guess.

I've ran into the same issue, any chance either of you have found the solution?

I was able to eliminate almost all of the clunking. My motor mounts were completely shot when I finally pulled them out. The 3000 RPM vibration was from the downpipe rubbing on the steering shaft when it heated up.