Light weight flywheels will cause the trans internals to chatter on deceleration. I ran a light aluminum flywheel on the Mazda trans for years and it was noisy.

Im about to the point that im going to have to do this, I played with the angles all evening last night after i got my driveshaft completely redon and it made no change at all... angle gauge reads zero as far as i can tell and as far as left to right i cant change that but it appears alligned with the car. Im hoping i can figure out some way to raise and lower it while im in the car maybe with a pry bar or a rope or something and leave a bolt loosely in there and just pull up on it or something. I don't like being under the quick jacks with the car off let alone with it running at 75mph.. All my changing last night really didnt help much unless its just suuuuper precise i was adding washers under the trans mount and ppf mount to move it around so basically working with hairs but everything i find says up to a degree or so is fine and im way under that and im checking with the flat spot of my trans mount and the face of the diff flange... Also seems my diff fluid gets dirty super fast so somethings accelerating wear i think

Also you mentioned you did the math on the heimjoint ppf delete, do you remember roughly how much force that thing is taking? im just worried ima twist the subframe or something i dont want that thing shooting up through my gas tank... I was debating putting it back on to test and ease of angle adjustment

Do you recall how far off they were with the angle finder? dont need exact numbers of course just like was it a few degrees or like .x's of a degree, i didnt get under there with it running just a bit too sketch for me on quickjacks. im still hunting down a weird vibration and i have them zeroed right now ive tried up and down a hair but doesnt seem to change much. i now have a weird effect at 55-60 where i get more of a really deep low pitchched vibration i can really feel throughout the car that is directly affected by throttle but it IS speed related which leads me to think that is the angles being off despite it being zero... im wondering if my ppf/diff setup is moving around a ton or something somehow.. Might stick a camera under there tomorrow and see, about to chunk this miata diff in the pond and just go with the 8.8 already...

Damn, I should've sub'd to this thread a long time ago. Lots of good information in here. I never thought about running the car up to 70 in a lift and messing with PPF angle on the fly to identify where it's happiest. Agreed that it's sketchy as f*ck but I suppose you could identify the ideal diff angle rather quickly haha.

After all the hours of adjusting PPF/trans angles to try and get my vibration sorted, I only found that most angles produce the exact same effect, with a couple more extreme angles making the vibration marginally worse.

It wasn't tenths of a degree, more like 2 degrees maybe.

Ultimately I had to set my drive shaft like the bottom diagram in this picture as I couldn't get the diff pinion angle low enough to match the second diagram. It says absolutely not even though it's just as good as the second one (assuming pinion to driveshaft angle is the same on both ends), both of which are better than the top diagram. Another example of garbage info on the internet. It's in effect a double cardan CV joint when angled like the bottom diagram.

Also take a look at your angle horizontally; crankshaft centerline may not be parallel to the diff pinion centerline when viewed from above.
https://cimg0.ibsrv.net/gimg/www.mia...a0ea7e5fcc.jpg

My issue with running something similar to the bottom one is the tkx is a bit large so i have to angle it down like 2.5 or so degrees to clear the tunnel. Also the stock diff is offset from the center a little bit, most diff's are i suppose but yeah i need to find a way to truly make sure they are still parallel to each other on the horizontal axis. Also theres no real way to rotate the diff to point it left or right if that is off anyhow, maybe point the transmission/engine around but its already dead center with the shifter hole and the shifter is center of the transmission thats center of the engine. unless the shifter holes offset but its not on a stock 5 speed transmission either and is also center of the trans/engine etc. I ordered a laser level maybe help determine that.

In another thread, @richbobby determined his Miata diff to be offset 16-17mm to the passenger side of the trans. Mine was about the same. We both used lasers to confirm and ended up hogging out the holes in our trans crossmembers to experiment with lateral alignment of the transmission. Rich ended up zip-tying some welding rod together to make an adjustable ruler to measure total angle.

https://cimg7.ibsrv.net/gimg/www.mia...c62225723.jpeg

I was not aware that the bottom diagram could be followed. +1 cat to @TurboTim for learnin' me something.

correct me if im wrong but my current thinking was even if they are offset 16-17mm left to right it shouldnt matter as as long as they are both pointing the same direction (at each other, hard to explain) even left to right angles offset/cancel out each other same way up and down do.. and im being dumb here Turbotim said like the bottom diagram i can do that aswell its just flipped per the diagram doesnt mean transmission has to be angled UP... its close to friday my brains fried for the week 😂. So i guess i can angle my transmission down my 2.7 degrees its at now AND angle the diff also down 2.7

Yeah, we're on the same page haha the point I was trying to get across is that it's ok that there's a lateral offset, it just adds to the "total" angle of the driveline.

I just fixed most All of my vibrations, I made that heimjoint ppf delete thing but never ran it much… well I have a full ppf on it now to my crossmember just bolted through the bottom holes and I guess it was bouncing around or wasnt very stiff… I drilled a hole in this ppf and threw that heimjoint thing on it bolted it up its solid now it actually makes less noise with the diff being hard mounted to the subframe than it did before the swap… picture this(pic below) but the ppf keeps going and not cut off. I can confidently say it fixed every vibration I had up to 85ish atleast I had one at 50-60ish then the one at 70-72ish that then never stopped from there. Now I got it up to about 87 and started to feel very slight something but at this point that’s probably something else entirely as my tires are pretty roached at this point. I feel a lot better doing it this way as if the Heim joint setup ever fails it hopefully won’t shoot up through my gas tank…i hope...
https://cimg4.ibsrv.net/gimg/www.mia...d6f9d2d70a.png

One of the last pieces to this puzzle, an NB cluster swap and a Dakoda digital speedo converter box. Swapped in the NA6 oil pressure gauge i took a chance at setting the needle and failed so i need to pull it back apart to do that but other than that its all in and working good. Its nice having VSS now for boost by gear and what not.
The Cluster swap wasn't too bad, followed car passions pinning guide, lots of wires to extend and stuff took a solid 3-4 hours for me at least.
https://cimg0.ibsrv.net/gimg/www.mia...de10b6acf4.png
https://cimg6.ibsrv.net/gimg/www.mia...52fac5e777.png

Lookin good. The TKX has mechanical and electronic speedometer outputs. Your Dakota box is the one that converts electronic signal of the TKX to what the NB electronic speedo wants for an input signal?

I'm not sure why the NB speedo was needed if there was a mechanical speedo on the trans, other than not needing to get the right speedo gear/cable/etc, that whole hassle. You could still use the digital speedo output to drive your ecu boost by speed/gear, or the digital cruise control output on the back of the NA speedo cluster (with a pull up/down resistor).

I looked into it a while back i want to say there wasn't a gear low enough for a 4.10 diff and small miata wheels and tires. I remember i spent a good bit on it but i cant remember how i calculated all that now, would have to go down that rabbit hole again.

Gotcha, that makes sense. IIRC I'm running the biggest T-5 speedogear with my 3.90's and it's still a bit too fast.

Safe to say the vibration is no longer a prominent issue then?

I wouldn’t quite call it completely fixed but I feel like I can drive the car without it feeling like something’s obviously wrong. Higher speeds it will start to give me a bit of a vibration but it could be anything at this point, as the alignment I’m pretty sure is off. I need to get it up faster to see if it goes away if it does then I don’t think it’s the same issue as before once it started it never got better only worse it plateaued after about 85. And before when I would give it throttle in 5th around 50-60 it would have a horrible hum and vibration that’s gone after bracing the ppf which was a big concern for me.

Tight, well good to hear that it's mostly solid then! I agree, once you're over 90-100mph, there's a lot of vibrational factors at play in these little cars lol. As long as it doesn't feel like something in the drivetrain is at risk, I guess you're good. Congrats on having the swap complete with the converter box too! I was going to go the same route before I got sucked into doing a PiDash haha.

I got it up to a little over 100 and I spoke a little too soon while it is better it’s still pretty violent.. I cant tell if its just in my head or what but if i slowly creep up to 85 it seems smoother but if i wot up to that it feels worse maybe its just me, i with i had some way to verify or something, might see if theres some accelerometer thing i can test with.. hoping to test it on jackstands yet again tomorrow. Certainly better than before but still something, maybe its my all round poly bushings really not sure.

So as i expected my paranoia would get to me on my welding on this bell housing. I think ima take another stab at it and built it in a bit of a different order and see if i can come across a bit higher amperage welder. This time im going to use a 5 speed bell as the auto ended up needing clearance inside to clear my flywheel, it all works currently but just to not have to worry about it and maybe avoid my transmission falling out of my car in the future. Most of the cost for me at least is mainly in time, Mostly just a couple hundred in materials at most.

sorry to dig up an old post but was reading back through this thread and was curious if you ever got anything going for your swap or found a housing? I was Probably going to be making another one soon, my old one would probably become a wall ornament, I just personally wasn't happy with how the welds came out not that it failed or anything just a v2. Not that i was really trying to make any to sell at the moment i dont consider myself that good of a fabricator yet but if you were still held up on all that money in swap stuff in the same situation i was figured id check and maybe see what i can do if you still were looking for one if the 2nd one turns out good.