also I guess would you say yours are still greatly reduced or tolerable since going to rubber diff bushings but just seeing the diff vibrate that that rpm and thats what your currently chasing or is it violent in the car still too? Debating ordering a set and ditching the poly ones... even with the poly ones my rear end stil clunks bad when backing up and is always just feeling clunky even tho backlash isnt crazy and nothing is loose...

 

Fosho. Lemme know what you find as far as runout goes if you check it tonight.

My vibration was greatly reduced just by going to rubber bushings. Like I said, I don't think it "fixed" anything, but the resonant frequency went up by 35mph and the vibration severity was probably only 2/3 as bad as before. If your car doesn't feel like it wants to vibrate apart until 95-100mph, swapping to the rubber bushings might even get you up to 125+mph before you start feeling it.

 

I jumped the gun a bit on ditching the adapters. The driveshaft shop I’m going through did not have the flanges on hand to make an adapter-less shaft. They did, however, have aluminum adapters for the transmission side, so I’m saving a couple pounds by going to one of those. Apparently the ZF5/6 transmissions share a bolt pattern with whatever came out of the mid-2000’s GTOs, which is probably useless knowledge



This adapter will also allow a 1350 flange to be used instead of a 1310 like before, and will widen the bolt pattern to make driveshaft removal and installation easier. The Allen bolts I had before could only be removed with the ball end of an 8mm Allen key due to being positioned right behind the u joints. It was a pain in the *** to install and remove. I’d get the ball end in and slide a 9mm socket with a couple extensions over the end of the Allen key to get the final torque down. Anyways…

I installed the adapters tonight so I could give the driveshaft shop my final measurements. Of course the trans adapter pilot cutout was larger than the last one. I “shimmed” the transmission output shaft pilot with some electrical tape and then got under the car while it was idling in 1st gear to mark where the runout was with a sharpie so I could readjust it. 30 or more minutes later, I got the adapter down to having only the slightest amount of visible runout. I think it should be fine. I checked the trans output pilot too, no visible runout there either.

While I was at it, I remembered @Gee Emm ’s quip about potential play in the output shaft. I checked that but there was none that I could feel by hand. I then took the trans diag one step further and warmed the car up then ran it through all the gears in my garage. Got it up to 6k rpm in 6th gear with no outrageous vibrations, aside from what you’d expect out of a BP with poly motor mounts and a fixed trans mount. That’s not to say the trans can’t be causing an issue when there’s load applied to it, but I can toss the gearbox into neutral at 115mph and the vibration doesn’t change so I think this rules out the trans.

I’m gonna call the driveshaft shop tomorrow morning with my flange-to-flange measurements. They told me if I did that, I’d have the shaft in hand by the end of the day. Pray for me, homies.

 

I just grabbed the new driveshaft and installed it. Vibration feels the same as it did after the install on sunday. Comes on even earlier now, maybe at 50mph.

I’m seriously contemplating parting this car out and buying a C5 corvette. I don’t have the time to keep doing this sh*t while getting nowhere.

 

I am no longer laughing.

I totally get the frustration but hope you find the willpower to stick with it and find a solution.

 

RIP.

I really thought the getrag was gonna be the magic ticket. What is different between your setup and greg peters in ?

And of course, pinon angles and whatnot checkout after the install?

 

That's really frustrating to see... i called and checked and dss wont even balance 3rd party shafts that arent theirs was hoping to have one balanced at higher speed maybe.. I got to thinking i wonder if we are seeing that miata shimmy speed shimmy thing and after getting rid of the ppf really upset the car, idk how structural it really was but miata being a wet noodle of a chassis already... Its weird that all your different driveshafts are changing the speed at which it comes on.. maybe its time for a cage 😆, part of me wanted to try some door bars and see if that changes the issue at all... I run NB2 sport brakes or else i was gona try and find dome stock na wheels and tires to test and see what happens

 

Yeah, this is past the point of being funny now. My "track car" is totally unusable. I checked the pinion and trans flange angles after the install and they were within 0.4* of each other. Maybe I need to get them closer, but the first time around I didn't note any difference in driveline vibration until the pinion and diff angles were well over 0.5* off from each other.

Maybe the trans flange adapter still has too much runout. I'll get it in the air before I leave work and check. I let the car idle in 1st on jackstands real quick before putting it back on the ground and the driveshaft didn't seem to have any substantial runout.

 

and im sure going from the tiny miata driveshaft to a larger diameter doesnt help anything balancing wise, more weight further from the center.

 

Alright, I've pulled myself back from the brink. Did some adjustments to how the driveshaft and pinion adapter were sitting. The vibration doesn't come on until around 65mph now and ramps up much less aggressively than before. It's still pretty bad at 95-100, but maybe not as bad as before. If I still had rubber bushings, it might be nearly gone.

Long story short, EVERYTHING between the trans and diff has a mild amount of adjustment/slop now. I found runout in the front of the driveshaft and in the diff adapter but noted both weren't centered on their respective components. I did a little bit of ghetto marking and adjustment (ran the car in 1st gear and marked the low spots on the diff adapter and front of the driveshaft with a marker), then loosened each component and just kinda... pushed it in the opposite direction. I did another ghetto electrical tape "shim" job on the pinion pilot shaft since there was notable runout there and a decent gap between that and the adapter. Got that nearly perfect and lined up the front of the driveshaft a bit better, but not perfect. The trans adapter runout still isn't perfect either, but it's minor enough to not be detectable on camera.

Here's a couple vids before I took before making the adjustments:



So this leaves me still kinda f*cked. Getting the alignment set up again is gonna be a nightmare if I have to remove the driveshaft at any point. Do I hit up another shop and have them build me an adapter-less driveshaft so at the very least I don't have to deal with the adjustment of the adapters? The local driveshaft shop I went to is pretty set on making steel shafts only and using adapters. I dunno. Next step will be further adjusting the shaft and adapters. If that doesn't work, one of the guys on the high HP Miata FB group said he went through my exact process to a T, and eventually found his adapters were out of balance. I'd still rather get rid of the adapters now, even if it means waiting weeks or more for a custom driveshaft.

Ah, also checked my driveline angles. 1.8* at the diff and 2.2* at the trans. Could be better but in my experience playing with angles when I first installed the trans, the vibration stayed the same until I got them up to about a 0.7 or 0.8* difference (had to try for science).

 

Damn Zak, hang in there dude.

i would get a dial indicator to center the parts. You should be able to get everything in to <.001” with some patience.

def thought about that though, if you have to do a trackside repair, dialing everything in will be a massive pain/timesuck. It should not be this hard! An adapter less shaft would be the way to go, as long as the flanges are tight fitting and well centered

I did not have my (single) adapter balanced, as the local shop said they could not easily adapt it to their machine.

I may try again next time it’s apart. I def still have some vibe at very high (shaft) rpm

 

Thanks dude. Yeah, no way around it, I still gotta see this through.

I’ll def bust out the dial indicator next week. Had only 45 minutes to get it in the air and check everything I could before the shop closed yesterday so I didn’t get too scientific with it. Based on what was done, though, I surmise with .001” runout, the vibration may actually subside..?

Yeah, I was curious how the adapters might be unbalanced even if they have zero runout, but it’s still worth checking I guess. Your vibration is still gone up until 130-140mph?

 

I have forgotten that using hose clamps to ghetto balance a driveshaft was a thing.

Just to start with, I'm gonna see if counter balancing the front of the shaft with a hose clamp makes a difference on Monday. I'm outta town this weekend and didn't take the **** rocket to work today unfortunately.

 

You guys aren't going to f*cking believe this lol (ignore the hose clamps).

 

did this fix it??? so old miata axles did it, new getrag axles also did it the same? what a coincidence

 

Well I just found this during my lunch break an hour ago. No fix yet. I'm suspecting this super-wobbly axle that came with my Getrag kit is causing my vibration now. Just messaged KP requesting to get it warrantied.

My old Miata axles had no runout issues. I ran it with two different sets of axles, no change in the vibration.

I'm just baffled at the odds of getting two bad driveshafts AND a bad axle. I thought The Driveshaft Shop was supposed to be on their game.

 

I have to laugh again. Dude. Once this is done - don't buy any more parts for a while. Clearly they're out to get you.

I really hope this is the final piece for you. It's incredible that you can go with such a well known name brand and still get QC issues like this.

 

Yeah man, I'm with you. We're back to laughing lol. This is just too ridiculous. I'm gonna be so happy once its all over

The whole last year, I was so bent on constantly upgrading and improving the car. After this whole saga, though, I'm gonna be so happy to have it problem free that I don't think I'll be doing much aside from maintenance for a while. Don't take your properly running cars for granted guys hahaha.

The good news is that this is kind of a smoking gun issue (I hope). I feel like I was able to mellow out the severity of it a little bit by adding hose clamps to counterbalance it, hopefully indicating that the axle is the issue. I also "counterbalanced" the front of the driveshaft by tossing some hose clamps on it and experimenting with different orientations. I feel like I was able to take a touch of the edge off of the vibration, but don't think the driveshaft is the issue at this point.

 

I really hope that's it, I agree that axle looks wonky and should be the next thing you replace for sure. Hope KPI feels the same and gets one out to you quickly.

The axles do spin at a much higher RPM than the driveshaft due to the gear ratio, so I could see an imbalance there getting pretty bad with RPM. I can't say I'm fully convinced that's the issue, but I'm hopeful for you.

Do you still feel the vibration in the diff when on the lift?

 

Yeah man, fingers crossed that it's the issue and that KP is able to get me a fix quick. Unfortunately, the axles are made to order by The Driveshaft Shop and took a month to make and ship the first time around. We'll see if there's a way around it but I'm assuming it'll probably be that long again until I can get a replacement. We'll see.

The vibration can still be felt in the diff, although less so than before. I only had an hour to mess with the car during lunch so I didn't stethoscope and feel everything like last time. I really need to spend a little more time checking everything out. That being said, the vibration in the car right now feels slightly different and is overall slightly less violent than before. Again, maybe that's an indicator that the issue is elsewhere after the diff swap. I'll have to play with it more to find out.

If I get a chance today, I'll throw a couple more hose clamps on the axle to try and counterbalance the runout and see if that makes any further difference in the vibration, for scientific purposes.