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Discussion Starter · #1 ·
Hi folks,

I've got a project I'm pretty excited about, but ran into a bit of a snag. 1993 Miata base model with 49,000 miles. Picked it up from my old neighbor who was the original owner and had babied it since new. It sat in my garage for 4 months while I slowly picked away at swapping all parts from my other 1993 onto new car (coilovers, sway bars, wheels, interior bits, small Momo steering wheel, swapped manual steering rack out of new car into old car and power steering onto new car, etc).

While I was at it, I figured I'd 'go for it', and found a 4.3 Torsen Type II that I installed. Put Energy Suspension urethane bushings in it as well as new seals, gear oil, cleaned exterior and interior of housing, etc. I bought new reman axles at NAPA as well as a used drive shaft.

Here's where the problem lies..... with the new driveshaft, axles and Torsen, I have a slight (but noticeable) vibration that irks the crap out of me! At first, it appeared at 60MPH, and got worse as speed increased. I checked the height of the PPF, and adjusted it so it is at exactly the 66mm from the front of the PPF to a straight edge straddling the "frame rails". Also, I returned my used driveshaft and exchanged it for another. This caused the vibration to appear at 65MPH instead of 60, but it certainly didn't alleviate it. This morning, I unbolted the driveshaft from the diff, and clocked it 90 degrees from where it had been bolted before. No noticeable difference.

I assume this is a driveline imbalance, and not a wheel balance issue. 1) I had the same 4 wheels on my other Miata, and it was smooth as butter to 100MPH +. 2) there is no issue with the front of the car. (the steering wheel is smooth, still and steady at all speeds) 3) I swapped a set of old wheels and tires onto the rear of the car to "give the Torsen a workout", and it didn't change the vibration issue at all. 4) the vibration would appear to be at the frequency of driveshaft rotation, not wheel rotation (ie: about 4x faster than a wheel imbalance isssue).

My question to you, dear Miata enthusiasts, is this: Have you experienced this after installing a TORSEN in an early car, and if so, what did you do to remedy this problem? Did you have your driveshaft balanced, and did it solve the problem? Is there a chance it's something with the differential I installed (it makes no noise, and behaves like I'd expect a good Torsen would!)

Any experience you've had with this issue, and any advice you're willing to give will be much appreciated!

Thank you
 

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had a similar issue but only after few spin outs on the track. The vibration was upon acceleration 85-100 mph. I was told i had flat spots. Swapped to different set of tires, same thing. I think it's the drive shaft as I can feel the vibration in the trans tunnel as well. Do you?


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It may be the Energy Suspension urethane bushings transferring too much NVH.
Note the disclaimer, may be!

I would suggest trying these Mazda Speed differential mounts from Moss Miata.
Link: http://www.mossmiata.com/Shop/ViewProducts.aspx?PlateIndexID=80808
They are stiffer than stock since you are going for performance but not as stiff as the Energy Suspension bushings. If you are really worried about NVH, go with stock differential mounts.

Also note that a Torsen rear end requires a different driveshaft length from your original 1993 Viscous rear end.
You can buy a NEW driveshaft from RockAuto at a reasonable price. If I remember correctly it was around $160.
You will want to search 1999 Mazda Miata and the part number should be Dorman 936251
The drive shaft is 39.375" long for the Torsen rear end. (Your old 1993 Viscous rear end driveshaft is 41.25" long)
Link for specs: http://www.rockauto.com/en/moreinfo.php?pk=5548881&cc=1356229&jsn=360
 

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Yeah you'll need a 1.8L driveshaft and bolts to fit it to your Torsen, which comes off of 1.8L cars. You probably have a 1.8L driveshaft and the appropriate bolts but I thought I'd reiterate in case you're using the 1.6L hardware. When I did a Torsen swap on my car the bolts must have fallen out of the box during shipping so I had to order new bolts since the 1.6L driveshaft bolts were too small for the 1.8L driveshaft.
 

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Discussion Starter · #5 ·
had a similar issue but only after few spin outs on the track. The vibration was upon acceleration 85-100 mph. I was told i had flat spots. Swapped to different set of tires, same thing. I think it's the drive shaft as I can feel the vibration in the trans tunnel as well. Do you?


Sent from my iPhone using Tapatalk
stevos555: I'll check the tunnel. I noticed that the shifter doesn't vibrate at all, but I'll check if I can feel it on the tunnel. - thanks
 

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Discussion Starter · #6 ·
Yeah you'll need a 1.8L driveshaft and bolts to fit it to your Torsen, which comes off of 1.8L cars. You probably have a 1.8L driveshaft and the appropriate bolts but I thought I'd reiterate in case you're using the 1.6L hardware. When I did a Torsen swap on my car the bolts must have fallen out of the box during shipping so I had to order new bolts since the 1.6L driveshaft bolts were too small for the 1.8L driveshaft.
Thanks guys - yes, I used a driveshaft from a 1999 Miata (and also exchanged it for another from a 2000, but same problem with each driveshaft). If I'm not mistaken, the driveshaft is the same in a 94-2000 (or so) car, whether you had a Torsen or an open differential, right? PS: also used the larger hardware to bolt the driveshaft to the differential.
 

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Discussion Starter · #7 ·
It may be the Energy Suspension urethane bushings transferring too much NVH.
Note the disclaimer, may be!

I would suggest trying these Mazda Speed differential mounts from Moss Miata.
Link: http://www.mossmiata.com/Shop/ViewProducts.aspx?PlateIndexID=80808
They are stiffer than stock since you are going for performance but not as stiff as the Energy Suspension bushings. If you are really worried about NVH, go with stock differential mounts.

Also note that a Torsen rear end requires a different driveshaft length from your original 1993 Viscous rear end.
You can buy a NEW driveshaft from RockAuto at a reasonable price. If I remember correctly it was around $160.


You will want to search 1999 Mazda Miata and the part number should be Dorman 936251
The drive shaft is 39.375" long for the Torsen rear end. (Your old 1993 Viscous rear end driveshaft is 41.25" long)
Link for specs: http://www.rockauto.com/en/moreinfo.php?pk=5548881&cc=1356229&jsn=360
Thanks MiataQuest. I'm hoping to exhaust a few other avenues before reverting to different bushings. I'm OK with added NVH from the bushings..... I don't mind that. But at a certain speed, its as if a switch is flicked, and a new vibration appears. It is not the 'ever present' added NVH that urethane bushings introduce in most applications (I've put urethane bushings in 3 of my other cars, and the NVH is changed at all times, not just when you hit a certain speed). I appreciate your note about the new driveshaft being available at RockAuto..... I may end up going that way first.
 

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Discussion Starter · #8 ·
had a similar issue but only after few spin outs on the track. The vibration was upon acceleration 85-100 mph. I was told i had flat spots. Swapped to different set of tires, same thing. I think it's the drive shaft as I can feel the vibration in the trans tunnel as well. Do you?


Sent from my iPhone using Tapatalk

PS: stevos555: did you ever solve your vibration situation, or are you still dealing with it?
 

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The NAPA rebuilt CV axles could also be suspect.
There are a lot of poor rebuilders out there and auto parts chains pick them by their price to improve their mark-up rather than by the quality.
 

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I have the same problem, torsen swap my 1.6. Have drivetrain vibration above 65mph, it's so bad the shifter shakes violently. Triple checked the ppf placement.

My guess is that it's the little rubber damper on the nose of the diff. I've heard of a lot of people cutting them off to reduce vibration. I haven't had time to bother since my car has been down for months.

Sent from my Nexus 6P using Tapatalk
 

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Discussion Starter · #12 ·
UPDATE: I figured a brand new driveshaft would probably solve my problem (thanks for the link, MiataQuest!) so I bought a new one from RockAuto. Interestingly, it was .25" larger in diameter. I figured that would likely change the harmonics of the driveshaft, but alas.... not so! Put it in excitedly on Friday night the moment it arrived. But the vibration is still there at 65 MPH..... Grrr..

I'm going to bring the car to a driveline shop nearby, and see if they can diagnose the problem. Will update once I've got it figured out.
 

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Discussion Starter · #13 ·
Hello again, folks!

I've had my brand new driveshaft balanced, and I re-installed it. Still no resolution. From 62MPH to 80MPH it has a pretty obnoxious thrumming. Not violent, but very buzzy. It is a pretty sudden vibration...... the rearview mirror is clear at 61MPH, and 62MPH everything in the mirror goes blurry (I mention this because some have suggested it is just more NVH due to the urethane bushings, but it happens all of a sudden, so I don't think this is something from the urethane bushings. Also, if I put the car in neutral at, say, 68MPH.... until it slows below 62MPH, the vibration is present. I changed the rear wheels & tires as well.... no change at all.

I'm deducing it's something different than the driveshaft, but that spins at the same speed as the driveshaft.

Interested to know if someone else has had the same problem and solved it. I bet there's an obvious solution to this that someone else has actually experienced.

I doubt it is the transmission output shaft, but I never drove the car more than 35MPH on the 6 miles I drove it before I tore it apart (remember, it is a senior driven car with only 49,000 miles on it).......

A few thoughts I had....
- would a bad pinion bearing cause this?
- might the rubber damper at the snout of the differential be a problem?
- I bought used driveshaft bolts..... they look pretty normal and they're all the same size....

Miata fans, thanks in advance for your help...... this is a pretty frustrating situation and I look forward to having it figured out!

Sincerely,
 

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Discussion Starter · #15 ·
Wow, I just stumbled onto my old post from a few years ago...... just to 'close the book' on this one..... I ended up removing the differential from the "urethane bushinged" housing, and put it back into another housing with OEM Rubber bushings....... it solved the problem completely...... it still doesn't make sense, but I wasn't going to spend time overthinking this one..... I'm happy I could get on the road and up to 100MPH without any vibration. It completely changed the car for me again.
 

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weird that it seemed to be the bushings. i had the same swap done with the same ES bushings last fall with no issues after.
 
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