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91 Miata Vibration When Shifting (For Street Car)


gsmith2424
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I recently bought a 91 Miata with 108k on it and I am slowly doing improvements and parts replacement. I have been getting a vibration in the clutch pedal and the transmission seems to shift harder/notchy/jumpy when I start to get above 4k rpm. When the rpms are lower than 4k it shifts without any issues and no vibration is felt in the pedal. I think it may be the motor mounts but has anyone else had an issue like this.

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Do you know if it has had the clutch replaced?  Sounds more like a pilot bushing/bearing issue then motor mounts. Quick short stabs on the accelerator. Watch the gear shift lever. It will move a bit. If it moves a ton then it would be motor mounts or rear diff bushings. I did polly bushings for the rear diff. Great upgrade. Didn't make a noticeable difference in noise as some folks claim it would. Drastic reduction in driveline movement,and better shifting. If you find it's the pilot bushing/bearing and have to drop the transmission,be sure and replace the rear main seal. No sense in having to do it later when you have all the work done to do that when you have already dropped the trans,

Edited by Ian Moone
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3 minutes ago, Ian Moone said:

Do you know if it has had the clutch replaced?  Sounds more like a pilot bushing/bearing issue then motor mounts. Quick short stabs on the accelerator. Watch the gear shift lever. It will move a bit. If it moves a ton then it would be motor mounts or rear diff bushings. I did polly bushings for the rear diff. Great upgrade. Didn't make a noticeable difference in noise as some folks claim it would. Drastic reduction in driveline movement,and better shifting. If you find it's the pilot bushing/bearing and have to drop the transmission,be sure and replace the rear main seal. No sense in having to do it later when you have all the work done to do that when you have already dropped the trans,

 

The clutch and rear main seal was just put into the car right before I bought it and from knowing the history of the car I think it has less than 5000 miles on it. I have also had the main/slave clutch cylinder along with the soft lines for the clutch also replaced.

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1 minute ago, gsmith2424 said:

 

The clutch and rear main seal was just put into the car right before I bought it and from knowing the history of the car I think it has less than 5000 miles on it. I have also had the main/slave clutch cylinder along with the soft lines for the clutch also replaced.

Can you be certain the pilot bushing/bearing was replaced? If you are, that eliminates that direction,unless it was bad from the get go

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Surf around here and see if you can find someone with  a similar problem...........................................

 

www.miataturbo.net

 

Good resource for all kinds of Miata stuff. Be sure you do the research BEFORE you ask the questions. Lots of high and mightys there though............first thing you'll get,............................................................................................................................

"did you do a search'?

Edited by Ian Moone
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3 minutes ago, tommytipover said:

Don't they have some weird setup where the diff is bolted to the back of the trans?  Bet that can cause some vibrations nobody who works on regular cars might recognize.

Yes through a part called PPF,power plant frame.There is no rear trans mount. The rear of the trans and the front of the rear end are linked with it

Exocet-Mazda-Miata-PPF.jpg

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Since we have been racing a 1.6 for three years I would seriously go to the motor mounts and as was said snap the throttle and watch the shifter. If it moves a lot head to the mounts.

They are so low on the motor they take a ton of load and can cause bad effects on the shifting. We added a short aircraft cable from the driver strut tower to the front lift point on the head and only allowed about 1/2" of movement. This completely removed the movement and never lost a mount.

 

As for the spigot bearing in the flywheel/crank they will easily seize and only make lots of squealing noise. Not seen that cause shifting or vibration issues. We have had several get stuck and the front input shaft just spins on the race and I put a small amount of anti-seize on that on assembly.

 

Do you feel the vibration in your butt or seat? That would begin some more looking and maybe driveshaft related or mount and diff related, also might look at halfshafts for a bad cv joint. Vibrations can move forward easily since this is all bolted to the truss.

 

Off the topic if you know anyone looking for a really strong freshly built 1.6 let me know. It has been dyno tuned and has about 18 hours of run time.

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11 hours ago, 55mini said:

Since we have been racing a 1.6 for three years I would seriously go to the motor mounts and as was said snap the throttle and watch the shifter. If it moves a lot head to the mounts.

They are so low on the motor they take a ton of load and can cause bad effects on the shifting. We added a short aircraft cable from the driver strut tower to the front lift point on the head and only allowed about 1/2" of movement. This completely removed the movement and never lost a mount.

 

As for the spigot bearing in the flywheel/crank they will easily seize and only make lots of squealing noise. Not seen that cause shifting or vibration issues. We have had several get stuck and the front input shaft just spins on the race and I put a small amount of anti-seize on that on assembly.

 

Do you feel the vibration in your butt or seat? That would begin some more looking and maybe driveshaft related or mount and diff related, also might look at halfshafts for a bad cv joint. Vibrations can move forward easily since this is all bolted to the truss.

 

Off the topic if you know anyone looking for a really strong freshly built 1.6 let me know. It has been dyno tuned and has about 18 hours of run time.

 

I'm going to get the mounts changed either way as I don't think they have ever been changed and they are known to fail especially the passenger one due to the oil filter location. As for the vibration I only feel it when I have the clutch pedal press in and its mainly only in the pedal. When the car is moving I don't feel much vibration even at the higher rpm. Also tried to see if I could hear anything with the pedal pressed in I heard nothing.

 

 

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