Nasty Vibrations!

Gerald Warner · Post by **Gerald Warner** » Mon Jan 07, 2008 1:37 pm

My 1989 NA has developed a vibration which sets in at about 105km/h.
It is coming from the rear. It is not the wheels (ie balance; out of round or distorted).
I suspect the inner CV joints as the prop shaft UJ seems tight enough.
I know its a difficult question but is there a common cause to such vibrations? Are MX5s prone to CV or UJ or something else failing? Thanks.

Post by **jif** » Mon Jan 07, 2008 2:06 pm

I have to say it does sound suspiciously like the infamous "65mph shimmy" ... believe some fixes are to check pressures or get it balanced very accurately. There's a comprehensive page about it here http://www.miata.net/garage/65_mph.html

Gerald Warner · Post by **Gerald Warner** » Mon Jan 07, 2008 2:42 pm

Thanks for that. Food for thought, although I still don't think it is the wheels I have been proved wrong plenty of times!

SLYDIT · Post by **SLYDIT** » Tue Jan 08, 2008 2:03 pm

very common problem on early Mx5's. Its just a natural harmonic in the chassis. Later MX5's had extra bracing in the rear subframe to cure this.
Can be caused by the alignment being out also.

it can be easily fixed by adding a brace to the rear subframe where the lower suspension arms bolt to the subframe. Also can be cured by adding a style bar/windblocker that bolt to the seat belt towers.