Structural Integrity

Donovan · Post by **Donovan** » Wed Feb 09, 2011 2:38 pm

I have done something recently that has given me concern that I have to consider whether I start looking for another donor car for my wee little project.

Yesterday for the first time in the 4 months I have had the car, I took the hardtop off it and went for a drive. The car went from being a nice well balanced chuckable thing to a Elvis Presley impersonator (shake, rattle and roll).

Now I realise the concept of convertibles being not as structurally sound as a tin top, but thought that since these car were designed from the ground up to be an open top, rather than something turned into one later on, that they would be much the same, whether the hard top was in place or not. I have never driven or been in a MX5 other than my one, so don't have a point of reference for this.

I am begging to think that this thing has been in a major biff, and not put back together right, which is going to be a bit of a concern for two reasons. 1 being the 300KW that is about to be injected into it, and the other that it will fail the cert process because something is amiss.

Is there something I should be look at/for, or should I just call it a bad buy and go looking for another one?

Keith Jones · Post by **Keith Jones** » Wed Feb 09, 2011 4:00 pm

The NA does has a bit of a reputation for body shake. Which is why the first thing peope do is add the two braces underneath, and Mazda introduced the behind seat brace on the later NAs.
Whether you have a dog or not is difficult to say, but you are welcome to come for a drive in my road car, which is an 89 with underbraces added.
PM me if you do.

sprsta · Post by **sprsta** » Wed Feb 09, 2011 5:01 pm

take the rubbers off along the front edge of the rear quarter panels (where the back edge of the doors would be) and have a look for spott welds

we had a BRG one come into the shop a while ago with the whole rear half replaced(cut and shut)

stop in at my workshop some time ill have a look if you like

Donovan · Post by **Donovan** » Wed Feb 09, 2011 8:09 pm

Thanks SPRSTA, will take a look and see if I can see anything, and also might drop by your workshop at some stage, for you to cast a professional eye over it.

Hate to go to the trouble of putting all this running gear in it, and then just have to pull it all out, and stick it in another body.

Gravelben · Post by **Gravelben** » Wed Feb 09, 2011 9:11 pm

The underbody braces make a big difference to rigidity, as does a rollbar in the back.

Another point is that if the alignment is out it will multiply any shake hugely, they're quite sensitive cars to alignment and wheel weight - overly heavy wheels can have similar nasty effects.

Donovan · Post by **Donovan** » Wed Feb 09, 2011 9:31 pm

The car is fitted with a rollbar with two cross beams in it, and anchored in four places, so it has made the back stiffer. It has pretty stiff suspension setup, but I had the dampers set to one of the softer settings at the time (which is still pretty stiff)

The mounting kit for the new running gear has two braces that run down either side, and then have a cross member underneath the transmission, I have also got a couple of boss frog arms coming in the container (http://www.bossfrog.biz/Miata_Performance.html) so hopefully that will help a bit more.

The places that I seemed to notice the most were at the back of the doors and the A pillars/windscreen. In fact I had my phone mount kit on the windscreen at the time, and is normally ok on it, but it was just jumping around like a pee in a washing machine. At the time was only doing about 80kph on a typical NZ (crap) road

I have only just had a wheel alignment done only a couple of weeks ago, so hoping that it isn't that.

Structural Integrity

Structural Integrity

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