Throttle shaft broke
 

My throttle shaft broke this weekend. Had towed around 3 hours to run a great event with the Renegade Miata club at Devens airfield in Mass. First run in second session, right when I was getting into the groove of the massive grip from the Hoosiers, FUCKING THROTTLE SHAFT BROKE! Apparently, it is common, there is a thread on m.net. Sucks. It broke at the pax side screw holding on the butterfly. Then the throttle bell crank fell out of the throttle body.

We rigged something to get it on the trailer to pull back home.

Sucks, I was just starting to go fast...

at least there weren't any stray pieces that made their way from the breakage to you cylinders...

+1

Hard to believe, still. I'm reading on it: http://forum.miata.net/vb/showthread.php?t=302371

I was buzzing the shit out of the car Saturday, that is surely the reason. I didn't really expect mechanical troubles out of 1.6 n/a power, but so be it. I hope there might be a fix for it.

what does "pax" stand for?

I've heard you can adjust the stop to prevent this from happening. Hopefully its true.

PAX is professional autocross index. It'd be better to call it RTP, which is 'racer's theoretical performance.' It's a way to index differently classified cars with a multiplier to equalize times. Some clubs use it to make a "Pro" class, some base season points on it. It is a reasonable way to figure your times versus others in your club to see where you stand in the rankings.

I have to check the throttle opening amounts to see if it was caused by the linkage trying to move the throttle crank beyond WOT. This would put stress on the shaft. If not, it's harmonics or something. I'm thinking maybe the brazed screws and butterfly would be good insurance.

I really was laying against the limiter for extended periods of time. It was just that type of course, and I'm on 13" wheels, so I'm gearing limited on longer courses.

Pax also stands for "Passenger"...

Years ago when I was driving my brother's turbo BP mx3, the throttle shaft broke on me while I was boosting in third gear. It was a FORD 70mm throttle body. Nothing is safe from it happening. :)

As violently as my whole car vibrates when I'm near redline, I wouldn't be surprised if a BP could break a throttle shaft from any application. I can't think of any other car I've driven that shakes so damn bad at high rpm.

Breaking news, BPs have harmonic issues. Throttle plate stop won't do anything. Rev it past 7k normally and it's just a maintenance item. I think Emilio has broken like 3 or 4 of them.

I read a post from somewhere about an EP builder who was spinning them to ~9200rpm. He said that they were breaking some crazy shit, like oil pan bolts and intake manifold studs. I broke a few IM studs on my old '99 motor.

I wonder if the B18 shaft is any better.

Sounds like a good candidate for balance shafts.

Guess that explains the IM brace that everybody always takes off. We may need it after all. haha.

dog shit > Miata motor

and pixel stands for picture element.

lol at the pax part of the discussion. I forgot I originally typed that.

Apparently guys have broken them even with the IM bracing in place. Mine is not present, so that's my data point.

Given what Sav wrote, the harmonics probably don't get any better at higher RPMs. I was sustaining ~7200 rpm when the problem happened, and I was hoping that a new 8k limit might bypass the problem. Probably not...

This is why I roll "low and slow", which is the same way I BBQ human.

Four years now of spinning my own engine to 7800rpm and it is still there, intact. It's my daily driver and I do make it feel uncomfortable any chance I get (pretty much most of the time).

One guy here in a 1.6l DP miata regularly sees 9000rpm he has had the oil pressure sensor brake off twice.

Bob

Petition for one of the smarter people on the forum to fab a balance shaft kit for our engines. :p

Jesse Prather Motorsports has a solution: an "alternate material" shaft with no screw holes and the butterfly is epoxied in place. His replacement shafts for 1.6 throttle bodies have the correct spline for upgrading to a 1.8 TPS. He charges $400 plus a core throttle body. You can contact Jesse at jprather34@cox.net and though this is not shown yet on his new site, the URL is: http://jesseprathermotorsports.com

https://miataroadster.com/brands/Jes...nt_400x300.png

https://miataroadster.com/brands/Jes...ar_400x300.png