I'll bite. It would look red in the threads where the shaft broke in half! Damn....

I guess I was lucky, but I never broke a TB on my motors. I never touched the screws either. I disassembled that throttle body a couple months ago and both screws broke in half before they threaded out of the shaft! Mazda stakes the ends of the screws. At least on mine, it would have been impossible for those screws to 100% vibrate out.

I could see them maybe getting loose a bit though, and then it vibrating around till something breaks though.

Either way, I am NOT a fan buying BS for these motors when it's not needed. But I would consider buying a different throttle body since that can be a safety item (throttle failure causing it to stick is bad) and if it fails it takes out a lot more $$$ parts.

 

We tried a slightly different design in that one, but yeah it still failed. We had three regular stock ones snap pretty quickly, (hell, two gave out in the same weekend) but this one lasted around two seasons worth of racing. Every time it's been fatigue cracks in the throttle shaft that released the screw. We got lucky. The first few times, the screw was pounded to slag without hurting internals or compression somehow. This time it took out cylinder four.

At this point, we're done with screws attaching the plate to the shaft. We plan to have only a slot for the plate to thread through the shaft and use some sort of adhesive like Loctite to hold it together, maybe brazing.

Yeah, it might still come loose, but there's no screws and a throttle plate isn't going to make it past the intake runners. The rules won't let us run something like a Skunk2.

 

By that I mean when you're creeping at 5mph in first with the clutch out just above idle its a bit jumpy, but not burnout jumpy. Its hardly noticable compared to a 1 cam later throttle body, but I was coming from the early complex linkage tb.

 

1994 TB? I want to change my '00 TB to it precisely to improve driveability as you describe.

Does it appear to have the same sucky breaky TB shaft and screws?

 

Yeah the 94tb. I believe it still has the same problem with the shaft as the rest of them. I wish I didnt leave the 94tb on the engine that I sold.

 

old af Bump..any fix for this on a 1.6 :( broke 2 this weekend

 

Skunk2 TB

Hate to push that piece of junk, but BTDT and while flawed, it is the only solution that seems to work in solving the issue. Fix the known issues with the Skunk (no great hardship), and you're home.

Some people have used a 70mm Ford TB, and I have heard of a Volvo TB but I'll let those who have tried these speak up for them.

 

Sk2 is only for 1.8 right? I'm 1.6 and not an EU 1.6

 

Double Post*

 

I have been contemplating replacing my OE TB with the S2, but my experience tells me that 99% of the time a broken shaft or lost screw is from an incorrect cable adjustment. I have read the theory behind the JB weld on the screw head and why the S2 is better since it is stronger. I have yet to read or discuss the cable adjustment with someone that understands how to do it correctly. The stop on the throttle shaft should not touch the boss/stop post on the TB body. At full throttle there needs to be a slight bit of clearance that is why the butterfly on most applications goes slightly past full open. Also the Miata has an inherent issue with the gas pedal stop which is very under built. It is very flexible and no match for the strength of the average persons foot.

 

"Originally Posted by blamkin
Jason the throttle stopper is not the issue. I'm not sure who came up with that.
Any stress from a really hard pull on the cable would be taken up entirely by the wheel where the cable is mounted. No stress goes from the cable to the shaft. The cable pulls the wheel, that's it. The shaft just rotates with the wheel - no stress there unless something is binding internally maybe. If we were breaking wheels or TB's the stopper might be the issue.
This really isn't a mystery. Go put your car on a dyno. (Try and) put your hand on the TB about 7K (or 8K) rpm. The vibration is so intense it's painful to the touch. I haven't broken one, but I hear they break at either butterfly-mount screw holes.
Some people are going back to the light steel flywheels instead of the incredibly light aluminum ones. It's entirely an engine vibration issue IMHO.
I have the hard factory motor mounts, so that ain't it. Again I've never broken one of these things, just the screws inside snap off the little pressed-on heads.
Amen. One dyno run, looking at the TB at high RPM, and there will no longer be any mystery.
Mazdaspeed has known about the problem (bad vibes above stock rpm) in EP cars for awhile, I guess they just never thought anyone else was having the problem. The EP racers solution? Braze plate to rod + braze screws to rod = no more breakage.
Since doing this fix (plus putting a randomly chosen durometer rubber gasket between TB and mani - which is probably not doing anything, but WTH) no more broken TBs (knock on wood). Before fix: 3 broken TBs, one ruined motor and 2 damaged motors, one just slightly."

 

This is not true. The shaft may not be in torsion but there is a bending moment. An average person cannot look at this design and say the strain from several hundred pounds of force is not the root cause. Vibration may increase the dynamic loading from the cable. My opinion is that without a cable there would be no breakage.

 

Here is a picture of what I'm trying to say could be the root cause or partial cause to this issue. What I see is that the shaft is in bending. This will put the shaft inside the bushing and main bore in bending. It will also put an axial load on the shaft. It might be when the shaft is loaded in a ridged condition that resonant frequency is different, or the vibration is applied in an axial direction because of the tensile loading. The axial load pulls the butterfly against the side of the main bore and puts the screws in shear My point is that if the cable is adjusted so that the throttle is not contacting stop it might prevent this failure.

 

In a fit of frustration, I took an angle grinder to my TB, so defo no contact with the TB stop. Still broke. I think that is when I got my first S2 TB. That went with the engine in my racecar part-out, and the second S2 was acquired as a preventative with the new car.

 

Any possibility that it was already on its way out before you modded it?

 

It is a while ago, but my memory is that it was spare, about to go on after its predecessor broke. Hence the frustration that led to that act of violence, and yes, I did feel better afterwards. Until it broke too ... and my life-changing decision to go with the S2, which saved me thousands in therapy fees ...