...and people with the LGT gears and newer 5 speeds STILL shred their gearboxes. They just take a little more force before they go.


The transmission weakness issue is twofold.
First is that the case is flexible under extreme loads (like that of an OEM powered car doing a high rev clutch dump, which is similar to a tuned up car going through a regular aggressive shift with a bunch more power)... those forces cause the input/output shafts to push against each other which in turn puts the load on the bearing surfaces, and then starts pushing the case halves apart from each other.

Once that happens, we see the secondary issue, which is that the gears are no longer fully engaged along their entire contact patch. So now you have a LOT of power, and a smaller contact patch to push on/connect across. Eventually the contact patch gets too small to hold up to the forces exerted on it and the gears break.

You can go about fixing the issue in various ways.
Make the gear ratios shorter - less resistance between the output/input shafts and therefore less deflection.
Make the gears stronger - they may be able to withstand running at the reduced contact patch under high load moments.
Make the case stronger - flexing less will keep the gears fully engaged and maintain the design specification contact patch. (blast plates may or may not be effective at doing this... I have not seen any evidence)
Change the shape/orientation of the teeth on the gears - this can change the direction of the outward forces from power throughput and make the gears much stronger (for better or worse).

 

Isn't this Moore Performance's take on things, too? Their 600+ WHP Forester was running a "glass" Bugeye 5 speed. The gears were new, they ran their blast plates, along with upgraded drive shaft and axles. But their theory is that it's not small/weak gears that destroys the 5 speeds. It's the twist/shifting of the case halves that allow gears to get out of alignment and snap teeth.

That's my poor, non-mechanical understanding of it.

 

Well that's been my take on the matter from my own experience but like anything take nothing as fact!

 

My knowledge-free deduction of the situation was that the differences in the gears basically contributed to this issue. Meaning, all of them experience case-flex, but, since the earlier gears are much smaller, there is less material to have the gears engaged to start, to spread the load across if you will, so they fail faster. With my 2002, it was not a launch or anything abrupt when it went. I was going up a hill in 3rd, rolled on the throttle, and was around WOT by ~4k rpm when things started sounding expensive. My car was purported to be making around 275whp at the time, around that rpm.

 

That pretty much summed up my experiences with different gears over the years with the exception being the PPG stuff as it looked rather beefy and spiffy yet shat itself with ease.

 

Interesting. Sounds like case flex is the real culprit.

 

This car was making ~240whp and ~320wtq when this happened.

 

Up2mtns!

 

Looks like something inside flexed and locked up, then BOOM. Again blast plates will help with this, will it solve all the problems...no. But as part of a good plan of cryo, blast plates, and proper mounts, it will help quite a bit.


besides:

1)I am not about to give up my 4.444 gearing
2)I want the only FXT with a DCCD 5 speed in CA

 

What. The....