Why do gears break on the stock transmissions?
#1
Why do gears break on the stock transmissions?
So on FlyinMiata's website, they say "the truth is that the teeth on the gears will rip right off because of the torque." In my mind, there are two things that come into play: gear material/design and movement of the clusters.
If the gears are structurally unsound for high torque, then the only option to keep the 5speed is to replace the gears.
If the clusters are flexing and moving apart, the gears spread apart and moves the contact area on the teeth from the inside (stronger, thicker) to the outside (thinner/weaker), then can something be made to keep the gear clusters together?
Am I totally out in left field with my train of thought?
If the gears are structurally unsound for high torque, then the only option to keep the 5speed is to replace the gears.
If the clusters are flexing and moving apart, the gears spread apart and moves the contact area on the teeth from the inside (stronger, thicker) to the outside (thinner/weaker), then can something be made to keep the gear clusters together?
Am I totally out in left field with my train of thought?
#2
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I recall FM's experience with Quaife suggested that flex was not an issue and the gears were just weak. You're welcome to search miata.net for those threads where they discussed it. Or call Keith at FM.
#5
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To OP: yes your train of thought is more or less correct in terms of the gears, however flex in the shafts shouldn't be am issues. You're forgetting one factor: helix angle. Mazda put a fairly high helix angle (load will be transferee parallel to shaft, not perpindicular) to keep gear noise down. Good for noise and 90hp, but not for strength and 200+ hp. Smallar teeth does not always mean weaker teeth, as again it depends on helix angle, as well as other factors. Teeth also do not mesh in the root of the tooth, but more towards the middle, called the contact patch, which is located on the pitch circle. The gears FM sells by qualfie are made no doubt from a better material, using modern hobing and grinding machines (more precise) and have less of a helix angle for more strength. I couldn't tell you whether or not they changed the hardeness however.
#7
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Can anyone tell me if the 6 speed box is more durable than the 5 speed? I'm on my 4th five speed box now in approx 16,000 street miles at 220 whp. If I knew that a 6 speed would solve the problem I'd shell out the extra cash for one, but 5 speed boxes here can be bought for £50 ($80).
#9
Can anyone tell me if the 6 speed box is more durable than the 5 speed? I'm on my 4th five speed box now in approx 16,000 street miles at 220 whp. If I knew that a 6 speed would solve the problem I'd shell out the extra cash for one, but 5 speed boxes here can be bought for £50 ($80).
#11
Can anyone tell me if the 6 speed box is more durable than the 5 speed? I'm on my 4th five speed box now in approx 16,000 street miles at 220 whp. If I knew that a 6 speed would solve the problem I'd shell out the extra cash for one, but 5 speed boxes here can be bought for £50 ($80).
What the heck are you doing with the damn thing?
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#16
I think I will try and find a cheap 6 speed until I can save the money for the Quafe. I still hate the gearing on the 6 speed. The problem I am having is I keep on getting 5 speeds for $75 or less and I haven’t found a 6 speed for less than $700.
Bob
#19
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It all depends on maintenance and use, just like a lot of other used car parts. It could of been beat to hell at the track, or it could have near new 1st-5th gears and a very worn 6th gear after 100,000 freeway miles. Of course the track'd transmission could be better, sine hopefully a driver skilled enough to track a car knows how to shift, opposed to the 16 year old who's daddy bought her a 6spd miata before teaching her how to drive it. 100,000 isn't a whole lot and although I'd probably trust it, I am on a 5spd with 120,000 fairly abusive miles, so anythings better. Any more info?
#20
It seems like the grinds start early, according to the poll results.