Gearbox options/experiences
#421
That's not 4th that's the primary drive gear set that broke. Drives the secondary shaft and every gear except 4th. 4th gear in the 5 speed just locks the input and output shaft together so no load actually goes through any gear teeth at all in 4th for a 1:1 ratio and the secondary shaft just spins freely with no drive load. Cant break 4th. The six speed does that in 5th.
Thanks Bob. Hope you get your transmission issues sorted out on a more permanent basis.
#422
WHP doesn't seem to be what kills them. Seems like north of 350tq the lifespan is measured in minutes. 320tq it's maybe a few hours. Below 300tq maybe a season. Lots turbo guys in the 250tq range have never broken an AZ6. I believe they are rated at around 200tq as implemented in the FRS.
Bob, what's your histogram or tq vs life?
Bob, what's your histogram or tq vs life?
#423
WHP doesn't seem to be what kills them. Seems like north of 350tq the lifespan is measured in minutes. 320tq it's maybe a few hours. Below 300tq maybe a season. Lots turbo guys in the 250tq range have never broken an AZ6. I believe they are rated at around 200tq as implemented in the FRS.
Bob, what's your histogram or tq vs life?
Bob, what's your histogram or tq vs life?
I’m getting short life like two 6 speed transmissions a year predominantly at under 300 ft-lbs.
I'm not exactly a pansy driver though. NASA TT2 lap records on all the northwest tracks I've driven and this year 4 out of 6 Northwest Region SCCA solo events I've gotten Overall top PAX running SSM in the same car.
Im guessing gear selection in the FRS box with the different primary ratio and tooth counts on 4th gear is good for about 10 to 15% more torque capacity than a the Miata.
#425
Fourth is the drive gear in this trans, and it is the one that broke, or more specifically the 4th counter gear is the one missing a tooth. Depending on how the gearset was made, you'll be replacing the countershaft if it's arranged like a stock gearset, which has the counter gears for 1-4 as one assembly, or counter 4th individually if the Quaife set is modular. I'd be happy to share a diagram for a stock transmission which illustrates that clearly.
#427
Also Subaru is putting a turbo in the BRZ I think for 2015 ~280hp from the factory.
I have an S15 SR20DET 6 speed box. I'm still debating about tearing apart and seeing what can be done. I still don't think the factory gears in it are strong enough just slightly stronger than the Miata version. Same gear ratios as the BRZ. Primary gear ratio it has sends higher speed and lower torque through the secondary shaft, tooth counts on 4th make for bigger teeth as well.
#428
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There was a big thread on this and the S15 Nissan box. It is a very similar AZ6 to the Miata center section looks identical with a different bellhousing and tail section. gears are all different but theory is a hybrid box could be made. Aftermarket gear sets are available for the S15 AZ6 box with claimed HP capacity in the 400 hp range with very optimimal close ratio 6 speed ratios.
Also Subaru is putting a turbo in the BRZ I think for 2015 ~280hp from the factory.
I have an S15 SR20DET 6 speed box. I'm still debating about tearing apart and seeing what can be done. I still don't think the factory gears in it are strong enough just slightly stronger than the Miata version. Same gear ratios as the BRZ. Primary gear ratio it has sends higher speed and lower torque through the secondary shaft, tooth counts on 4th make for bigger teeth as well.
Also Subaru is putting a turbo in the BRZ I think for 2015 ~280hp from the factory.
I have an S15 SR20DET 6 speed box. I'm still debating about tearing apart and seeing what can be done. I still don't think the factory gears in it are strong enough just slightly stronger than the Miata version. Same gear ratios as the BRZ. Primary gear ratio it has sends higher speed and lower torque through the secondary shaft, tooth counts on 4th make for bigger teeth as well.
#429
It does not look that bad in the new photos. I'll stick with my previous thought regarding the replacement of both halves of that affected gear pair and using the transmission. There does not appear, at least in the photos, to be any horrible smearing or damage to the teeth otherwise.
Fourth is the drive gear in this trans, and it is the one that broke, or more specifically the 4th counter gear is the one missing a tooth. Depending on how the gearset was made, you'll be replacing the countershaft if it's arranged like a stock gearset, which has the counter gears for 1-4 as one assembly, or counter 4th individually if the Quaife set is modular. I'd be happy to share a diagram for a stock transmission which illustrates that clearly.
Fourth is the drive gear in this trans, and it is the one that broke, or more specifically the 4th counter gear is the one missing a tooth. Depending on how the gearset was made, you'll be replacing the countershaft if it's arranged like a stock gearset, which has the counter gears for 1-4 as one assembly, or counter 4th individually if the Quaife set is modular. I'd be happy to share a diagram for a stock transmission which illustrates that clearly.
Input primary gear is one piece with the input shaft. The other side of it is one piece with the secondary shaft. So fixing it involves replacing the two shafts.
#432
Thanks Bob. Second order of business, given that my replacement tranny should be here next week, is what gear oil to use.
Bob, I think I read you were going to try the Amsoil. Given that you just blew up another 6-speed, it apparently isn't a panacea. Do you think it helped extend life at all? How was shifting (hot and cold)?
- Redline Shockproof (unadulterated or mixed with something else)
- Amsoil Severe Gear SAE 250
- Something else?
Bob, I think I read you were going to try the Amsoil. Given that you just blew up another 6-speed, it apparently isn't a panacea. Do you think it helped extend life at all? How was shifting (hot and cold)?
#433
No that is not 4th gear it is the primary gear set that drives the secondary shaft for every gear but 4th. There is no 4th gear set in the 5 speed box so it can't be broken. When you shift to 4th the selector ring just locks the input and output shafts together and all the drive just goes straight down the two in line shafts 1:1 and the rest of the gears and the secondary shaft just spin with no load at all being transmitted through them.
When you tell someone to upshift from 3rd to the next higher position, what would you call the position where the shifter ends up? We are talking about the same thing and using different terms.
Call it what you will: direct drive, 1:1, 4th, Main drive… Mazda refers to the hub/sleeve assembly which locks the input gear to the output side as the “Hub set, Clutch – 3rd & 4th”. It also refers to the input gear as “Gear, Main Drive”, not 4th, and 5th gear as “Gear, Over Top”. If this were a highly technical discussion then using the exact nomenclature offered by Mazda would be appropriate, but given the relative lack of knowledge by the casual reader then I don’t think it’s a big oversight to refer to the broken tooth to be relative to the “Counter 4th“. We both know what they do, but everyone else reading this may not so I simplified it a bit.
Originally Posted by DeerHunter
What kind of expertise is required to change out gears and reassemble? Can any competent shop do it or should it go to specialists?
#434
Thanks Bob. Second order of business, given that my replacement tranny should be here next week, is what gear oil to use.
Bob, I think I read you were going to try the Amsoil. Given that you just blew up another 6-speed, it apparently isn't a panacea. Do you think it helped extend life at all? How was shifting (hot and cold)?
- Redline Shockproof (unadulterated or mixed with something else)
- Amsoil Severe Gear SAE 250
- Something else?
Bob, I think I read you were going to try the Amsoil. Given that you just blew up another 6-speed, it apparently isn't a panacea. Do you think it helped extend life at all? How was shifting (hot and cold)?
#435
I sent a sample of my 5K-mile 6-speed oil (Redline MT-90) to Blackstone just before Laguna. This was with the now-dead 2560, so only 260-270 ft-lbs of torque, but they didn't identify any particular issues with the oil. That said, iron was at > 50% of their "universal average" after 5K miles, with the "universal average" being about 24K miles.
Bob, have you ever had a tranny stay together long enough to change the oil on it and do an analysis?
--Ian
#438
I know how this trans work, but I’m sure someone here appreciates your time to explain it.
When you tell someone to upshift from 3rd to the next higher position, what would you call the position where the shifter ends up? We are talking about the same thing and using different terms.
Call it what you will: direct drive, 1:1, 4th, Main drive… Mazda refers to the hub/sleeve assembly which locks the input gear to the output side as the “Hub set, Clutch – 3rd & 4th”. It also refers to the input gear as “Gear, Main Drive”, not 4th, and 5th gear as “Gear, Over Top”. If this were a highly technical discussion then using the exact nomenclature offered by Mazda would be appropriate, but given the relative lack of knowledge by the casual reader then I don’t think it’s a big oversight to refer to the broken tooth to be relative to the “Counter 4th“. We both know what they do, but everyone else reading this may not so I simplified it a bit.
Thus my admission of having seen neither the inside of a Miata trans, nor a Quaife gearset for one, and my guess as to whether the Quaife set was modular. It looks like Deerhunter got lucky and it is, based on the pic he posted, and can replace only the two items I had suggested a couple of posts ago.
Do you not trust that the guy who got it this far can handle the rest of it? Looks like they have a decent handle on how it comes apart.
When you tell someone to upshift from 3rd to the next higher position, what would you call the position where the shifter ends up? We are talking about the same thing and using different terms.
Call it what you will: direct drive, 1:1, 4th, Main drive… Mazda refers to the hub/sleeve assembly which locks the input gear to the output side as the “Hub set, Clutch – 3rd & 4th”. It also refers to the input gear as “Gear, Main Drive”, not 4th, and 5th gear as “Gear, Over Top”. If this were a highly technical discussion then using the exact nomenclature offered by Mazda would be appropriate, but given the relative lack of knowledge by the casual reader then I don’t think it’s a big oversight to refer to the broken tooth to be relative to the “Counter 4th“. We both know what they do, but everyone else reading this may not so I simplified it a bit.
Thus my admission of having seen neither the inside of a Miata trans, nor a Quaife gearset for one, and my guess as to whether the Quaife set was modular. It looks like Deerhunter got lucky and it is, based on the pic he posted, and can replace only the two items I had suggested a couple of posts ago.
Do you not trust that the guy who got it this far can handle the rest of it? Looks like they have a decent handle on how it comes apart.
But when somebody says they broke a gear that is the 1:1 ratio for the transmission it's not possible. You can take every gear out of the transmission and still ingage 1:1. as long as the selector mechanism isn't fubar.