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Old 01-08-2021, 04:10 AM   #43
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Originally Posted by Irace86.2.0 View Post
It probably depends on how someone drives.
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Do they just let go all of a sudden? My trans feels fine after 14k Edelbrocked miles.
Very little audible/kinesthetic warning, typically, although you can see warning signs on fluid changes.

I'm not exactly abusive with my shifts; I have a high degree of mechanical sympathy. I have no desire to pay for transmissions.
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Old 01-08-2021, 08:15 AM   #44
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It's probably a heat thing. Even if you're super smooth and sympathetic ( ) to your transmission, I'd imagine the extended track use (and higher than stock torque) you see is generating much higher than normal heat internally (i.e. transmission losses we see mostly manifest in heat). I'm sure you use good fluid and change often, but you'll also see expansion/change of clearances internally as things heat up, seals can break down earlier, etc. Do you use any additives?



Street folks with turbo/supercharger kits will likely have less of a heat problem, unless maybe they are doing some really hardcore canyon driving.
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Old 01-08-2021, 10:36 AM   #45
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It's probably a heat thing.
This goes quintupled for those running a kit that moves the exhaust closer to the transmission. The exhaust is superheating part of the transmission, the fluid has to deal with that external heating as well as internal.

Anyone who wants to save their transmission should terminate the exhaust at the front axles
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Old 01-08-2021, 12:55 PM   #46
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Quote:
Originally Posted by CSG Mike View Post
Very little audible/kinesthetic warning, typically, although you can see warning signs on fluid changes.

I'm not exactly abusive with my shifts; I have a high degree of mechanical sympathy. I have no desire to pay for transmissions.
Mike, can you elaborate on what transmission failures you have had? Has it been syncro issues, the more infamous 4th gear circlip, or other ?
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Old 01-08-2021, 01:47 PM   #47
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There are oil coolers for manual transmissions like on the Porsche GT3. Obviously too much heat could be a problem. It would be nice to have data on transmission oil temps or from people disassembling their transmissions, but I haven’t seen too many. In the end, the damage seems inherent in the limitations of the components, so people just chalk it up to that. I’m definitely beyond the limits of the transmission, as stated by Aisin, so if mine broke I wouldn’t be surprised. If I opened mine open now then maybe I would find some deformation or stress points. Track conditions might just fatigue cycle the metal more often to get it to snap in a timeline that is much shorter than a street car. This is true of all components, is it not?
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Old 01-08-2021, 03:31 PM   #48
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It's probably a heat thing. Even if you're super smooth and sympathetic ( ) to your transmission, I'd imagine the extended track use (and higher than stock torque) you see is generating much higher than normal heat internally (i.e. transmission losses we see mostly manifest in heat). I'm sure you use good fluid and change often, but you'll also see expansion/change of clearances internally as things heat up, seals can break down earlier, etc. Do you use any additives?



Street folks with turbo/supercharger kits will likely have less of a heat problem, unless maybe they are doing some really hardcore canyon driving.
My last transmission failed on the 27th of december, 2020, on the 1st lap of the 2nd session of the day on a rather cold day!

I'd correlate the typical transmission failure more to tire grip and shock loading, rather than heat.

While this is highly anecdotal, I had just swapped in a stock torsen diff recently, due to selling my ATS LSD. My Drexler wasn't ready to put in yet. The track in question has rather large, painted berms, and my AIM data shows a lot of one tire fire when I get on the berms at WOT. This is the same type of load that shredded my OEM axles.
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Old 01-08-2021, 03:34 PM   #49
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Mike, can you elaborate on what transmission failures you have had? Has it been syncro issues, the more infamous 4th gear circlip, or other ?
I've had pretty much all the common ones.

- 3/4 shaft dead
- input shaft failure (most common for me)
- 3/4 fork bent (and subsequently stuck in gear)
- 3rd gear teeth broken
- 4th gear teeth broken


After converting to rising rate boost, I've only had input shaft failures. Even my spoolup is intentionally mellowed out to reduce transient load.
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Old 01-08-2021, 03:51 PM   #50
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My last transmission failed on the 27th of december, 2020, on the 1st lap of the 2nd session of the day on a rather cold day!

I'd correlate the typical transmission failure more to tire grip and shock loading, rather than heat.

While this is highly anecdotal, I had just swapped in a stock torsen diff recently, due to selling my ATS LSD. My Drexler wasn't ready to put in yet. The track in question has rather large, painted berms, and my AIM data shows a lot of one tire fire when I get on the berms at WOT. This is the same type of load that shredded my OEM axles.
That makes sense too - I didn't think about tires. I bet we see a lot of failures in drag racing where we see high grip tires + shock/wheel hop. Temperature failure I would think would more of a long term thing than a sudden heat event right before failure. Just speculation though - as Irace mentioned it would be nice to have some temperature metrics on your setup compared to a normal car. Maybe a blackstone analysis over time too?
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Old 01-08-2021, 05:12 PM   #51
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That makes sense too - I didn't think about tires. I bet we see a lot of failures in drag racing where we see high grip tires + shock/wheel hop. Temperature failure I would think would more of a long term thing than a sudden heat event right before failure. Just speculation though - as Irace mentioned it would be nice to have some temperature metrics on your setup compared to a normal car. Maybe a blackstone analysis over time too?
I have both. Nothing out of the ordinary.
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Old 01-08-2021, 09:11 PM   #52
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I don't have any definitive proof, but I highly doubt the transmission oil is overheating to the point of failure leading to transmission failure - in our specific situation.

the AZ6 unit is exposed to significantly less thermal stress (relative to the oil's limits) compared to the mechanical stress limits.

Our unit uses a 75w-90 gear lube - were talking capacities of above 300°F. And if you're using higher quality oils, we're talking around 400°F or more.

And as CSG Mike explained - normal oil analyses - and he tracks regularly (I need to learn from this man (or women, who knows) one day).
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Old 01-09-2021, 12:09 AM   #53
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I wouldn't say heat is the direct cause of the failures, but it's certainly a contributing factor.

Even after long highway drives (4+ hours), the trans doesn't feel the same, but feels normal after sitting overnight.
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