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gearhead
 
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And a thread worth reading.
3rd gear teeth gone! is this common?

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Old 10-27-2014, 11:02 AM
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I remember in the early 1990's running with POC back in the Martin Snow days Sergio Nardi would run his turbo car with a 915 gear box and would go through two or three over a weekend.

I did the mods and am running a G50 in my early turbo canyon runner.
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Old 10-30-2014, 12:23 AM
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what exactly is weak about the 915- as in, if the 930 4 speed is ostensibly a 915 casing with 4 beefed up gears inside, what parts were beefed up in the change over?
Old 10-30-2014, 12:28 AM
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Thanks for all the info Matt Monson!

I actually took my car to a local Porsche expert & racer last night. He actually pointed out that my 915 trans has the reinforced side covers, which is a small relief but I'm still going to be very cautious and careful with it.
Old 10-30-2014, 02:39 AM
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The weak points of the 915 are:
> small bearing retainer - torque warps the retainer causes the pinion to move.
> side plate cover - as the torque moves the assembly towards the side plate the shims are crushed and the side plate cracks.
> LDS - this will more equally load both sides easing the pressure on the side plate.
> small gears/teeth - the long throw on boost from 2-3 can shuck the teeth right off 3rd gear.
> wheel hop - can instantly warp the bearing retainer smash the shims and crack the cover plate.

The worst I have seen is a drag racing incident where the actual housing cracked on the 1-2 speed shift.
To combat these things I used a WEVO bearing retainer, HD side plate, custom gears, LSD, and made a cradle surrounding the R&P housing. That held 400HP on the street. Still not the strength of the 930/4spd.
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Old 10-30-2014, 03:53 AM
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thanks!
Old 10-30-2014, 04:14 AM
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Quote:
Originally Posted by clutch-monkey View Post
what exactly is weak about the 915- as in, if the 930 4 speed is ostensibly a 915 casing with 4 beefed up gears inside, what parts were beefed up in the change over?
A 930 transaxle is about 1.5 heavier than a 915. They are very much heavier, if you ever see 2 side by side, try to pick up both. I didn't weigh them but was quite astounded by the weight difference.
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Old 10-30-2014, 05:01 AM
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Quote:
Originally Posted by clutch-monkey View Post
what exactly is weak about the 915- as in, if the 930 4 speed is ostensibly a 915 casing with 4 beefed up gears inside, what parts were beefed up in the change over?
A 915 and 930 2nd gear side by side.

930 ring and pinion is also much larger and the bearing on the ring gear side it larger and stronger to prevent deflection. A common feature of all aftermarket sidecovers is every one of us upgrades it to the 930 size bearing.

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Old 10-30-2014, 07:11 AM
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Awsome!!!
Quote:
I must have the best 915 ever built! my 84 Carrera has been turbocharged for 5 years and I beat on it like you wouldn't believe. I drop the clutch spinning first into second all the time, heck the other day I did four donuts then grabbed second spinning the whole time till 3rd gear lol. borrowed time I guess
Some great 915 info! Thanks matt

Last edited by northstarbeetle; 11-07-2014 at 11:56 AM..
Old 11-07-2014, 11:30 AM
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Quote:
Awsome!!!

Quote



I must have the best 915 ever built! my 84 Carrera has been turbocharged for 5 years and I beat on it like you wouldn't believe. I drop the clutch spinning first into second all the time, heck the other day I did four donuts then grabbed second spinning the whole time till 3rd gear lol. borrowed time I guess

Again I think your saving grace is the loss of traction. If you were hooking up your gearbox would be even more pissed than it probably is now.
Old 11-07-2014, 11:54 AM
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I've been driving my car with the wider tires for about one month. More traction means more grip. More grip stresses the gears. Today my second gear let go again. Same scenario, load up boost and boom. Second gear gone baby gone.
I still don't know exactly how much power the car has, I'd say 325-350hp but it has big torque down low. My boost is full (.8bar) by 2900rpm. It pulls very hard till 6000rpm. It's a good turbo. Perhaps too good? Something's gotta change and it's not going to be the turbo. But I just can't afford the g50.
I'm lost here with this delema.
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Old 11-15-2014, 07:52 PM
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Originally Posted by quattrorunner View Post
Today my second gear let go again.

I'm lost here with this delema.



Old 11-15-2014, 08:42 PM
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That won't hold. Tried it. Silicone glue maybe?
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Old 11-15-2014, 08:45 PM
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At least with the silicone you'll be able to spot gear oil leaks!
Old 11-15-2014, 08:56 PM
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Puddy,

I am running a similar set up. I have a hot rodded 930 motor in my Carrera and running an unmodified 915. I am taking it easy on the trans while I break the motor in, but I would suggest building up the trans as mentioned in the thread or best option move to a 930 4speed and don't worry about it and enjoy the car. That is my future plan or possibly a G50 to keep the 5 speed option, although the 4 speed is a much better option as far as keeping it simple. From my vantage point I am going to spend the money one way or the other.
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Old 11-16-2014, 04:35 AM
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Quote:
Originally Posted by quattrorunner View Post
I've been driving my car with the wider tires for about one month. More traction means more grip. More grip stresses the gears. Today my second gear let go again. Same scenario, load up boost and boom. Second gear gone baby gone.
I still don't know exactly how much power the car has, I'd say 325-350hp but it has big torque down low. My boost is full (.8bar) by 2900rpm. It pulls very hard till 6000rpm. It's a good turbo. Perhaps too good? Something's gotta change and it's not going to be the turbo. But I just can't afford the g50.
I'm lost here with this delema.
haha feels weird saying this but.. maybe some lag would help?
Old 11-16-2014, 12:06 PM
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I was looking at an electronic boost controller that would use the rpm as one of the inputs. My thought was .5bar to 4000rpm and then all in.
Or..........a stronger transmission. Brian bodart has been saying the same thing for a long time about strengthening the 915 and handling 360hp for a long time. I'm getting that but I di t just want to go to 360hp. I want to raise the boost and see where 1.2 or 1.3 bar gets me provided I have fuel which I doubt I will. But I'd like to see. I just can't with this weak link.
Old 11-16-2014, 12:35 PM
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Quattro, from the YouTube vids your car seems like a blast. If I were you, I'd seriously try to harness myself and enjoy what I have. While doing that save up for a G50. Everything else seems like ignoring the obvious. More HP isn't worth anything if you cannot put it down.

You already got more than most, you need to plan out how to proceed.

Just my 2C.
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Old 11-16-2014, 01:27 PM
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Quote:
Quattro, from the YouTube vids your car seems like a blast. If I were you, I'd seriously try to harness myself and enjoy what I have. While doing that save up for a G50. Everything else seems like ignoring the obvious. More HP isn't worth anything if you cannot put it down.



You already got more than most, you need to plan out how to proceed.



Just my 2C.
I know what your saying. But what you don't know is that I'm always worried about this issue. It may not seem like it but it's always in my mind.
It would be nice to not have the big issue on my mind when I'm wanting to go.
And now that I'm running larger section tires it's even more an issue.
Old 11-16-2014, 02:30 PM
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Quote:
Originally Posted by quattrorunner View Post
I know what your saying. But what you don't know is that I'm always worried about this issue. It may not seem like it but it's always in my mind.
It would be nice to not have the big issue on my mind when I'm wanting to go.
And now that I'm running larger section tires it's even more an issue.
Know where you're coming from. Babying the 915 gets old. Problem is, it's a high-stakes craps game and the house will always win. Eventually.

The compromises on the 915 clutch to hold the power are a massive PITA if caught in stop-go traffic, too.


Even if you spend $$$ on building a high-spec (WEVO bits, LSD, spray bars) 915 and treat it well, it'll still find the weakest link and do stuff like this from time-to-time:



G50 is an expensive conversion - and one you'll probably never see a realistic return on.



If you drive/keep the car long enough, the G50 should eventually work out cheaper than fixing prematurely worn/broken 915's, clutches, gearsets and other ancillary stuff.. Take a while though....

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Old 11-25-2014, 07:57 AM
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