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915 transmission in a 930

I have an 86 930 that I would like to put a 5 speed 915 transmission in. I have an SC flywheel and clutch, but I am not sure what it takes to adapt the CV joints. Will the larger 930 drove yolks fit in the 915 transmission? Any advice from someone who has done this mod would be appreciated.
Old 06-18-2007, 06:51 PM
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I believe the M491 cars came stock with 930 axles and a 915 tranny so there are flanges out there that will fit the 915.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 06-18-2007, 08:01 PM
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A stock SC clutch won't hold the power for very long. KEP has an upgraded PP that should work.
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Old 06-19-2007, 03:58 AM
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IMHO, I would stay away from the 915 gearbox. I had one in my car and snapped the main shaft into two. The 915 was never meant to handle that kind of HP or torque.. If you want 5 speeds, by a G-50. Do it right the first time, otherwise you will be doing it again... trust me learn from other peoples mistakes. The gear ratios on the 915 box are also not perfectly matched for a turbo motor anyways. The clutch is smaller, and is still cable operated. If you go with a G-50, you will love the way the trans shifts.... and have hydraulic clutch. Its the best of all worlds.. trust me...drive a car that has a G-50/50, then go drive a 915...there is no comparision
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Old 06-19-2007, 08:49 AM
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Re: 915 transmission in a 930

Quote:
Originally posted by tx93086
I have an 86 930 that I would like to put a 5 speed 915 transmission in. I have an SC flywheel and clutch, but I am not sure what it takes to adapt the CV joints. Will the larger 930 drove yolks fit in the 915 transmission? Any advice from someone who has done this mod would be appreciated.
Oooh, good question.

The later 3.2 drive shafts are different (bigger flanges) than the SC ones, but I'm not sure that they're the same as 930, although they might be.

I know when I replaced the mag case 915 on my car with a late 3.2 alu cased-915, we swapped the fine-spline S type stub axles into it.

The Sachs power clutch seems to hold a 930 just fine, the standard one will live for a while at least.

Renegade do kevlar-faced clutches that hold V8 power through a 915, and Wayne said that they were one of Pelican's suppliers in a thread a couple of years ago - so should be able to get them through our host.

http://www.renegadehybrids.com

In fact, you might want to talk to them about beefing up the 915 or other gearbox conversions - an SC 915 is much better than a mag-cased one, but the later ones - later the better - are stronger.

My mag-cased 915 was quite unhappy after about 230,000 miles in the car (it'd been gone through before), with 25,000 of those in front of a mild 930. You should consider a spray bar kit if you're going to track it - my 5th gearset was blue when it came out, we figured from oil starvation (slosh) under prolonged boost...

Remember, 1st is pretty much for traffic and parking lots only, launching hard really isn't a good idea.

You might also prefer a taller 5th gearset than an SC comes with, I found' 5th pretty buzzy at highway speeds. Short-geared like that, it does go like hell 50-150 though...

I ended up raising 2nd as well, which makes 2-3-4 pretty close, and my 5th is now a good cruising gear (80 @ 3000 in top).
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Old 06-19-2007, 10:21 AM
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turbobrat930 makes a good point.. gearing is all wrong.. you think you have turbo lag now?

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Old 06-19-2007, 01:00 PM
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The level of engine modifications combined with your driving habits will dictate what gearing you like best.

A 915 won't work for you if your engine is modded past 300RWHP and you don't like to buzz the motor.

If your engine is stock you will think you picked up 100HP with the 915. Turbo lag goes away with the short gears.

The 915 is weak. It will not take drag racing starts or sustained torque levels of much more than 300ft/lb for the long haul. If you have a stockish engine and drive reasonably the 915 can be a lot of fun for many years. If not you will blow it up in short order.
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Old 06-19-2007, 06:51 PM
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Thanks for all the good advise. I have a good aluminum case 915 on the work bench just asking to be installed, my motor is stock, and I don't get out on the track so I am leaning on giving it a try even if it is marginal on reliability. It sounds like others have tried it before so someone must know the easiest way to match up CV Joints/axles. Any shared experience on the CV Joints would be appriciated.
Old 06-27-2007, 03:52 PM
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tx,

I had a 915 gearbox in my car for awhile. In contrast to others' advice, I'd suggest it would be fine to give it a try -- especially since you already have one. I loved the gearing; in my opinion it was much better than stock 930 gearing -- which, for my purposes, was worthless. The 915 first is pretty short, but if you consider it a gear just to get started with, second through fifth are great. The problem with the 930 is that the spacing between the gears is too wide. This is solved with the 915. On the track (which is my interest), even the 930 first is too short to be useful. Then there's a huge, lag-inducing gap between first and second. To cap it off, the 930 fourth was too tall to be useful to me under any circumstances. On the 915, first might still be too short for any significant driving, but the other four gears will be perfect, unless you want to go faster than about 160. Yes, it's a little buzzier at highway speeds (because you lose the super overdrive of the 930 fourth gear), but for most fun excursions, I think it's very nicely geared. After all -- it's just the same as a 911.

Yes, the 915 may not be as strong as a 930 box, but even for track use, if you put it together right and treat it with respect, it should last you a while. If you mod the engine to a significant degree, you might want to be careful, though. If you're interested in drag racing starts, or anything that shocks the drivetrain excessively, then forget about the 915. But if you're one who will apply the power smoothly, it should be fine. I know a local road racer who used one with his 500 hp EFI engine very successfully for several seasons. Once he upped it to about 550 hp, he started to break 3rd gear and went to a G-50. If you're going to install a 915, I'd consider at least putting a temp gauge on it (you can do this easily by modifying the reverse light switch to become a temp sender location). That way you can monitor the temps and decide if you need extra cooling. For street use with a few blasts on boost, you'll probably be fine. On the track, you may need more cooling.

To install a G-50 is so expensive that it can't really be considered an alternative to the 915. Unless you want to spend $10-12K to convert, I'd consider the 915 to be a viable option if you want five gears. It sounds like you have an aluminum 915, probably with the 8:31 R&P, which is the best 915 to use.

As far as installing it, it should go in without too much trouble You need a 915 shifter, which just bolts in. I think the shift rod that goes through the tunnel from the shifter to the transmission is identical, but you might want to verify that. The halfshafts just bolt on, as I recall; I think the flanges and bolt patterns are identical. The trick is to get the transmission mounted fore-and-aft in the right location. Neither the 930 nor the 915 stock front mount will work without modification. I can't describe the best way to make this happen; you just need to get some help from a fabricator (if you're not one yourself). My front mount was based on a 915 mount, but it had to be moved about 3/4 of an inch either forward or backward, as I recall. I may have flipped it 180 degrees to help make it reach. In so doing, it interfered with my rear sway bar, which was a small problem. What's important is to locate the transmission so the halfshafts and shift linkage are in the correct locations. That means the engine will be in a different location -- and will be farther forward by about 3/4 of an inch, I think. To accommodate this, I had to make a spacer for the rear engine mount, and use longer bolts, so that the crossbar mount stood rearward from the engine by that amount. The clutch cable worked fine, as did the throttle linkage. All the oil lines, fuel lines and wiring reached just fine. I think the rear engine cavity seal barely touched the rear tin, though. For a clutch, try Kennedy Engineered Products, in California. They make a clutch for the 225 mm 911 flyweel that worked just fine.

Good luck.

Rob

Last edited by Rob 930; 06-28-2007 at 03:45 PM..
Old 06-27-2007, 04:51 PM
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Rob,
Thanks.
y terminology may be a little off when it comes to "half shafts/drive yolks/stub axles", but are you saying that you can remove the output drives from the 930 box and insert them in the 915 so it will bolt up to the CV joint? I have the gasket sets and they have the same diameter seals so I thought it might be possible.

Thanks
Richard
Old 06-27-2007, 05:45 PM
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Richard,

Frankly, I've forgotten the detail on the CV joint swap -- it was about 5 years ago. I know I used 930 axles and CVs with the 915 transmission. Pelican shows a different part number for 915 and 930 CVs, so the 930 CVs are probably larger and maybe won't bolt right to the 915 drive flange. This is something you'll have to verify. If so, I must have put 930 drive flanges on the 915 transmission. But I'm sure that the drive flanges must be completely interchangeable -- because it was so little effort to do this that I forgot I had to do it! I know that the aftermarket Guard LSD is identical for the late (fine spine) 915 and the 930. That's further proof that the drive flanges must be interchangeable (if they need changing at all).

Rob
Old 06-28-2007, 03:43 PM
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Don't do it, you will be braking lots of 3rd gears, btdt,Candy.
Old 06-30-2007, 08:31 PM
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Third gear is not the weak spot of the 915 gears, 2nd gear is.
If you've got enough power to break 3rd gear then 2nd doesn't have a prayer.
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Old 07-01-2007, 07:21 AM
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That's funny, the only gear that I have broken a few times is third gear, in different trannys!!!, using 400hp. max., cheers, Candy.
Old 07-01-2007, 01:33 PM
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I guess the general concensusis that: We all know Porsches are allot of money... PERIOD!!! that being said.....

I thinkw e would all agree that if you had say.... 7 to 10 grand burning a hole in your pocket... then the only way to go is a G-50 or G-50/50 conversion.... it is also the best option.

But allot of us don't have that kind of money available to blow... then for those guys...the only solution is the 930 4-speed or the 915. The 915 being the cheapest of the 4 choices.

It may not be the best choice, but if its the only one you can afford, then there is no question.

However, I have gone down that road before....and have wasted more money than if I just had bit the bullet and did the G-50/50 conversion the first time. I did not "drag race" my car, but was not easy on it either. I had about 400 to 450 Hp at the wheels...
The G-50 series of transmissions shift better, last longer, are beefier, have a larger clutch, and have better gearing suited for a turbo motor.... its your choice......
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Old 07-01-2007, 01:57 PM
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2nd gear is notorious for shucking teeth during a power shift in the 915. Big turbo torqe can peel them off even after the clutch is fully engaged.

400WHP will break every gear in a 915 and bust the housing as well. At that point it is past questionable and a firm given that you can bust the tranny at will.

300 ft/lb is the limit of what the 915 can take long term, and at that you have to treat them with respect. I've seen one 915 grenade with a 225CHP 3.2L Carrera engine behind it during a burnout "demonstration". It was the cool $1000 set of black marks though.
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Old 07-01-2007, 05:23 PM
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A little off topic, but related...

What's a fair price for a 930 transaxle in good condition? I thought perhaps some of you have bought or sold them in the past and could provide some insight.

Thanks!
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Old 07-06-2007, 09:06 AM
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Sell the 915 box and your 930 box and take that money to put toward a 5 speed conversion.. if the 930 box has a LTD in it you can probably get 3500-4500 or so for it depending on who needs it for what at the time... then go put a proper 5 speed in your car..that being said the parts will swap off your 930 box so your turbo axles will bolt up .. I have seen this done many times over the years with poor results... if you decided to roll that way maybe give Hayden at WEVO a call. He has developed some good strengthening parts for the 915 box.
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Old 07-07-2007, 08:10 PM
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I agree with the last poster. Go with the G50 conversion.
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Old 07-08-2007, 05:08 AM
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http://sfbay.craigslist.org/eby/car/368725126.html

I just solved your problem...86 turbo with rebuilt motor 3000 miles ago with a G50 already in it...25K if that car checks out that is a heck of a price IMHO
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Old 07-08-2007, 09:47 PM
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