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Old 01-26-2011, 02:32 AM   #1
thenewwazoo
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Default Picking a transmission for some blasphemy

Hello there Convertards.

Today I ordered an EZ30D for my Porsche 914 project, and it's time to start considering a transmission. Given the light weight of the car, the 2WD nature, and the fact that I'll be running 215-wide tires at the widest, I don't think I need a beefcake gearbox. Essentially, my requirements are:
- must have hydraulic clutch operation
- must be cheap

Which transmissions were hydraulic (and are conversion parts easy to find)?
I should be able to use a WRX flywheel/clutch/pp with any transmission, right?
Could I reasonably get a hydraulic FWD box and use a WRX clutch setup on it?
What halfshafts/axles work with which transmissions? Are they all interchangeable?

Any and all guidance would be appreciated, as searching hasn't proved all that fruitful.
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Old 01-26-2011, 04:12 AM   #2
kcpaz
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Your clutch set-up has to match the transaxle you use so if you use a stock 901 Porsche gearbox with an adapter kit, you will need to run a Porsche clutch. If you use a 2wd converted Subie 5 speed WRX gearbox, you will be able to run a Subie clutch. Obviously the 901 is not a hydro actuated clutch, so that is out... and besides, they suck. The Subie has been done before, but the problem with that set-up in a 914 is you usually have to hack the rear trunk bulkhead to clear the intake manifold and the starter because the distance from the center of the CV flange to the engine is so short compared to a real mid-engine transaxle. Search around on the 914 World Forum and you will find a lot of information... a lot more than you will find here. Come here for the Subaru specific stuff, but go to the 914 forums for chassis specific stuff.

Another option is to use a Porsche Boxster transaxle with an adapter kit (that I will be releasing in the next few months). Take a look at this thread... http://forums.nasioc.com/forums/show....php?t=2047734 for more info.

Highlights include...

- The transmissions are affordable. 5 speeds can be found for $800-$1000 and 6 speeds for $1500-$2000 (both use the same adapter kit.
- They both use a hydraulic clutch
- They come from the factory with a cable shift mechanism, where as the Subie would need some sort of custom linkage and cable system.
- They shift like butter and they are relatively light weight.
- LSD's are readily available
- They already use Porsche CV's so axles would be easy and just a matter of ordering custom length shafts from someone like Sway-a-way. And BTW, the Boxster 5 speed axles use the same wheel bearings as the 914's from what I've heard...

If you have some time, I already have a straight, rust free 914 chassis that I will be using to mock-up an engine cradle system on as soon as the Boxster is finished, so if you aren't able to, or don't want to do your own fab work, it would be mostly bolt-in.
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Old 01-26-2011, 10:25 AM   #3
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^^^yeah but he'd need to be able to guy the adapter to make it work
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Old 01-26-2011, 11:30 AM   #4
thenewwazoo
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Lots of good information kcpaz, but I'm specifically looking for Suby info - a 2WD converted suby gearbox is still cheaper than an Audi/Boxster gearbox and an adapter, and with no weird clutch issues to deal with. Axles are easy and cheap to have made.

So, can clutches be interchanged amongst different gearboxes? Halfshafts? And which years/models came with hydro setups?
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Old 01-26-2011, 01:46 PM   #5
RallyColtTurbo
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IIRC, there were no hydraulic FWD transmissions. At least not in North America. Converting a AWD trans is likely the best choice.
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Old 01-26-2011, 02:18 PM   #6
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phase 2 (99+) are all hydraulic clutches. Turbo models up to 05 cam with pull style clutches and slave cylinders. All others (turbos 06+) are push style clutch and slave cylinder. The flywheels are interchangable...

To convert an AWD trans to front diff drive (relative term) requires locking the center diff via welding or a spool. You then need a block off plate for the rear of the center diff or a plug for the tailshaft. Then, most all 5-spds have open front diffs, so you'll want to upgrade that.

The 6-spd is slightly different but they aren't cheap, so you aren't asking about them.

See this thread for some recent details http://forums.nasioc.com/forums/show....php?t=2093090
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Old 01-26-2011, 02:50 PM   #7
thenewwazoo
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Very nice! That makes things nice and easy. I've been all over the 914 forum for a while now, so am fairly familiar with all the 914-specific aspects of the conversion, such as the Bremar/Subagear FWD conversion, etc. Now I'm in "buying parts" mode.

Do you know if the 96+ 2.5L Legacy transmissions were hydro?

Edit, google appears to think that all the transmissions mated to 2.5Ls were hydraulic. Nice. Anyone wanna sell me theirs?

Last edited by thenewwazoo; 01-26-2011 at 03:03 PM.
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Old 02-13-2011, 01:27 PM   #8
thenewwazoo
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Just as quick follow-up, packaging requirements meant that I had to go with a push-style clutch slave cylinder (unless I wanted to cut my chassis), which meant a 96+ Legacy 2.5 trans or a 98+ Impreza 2.5 trans, but excluded JDM transmissions or the 02-05 WRX transmissions. The 06+ WRX boxes are still waaaay expensive, and I was discovering that high-torque clutch solutions for the N/A boxes basically just don't exist.

My current plan is to use the 05 Impreza Outback transmission I ordered, and mate it to an 06+ WRX flywheel/clutch/pp, using the non-turbo slave cylinder and clutch fork. That means I get to choose amongst clutches that can hold as much power as I will ever make, and still mount the slave cylinder as far toward the engine as possible.
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