One for the transmission gurus

[evolutionmovement]

Probably a long shot, but does anyone know if the front differential gears can be rotated (so that the axles would turn in the opposite direction)? This is supposedly doable on the rear diff and gave me the idea.

[gijonas]

Someone is going rear engine eh?

[fishbone79]

I'm inclined to say "sure, why not?" after having been in several 5MT's numerous times... but I'm wondering if you could actually set up the diff and reassemble successfully with it in the other half of the case... Adjusting the fore-aft position of the pinion shaft would be very difficult, if not impossible, and re-meshing the gears on reassembly would require some acrobatics. If you could set the position of the pinion shaft within tolerances, adjusting the lash through the drain hole when she's all buttoned up tight (as you are supposed to) would be tough with the diff on the other side. Other than that, it is physically possible.

Oh, you might have to move the dipstick hole too.

[evolutionmovement]

So you think there's the chance? Might be worth getting a beat transmission to try, then.

For the curious, I'm thinking that making Tigershark fwd might just add a couple years on the end of my life (though those are probably useless years where I'm shitting myself and forgetting my name anyway) instead of having to figure out and put together a CV joint driveshaft setup that passes under the seats, between the double floor (the passenger floor of which will be armored!) to the Goldwing swingarm which may or may not live with the extra power and weight strain I'll be putting on it and will be more difficult to modify to accept my unique (as far as I know, though everything seems to have been done before somewhere at sometime) rear suspension, and still have less than 500 lbs. of tractive force on a good day (damn car might end up being lighter than 1500 lbs., which is actually a little bit of a problem in this case), and, oh, yeah I live in friggin' New England, so fwd makes more sense. Being that it is a 3-wheeler, fwd will be a little different experience than with a 4-wheel car and my fwd GLs were fun and full of steering feel (with an aftermarket wheel) at an easy 800 lbs. more weight, so I probably won't notice any loss of intimacy vs. rwd, but I do lose the ability to power oversteer at will. That's probably a good thing too, now that I think about it. There's also the need for 70% or more of the weight on the front with this type of vehicle, which leans to fwd again. So the idea is to try a Subaru fwd drivetrain backwards (yes, Saab style, but at least not with the transmission under the engine), using as much of the suspension parts as possible (everything but the struts, which would be replaced by brackets on the spindles for custom upper control arms with brackets for inboard suspension, which should fit nicely over the transmission. I even came up with a way to make the axles aerodynamic (but I probably won't bother as it will make replacing them too much of a PITA. Would look damn, cool, though). Allows me to keep the whole vehicle lower, as well, since there's no driveshaft to sit on top of.

[fishbone79]

I think there's a pretty good chance... I think the only real issue is going to be adjusting the ring and pinion lash... If you can snake a dial indicator through the drain hole to a tooth on the ring gear, you might have a chance. However, now that I think about it, the case might not have flutes/buttresses to support the lateral stresses produced by the ring gear. I think it probably depends on the year... I think the 1st gen legacy might be OK, but the e.g. WRX case looks like it may not be well-enough reinforced on that side... Also, the support buttresses will need to be ground to accommodate the ring gear. See the top part of the right case half here:



I think the only consequence that might be noticeable is a little goosieness in the drive line.

Also, that post on the Dune Buggy forums is pretty useful. Apparently it's much simpler to just buy the correctly machined ring and pinion (I'd agree with that 100%) but I'm not sure it will do exactly what you want. I also notice that Matt Monson is cited in there a few times, wonder if he's ever chimed in?

[fishbone79]

Here's a shot of his reversed machined ring and pinion. Looks worth the $$$ to me, I think that would do exactly what you want... The idea is not very new.

[evolutionmovement]

Thanks for that link. I'd be using a 1st generation fwd transmission anyway. Could I drill and tap another hole for a second plug to use as access on the other side? That custom made gear set looks good, if a little pricey, and I'd have to call inquiring about the older transmission fitment. He mentions them being weaker than 4wd versions, but with half the weight to accelerate and ~2/3 the aerodynamic drag at speed, I'm not remotely worried. The gear ratio isn't bad, either (actually stock fwd 5MT 3.7). Surprising, as I'd figure those offroad guys would want something really short, which I definitely don't. Now I wonder if there were any OBDII fwd Subaru Imprezas made. I think they were discontinued by then.

[gijonas]

Porsche trans better for this??

[evolutionmovement]

The ones I've seen are as much as a bullet-proof transmission for Duchess, I don't like the gear ratios, an adaptor also has to be purchased to mate it to the engine, and I don't want anything German in my car if I can help it. Some of those cases were magnesium, too, and I don't want that either. I want to get as much as possible from a single donor car. So far, not knowing what I'll end up doing with the HVAC (probably have to be mostly custom), the only other donor I'll be using is possibly new Audi TT or similar for parts of the taillights, unless I can make something similar myself (I need to actually get a taillight unit to inspect to know). There's my no-German rule and an Audi of all things, but I love those rectangular lighting elements and they'd fit my design so perfectly and really help the vehicle stand out as something that doesn't look built-in-a-shed.

[gijonas]

I dont see why you couldnt make the subaru trans work for this really.But i do wonder about some of the details such as how the pinion may be under different loads being reversed and such,would the thrust loads be reversed as well (the direction it sees in reverse)??? too much to think about.

[evolutionmovement]

I would think they'd be the same if I buy that kit. Seeing as going fwd probably works out saving me somewhere in the neighborhood of $3k over rwd, I guess I could justify picking up the gear. Still, I'd like to tear apart a transmission to see if I can reverse it first, even if just out of curiosity. If it works, it might be worth seeing how long it lasts as the transmission should be pretty easy to swap out and the less stress of lighter weight, it might not be an issue. But if I ever get a hold of a DI Subaru engine, I might want to upgrade then.

[fishbone79]

The pinion gear does not drive the ring gear directly at it's center, but is offset from the centerline by ~2cm. I'm wondering what difference this will make because you will not actually be simply spinning the ring gear around the pinion to reverse it... you will be mirroring the geometry as well. It may work out that the gears are cut so this does not make a difference, but I have a feeling it does.