I had a crazy dream about homemade AWD.

A couple of weeks ago I had a very vivid dream about a homemade AWD Rally X car, with some similarities to kevlarcorolla's AWD Geo with a motorcycle engine.

In the dream the car was an indistinct light weight econbox that was a wagon or hatchback, but that's not the important part.

The thing that has kept it running through my mind is the drive system. Kevlarcorolla's Geo uses a chain drive to power the front wheels, but in my dream the car that I was building had a shaft drive, running uninterrupted from a rear differential up to a front diff. Both differentials looked like they came from the rear section of a cute-ute AWD system, like an Escape or CRV. I just flipped one to use it in the front. The steering and front suspension were whatever came with the car. The rear may have been the whole rear sub-frame from the cute-ute, but that's not real important either.

I had a chain sprocket attached to the yoke of the rear differential to drive the whole system from a cycle engine.

In the dream I was stuck on the last few details of the build. First was what engine to use, I wanted to use a V-max because its compact and had a lot of torque & and a low CoG, but the shaft drive would require another piece of hardware to connect to my drive system. I was also considering a goldwing engine, but that would have the same problems. My other choice was a 'busa engine, but I felt that I would wind up mounting it too high, and that engine already has a high CoG.

What I've come up with in the time that I've been pondering this is a chain intermediate drive in-between the sprocket on the rear diff yoke and the cycle engine. The advantages of this would be that I could mount the intermediate drive's input shaft below the diff at the 4 o'clock or 8 o'clock position to bring the whole engine mounting position down, and I could adjust overall final drive ratio by changing the sprocket size on the input of the intermediate drive. The input of the intermediate drive could be set up with a flange for a shaft drive or a sprocket for a chain drive.

As I was writing this I realized that a Harley primary drive belt would be perfect to use for the intermediate drive. I wonder if they have multiple pulley sizes available?

Does this whole scheme seem like it could work? Would the lack of a center differential make it hard to drive at high speeds? What kind of gear ratios do those cute-utes have in their rear diffs, because that could make or break this scheme.

Was this just a stupid dream, or inspiration?

I don't have the answer to any of these questions, but I'd love to hear other's input.

If that was a dream what can you think up when your awake? Holy cow that is detailed and the fact that you remember it with that much clarity is amazing. It is a sign!!! You have to build it.

HappyAndy wrote: Does this whole scheme seem like it could work? Would the lack of a center differential make it hard to drive at high speeds? What kind of gear ratios do those cute-utes have in their rear diffs, because that could make or break this scheme.

I think the lack of a center diff is likely to be a major problem.

I think small SUVs typically have similar final drive ranges to the economy cars with which they share engines -- high 3s, low-to-mid 4s.

HappyAndy wrote: I just flipped one to use it in the front.

Won't work, the front diff will spin backwards.

When you put a rear diff in the front, the ring gear sits on the other side of the pinion gear, so the axles will still turn in the correct direction. The only difference between "normal rotation" and "reverse rotation" gears is how the gear is cut, they flip the drive and coast sides of the teeth around. You CAN run a normal rotation gear on the front but it will lose strength.

codrus wrote: I think the lack of a center diff is likely to be a major problem.

Not so much as you'd think. Audi LWB and Sport Quattro rally cars used a locked diff in the center. I forget what they did for the S1 E2 (the winged monster) but it wasn't locked.

Current WRCars also don't have center diffs, by rules. They are only allowed to have a rear axle disconnect.

THAT SAID. Most of the mini-utes/cuteutes use a Haldex or some variation, and IIRC those are 1:1 drive ratio. (I'm not sure what the CRV has other than being so toothpick like that it is not worth considering for anything) 90% of the time they just have a takeoff from the front differential's output and send it back through a right angle drive, and the Haldex unit is really simple: power on and it is locked, no power and it isn't, and modulate power for varying degrees of "lock".

As far as drivability. My Subaru had a FWD/4WD transmission (no center diff) and you couldn't really tell a difference in anything when in 4WD unless you were trying to turn in a parking lot. That car spent 90% of its life in 4WD, rain or shine or snow.

My current AWD car has lockable open diffs and you can't tell a difference on dry pavement. In the rain and especially the snow, the car is very sketchy and unstable with the diffs unlocked, but lock the center diff and the car is connected to the ground like a 10 ton block of granite. Just unflappable. It also STEERS like a 10 ton block of granite. Probably has something to do with having 400lb of engine sitting between the bumper and front wheels, and 175lb of transmission over the front wheels, and steering geometry like a J-car.

AMC Eagle had a vacuum operated, single-speed t-case w/ viscous coupling, IIRC NP195. Adapt the input shaft to the MC shaft drive. Should handle reasonable MC engine power.

Anything like that work for ya?

just my .02

dean1484 wrote: If that was a dream what can you think up when your awake? Holy cow that is detailed and the fact that you remember it with that much clarity is amazing. It is a sign!!! You have to build it.

Well, the intermediate drive and the H-D belt & pulleys didn't come from the dream.

I've also been thinking of home brewed AWD for years. I've though of putting a FWD in sideways in the middle, but couldn't get past the conundrum of double final drives. Maybe this was my subconscious minds way of solving that problem. Oh, and I love kevlarcorolla's AWD Geo, but all those chains freak me out.

HappyAndy wrote: I've though of putting a FWD in sideways in the middle, but couldn't get past the conundrum of double final drives.

Haldex front and rear. Weld up the center differential and perma-lock the rear diff. You can control the front diff with a switch or you can rig up a controller, but that looks like it may have a steep learning curve as far as determining WHAT the car wants. Basing lockup percentage off of throttle position or manifold pressure probably wouldn't be too far off, though.

This, incidentally, is where I'd been thinking for my GTI. A transverse trans would work too (02A/J for strength - the 020 probably lives only because light FWD cars have no traction) but longitudinal mounting reduces effective available interior room. Shoving the engine behind the passenger seat sideways with a "longitudinal" transmission means that, theoretically, there can still be trunk space. (This is how the 205 T16 was built, incidentally)

The next problem is that Haldexes are flippin' expensive used. Granted they were put in just about every GM transverse AWD minivan but they also have a bad habit of going wonky with age so there is a good demand for them too.

You know what? Nevermind. I found some Rendezvous rear diffs for $300-400 a pop, and apparently front-drive Passat transmissions go for stupid cheap.

ARG. Okay, first get Quantum put together, then get RX-7 rebuilt, THEN worry about making a Rabbit T16.

Just because I geek out about this sort of thing:

Now, that center diff needs an explanation. Power from the center crownwheel goes through a hollow shaft to power the diff. It's an epicyclic diff with a viscous coupling on top, similar to some Subarus. Power to the front goes through the hollow shaft, power to the rear goes straight back.

We don't have the engineering/fabrication might that Peugeot had but we do have access to other things. The one possible sticking point is driveshaft rotation - I don't know if Haldexes are "reverse rotation" or not. (Audi longitudinal rear diffs are ALL reverse rotation but then there's the double final drive problem)

Why not put an engine out of a snowmobile along with the CVT set up instead of a bike engine?

Sure it wouldn't allow you to shift gears, but it could be mounted low and weighs almost nothing.

An 800cc triple with triple tuned pipes would sound incredible, and probably puts out close 160hp stock.

Not to mention many of the sleds had reverse, so you could have reverse with minimal engineering.

Couldn't you use a transfer case with sprocket on the front input where the trans would be?

MrJoshua wrote: Couldn't you use a transfer case with sprocket on the front input where the trans would be?

Only if it has a bearing and not a bushing.

Granted, I don't remember if any transfer cases were made with a front bushing instead of bearing, but it'd be something to check for sure.

Or find a divorced transfer case. I think Samurais had those. I seem to recall people putting 12As in those by doing some jiggery-pokery with an RX-7 front driveshaft yoke and a Samurai spud shaft yoke.

You've been looking at Ford RS200s haven't you? Engine in back, drives transaxle in front, then power goes back to rear diff.

Or just use your favorite transverse engine/trans combo and turn it 90 deg. Output shafts become drive shafts going to the front and rear. There's your center diff.

In reply to Appleseed: And then you run straight into the double final drive conundrum.

You need a center diff or it would chuff-chuff-chuff on pavement. A locked center doesn't always feel good on slick stuff either, under certain conditions you get "binary" handling where the vehicle's behavior is night and day between accel/decel. Having zero steering control when on the gas and very sharp steering when off the gas for example, something my sammy does in very "greasy" mud.

Looks good other than that.

Locked center.

I just drove 150 miles with the center locked. No issues...

In reply to Knurled: what exactly is this "Haldex" that you are talking about? Haldex makes all sorts of mechanical, hydro-mechanical and electro-mechanical devices.

Haldex made the rear differential/clutch pack unit for a lot of transverse AWD setups. The ones that stick in my head the most are the ones in transverse engined VWAG products like R32s and TTs, and the minivan based GM AWD products (Aztek/Rendezvous/etc).

Now I wonder what the Honda Ridgeline uses in the back. I remember that it doesn't look like the unit in the above mentioned vehicles but it functions the same way.

Honda uses the SHAWD system in the MDX, which can vector torque F-R, L-R. The Ridgeline uses a VTM-4 which can only engage when it detects front wheel slippage.

i once did some dreaming/measuring to scope out the possibility of putting the AWD setup and front subframe from an Astro van under my 74 Monte Carlo... the measurements lined up almost too well... thankfully i was in the middle of moving across the state at the time and i know that i don't have any experience in making such dreams become a reality, so i never started cutting things apart..

but this car has me thinking evil thoughts about my T Type...

I wonder if it'd be easier to start with an Eldorado/Toronado/Riviera. It looks for all the world like the 4wd S10 and derivatives are based off of that frontend. Adding a bigger trans tunnel and grafting in a rearend is probably a lot easier than grafting the frontend stuff.

That's assuming that you wanted a heavy, clunky system. The kind of system that made the FIA say "What, you want to make 4wd legal for stage rally? Suuuuuure, why not?"