I once saw a differential that was electronicly controlled with some sort of magnetic pickup coil or something that allowed you to lock or unlock the differential at the flip of a switch. Not sure what the heck it was for and since it wasn't what I was looking for, I continued clicking on. I'll look for it again and maybe post the url here for you and others to see. But from memory I think it was the ability to lock it in positrack mode and switch to either limited slip or full diff mode, not to engange or disengage it's drive, but the theory was there. Possible that it is a modification of what I saw that day. It was built for FWD DSMs to lock the front diff for straight line racing and then unlock for normal street driving and turning. I would think something like this would be a strain on the viscous coupler. I've seen stickers that state not to turn any wheel or start the car when any wheel is off the ground as damage to the viscous coupling could result. He may have also remove the viscous coupler and replaced it with a direct drive or solid coupler to offset any shaft rotation or power that would be transferred.

 

I will call that guy again and see if I can get his son to come here to dsmtalk.com and explain exactly what he is doing. He lives in utah by the way. near salt lake city

 

best thing is like the switchable FWD/AWD tranny


however by switching to RWD you are NOT gaining much efficiency. the drivetrain loss does NOT increase much.

you are still carrying the weight and the front drivetrain is still spinning.

Even though Subaru claims they have achieved better fuel milage with devoation of more torque to front wheels in normal condition in its AUTO Legacy GT's, the theory behind it is more flawed than you can think.

 

i think that skylines can do this with some sort of electronic control geting as much as 90% torque (i think) to the rear wheels.
i think i read that HKS makes this electonic control for skylines.

not sure how it would be done on a dsm...

 

i think that skylines can do this with some sort of electronic control geting as much as 90% torque (i think) to the rear wheels.
i think i read that HKS makes this electonic control for skylines.

not sure how it would be done on a dsm...

Skylines have a much different center differential setup than DSMs. Along with the fact that they are designed as RWD cars unlike DSMs which are designed like FWD cars.

 

In a drag racing sense, the "dsm switchable tranny" if it existed would be fantastic. Awd till after you shift into 3rd, then switch to the front wheels for the rest of the run for minimum driveline loss.

 

there is such a thing as a "dsm switchable tranny," the only problem is its not electronicly controled, check the VFAQ

 

Man, I thought I was the only one with one of those

The only fun I could have with it is if I smoked the fronts say at a 40-50 mph roll, then engaged awd at the light and just anihlated the sucker next to me.

There is no benefit to be seen by selecting fwd in a race. You are still rotating the entire drivetrain. So you won't be using the tcase to power the rears, you'll be using the fwd to power them (same rotational resistance). Now if you could make axles that disengaged at the hubs, and still disengage the tcase, then you'd be saving (a guess here) 60 lbs rotational parasitic loss.

On the other hand, I don't think these could handle being reengaged while moving. I think it'd be ok to disengage, but definitely not to engage the awd (no synchro's,...).

I think you could just get some door lock actuators and mount them onto the tranny(tranny would be optional)/tcase, and have an electric switch from inside the car.

It wouldn't really be a sleeper since you would roast your fronts at a high speed, but the ability to launch with little to no slip would leave them speachless.

I don't know how strong the switchable diff is, when its in locked (intended for fwd) position. It would act the same as a welded, but has external teeth that mesh to the vc.

 

I was thinking about this a little more. I don't know if the tcase could handle being engaged while coasting at any speed. Ideally both ends are spinning the same speed (driveshaft powering the output). Coasting would take off any loads from the engine. Its the same principle as rpm matching shifting. I just don't know how stout it would be.

 

Subarus and Skylines have inline transmissions. basicly they are RWD trannys where the output shaft has a gear running off of it to FWD ring/pinion. (think about the old ford/chevy trucks with a NP205 gear driven transfercase that was selectable...)

the DSM is a traditional sideways mount FWD transmission that has an extra gearshaft between the 'countershaft' and the ring gear that shoots over to a transfercase. its not a normal transfercase tho, its just a gear reduction angler unit that goes to the rear end. making a DSM disengage the REAR end would be somewhat easy but disengaging the FWD part of a DSM would require EXTENSIVE modification to the transmission and the viscious coupling would have to be compeltely eliminated.

 

after traction is taken care of wouldnt fwd be better than rwd because of less rotating mass (longer driveshaft)?

 

Now if you could make axles that disengaged at the hubs, and still disengage the tcase, then you'd be saving (a guess here) 60 lbs rotational parasitic loss.

That's basically how a four wheel drive truck works. If you could do that it'd be great. You would have a lot less drag then but like all the other posters said, just because it isn't "locked in" it still woud have all that parasitic loss.

You would have to waste just as much torque getting those wheels and axles moving that didn't have any power going to them. In a truck you unlock the hubs and take the transfer case out of four wheel drive to have 2wd. You can leave the hubs locked in but then you are spinning those axles and front drive shaft with the tires on the ground. The only time you are saving any gass or torque is when you shift the transfer case into 2wd and have the axle to hub conection unattached. It isn't like you are pulling the axles and drive shaft out to run only in 2wd.

The best way to do this would be to make some lock on lock out hubs like an old ford or chevy truck. But jeep did this for a few years (still does?) and they had a shit load of problems with it. They would freeze in the cold or not even ingage. Imagine a chrysler having problems with four wheel drive?

Oh man I got way off subject.

 

don't the mighty max trucks have 4wd that works like that? if so i imagine something could be worked out with the transmission and everything. but then it just sorta gets to a point of, "is this really worth it?"

 

after traction is taken care of wouldnt fwd be better than rwd because of less rotating mass (longer driveshaft)?

that is what I think too.
However some might argue that RWD is better in handling because of over steer.

This lock engagement disengagement thingy is really going to work on Luck and will earning nothing. It will add as much weight to the car.

 

other than being able to smoke the rear tires and have fun drifting, I dont really see the purpose of switching off the AWD....

Most people with RWD or FWD wish they HAD awd. lol.

Personally, I'd like a pure RWD dsm. I'm probably going to start that project in a year when I get out of college. The hardest part is going to be finding a clutch and a way to start it. I was looking at using a ford T5 (or a variation of it) and a corvette or mustang cobra fully independent rear end with a custom CF driveshaft.

talk about being a thread nazi...

 

Dunno if you guys have seen this video but its an AWD dsm with RWD..Stock tranny and drivetrain.. Someone plz explain this to me and if anybody knows what kinda exhaust that is just by listening to it plz let me know..thnx

If link doesnt work just copy and paste..



http://sddsm.org/pages/movies/CARVIDS/RWD.mpeg

 

im a n00b but i dream big. being stuck with my fwd gs eclipse i love so much, im constantly dreaming of anything that can relieve me of my fwd delemia(my opinion about fwd ever since i learned of awd) and one day it hit me. sure i was inspired by this top secret del sol i read about in super street but it would still be quite revolutionary on a dsm(i think).....move my go fast parts up front to the back. sure it would be TOTALLY fabricated and a HUGE undertaking, but doesnt a RR (rear-rear) car work pretty much the same as my transaxle, just to the rear wheels?? wouldnt that be the best alternative to awd for us fwd'rs?? and definately more realistic than the eternal question "How do i convert my 1.8 RS into an awd??". i dont know just a thought and hopefully some inspiration... hopefully not too off topic...=)

 

im a n00b but i dream big. being stuck with my fwd gs eclipse i love so much, im constantly dreaming of anything that can relieve me of my fwd delemia(my opinion about fwd ever since i learned of awd) and one day it hit me. sure i was inspired by this top secret del sol i read about in super street but it would still be quite revolutionary on a dsm(i think).....move my go fast parts up front to the back. sure it would be TOTALLY fabricated and a HUGE undertaking, but doesnt a RR (rear-rear) car work pretty much the same as my transaxle, just to the rear wheels?? wouldnt that be the best alternative to awd for us fwd'rs?? and definately more realistic than the eternal question "How do i convert my 1.8 RS into an awd??". i dont know just a thought and hopefully some inspiration... hopefully not too off topic...=)

there is a whole lot more to this...and with a gs i dont believe you will be making enough power to shell out big cash for such a conversion. the fwd cars are built different, there is no place for the driveshaft to go and the gas tank is in the way. it's just not worth all the fab work.

 

i don't understand why anyone would want to go through all the trouble of engineering different drivetrains for our cars when there are already awesome chassis's out there. you want a rwd turbocharged four banger with impeccable handling, get a 240sx. you want a midengined turbocharged 4 banger with even better handling, get an MR2. simple as that.

this is so funny because i bet there are 240 and MR2 drivers that would kill to have their cars with AWD.

 

to everyone their own... every design has its flaws. im fine with my fwd

 

i stumbled on this thread while searching for something else.

Nobody probably cares anymore,
but the guy who claims his son did something to "turn off" power to the front wheels has no idea what he is talking about. If you weld your center diff you can remove the front axles and have a very inefficient rwd car. Unless you went through painstakingly difficult custom work to fit electronic locking hubs on the front wheels there would be no way to change between AWD/RWD without installing and removing the front axles.

Furthermore, there would be no benefit in power or fuel economy if you did all this. Basically Terrible already explained this, but unless the front diff and drive axles were completely disengaged (a complete impossibilty do to the design of the tranny) your motor would still be forced to spin the mass of all of the front wheel drive components and you would still experience the same friction from spinning these components.

Case Closed?

 

AMEN brotha!

 

There's one more disadvantage. The stock axles are not built to handle the power transfered to them specifically. Throw slicks on a 350+ HP RWD DSM with stock rear axles and I can see some snapping taking place with ease.

 

Let's just say the old man was full of crap... Case closed.