Dyno in 2WD mode

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Postby nfn15037 » Fri Sep 22, 2006 9:22 pm

Why not just go to an AWD dyno? Seems like a lot riding on your hypothesis, with very little real information known about the subject.
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Postby gearhead313 » Fri Sep 22, 2006 11:00 pm

There is a normal mustang dyno 5min from my house.

The closest AWD dyno that doesn't have idiots working it is 6 hours.
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Postby nfn15037 » Sat Sep 23, 2006 4:24 am

Bleh, stupid dyno shops.

To me, it seems the reason the BGB says only to use the higher gears is because the torque miltiplication in 1st and 2nd gear generates thousands of ft/lbs more torque. As someone stated earlier, the front diff is only designed to handle 50% of the torque, with the rear diff handling the remainder. It should be fine on a chassis dyno, just do some steady state to dial in everything but WOT then do some swept runs in 4th. It shouldn't take too many pulls to get WOT dialed in properly, which sould save wear on the diff and front driveshafts.
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Postby coyoteboy » Fri Nov 10, 2006 12:32 pm

From what i see in the Toyote manuals you shouldnt use the 2wd mode above certain speeds and presumably not above set torques. Its there to let you run basic tests at low speeds, not for power transmission. You might not kill your viscous unit immediately but you will damage the fluids in it by overheating them which will all add up to reduce the lifespan of the parts.

I have been tempted to do this a few times but then realised the lower cost of 2wd dynos is not worth the extra expense if the transmission fails and i have to pull the box out.
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Postby alltracman78 » Sat Dec 30, 2006 10:57 pm

It's not too much power for the front diff.
With the way our drivetrains are overbuilt do you seriously think it[front diff] couldn't handle 200 hp/ft/lbs torque?
Or even quite a bit more?

"Shifting" that lever is just like when you shift the trans.
It slides a sleeve in the T case, locking and/or unlocking.
I forget exactly what shafts are actuated. It's been a while since I tore one apart.
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Postby coyoteboy » Sun Dec 31, 2006 12:27 am

I know the design work that goes into such items, and I know they are not "massively" over-engineered despite what common misconceptions there are flying around. Shifting the lever is nothing like shifting the gear lever and although the mechanism for locking/unlocking the viscous coupling may be perfectly happy to be moved, the transmission of all the torque through one end of the driveline was never invisaged OR designed for. And whats more the failure of several that I know of that were used for only a matter of weeks in the 2wd mode and thats in the UK alone leads me to believe this is the case.

You take the risk if you think you know more than the Toyota design team, who will have specified that it should not be used in those circumstances. But for the sake of my transmission I wont be so presumtuous despite (or, maybe, because) mech eng being my career :)
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Postby alltracman78 » Sun Dec 31, 2006 11:44 pm

I don't suggest using the 2WD mode.
In fact I never even hinted at it. ;)
I simply stated it was not to protect the front diff...
You might want to work on your reading comprehension. ;)

The physical action of engagement is very similar.
There is no cable, but there is still a shift fork that slides a sleeve to lock or unlock. Same thing the gears do.
Pretty similar to me, though I don't have a piece of paper telling me how smart I am...

And I fail to see how the front diff cannot handle all the power being transmitted from a stock engine when it has no problem handling it's HALF of 6, 7, and 800 hp engines....
Half would of course be much more than 200 in case you don't have your calculator on you.

:shrug:
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Postby ummmiono » Fri Aug 31, 2007 3:47 am

i think what we have to do is figure out exactly what part is breaking when these cars are being run in 2wd mode. if it is in fact the front diff then wouldnt a beefed up diff help with this? i realize most people dont care about driving in 2wd mode but i just think it would be cool to have it as a reasonable possibility due to benefits such as: gas saving, possibilty of remaining mobile in case of broken rear axle, functionality in case of busted center diff or rear diff, dyno tuning, emissions testing. these are just a few ideas that i think would be worth the effort of making a reliable 2wd mode possible for all of us, especially beneficial for rally racers just trying to finish a race after breaking parts. so which part exactly is breaking? it would be nice if it was just a small part, maybe our mech engineer could think of a solution. if it was reliable id do it just for commuting/dd purposes.
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Postby yellowtuner » Thu Sep 13, 2007 6:12 pm

do you guys switch it to do the smog tests? i need to know cuz im going to smog mine and ive never done it! whats the easiest way to get to it if i do need to switch it? :shrug:
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Postby Carolina91GT-S » Sat Oct 27, 2007 7:36 pm

This topic is especially interesting to those of us who are FWD Celica owners that are doing the 3SGTE swap. My engine clip came with the AWD XMSN and I am hoping to use it in my FWD 91 GT-S. I have looked at the drawings/diagrams in detail and cannot see immediately see why it could not be a long term usable solution in my particular application. I think that the warning in the BGB takes into consideration that the rear portion of the drive train is in place and causes drag on the system. So, I just the transfer gear off and put a blank off plate on the center portion, then I put the lever in FWD mode...we'll see what happens. I hope to get it back in the car and running in the next month or so. I am doing the work in a relatives shop a couple of hours away so I can only get there on the occasional weekend. I am finishing up the wiring stuff now, so I can use the RH drive harness with a LH drive car.

With that being said the same should be true if you happen to be in the situation where you have a rear drivetrain malfunction on the All trac and need to drive the car.
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