Competition launching in 4wd

[RichBennett]

Just curious exactly how its done ?! when and how do youshift back to 2h and does it do any harm to the T case ? can AT and MT launch like this ?

 

[Rhondasway]

Don't go there, girlfriend...

Rich, there are other threads covering this in this Forum (see "Cases' case" http://www.tdr1.com/forums/showthread.php?s=&threadid=81515&perpage=15&pagenumber=1), but yes, it can be done with both AT and MT.

(saying a prayer that I am not cursing myself here) I've run my truck for an entire season launching in 4x4. Words of advice:

1. Be prepared for stuff to break

1a). Check your drivelines and U-joints.

2. Make sure 4x4 is fully engaged (4WD light on does not always indicat this).

3. Launch at whatever boost you deam appropriate (can open, worms everywhere... ), unless cursed with a Manual, in which case launch in 3rd.

4. I shift out of 4WD after 1-2 shift (hubs will remain locked, but you'll no longer drive the transfer case).

In the 1/4 mile, launching in 4WD over 2WD will buy a couple of seconds, and is the best way to bring trauma to little ricers at the light...

 

[R-N-R]

and is the best way to bring trauma to little ricers at the light...

simply priceless... . Oo.

 

[MCummings]

'02's will still drive the axle... .



After 10PSI, you risk serious part breakage.



Merrick

 

[Duluth Diesel]

First off, since it's been said a hundred times. . WE DON'T HAVE LOCKING/UNLOCKING HUBS!!!!!!! I don't know why people can't learn this. Up until mid model year 2002, our Dodge's had a center axle disconnect. My 02 has nothing, meaning I have a live front end. In 2wd, my front axle and driveshaft are turning. When I put the truck from 4 back into 2, there is no more power being input to the front end. Same for earlier trucks - so the c. a. d stays locked, so what? If the transfer case is in two, your front end is safe. Now, the only way I can see this being a problem is for guys with dial-a-drive 4wd. When under heavy acceleration load, and switched back to 2wd, the electronic actuator usually cannot take the t-case out of 4.



Didn't mean to get excited guys, just this whole hubs thing drives me nuts. I think dial-a-drive is for sissies. If I had a c. a. d on my truck, I'd convert it to manual so I could control it, AND have 2-low. The only bummer about the live front end it that I can't have 2-low.

 

[Rhondasway]

teach me

Well, I'm openly admitting my ignorance, so Duluth would you please explain what is c. a. d. ? What is "dial-a-drive"? I do understand that I don't get out and lock my hubs, but something stays engaged even when I push out of 4X4, both on the track and on the street (for example while driving on snow) until I let out of the throttle.

So, in my case, when I have moved the lever to the 2WD position, is any part of my system inactivated?

If I have one of those "sissy" setups, please don't tell my truck as it thought it was pretty tough racking up about 150 brutal 4X4 1/4 mile races and enough daily driving to rack up over 30,000 miles last year...

Thank you for sharing your wisdom.

 

[Rob Thomas]

The CAD is Central Alxe Disconnect, when you engage 4 wheel drive, vacuum operates a fork in the axle to actuate 4x4. When under a load in 4x4 and you push the 4x4 lever into 2 wheel drive you loose any power applied to the front alxe, but the CAD remains locked, until you remove the load from it.



BTW, the same applies to trucks without the CAD, when you move into 2 wheel drive, no power is driving the front axle, even though everything in the front is still turning.



Rob

 

[Rhondasway]

Thank you very much, Rob. Another question if you don't mind (sorry to evolve the subject, Rich):

If the truck does not seem to "let go" of 4WD after shifting into 2WD, sometimes having to go to Reverse to disengage, does that indicate wear/problems, and if so, what?

Thanks much!

 

[fest3er]

Originally posted by Rhondasway
Thank you very much, Rob. Another question if you don't mind (sorry to evolve the subject, Rich):
If the truck does not seem to "let go" of 4WD after shifting into 2WD, sometimes having to go to Reverse to disengage, does that indicate wear/problems, and if so, what?
Thanks much!

Rhonda,

The reason 4x4 doesn't always disengage is that there is pressure on the driveline preventing the components from releasing. Usually, when you shift out of 4x4, the transfer case immediately releases the front axle. But this doesn't always happen. Most likely cause is the truck is turning a little, which puts pressure on components in the t-case.

With my truck, I've found that it almost always disengages quickly if I'm movingat least 15 MPH, shift out of 4x4, then gently work the go pedal between decel and accel.

But then, I havne't changed the t-case lube in quite a while. I should check it.....

N

 

[Rob Thomas]

Neal, of course it could be because you have the Amsoil in there. J/K LOL

 

[fest3er]

Originally posted by Rob Thomas
Neal, of course it could be because you have the Amsoil in there. J/K LOL

Well, yes, that snake oil *can* make odd things happen. I'm surprised it hasn't all leaked out already.

N

 

[Duluth Diesel]

fest3er is correct. Some driveline components cannot actually shift out until there is no load, or no torque input. Dial-a-drive is for people with electronic shift transfer cases. These cases have the problem of not pulling out of 4 when asked if there is torque input (meaning you're still on the throttle). If you have a manual transfer case, and you shift from 4 to 2, even though you center axle disconnect (c. a. d. I explained what this was in my original post) may stay engaged due to sustained torque input (meaning you're still hammering on the throttle 'cause you're drag racing), your transfer case and front end are safe from binding and breakage due to the fact that they're disconnected from the active driveline.



Rhondasway, you're truck is fine. You have a manual shift transfer case, and you have the c. a. d. If my truck had the c. a. d. I would convert to manual with a cable pull. But even the cable pull would not disconnect the c. a. d. if there was torque input. It would give you a 2 low selection. And that is what I wish my truck could do, is have 2 low.

 

[thejeepdude]

Re: Don't go there, girlfriend...

Originally posted by Rhondasway

launching in 4WD over 2WD will buy a couple of seconds, and is the best way to bring trauma to little ricers at the light...

It's also a way to make a lowly ~250HP truck beat a C5 Corvette off the line... in the rain! hehe. . should have seen him fishtailing tryin to keep up with my 4WD 14psi launch

 

[Timebomb]

In my case it was imposable to shift out of 4wd on the fly at the dragstrip. unless i could mash the throttle with my left foot and kick the 4wd shifter foward with my right foot just to hope it goes into 2H and not N... . I just launched at 2500rpm and ran it out the whole way in 4wd. . thought i cut good 60fts for an old rotary truck.

 

[Rhondasway]

Originally posted by Antrim93

In my case it was imposable to shift out of 4wd on the fly at the dragstrip. unless i could mash the throttle with my left foot and kick the 4wd shifter foward with my right foot just to hope it goes into 2H and not N... .

I'm visualizing that... LOL



Thanks again for the info Duluth; I'm learnin' slowly...

I will continue to shift out of 4x4 after launch if it's lessening wear and stress.