Shiftable AWD ?

[Lynn D. Brown]

Dear Clonephoons, (kinda close to Clownphools)

I posted something on this a few months ago and here is a follow up. While I am at fixing my cracked Front Diff. case, I thought I would investigate whether our AWD can be converted to shiftable 4WD. This might be really useful to get some mileage out on the road. I've never been too crazy about my 13-14 MPG around town and 16-17 on the HiWay.

I just picked up a Front Diff and axles @ the J-Yard for $250 (Good/Bad ?) from an '85 S-10 blazer. The Front Diff appears to be identical to ours except GM added a few things on the Pass side to make it shiftable. The diffs R :

1.) The plate that the axle goes thru has an xtra hole in the bottom for the vac shifting cable to go thru.

2.) Inside there is a shifting collar and fork, which connects/disconnects the two axles.

3.) The Pass side (long) axle is different so that it can be disconnected.

I thought that those were the only differences that made the 4WD shiftable. But when I went to the JY again, I noticed that they also have a shiftable Transfer Case. Don't know if, like on the Front Diff, the TC is just like ours w some minor mods, and will bolt into our trucks. They look different in the two manuals - Main and Supplement - in which case our TC would then be SyTy specific. Don't know if the 4WD TC would take our torque output or not. There must be some reason GM made us AWD instead of 4WD.

I see in the Truck Shop manual that there were 2 different shift types - a floor mounted mechanical (probably on older trucks) and a push button electronic type.

 

[syclonekid43]

i know a guy pushing around 450 hp out of a s-10 pick up. it has the stock 700r4 and TC with manual 4+4. i think it might hold the power. i also think it would be a cleaner install with the push button TC. i have a 93' jimmy with the push button 4+4. and so far so good. i never really liked the push button. i quess you have to try it to like it , but i think the front diff. is set up diffrent for the manual TC and the button TC.

 

[rockvillespeed]

i just did a front diff from a 4x4 and thought hard about it - decided against.
you cant shift under load, so u r stuck in 2wd till u stop.
for just cruising on teh highway, i dont think itll matter as we dont have unlockable hubs.
also, obv, its full time outta the t case.
u can use the diff - just switch the pass side tube, etc out.

 

[Lynn D. Brown]

Shiftable AWD

Shiftable AWD

I don't know anything about it, but the manual says there is a 4WD Lo and Hi. It says that U can shift back & forth between 2WD and 4WD-Hi while moving, but U have to stop to go into or out of 4WD-Lo. I doubt if U would be able to, or even want to, do any shifting at WOT, so it wouldn't do U any good at the track..

R the Hubs different at the front wheels also ?

 

[syclonekid43]

the hubs are the same on the ty- sy and reg. blazer. when you put it in 4 wheel drive it locks the TC and the front dif. the axles are always spinning no matter what. so really the front drive train is set up like a front wheel drive car.as far as the hubs goes.

 

[rockvillespeed]

yup, just like front drive.
the hi lo is in teh t case of the 4wd

 

[ericguy320]

but i think the front diff. is set up diffrent for the manual TC and the button TC.

nope its still the same vac operated, i think there is a conversion in summit to make it cable opetated from inside the cab, still even if you could unlock the front diff i would worry about burnning up the viscuse clutch from extended driving in 2wd

 

[InvisiBill]

In addition to the Sy, I also have a 93 S-10 4.3L 4x4...

The transfer case and front diff both engage/disengage for 4WD.

You CAN shift between 2WD and 4WD while it's moving, but it won't actually engage/disengage under load. Sometimes I even have to throw it in reverse to get it to disengage (though that's most likely due to the 215k+ on it).

With both the diff and the transfer case disengaged, all the same parts are turning except the front propshaft. As was stated, the AWD transfer case will be turning the propshaft constantly to "equalize" front and rear unless you make that switchable also.

I don't think it would actually aid anything in a SyTy, and might even make things more difficult in some cases. You should be able to swap the parts in fairly easily, but I don't think it would do much. tloof had a nice post(s) a while back about what he was doing with one of the new auto-switching AWD transfer cases. I think that would work a little better way to do things, but I still don't think it would do enough to warrant all the swapping. Building a clone from scratch, possibly, but not swapping into a stock SyTy.

 

[tloof]

Invisibill is not exactly right when he says that adding the shiftable front differential to a Sy/Ty will do little to improve it; however, doing so will ultimately cause the viscous coupling in the t-case to fail sooner. The reason the disengageable front diff is put in the 4x4 version S10's is to stop the front propshaft from rotating when the shiftable type 4x4 t-case is in 2WD. This stops the front propshaft from vibrating due to the cheaper u-joints being used on both ends of the shaft as opposed to the CV jount used on the full time AWD that the Sy/Ty has, and also reduces the drag in the driveline while cruising down the road. It does make quite a difference in fuel efficiency (2-3 mpg) when both the t-case & front propshaft are stopped, so obviously there is a substantial amount of added drag in the system when the front drive is engaged. Unfortunately, the viscous coupling type t-case does not lend itself to using a disengageable front diff in the Sy/Ty.

On the otherhand, if one of the newer generation Smartrac t-cases (NV-136 from a '98 up Bravada) were to be used, then the disengageable front diff would be VERY useful in a Sy/Ty to improve fuel efficiency (it would also allow 2WD burnouts in the Sy/Ty when disengaged). A two speed Autotrac t-case (NV-236 from a '99 up Jimmy) would also work well in the Sy/Ty, but the low range gearing (which adds another 8 lbs to the weight of the t-case) couldn't really be utilized in a Sy/Ty, but wouldn't really hurt it either. As a side note, a 4x4 S10 on the otherhand, would be able to use the low range gearing of the Autotrac t-case for off road use, so it would be the better choice for any 4x4 S10 conversion. Both the Smartrac & Autotrac t-cases would be a great choice for a modified Sy/Ty, and would also give higher trap speeds and a lower 1/4 mile time since they can shift out of the AWD mode into 2WD mode under power (the front diff would NOT be able to be disengaged under power, so that function is really only good for fuel efficiency when on the highway; but then again, when the Smartrac or Autotrac t-case reverts back into 2WD mode due to rear wheel traction being regained after launch, then there is really no load on the front diff to prevent disengaging it, especially if a manual cable shift mechanism like Summit sells is used).

The only downside to the use of the Smartrac or Autotrac t-cases in the Sy/Ty is the electronics that need to be wired up, and the requirement of using a late style 6-bolt tailshaft 4L60E auto trans (the t-case adapter for the NV-136/236 will only mate up to that auto trans, unless a special custom t-case adapter is made by someone like Advanced Adapters to fit them up to a 700R4). Also, a VCM from a '98 up S10 is required that some of the Sy/Ty's engine sensors are wired up to in order to get the TCCM (transfer case control module) to work correctly. This is so that the TCCM will automatically engage the front drive at launch when the throttle is pushed wide open below 5 mph (to get a jump on preventing potential rear wheel spin). All in all, it does require alot of effort & expense to convert to these later style t-cases, but if you already have to replace a stock viscous coupling t-case that has gone bad, then it is a great setup to consider (and other than the auto trans issue, will actually be cheaper to do than rebuilding the stock Borg Warner viscous coupling t-case).

By the way, for anyone that is interested, I have an entire extra low mileage NV-236 Autotrac conversion for sell that will fit into any Sy/Ty (or 4x4 S10 for that matter). It includes the Autotrac t-case, Autotrac specific front propshaft, TCCM, custom wiring harness to fit in the Gen 1 S10 (which includes Sy/Ty's), '98 VCM (for download data), and mounting adapter to fit a late style 4L60E. It does NOT include the 4L60E auto trans. For a Sy/Ty conversion, it would be best to have a custom adapter made by Advanced Adapters to fit the 700R4 (unless you are willing to convert to the 4L60E, which the VCM could be used to act as a stand alone controller to operate it...of course that will require additional wiring, as well as a few extra engine sensors to be wired up to the VCM in order to get it to control the 4L60E auto trans). Let me know if any of you are interested at:
travis.loofbourrow@airliquide.com

 

[jwaller]

On the otherhand, if one of the newer generation Smartrac t-cases (NV-136 from a '98 up Bravada) were to be used, then the disengageable front diff would be VERY useful in a Sy/Ty to improve fuel efficiency (it would also allow 2WD burnouts in the Sy/Ty when disengaged

this is exactly why I'm using one...

my track here gets crap all in my tires...and these nittos need heat to work properly anyway,...I think it'll be cool....

 

[tloof]

jwaller,

Which transmission are you using with the NV-136 conversion? If it is the 700R4, did you get Advanced Adapters to make you a custom adapter to fit the NV-136 up to it? Also, did you wire up a VCM for all the download data to get the TCCM to function? (The factory service manual explains that all of this is necessary for the TCCM to function).

Just curious how your conversion is working out...

tloof

 

[jwaller]

jwaller,

Which transmission are you using with the NV-136 conversion? If it is the 700R4, did you get Advanced Adapters to make you a custom adapter to fit the NV-136 up to it? Also, did you wire up a VCM for all the download data to get the TCCM to function? (The factory service manual explains that all of this is necessary for the TCCM to function).

Just curious how your conversion is working out...

tloof

what I'm goin to do is use the 94 model elec shift case. not the smartrac unit. then I'm using a shiftable (welded) front diff with a cable pull. this way I can do the burnout, flip the switch, pull the cable, have true 4wd or awd; whatever you like to call it and actually have all 4 wheels pulling. not just 2 or 3..

 

[tloof]

jwaller,

With that type of system you WILL NOT be able to go thru a turn in 4WD on the pavement without dragging your front tires severely, since the elec shift NV-233 4x4 t-case that you are going to use will have both the front & rear output shafts locked together as a unit (there is no slip allowed between them when going thru turns...that is why they are considered part time t-cases). Such a t-case only works off road due to the dirt surfaces allowing the tires to slide in turns, which is considered tolerable, but on hard paved surfaces that is a recipe for quick tire wear, and is extremely hard on the drive components! Also, by welding your front differential carrier, you will drag the tires even worse thru turns, as there is no way for the opposite side wheel to turn a different diameter radius than the other wheel (this will really kill tires quick!); and your front propshaft will always rotate even when the t-case is in 2WD & the front diff disengaged due to the drivers side wheel continuously driving the propshaft input yoke. With an open carrier in the front diff, the propshaft stops rotating when the front diff is disengaged due to the fact that the spyder gears in the carrier free float around the pinion gear because it has more drag to prevent rotation.

Of course, I understand that you are probably planning to only use the front drive when drag racing in a straight line, and the rest of the time only running in 2WD (thus the reason for disengaging the front diff so that you can drive on the street without dragging front tires). Who knows, maybe that isn't such a bad idea after all, but you could still achieve all of that plus the added AWD "on demand" with the NV-136/236 Smartrac/Autotrac series t-cases and have a better all around vehicle (athough it wouldn't be as cheap as what you are planning!).

 

[jwaller]

jwaller,

With that type of system you WILL NOT be able to go thru a turn in 4WD on the pavement without dragging your front tires severely, since the elec shift NV-233 4x4 t-case that you are going to use will have both the front & rear output shafts locked together as a unit (there is no slip allowed between them when going thru turns...that is why they are considered part time t-cases). Such a t-case only works off road due to the dirt surfaces allowing the tires to slide in turns, which is considered tolerable, but on hard paved surfaces that is a recipe for quick tire wear, and is extremely hard on the drive components! Also, by welding your front differential carrier, you will drag the tires even worse thru turns, as there is no way for the opposite side wheel to turn a different diameter radius than the other wheel (this will really kill tires quick!); and your front propshaft will always rotate even when the t-case is in 2WD & the front diff disengaged due to the drivers side wheel continuously driving the propshaft input yoke. With an open carrier in the front diff, the propshaft stops rotating when the front diff is disengaged due to the fact that the spyder gears in the carrier free float around the pinion gear because it has more drag to prevent rotation.

Of course, I understand that you are probably planning to only use the front drive when drag racing in a straight line, and the rest of the time only running in 2WD (thus the reason for disengaging the front diff so that you can drive on the street without dragging front tires). Who knows, maybe that isn't such a bad idea after all, but you could still achieve all of that plus the added AWD "on demand" with the NV-136/236 Smartrac/Autotrac series t-cases and have a better all around vehicle (athough it wouldn't be as cheap as what you are planning!).

yeah I realize I will be making it only for the drag strip.. and I would LOVE to have the system you are trying to sell but I just dont have the $$$ for that. this syetm is much simpler and cheaper although I'd really like to have the smartrac system.

with the front being welded and unlocked it will be the same as what we have now on our trucks. and with the shiftable xcase I will be able to do everything that I can now plus burnouts and true AWD. what or how much do you want for that system? anything like this xcase form the 94 I can trade you?

 

[tloof]

I'm looking to get what I have into it out, which is $650. The custom wiring harness to fit the Gen 1 S10 requires ALOT of hours to make (not to mention the number of hours studying the wiring diagrams in order to determine what to wire up!), and it is being thrown in for no extra charge. It also requires two '92-'94 electric shift 4WD harnesses as a base to make the custom harness, and I had to pay $50 apiece for them as I recall, so I am really going deep in the hole at that price! Oh well...

tloof

 

[jwaller]

sent you a pm tloof