Shiftable Front Diff. on SyTy's ?

L

Lynn D. Brown

New member
Hey Guys,

Gotta small dent in the the Pass side of my Front Diff. I had a bad leak in the Diff., Don't know if that was the cause, but I would just as soon replace the Pass side case to be sure while I'm at it, and maybe put a drain plug on it while I'm at it.

I found a Front Diff in a J-Yard from an '84 S-10 Blazer, and it appears to be identical to ours except it has a switching mechanism on the outside (Pass side) and an extra gear inside of the case to switch in & out of 4WD. Just like it shows in the '93 Sonoma/Jimmy shop manuals and the Typhoon supplement.

This switching capability could be added to our trucks. Does anybody see any advantage to having the capability of switching in & out of AWD ? I know some of our serious racers have gone RWD only for better ET due to friction reduction @ the Top End. But do they also have to remove the Front Diff and Axles, Transfer Case and Propshaft to get this friction reduction ?
 
jwaller

jwaller

Evil Genius/SyTy Guru
the shftable front diff.... it is a good idea but you cannot unlock the RF axel while the vehicle is under load..... so it would provide some benifit like being able to do a burnout and being able to dyno without R&R the poopshaft but thats about it... oh yeah you would also have much better fuel economey and much better highway speeds...
 
Christian Dionne

Christian Dionne

Member
How would you get better economy? You still drive the axles and the propshaft, so I can't see much improvement from disconnecting the frontend.

If you dyno once a month, I could see it worth while.

If you run drag radials on the rear and would like to heat them up, then maybe that too. Wouldn't that hurt the clutches in the transfercase a little?
 
jwaller

jwaller

Evil Genius/SyTy Guru
the pain and agony on the xcase is a whole other topic... and not having to drive the front end bc's it is now an open diff would be just like removeing the PS....so thats where the gain would come from....
 
Will_in_China

Will_in_China

Truckless Wonder
I just want some drama, like burnouts and shit....
Miss my nova's lack of traction.

Call me a chick or a mustang-type, but every once in a while I like to fuck around and do stupid shit on video.

I was honestly considering doing 4 "spare tires" on the Ty, just for "video purposes"...

-Will
 
L

Lynn D. Brown

New member
Shiftable Front Diff

Shiftable Front Diff

Guys,

I was looking at the '93 Jimmy manual, and it looks like the longer axle on the
Pass side is different than the SyTy's, and that's where the disconnection takes
place. The other axle looks the same. The manual says "the central disconnect
system allows shifting in & out of 4WD while the vehicle is moving under most
driving conditions".

Not sure what this means exactly. Maybe U can't do it @ WOT. I'm thinking that it
could be useful at the top end at the track to disconnect, but it might be tough on the system at WOT. Apparently it has some kind of vacuum shifting cable under the hood.

Just a thought if I have to buy the whole Front Diff. I tried to drill and tap a hole in the smaller damaged case portion for a Drain plug. Good thing I experimented on this piece, because it didn't work, so I guess I'll scrap that idea.
 
L

Lynn D. Brown

New member
S10/15 Front axle.

S10/15 Front axle.

Now that I think about what shows in the Shop manuals - '93 S/Jimmy and Typhoon - it doesn't make sense. It looks like the Pass side (long) axle can disconnect on the 4WD's, but I see no way 4 the other axle to disconnect. Surely it has to or it would still be driven.

Does anyone know how this thing works ?
 
S

Sy769

Donating Member
It is a open differential.
Think of it like this. Pretend there is no rear driveshaft installed. You can jack up the right front of the Sy and the left side will get no power and not try to turn.. The right side will get all the power. The 4X4in effect does this when it disengages the right side axle.
 
L

Lynn D. Brown

New member
Shiftable Front Diff.

Shiftable Front Diff.

Patrick and Guys,

I was looking at the manuals again, and the pieces laying in the garage, and I still have some questions :

1.) The Transfer case puts power to the Propshaft and front Pinion and the Pinion drives the Ring Gear.

2.) The axles both spline into separate ends of the 4 gear Differential set, so they must turn together since these gears are always meshed. Unless of course the Pass side axle is disconnected, as it can be w the 4WD axle - then the 2 axles are no longer connected.

3.) However, the Differential gear set rotates independent of the Ring Gear, so I'm wondering how the torque from the Ring gear gets to the axles and Diff gears. I guess the Rear Axle works the same way, so I guess I don't understand how a Differential works.

But, anyway as far as me switching to a switchable 4WD, there doesn't appear to be any point. When it's disconnected, the front wheels still drive the axles and Diff gears, and the Trans still drives the Transfer Case, Propshaft, Pinion Gear and Ring Gear. So, U still have all of that friction, but just aren't getting any torque out of it. There doesn't appear to be any savings in drag, huh ? And all the torque now goes to the Rear Diff., and it may not be able to take it.
 
P

peterpaw

New member
hi there,
the front of assembly of a 4x4 is exactly the same except that the 4x4 has a system that locks the diff into gear. you can get the diff with the cable and just tie it in the engaged position.
or,
jegs sells a kit to have manual control over the front diff. you have a locking cable in the cab that you can engage the front diff whenever you want.
in that way you could have 2wd for going on a dyno and AWD for the road.
i put AVD in a '97 ZR2 and simply tied the front diff into gear. i am going to relocate the batery to under the bed (ala kenne bell kit) and then will have direct access to the control of the front diff. (it is located under the battery tray)
yea, buy cheap and tie it into gear, just make sure that you get the cable actuator as well when you get the junker front diff.
oh yea, not from a bravada; they have 3.73 gear not our 3.43.
have fun
peter
sy
ZR2
nyc
 
F

FLSY2730

New member
peterpaw said:
hi there,

the front of assembly of a 4x4 is exactly the same except that the 4x4 has a system that locks the diff into gear. you can get the diff with the cable and just tie it in the engaged position.

or,

jegs sells a kit to have manual control over the front diff. you have a locking cable in the cab that you can engage the front diff whenever you want.

in that way you could have 2wd for going on a dyno and AWD for the road.

i put AVD in a '97 ZR2 and simply tied the front diff into gear. i am going to relocate the batery to under the bed (ala kenne bell kit) and then will have direct access to the control of the front diff. (it is located under the battery tray)

yea, buy cheap and tie it into gear, just make sure that you get the cable actuator as well when you get the junker front diff.

oh yea, not from a bravada; they have 3.73 gear not our 3.43.

have fun

peter

sy

ZR2

nyc
Click to expand...






What is AVD?
 
F

FLSY2730

New member
I have a ZR2 , the front diff has the little actuator on it, WHY does it need this, when you shift into 4 wheel drive it is putting it in 4x4 mode at the transfer case , right? So if you had a transfer case in a sy that you could switch from 2x4 to 4x4 and did not swap the front diff out what is the difference not having the actuator, why did GM even put this there? When my front diff broke i got one from a blazer 4x4 and just swapped the right side axle tube and installed.

I know the actuator is on all the full sizes also , but if it was not there the gears would always be locked up, is that why? Is it just so the front dif can free spin easier when not in 4x4 or what?
 
E

ericguy320

Stupid Member
FLSY2730 said:
I have a ZR2 , the front diff has the little actuator on it, WHY does it need this, when you shift into 4 wheel drive it is putting it in 4x4 mode at the transfer case , right? So if you had a transfer case in a sy that you could switch from 2x4 to 4x4 and did not swap the front diff out what is the difference not having the actuator, why did GM even put this there? When my front diff broke i got one from a blazer 4x4 and just swapped the right side axle tube and installed.

I know the actuator is on all the full sizes also , but if it was not there the gears would always be locked up, is that why? Is it just so the front dif can free spin easier when not in 4x4 or what?
Click to expand...
it is for better fuel econ and less were on parts.. also the front diff cannot be locked under load it will just grind untill the gear catches, there are no blocking rings or syncro like a tranny, it is just a bevled gear that slides onto another gear. it normally wont unlock under load, in my blazer i sometimes have to drive a while or stop and back up to unlock it.
 
Will_in_China

Will_in_China

Truckless Wonder
So is the consensus that it can still be done, in benefit of dyno ease and such?

Or is the passenger side axle limitation a reality?

-Will
 
L

Lynn D. Brown

New member
Shiftable Front Diff

Shiftable Front Diff

Is it just so the front dif can free spin easier when not in 4x4 or what?

TL2730,

I guess so. There must be some reason for being able to shift out. So, I guess it is for shifting out of 4WD out on the road so that U can reduce drag and increase mileage. I'm thinking that U couldn't use the feature at the strip because U can't shift out @ WOT. So, unless I have to get one because of my blown halfcase, I won't bother w it.
 
L

Lynn D. Brown

New member
Shiftable Front Diff.

Shiftable Front Diff.

Is it just so the front dif can free spin easier when not in 4x4 or what?

TL2730,

I guess so - it must be there so that U can shift out of 4WD out on the road to reduce friction and increase mileage. I don't think U can do it @ WOT on the track.

So, unless I have to buy the shiftable unit from the J-Yard because of the damage to half of my case, I won't bother w it.[/i]
 
InvisiBill

InvisiBill

Active member
ericguy320 said:
it is for better fuel econ and less were on parts.. also the front diff cannot be locked under load it will just grind untill the gear catches, there are no blocking rings or syncro like a tranny, it is just a bevled gear that slides onto another gear. it normally wont unlock under load, in my blazer i sometimes have to drive a while or stop and back up to unlock it.
Click to expand...

Just seconding this. Sometimes the PoS-10 will unlock by itself while driving, other times it needs Reverse... It wouldn't really be useful in our situation, I don't think (performance-wise). tloof did some research on the automatic transfer cases a while back, and had lots of cool info. If I remember correctly, it would disengage the propshaft, and the open diff would have the same effect up front, so it wouldn't turn the propshaft, giving a bit of improvement...

And yes, the S-10 4x4 system is a pain. There's a little ball-switch on top of the transfer case. When you move the lever, it pushes the ball and redirects vacuum to the diaphragm actuator under the battery (looks like the cruise actuator). That flattens and pulls the cable, which locks up the front diff. Been there, replaced that. =(
 
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