Thermal locking front diff question

[sctrailrider]

Hi everyone, I am having a little trouble getting the front diff to lock, I know there is a broken wire somewhere in the wiring for the thermal plunger in the front diff and it will lock sometimes and other times it doesn't lock....

My question is.... my thermal plunger has 2 black wires going to it, if I connect new wires to it and feed 12v to it with a toggle switch will it matter witch wire I connect the 12v to???

I have a posi lock coming but it will not be here before my trip and I would like to be able to use the 4x4 if needed....

[jamesm]

What a terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible terrible

design.

The wax pellet uses electrical heat to melt and expand, very similar to the way the coolant thermostat operates.

DC motors, LEDs, and diodes require the wires to be connected to the proper polarity wire. A resistor (as in the heat coil in the actuator) or filament light bulb does not have an "in" and "out" wire. Connect one actuator wire to ground, and the other to a +12 source, and you should be good to go.

terrible terrible terrible terrible terrible terrible terrible terrible terrible

[sctrailrider]

Thanks, I wasn't sure about that, I will try that today....

[Robyn]

http://www.4x4posi-lok.com/

Here is a permanent fix for the issue.

This system is a perfect fix

Even when the TLA is working, every time you turn the key off, the front end drops out.
The posilock gives you the control that is needed for safe operation.

Try getting out in the pucker bushes, miles from nowhere, and have the TLA quit or a wire break. your screwed.

The $160 for the cable system looks real good after you think about it.

MISSY

[More Power]

GM introduced a upgrade kit in the late 1990s for all of the earlier Central Axle Disconnect (CAD) equipped trucks that replaces the thermal actuator with a solenoid actuator. We did an install article on it way back in 1999, which is now available in the 6.5L Turbo Diesel Volume I.
GM part #12376316 & #26060073 (harness & actuator)

As an aside, the Posi-Lok is discussed and shown (and was tested) in that article, but personally, I wouldn't want the front driveshaft spinning all of the time when 4x isn't needed. There's a small effect on fuel economy, on wear & tear on all 4x parts, and additional noise and vibration that I'd rather do without.

[phantom309]

GM introduced a upgrade kit in the late 1990s for all of the earlier Central Axle Disconnect (CAD) equipped trucks that replaces the thermal actuator with a solenoid actuator. We did an install article on it way back in 1999, which is now available in the 6.5L Turbo Diesel Volume I.
GM part #12376316 & #26060073 (harness & actuator)

.

Can you confirm that this will work with the 8 bolt hub axle on my 1994 K2500 8600lb truck?

info i read says it won't work,.??

Thanks
Nick

Nick

[BrIONwoshMunky]

GM introduced a upgrade kit in the late 1990s for all of the earlier Central Axle Disconnect (CAD) equipped trucks that replaces the thermal actuator with a solenoid actuator. We did an install article on it way back in 1999, which is now available in the 6.5L Turbo Diesel Volume I.
GM part #12376316 & #26060073 (harness & actuator)

As an aside, the Posi-Lok is discussed and shown (and was tested) in that article, but personally, I wouldn't want the front driveshaft spinning all of the time when 4x isn't needed. There's a small effect on fuel economy, on wear & tear on all 4x parts, and additional noise and vibration that I'd rather do without.

Posi-lok offers a kit that's switchable. I just finished installing mine (800 kit for my 8 lugged K3500) after having fuse blowing fits and trying a new TLA. In is front axel disengaged, out is engaged. 4x4 works excellently now. Exactly when I want it to, no waiting, no off after shut-down. Hardest thing to do was poke propperly sized holes in things, and fish the cable through the firewall.

[Robyn]

Yesss this is the kit I was refering

They do make the one called "fleet operations" or ??? and it just locks it up all the time.

The cable certainly eliminates the issues with the Thermal mickey mouse unit.


During bad weather I always want to leave the unit in 4x4, and with the thermal unit or even the solenoid motor unit, the thing unlocks as soon as the key is switched off.

I am a HUB type of girl. When things look the least bit hinky, I screw in the hubs and then let the chips fall where they may.

The more they overthink the plumbing the easier it is to plug up the drain

Last winter we had some snowy stuff and the weather up at the ranch was nasty compared to in town. I was at the grocery store and decided to give the hubs a twist while life was easy. (89 K5)

A young fellow was watching me twisting the hubs and came over to ask what I was doing ????????????

I explained the process to him and the reasons. His reply was, don't you find that EMBARACING to have to do all this stuff, and to get your hands dirty.

OMG
I laughed and explained to him that I would not be embaraced to do it butt naked in a blizzard, as it is positive and its nearly 100% reliable.

The electric units that the GMT 400 trucks came with always made me nervous every time the weather was bad.

Just not much you can do out on the road if the electric Gizmo quits.

Winter of 08 here saw nearly 4 feet of snow and I had the front end drop out on the BURB due to a broken wire.

Luckily it happened here at home and I was able to fix it.

Large hunk of ice/snow had gotten crammed over the front diff, and snagged the wires.

Overall a terrible design.

Just can't really say too much good about the IFS system.

Local fellow here has his 95 Burb converted to a 60 series Dana and leaf springs.
Has the large hubs too.

Now thats how it should be. simple and easy to use.

He took the concept of no electronics all the way.

He rewired things a bit and has a carbureted 502 BBC under the hood, running a no frills HEI distributor, a TH 400 tranny with an add on OD unit aft of the T case.

Just like the good old days, simple, reliable and no $#@!~ SES light to come on when your in the thick of it.


My vote goes for the cable system.


Missy

[More Power]

Can you confirm that this will work with the 8 bolt hub axle on my 1994 K2500 8600lb truck?

info i read says it won't work,.??

Thanks
Nick

Nick

Nick, I installed that GM kit in a 1994 K3500 SRW. Aside from rear spring rates and badging, the truck I owned at the time was the same as yours.

Correction: It was the P.A.D. I was referring to in an earlier post, not the Posi-Lok. My bad..



Clip from my writing about it: Precision Auto Parts produces an aluminum actuator called "PAD" (Positive Actuation Device), that will positively engage the front axles. Being made from machined aluminum, these actuator replacements would be more durable in rough four wheeling situations. The PAD actuator replacements keep the front axles engaged all the time. This means your front differential, front driveshaft, and transfer case chain will be turning whenever the truck moves, whether in 2WD or 4WD. The penalty for an always engaged 4x4 front differential is a slight reduction in fuel economy and possibly some additional drivetrain wear.

Note: The transfer case shifter in the cab will still disengage the front differential in 2WD, but all the associated drivetrain parts will still turn. Here's their address back in 1999... I couldn't find a current source online....
Precision Auto Parts
210 Suite 4 Highway 20 South
Thermopolis, WY 82443
307-864-3490

[Kennedy]

GM introduced a upgrade kit in the late 1990s for all of the earlier Central Axle Disconnect (CAD) equipped trucks that replaces the thermal actuator with a solenoid actuator. We did an install article on it way back in 1999, which is now available in the 6.5L Turbo Diesel Volume I.
GM part #12376316 & #26060073 (harness & actuator)

As an aside, the Posi-Lok is discussed and shown (and was tested) in that article, but personally, I wouldn't want the front driveshaft spinning all of the time when 4x isn't needed. There's a small effect on fuel economy, on wear & tear on all 4x parts, and additional noise and vibration that I'd rather do without.

The answer lies above. Works like a charm like every other modern GM 4x4.

[phantom309]

The answer lies above. Works like a charm like every other modern GM 4x4.

again,. everythign i read about the conversion,. points to it not working on the 94 axles,.

BUT i did read somewhere,. if you slip and old 14mm socket over the Thermal doohickey,. it effectively keeps the front end engaged all the time too,.

but my 14mm sockets are like gold when i cant find a 9/16ths,.

Nick

[More Power]

again,. everythign i read about the conversion,. points to it not working on the 94 axles,.

BUT i did read somewhere,. if you slip and old 14mm socket over the Thermal doohickey,. it effectively keeps the front end engaged all the time too,.

but my 14mm sockets are like gold when i cant find a 9/16ths,.

Nick

It worked perfectly on the 1994 I owned. Plus, the 1989 K1500 I have was upgraded with the solenoid actuator as well sometime before I got it. So... it works on older axles.

[Robyn]

The cable kits will work dandy on all the IFS front ends from 88-98 and I would venture that even later ones will work too.

I know for fact that the 94 will do fine


Missy

[chvycmnslvr68]

Nick, I installed that GM kit in a 1994 K3500 SRW. Aside from rear spring rates and badging, the truck I owned at the time was the same as yours.

Correction: It was the P.A.D. I was referring to in an earlier post, not the Posi-Lok. My bad..



Clip from my writing about it: Precision Auto Parts produces an aluminum actuator called "PAD" (Positive Actuation Device), that will positively engage the front axles. Being made from machined aluminum, these actuator replacements would be more durable in rough four wheeling situations. The PAD actuator replacements keep the front axles engaged all the time. This means your front differential, front driveshaft, and transfer case chain will be turning whenever the truck moves, whether in 2WD or 4WD. The penalty for an always engaged 4x4 front differential is a slight reduction in fuel economy and possibly some additional drivetrain wear.

Note: The transfer case shifter in the cab will still disengage the front differential in 2WD, but all the associated drivetrain parts will still turn. Here's their address back in 1999... I couldn't find a current source online....
Precision Auto Parts
210 Suite 4 Highway 20 South
Thermopolis, WY 82443
307-864-3490

Hey guys .. I am new on here ...
Back in the early 70's and on up into the eighties the Full time 4x4 was quite popular with GM vehicles and it was proven that with all four wheels driving all the time the driveshafts and all other components actually lasted longer and goodyear and michelin put out articles about tires actualy having 12%less rolling resistance when under a positive torque ... thus actualy increasing the fuel mileage of a vehicle by having full time 4x4 ...

I had a '75 K5 blazer .. my first vehicle ... and I found that once I had the front driveline rebuilt where it did not vibrate that I actualy got about 1-1.5 m[g better with the front driveline in place ... before I had it rebuilt I got less mpg with it in .. with the FT 4x4 you actualy had to pull out the driveline to and remove the plugs from the front hubs to stop things from turning ..

so the point that i am trying to make is that if you locked up your front end to turn all the time wouldn't it make sense to install a FT T-case to go along with it to keep a positive torque on things thus actualy improving your fuel mileage ... by reducing the rolling resistance of the tires ... This is something I have been planning on going to for quite some time...

[JohnC]

I don't know if I believe that. My wife's Yukon has an automatic 4wd transfer case and it definitely gets worse mileage when it is engaged than when it is not engaged.

I don't think this is what you were suggesting, but a transfer case that does not allow slippage between the front and rear axles would not be suitable for full time use.

[Robyn]

The full time transfer case spoken of was the NP203 These were offered from 73-79 in the Ford, Dodge, GM rigs

These cases had an open differential in them that allowed power all the time to all four wheels.

When on slippery stuff the shifter could be moved to the LOCK position and this made the T case work like any other 4x4 with equal power to both front and back.

The 203 was a marvelous setup that made rigs handle great and unless you were in real nasty stuff, you many times just needed to drive.

The system thats in the Astro AWD VANS is similar with the exception that these units do not have a shifter and have a viscous coupling that maintains a torque split of 65%/35% back/front

The idea is not new at all. LARGE CLASS 8 trucks use a power divider in the rear tandem drive axles that works about the same with equal power to both axles as long as both have traction. A lock up is also in the system if one axle slips.

Missy

[JohnC]

These cases had an open differential in them that allowed power all the time to all four wheels.

Three total open differentials? Sounds like it would deliver all the power to the one wheel on the ice!

In 1990 I had an Eagle Talon with viscus couplings in the transfer case and rear axle. You could drive 3 wheels at a time. Worked great until you spun them, then it felt like the deer on the ice in Bambi...

The Yukon has some sort of active, computer controlled case. All I know is it goes good in the snow...

[a5150nut]

The idea is not new at all. LARGE CLASS 8 trucks use a power divider in the rear tandem drive axles that works about the same with equal power to both axles as long as both have traction. A lock up is also in the system if one axle slips.

Missy

What? No more air switch on the dash to lock em up?

[DmaxMaverick]

What? No more air switch on the dash to lock em up?

I think that's what Robyn meant. If there's another option (common), I've not seen it. Flip the switch, lock the drivers.

[Robyn]

John

Yes, three Differentials ( open unless lockers were ordered)
Yessss, all the power could go to one wheel if it had zero traction "ice"
The shifter would be placed in either LOW LOCK OR HIGH LOCK to lock the diffy in the T case, then the system would operate like any 4x4


Unless you were in the really snotty stuff the full time drive gave a wonderful ride with no need to flip hubs or yank levers.

Once the going got nasty you had options.

Another plus was the ability to use the low range on the asphalt to drag a heavy load, and have both front and rear axles pulling and not bind it up.

I owned a 75 K5 Blazer with the 203 t case as well as a 76 F250 4X4 with it.

Simple and reliable system all around.

My F250 had a locker in the rear, so with it all hangin out there were at least 3 a diggin.

5150

OHHHH yes, still have the air switch. That only locks the divider up to stop the interaxle diffy from working.

My Western Star had the normal interaxle lock switch, but also a lock switch for each axle too.

I could lock the divider, then lock the front diffy and the rear one too if need be.

With all four sets of duals pulling, it would rarely not walk out of a bad spot.

All tandem drivres use the air lock on the power divider.

Nothing has changed much in the last 40 years or so in that department.


The full time 4x4 drive on pickups and SUV's was great, but too many people simply did not understand it and the aftermarket worked overtime to devise gizmos to defeat it and make it like the regular part time systems.

The overall superior handling and control of the FT systems far outweighed any small loss of mpg

My buddy had an F250 of the same year and such with standard PT 4X4 and our mileage was near identical.

The most noticeable handling perk was on dry gravel roads. The FT system would pull you through the corners, without the usual BS of the thing trying to swap ends on the loose road surface.

Over the years, I have heard more strange explanations of how the FT 4X4 WORKED.
From, it kicks in when you "floor it" to the front axle kicks in once the rear axle speed exceeded the front axle speed by 50%

I even had one explanation that had the front end doing the work unless the truck had a load in the bed
Good GAWD, where did these clowns come from?????

The system of 3 differentials, to allow all parties participating in the task, to do so without getting their shorts in a knot is just way to simple to even worry about.


The new all wheel equipment used today is just a retread of the NP203 setup with some viscous couplers, and, in some cases electrically opperated clutches controled by the computer added to the mix.

These new systems are far too complex, with too many things to fail.

I really don't see why the auto makers have gravitated towards adding electronics and computers to every system.

A 4x4 is supposed to be a getcha through the tough crap under the most severe conditions.

Now the most severe conditions can very well render the vehicle incapable of functioning.

Yup, case in point, just let the Thermal actuator take a dump and you are fouled.

Add more wires, processors and other superfluous crap and the true functionality of the vehicle is questionable.

Now, add to the mix, a batch of youngsters that have no clue about the fact that "traction control" has zero effect on the coefficient of friction between the tires and the road surface (snow ice) and all bets are off.

Now, lets go one step farther, lets add a couple years of salt spray ( for you poor souls who live where cars rust out before the warranty is up)

The salt corrodes the electrical connections on the 4x4 Gizmos, ABS systems and the T case, now things are looking pretty bleak, indeed.

Its snowing sideways and the convenient flip of a switch or press of a cute dash button does nothing.

No 4x4 lamp on the dash, and worse yet, your stuck.

A $40k +++ vehicle has been rendered inert and near useless.

TRIPLE A gets another call.

Solution, keep it far more simple.

I know, it's embaracing to the young ones to have to twist hubs and have that unsightly lever on the floor of the car, sorry about their vanity, but the stuff works, and works well.


HEY

Rant off

Missy