90 Chevy 1/2 Ton xfer case q

today was the first snowfall, and I discovered two things about my truck...

1) the tires suck. they looked in better shape before I owned it
(father-in-law's old truck) and they'll need to go.

2) there's something "broken" in the 4wd system.

These are really embarrassing when you get stuck moving your truck so
you can snowblow your driveway. (We got hammered with a foot of snow...)

Anyway, the problem is when I put it in 4hi or 4lo I discovered
(minor) the linkage needs some (a lot of) grease
(major) 4wd doesn't work. Well, it does, then it doesn't. The 4wd
indicator light goes on and off and dim and bright, which I believe
comes on when the front axle is engaged. After getting major stuck and
letting the truck warm up I think the front axle finally engaged and I
got out of the ditch.

I dug out the shop manual, and am a bit confused as to how the transfer
case/front axle electrical works. I know 4wd works - I used it in 4low
in my yard to move some engines a couple of weeks ago. (fluid levels
are fine, the rear seal on the xfer case leaks but I just checked the
levels on it and the diffs.)

According to the shop manual: There's the xfer case switch and a front
axle switch, the solenoid/thermal activator in the front axle, and a
clutch coil relay and a clutch coil. The description doesn't explain
how all the parts work. I _think_ the xfer case is sending power to the
front and the front hubs aren't locking, but not 100% sure. I'm going
to go out tomorrow and see if the front driveshaft turns when I engage
4hi and the front tire isn't spinning on ice. (obviously a 2 person
job... or I need to get all 4 tires in the air..)

I guess I'm wondering what the clutch coil relay and clutch coil do
before I start replacing parts at random... (the truck is a stick shift
if that makes any difference.) - do the front axle actuators "wear out"
or stick as they get old? It was about -5C at the time and the truck
had only gone about 50 feet before I got stuck...

I'm also thinking that the xfer case is a chain drive, so if it was
busted it would be BUSTED and not work some of the time...

and upon further reading, it appears the clutch coil is only used for
the "pushbutton 4wd" system, so my problem with the front axle light is
probably the thermal actuator for the front axle? (it came on, then
off, then on dimly, then off, then on and so on for a couple of minutes
and finally came on solid...)

What do the experts think?

Ray

news wrote:
>
> today was the first snowfall, and I discovered two things about my truck...
>
> 1) the tires suck. they looked in better shape before I owned it
> (father-in-law's old truck) and they'll need to go.
>
> 2) there's something "broken" in the 4wd system.
>
> These are really embarrassing when you get stuck moving your truck so
> you can snowblow your driveway. (We got hammered with a foot of snow...)
>
> Anyway, the problem is when I put it in 4hi or 4lo I discovered
> (minor) the linkage needs some (a lot of) grease
> (major) 4wd doesn't work. Well, it does, then it doesn't. The 4wd
> indicator light goes on and off and dim and bright, which I believe
> comes on when the front axle is engaged. After getting major stuck and
> letting the truck warm up I think the front axle finally engaged and I
> got out of the ditch.
>
> I dug out the shop manual, and am a bit confused as to how the transfer
> case/front axle electrical works. I know 4wd works - I used it in 4low
> in my yard to move some engines a couple of weeks ago. (fluid levels
> are fine, the rear seal on the xfer case leaks but I just checked the
> levels on it and the diffs.)
>
> According to the shop manual: There's the xfer case switch and a front
> axle switch, the solenoid/thermal activator in the front axle, and a
> clutch coil relay and a clutch coil. The description doesn't explain
> how all the parts work. I _think_ the xfer case is sending power to the
> front and the front hubs aren't locking, but not 100% sure. I'm going
> to go out tomorrow and see if the front driveshaft turns when I engage
> 4hi and the front tire isn't spinning on ice. (obviously a 2 person
> job... or I need to get all 4 tires in the air..)
>
> I guess I'm wondering what the clutch coil relay and clutch coil do
> before I start replacing parts at random... (the truck is a stick shift
> if that makes any difference.) - do the front axle actuators "wear out"
> or stick as they get old? It was about -5C at the time and the truck
> had only gone about 50 feet before I got stuck...
>
> I'm also thinking that the xfer case is a chain drive, so if it was
> busted it would be BUSTED and not work some of the time...
>
> and upon further reading, it appears the clutch coil is only used for
> the "pushbutton 4wd" system, so my problem with the front axle light is
> probably the thermal actuator for the front axle? (it came on, then
> off, then on dimly, then off, then on and so on for a couple of minutes
> and finally came on solid...)
>
> What do the experts think?
>
> Ray

For a '90 it has auto locking hubs which are known to have some
weaknesses or manual locking hubs. The auto locking hubs are 100%
mechanical, they do not have any electrical actuator(s) like the later
models with the center axle disconnect with the troublesome thermal-wax
actuator. The 4WD light is operated from a switch in the transfer case,
a NP241 I think.

If the transfer case is difficult to shift and the 4WD indicator blinks
out I would expect your problem is with a binding shift linkage probably
due to worn out transmission mounts allowing the transmission and
transfer case to shift under load which is binding the transfer case
linkage and knocking it out of 4WD. Since the transmission shift is
straight out the top of the transmission without any linkages you aren't
likely to see the problem there.

This is from owning a '90 full size Blazer so it may or may not apply.
If they switched to the center axle disconnect for your truck by the '90
model year then the thermal-wax actuator which is the black cylindrical
thing screwed into the side of the front differential is the prime
suspect.

Pete C.

>
> This is from owning a '90 full size Blazer so it may or may not apply.
> If they switched to the center axle disconnect for your truck by the '90
> model year then the thermal-wax actuator which is the black cylindrical
> thing screwed into the side of the front differential is the prime
> suspect.
>
> Pete C.

doing some further reading it's probably the thermal actuator. Sounds
like if I was ever going to do some real offroading this part would have
to go. Sounds like when it's -40 it's going to be a while before the
front axles lock.

Ray

ray wrote:
>
> >
> > This is from owning a '90 full size Blazer so it may or may not apply.
> > If they switched to the center axle disconnect for your truck by the '90
> > model year then the thermal-wax actuator which is the black cylindrical
> > thing screwed into the side of the front differential is the prime
> > suspect.
> >
> > Pete C.
>
> doing some further reading it's probably the thermal actuator. Sounds
> like if I was ever going to do some real offroading this part would have
> to go. Sounds like when it's -40 it's going to be a while before the
> front axles lock.
>
> Ray

It it's -40 I'm not going to be in my truck, I'll be in my house under a
pile of blankets.

Pete C.

Pete C. wrote:
>
> If the transfer case is difficult to shift and the 4WD indicator blinks
> out I would expect your problem is with a binding shift linkage probably
> due to worn out transmission mounts allowing the transmission and
> transfer case to shift under load which is binding the transfer case
> linkage and knocking it out of 4WD. Since the transmission shift is
> straight out the top of the transmission without any linkages you aren't
> likely to see the problem there.
>
> This is from owning a '90 full size Blazer so it may or may not apply.
> If they switched to the center axle disconnect for your truck by the '90
> model year then the thermal-wax actuator which is the black cylindrical
> thing screwed into the side of the front differential is the prime
> suspect.
>
> Pete C.

I'm going to clean and lube the xfer case linkage, and yeah, the thermal
actuator may be replaced as well. I say may be because the dealer
wanted $400CDN for it. gmpartsdirect.com wants $100 US. I may go with
the kit which manually locks the front hubs with a pushbutton. We'll
start with checking stuff and lubricating linkages first before spending
hundreds of dollars on parts I don't need.

Oh, and I bought tires - like night and day. Even in 2wd with an empty
bed the truck is driveable. In 4wd and with a couple hundred pounds of
patio blocks in the bed the truck feels like my Jimmy did. Of course,
my front driveway is still buried under 2 feet of hardpacked snow now.
(I have a side entrance...)
I hate winter.

Ray
(who lives in Winnipeg and hates winter but the wife won't move...)

> It it's -40 I'm not going to be in my truck, I'll be in my house under a
> pile of blankets.
>
> Pete C.

I wish. I'm ready to move south. The wife won't go. BUt that's
another story.

But fwiw, It was about +5C (about 40F) a week ago, and last night it was
-20C (-4F) and in January, we can go a week where it doesn't go above -20C.
Ick.

And my truck is literally too long for my garage. (long box... it fits
if I stop when I hit my workbench.)

That's why a thermal actuator won't work in Winnipeg.

It's like an electric car in Winnipeg -> we have plugins at all the
parking lots for your block heater, but at -30 you're not going anywhere
with an electric car. (and diesel cars don't do so hot here either at -40.)

Ray

ray wrote:
>
> > It it's -40 I'm not going to be in my truck, I'll be in my house under a
> > pile of blankets.
> >
> > Pete C.
>
> I wish. I'm ready to move south. The wife won't go. BUt that's
> another story.

Already did that last year, CT to TX. 70 degrees on New Years eve worked
for me. Had a total of three days of snow around Xmas.

>
> But fwiw, It was about +5C (about 40F) a week ago, and last night it was
> -20C (-4F) and in January, we can go a week where it doesn't go above -20C.
> Ick.

Got cold here, was mid 70s day and now mid 50s. Brrr.

>
> And my truck is literally too long for my garage. (long box... it fits
> if I stop when I hit my workbench.)

Same here, crew cab and long bed. 22' truck, 19' garage. Got a 30'
carport along side the shop though.

>
> That's why a thermal actuator won't work in Winnipeg.

2wd - 4wd in about six months.

>
> It's like an electric car in Winnipeg -> we have plugins at all the
> parking lots for your block heater, but at -30 you're not going anywhere
> with an electric car. (and diesel cars don't do so hot here either at -40.)

I've noticed the outlets in the parking spaces when I've been in
Montreal and Toronto. In those temperatures the electric car would
probably go, but require the slow vehicle warning triangle at 5 mph.

>
> Ray

Pete C.

ray wrote:
>
> Pete C. wrote:
> >
> > If the transfer case is difficult to shift and the 4WD indicator blinks
> > out I would expect your problem is with a binding shift linkage probably
> > due to worn out transmission mounts allowing the transmission and
> > transfer case to shift under load which is binding the transfer case
> > linkage and knocking it out of 4WD. Since the transmission shift is
> > straight out the top of the transmission without any linkages you aren't
> > likely to see the problem there.
> >
> > This is from owning a '90 full size Blazer so it may or may not apply.
> > If they switched to the center axle disconnect for your truck by the '90
> > model year then the thermal-wax actuator which is the black cylindrical
> > thing screwed into the side of the front differential is the prime
> > suspect.
> >
> > Pete C.
>
> I'm going to clean and lube the xfer case linkage, and yeah, the thermal
> actuator may be replaced as well. I say may be because the dealer
> wanted $400CDN for it. gmpartsdirect.com wants $100 US. I may go with
> the kit which manually locks the front hubs with a pushbutton. We'll
> start with checking stuff and lubricating linkages first before spending
> hundreds of dollars on parts I don't need.
>
> Oh, and I bought tires - like night and day. Even in 2wd with an empty
> bed the truck is driveable. In 4wd and with a couple hundred pounds of
> patio blocks in the bed the truck feels like my Jimmy did. Of course,
> my front driveway is still buried under 2 feet of hardpacked snow now.
> (I have a side entrance...)
> I hate winter.
>
> Ray
> (who lives in Winnipeg and hates winter but the wife won't move...)

There are several companies that sell replacements for the thermal-wax
actuators. One is a fully mechanical cable operated system and the other
is a motor drive. Should be able to find the adds in 4Wheel and Offroad
or similar. One note is that the hubs do not lock on these axles, they
are solid. This is a center axle disconnect that operates on the
differential.

Weight helps a lot in snow. Back when I dealt with snow in my K3500
dually, I would line the bed with a layer of the 4"x8"x16" concrete
blocks at 30# ea for a total of a little over 1,000#. Sounds like a lot
of weight, but with the duallys and the 4,000# capacity it's not really.
Made a huge difference in the handling.

I never bothered to clear snow, I just drove over it. Add a little sand
now and then when you're getting the compression ice.

Pete C.

Pete C. wrote:

> There are several companies that sell replacements for the thermal-wax
> actuators. One is a fully mechanical cable operated system and the other
> is a motor drive. Should be able to find the adds in 4Wheel and Offroad
> or similar. One note is that the hubs do not lock on these axles, they
> are solid. This is a center axle disconnect that operates on the
> differential.
>
> Weight helps a lot in snow. Back when I dealt with snow in my K3500
> dually, I would line the bed with a layer of the 4"x8"x16" concrete
> blocks at 30# ea for a total of a little over 1,000#. Sounds like a lot
> of weight, but with the duallys and the 4,000# capacity it's not really.
> Made a huge difference in the handling.
>
> I never bothered to clear snow, I just drove over it. Add a little sand
> now and then when you're getting the compression ice.
>
> Pete C.

Yeah, I saw the replacements for the actuator. I'll probably do that if
it goes. I apologize for screwing up the terms for the front axles -
I'm new to this truck. I guess I'm just used to the phrase "locking the
front hubs"...

I've joked I don't need to clear my driveway, I have 4wd.
Unfortunately, no one else does - my buddy almost took off his PT
Cruiser's air dam last winter...

New tires + about 400 pounds of patio blocks = much better traction.