88 Chev K2500 4x4 problem, 4wd not engageing. & indicator not showing.

Hello all,

The main point,
i need information concerning the 4wd system on an 88 chev k2500
so i can atlest try to isolate the problem. All i have is an haynes
manual, and it has very little information. Any schematics for the
electronics involved would be very usefull too

Ok in a nut shell,
recently i was unable to engage the 4wd on my 88 chev k2500. (going to
pull some one out). The next day(in a vain trouble shooting attempt),
on dry asphalt, i was able to engage it, but the indicator lite's by
thte xfer case shifter did not come on. was able to shif in a out of
4hi 4lo and 2hi with no problem. checked the bulbs, bulbs are fine,
but no indicator.

Basicly id like some info on the 4wd system on this truck, how what
engages what to get power to where and what not. is it the front diff
that engages/disengages and if so, what controls that.

Thank you all

Please reply to;
[email protected]

On 6 Dec 2003 21:50:15 -0800, [email protected] (Daniel)
wrote:

>:|Hello all,
>:|
>:|The main point,
>:|i need information concerning the 4wd system on an 88 chev k2500
>:|so i can atlest try to isolate the problem. All i have is an haynes
>:|manual, and it has very little information. Any schematics for the
>:|electronics involved would be very usefull too
>:|
>:|Ok in a nut shell,
>:|recently i was unable to engage the 4wd on my 88 chev k2500. (going to
>:|pull some one out). The next day(in a vain trouble shooting attempt),
>:|on dry asphalt, i was able to engage it, but the indicator lite's by
>:|thte xfer case shifter did not come on. was able to shif in a out of
>:|4hi 4lo and 2hi with no problem. checked the bulbs, bulbs are fine,
>:|but no indicator.
>:|
>:|Basicly id like some info on the 4wd system on this truck, how what
>:|engages what to get power to where and what not. is it the front diff
>:|that engages/disengages and if so, what controls that.
>:|
>:|Thank you all
>:|
>:|Please reply to;
>:|[email protected]


here goes:

in GM IFS trucks the front axle has a Central Axle Disconnect (CAD)
system. there is an actuator on the front of the axle, above the axle
centerline that engages the passenger side (if memory serves) axle.
there is a 99% chance that your actuator (which is of a very failure
prone thermal design) has failed. if you have a 7200# K2500 you can
use the revised electomechanical acuator from a 98+ truck (which I
have in my 88 K2500). if you have a 8501# or heavier (GVWR) truck,
you are stuck with the thermal actuator. I can give you the part #'s
if you like.

to check the CAD, you'll need to get under the truck and unscrew the
thermal actuator ( you don't need to drain the diff) and use a wood
dowel about 12" long and push the plunger in. if you do this with the
key on and a friend watching the indicator, the indicator should light
up. if it doesn't, your problem lies elsewhere. the plunger should
also move smoothly, although you may have to rotate the tires to get
the splines to line up.

HTH,
Bret

On Sun, 07 Dec 2003 09:57:10 -0500, Bret Chase <[email protected]>
wrote:

>if you have a 7200# K2500 you can
>use the revised electomechanical acuator from a 98+ truck (which I
>have in my 88 K2500). if you have a 8501# or heavier (GVWR) truck,
>you are stuck with the thermal actuator. I can give you the part #'s
>if you like.


Isn't there a manual version available for all the GM trucks of this
vintage? I know the aftermarket offers some type of cable system for
at least some of these trucks. Sounds like a better and cheaper
solution if available.

Matt
99 V-10 Super Duty, Super Cab 4x4

On Sun, 07 Dec 2003 08:30:40 -0800, Matt Mead
<[email protected]> wrote:

>:|On Sun, 07 Dec 2003 09:57:10 -0500, Bret Chase <[email protected]>
>:|wrote:
>:|
>:|>if you have a 7200# K2500 you can
>:|>use the revised electomechanical acuator from a 98+ truck (which I
>:|>have in my 88 K2500). if you have a 8501# or heavier (GVWR) truck,
>:|>you are stuck with the thermal actuator. I can give you the part #'s
>:|>if you like.
>:|
>:|
>:|Isn't there a manual version available for all the GM trucks of this
>:|vintage? I know the aftermarket offers some type of cable system for
>:|at least some of these trucks. Sounds like a better and cheaper
>:|solution if available.
>:|
>:|Matt
>:|99 V-10 Super Duty, Super Cab 4x4

yeah there is, it's called a 4x4 Posi-Lok, but for $179, I can replace
my 98+ electromechanical actuator twice and never have to worry about
exposed bellcranks and cabling. the 98+ actuator has almost instant
(<1 sec) engagement and is impervious to the cold (I've used at -15F).

-Bret

On Sun, 07 Dec 2003 15:23:27 -0500, Bret Chase <[email protected]>
wrote:

>yeah there is, it's called a 4x4 Posi-Lok, but for $179, I can replace
>my 98+ electromechanical actuator twice and never have to worry about
>exposed bellcranks and cabling. the 98+ actuator has almost instant
>(<1 sec) engagement and is impervious to the cold (I've used at -15F).
>
>-Bret

Well, I guess I can see value to both. Personally, I think I'd like
the manual system just because I think I could fix it trailside if it
didn't work right.

Matt
99 V-10 Super Duty, Super Cab (who has "issues" with his vacuum
operated hubs!)