# 1991 Chevy 4wd problem



## Little Jay (Dec 12, 2001)

While continiuing to go through and get all the trucks ready I discovered a problem. Heres the problem and what I've done;
1991 Chevy 2500 wont go into 4wd
-transfer case is in 2hi-things are normal
-shift trans into 4hi, nothing happens. The light doesnt come on and you still spin only the rear tires
-to eliminate the trans case as a problem, you can disengage it like normal (trans case in neutral, transmission in drive and nothing moves-working properly.) when I engage 4 low, only the rear tires again are powered.
-I checked the fuse which was fine and replaced it anyway;which solved nothing
-I replaced the acuator on the front axle, which did not fix it
-I did drain and refill the the front diff as part of the pre-season maint. I checked the fluid level just to double check, and it was fine-not that it would be the problem but just to check

Any suggestions ?

J


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## wyldman (Jan 18, 2001)

When you put it in 4WD,can you turn the front driveshaft ? (wheels must be off the ground).If you can then the problem is inside the transfer case.If not,it something with the front axle not engaging.At least that will narrow it down and point you in the right direction.


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## JohnnyU (Nov 21, 2002)

J-

It sounds like the thermal actuator on the front axle is bad. That is a very common problem on the early IFS trucks. GM recently changed to a totally electric actuator, which is much faster engauging and more reliable than the older thermal style.

The parts will cost you about $125-$140 depending on what your dealer wants to charge you. 

 Glad you found it now and not in the middle of a snowstorm!


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## tovoninc (Nov 1, 2001)

I would check to see if the connections are secure. there is a connection at the fuse box, and another one under the carpet near the floor shifter. I have had the same issue and it was as simple as a loose connection!


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## Little Jay (Dec 12, 2001)

Snowybowtie,
I thought it'd be the actuator too, and I replaced it. It didnt solve the prob:realmad: 
What really troubles me is that I did find this and it isnt snowing with calling customers and the shop heat broke. If Im having issues before the season starts, whats in store later ?! If the lowballers would collectivly drive off a cliff, i could afford to replace these older trucks !!


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## Little Jay (Dec 12, 2001)

Ill do as wyldman suggested to further rule out the trans case.
I did check the fuse box connection but did not know 'bout the second one. Ill try that too!


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## Little Jay (Dec 12, 2001)

nope.still broke.connections are all fine and trans case is fine..ugh


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## wyldman (Jan 18, 2001)

So when you put it in 4WD the front shaft won't turn,correct ?

If that's the case,check for power at the actuator when it 4WD.If it has power,then the actuator is bad,or there is a problem inside the diff.If there is no power,then it's an electrical problem upstream of the actuator.


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## CARDOCTOR (Nov 29, 2002)

1-blown htr-ac fuse
2-faulty transfer case switch--probaly this part
3-transfer case linkage
4-faulty transfer case
5-faulty front axle



if i had a choice i bet the switch that screws into the transfer case is stuck
if you have 12volt to the switch jump it if it engages the switch is bad




cardoctor


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## Little Jay (Dec 12, 2001)

I've determined that the problem is eletrical and not mechanical. The front drive shaft does not move when engaged in 4wd and the front tires off the ground. I have no power to the actuator up front. I have no power to the switch screwed in to the trans case. The wires that run under the driver's feet, while being a poor design, are fine and look like new. The fuses are all good. Then the pizza guy came and I packed it in for the night. I guess my next step is to check for power at the 4wd fuse. If there is none, Ill keep poking around. My Children's (Chiltons) book does not say anything about a relay or anything electrical pre 4wd fuse. I suppose I can run a wire around the 4wd fuse to check the switches and acutaor to narrow down a potential source of the problem...


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## staley52 (Dec 17, 2001)

you had the key on right? I chased a front end problem for a couple weeks and finaly realized had the key off with it in 2wd:realmad: 
ended up needing the tcase switch


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## Little Jay (Dec 12, 2001)

Yes. I had the ignition on and the lever in 4wd 
I have power at the 4wd fuse, the wires running under the driver's feet are fine, and no power at the trans case switch. I tried to find any relays between the the fuse and the switch but didnt.


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## ptllandscapeIL (Jan 15, 2004)

im also having this problem on my 89 same design and you have jsut given me alot of good adive im almost positive that the transfer case si just fine ive been having alot of electracl problems with that truck first witht hew brake lights..now the 4x4 also on the chevys my light wont turn on at all when i engage he 4x4 so i dunno anymor ehelp would be greAT


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## bigdaddyracing (Jan 9, 2005)

Had a similar problem 2 years ago... turned out to be the ignition wiring block underneath the steering column. It had heated up and melted and 2 wires shorted out, replaced and no problems since...


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