Four Wheel Drive Not Locking In

[LovinMyTruck]

I have a 1991 GMC Sierra 1500 SLE 4X4 V8 5.0Liter Automatic with overdrive. Automitc 4 wheel drive locked in by shifting the 4 wheel drive llever in the floor. The front wheel are supposed to light up when you shift into four wheel drive ( The display lights in the floor around the shifter)

Anyway we are having a very aggravating issue with it. When you shift it into 4 wheel drive it won't lock in (and the display lights in the shifter do NOT light) We have replaced the accutuator twice one withn a used one and then bought the new one...My husband and I believe we are shifting into 4 wheel drive corectly but it still does not lock in...any ideas?

By the way the truck is a shortwheel base with an etended cab(or king cab i am not sure...it does have the full seat in the back but does not have 4 doors like a crew cab)

[maxwedge]

Welcome to AF. Do you have the proper vacuum to the frt axle actuator?

[LovinMyTruck]

Actually seems like (hears like) it's locking in outside but the shifter does not indicate change and of course it doesn't lock in. As for the vaccum lines my husband says it is a wire connection only he says in the process of replacment he did not remove any vaccum limes to his knowledge.

[Z15]

There a redesigned actuator. Did you install one of these or just replace with original type?

The new ones have been available for years from GM dealers but other sources may still be selling the problem type.

History
The oem unit uses electricity to heat up a gas in the actuator which in turn forces a plunger to engage the front axles. These sometime take up 10+ secs to work when they are failing or may not work at all.

The new kit uses a electrically controlled actuator (no gas) to engage the axle and is instantaneous. To use this new type, you have to get it from a GM dealer along with a new wire harness that has to be connected up to the shifter and requires soldering of wires.

Did your husband do this whe he fixed it?


If not then you need to go see a GM dealer about this, check out what parts are needed and weather or not you are up to the task. Last I checked the parts run about $100 and its about a 1 hr job. There may be after market parts available but I don't trust as lot of this stuff because its often sourced from cheap far east sources. The GM parts work and thats what I would recommend.

ALSO NOTE--After intalling the new actuator it may not appear to work. If that happens, move the truck a few feet and try again. It will engage. I know someone who messsed with it for a whole day, called the dealer parts dept and made a big stink so they gave him a new switch. Installed it and same thing, would not work. All the while he was doing this he never started the truck or moved it. I was riding by his shop and saw him working on the truck, stopped in and heard all about the problems he was having. So he asked, jump in there and see if it works when I try this. No work. So I said, have you tried it with the truck moving? What? No, so I started it up and moved it a few feet and it worked. He had been screwing around the better part of a day and he thought to try to move the truck! The gears were not meshing.

[LovinMyTruck]

No we put the original acuator back on it...I will call the GM dealership to see what it takes to get those parts and what it takes to put them on

Thanks A Bunch we have been buttin our head on the wall witht this one for over a month. :')

[Z15]

Here's the TSB for those that don't know about it

SLOW OR NO ENGAGEMENT OF FRT. AXLE WHEN 4WD IS SELECTED

TSB#76-43-01A - (09/18/1998)
REVISION: 09/17/98 DIVS INVL 1 5 7

THIS BULLETIN IS BEING REVISED TO ADD INFORMATION TO THE SERVICE PROCEDURE, ADD A NEW PART NUMBER, AND INCLUDE SCHEMATICS. PLEASE DISCARD CORPORATE BULLETIN NUMBER 76-43-01 (SECTION 4 - DRIVE AXLE). __________________________________________________ ____________________

SUBJECT: SLOW OR NO ENGAGEMENT OF FRONT AXLE WHEN 4WD IS SELECTED (REPLACE FRONT AXLE ACTUATOR)

MODELS: 1988-97 CHEVROLET AND GMC K MODELS EXCLUDING 1988-93 MODELS OVER 8500# GVW

CONDITION:

SOME OWNERS MAY COMMENT THAT THE COLDER THE OUTSIDE TEMPERATURE IS, THE LONGER IT TAKES FOR THE FRONT AXLE TO ENGAGE WHEN 4 WHEEL DRIVE IS SELECTED, OR THE FRONT AXLE DOES NOT ENGAGE.

CAUSE:

THE FRONT AXLE ENGAGEMENT ACTUATOR IS A THERMALLY ACTIVATED COMPONENT. BECAUSE OF THIS CHARACTERISTIC, THE TIME REQUIRED FOR THE ACTUATOR TO COMPLETE 4 WHEEL DRIVE ENGAGEMENT IS EXTENDED AS THE TEMPERATURE DROPS.

CORRECTION:

REPLACE THE FRONT AXLE ACTUATOR AND INCLUDE THE APPLICABLE WIRING HARNESS KIT. REFER TO THE PARTS INFORMATION IN ORDER TO DETERMINE WHICH WIRING HARNESS KIT IS NEEDED.

1996 MODEL TRUCKS WITH A BUILD DATE ON OR AFTER JANUARY 2, 1996 ARE CONSIDERED AS "96I". IF THE BUILD DATE OF THE TRUCK IS UNKNOWN, VERIFY THE 3 CHARACTER "AXLE CODE" ON THE FRONT AXLE LABEL IN ORDER TO DETERMINE WHICH WIRE HARNESS TO ORDER.

THIS NEW ACTUATOR USES A MOTOR TO ENGAGE THE FRONT AXLE AND IS NOT AFFECTED BY TEMPERATURE. ON 1988-93 MODELS WITH A GVW RATING OVER 8500#, THE NEW ACTUATOR CANNOT BE INSTALLED AND THE THERMAL ACTUATOR WILL REMAIN THE SERVICE PART.

SERVICE PROCEDURE

1. REMOVE THE FRONT DIFFERENTIAL CARRIER SHIELD, IF EQUIPPED.

2. IF NECESSARY, CLEAN THE AXLE HOUSING IN THE AREA AROUND THE EXISTING ACTUATOR. DISCONNECT THE ACTUATOR'S ELECTRICAL CONNECTION AT THE FRONT AXLE HOUSING.

3. REMOVE THE FRONT AXLE ACTUATOR BY UNTHREADING THE ACTUATOR FROM THE AXLE HOUSING.

4. INSTALL THE SPACER FROM THE WIRING KIT INTO THE AXLE TUBE WITH THE FLAT SIDE SEATED AGAINST THE SHIFT FORK.

5. INSTALL THE ACTUATOR MOTOR AND TIGHTEN UNTIL THE SHOULDER OF THE ACTUATOR SEATS AGAINST THE AXLE TUBE.

IMPORTANT: IF BINDING OCCURS BEFORE THE ACTUATOR IS SEATED, REMOVE THE ACTUATOR AND RESEAT THE SPACER BY PUSHING ON THE SPACER WITH A SCREWDRIVER. THEN REINSTALL THE ACTUATOR.

ON K3 MODELS WITH THE CAST IRON AXLE TUBE, THERE MAY BE A CASTING BURR WHICH MAY CONTACT THE EDGE OF THE ACTUATOR. THIS SHOULD NOT CREATE A CONCERN AND THE ACTUATOR SHOULD SEAT AGAINST THE AXLE TUBE. IF THIS CONTACT REMAINS A CONCERN, USE A DIE GRINDER IN ORDER TO REMOVE THE BURR.

6. CONNECT THE SERVICE HARNESS CONNECTOR TO THE ACTUATOR AND CONNECT THE 2-PIN CONNECTOR TO THE MATING CONNECTOR AT THE AXLE. FOR 1994 TO CURRENT MODELS, IN THE CASE OF A COMPLETE AXLE REPLACEMENT, REFER TO FIGURE 1.

7. ROUTE THE WIRING HARNESS ALONG THE EXISTING HARNESS ON THE RIGHT SIDE OF THE VEHICLE. ROUTE CKT 241 (BRN) OVER THE TOP AND TO THE LEFT OF THE TRANSMISSION. SECURE THE HARNESS USING PLASTIC TIES.

8. FOR 1995-97 INTERIM VEHICLES, LOCATE THE 4-WIRE CONNECTOR (C120) ON THE LEFT SIDE OF THE TRANSMISSION. SPLICE THE BRN WIRE OF THE ACTUATOR HARNESS INTO CAVITY D OF CKT 241 (BRN) ON THE ENGINE SIDE OF CONNECTOR C120. FOLLOW THE SPLICING PROCEDURE DESCRIBED IN SECTION 8A (ELECTRICAL DIAGNOSIS REPAIR PROCEDURES) OF THE APPLICABLE SERVICE MANUAL.

IMPORTANT: THE NEW FAST AXLE ACTUATOR REQUIRES ONLY 1 SPLICE. - FOR 1993 AND PRIOR VEHICLES, SPLICE INTO CKT 50 (BRN) BETWEEN CONNECTOR C152 AND GT101 (FIGURES 2,3,4). - FOR 1994 VEHICLES, SPLICE INTO CKT 50 (BRN) BETWEEN CONNECTOR C152 AND P101 (FIGURES 5,6). - FOR 1995-97 VEHICLES, SPLICE INTO CKT 241 (BRN) BETWEEN CONNECTORS C120 AND C100 (FIGURE 7).

NOTICE: CONNECTIONS MUST BE WATER TIGHT IN ORDER TO PREVENT WATER FROM ENTERING THE CIRCUIT AND CAUSING DAMAGE TO THE COMPONENTS.

9. ON K3 MODELS, INSTALL THE DELAY RELAY, INCLUDED AS PART OF THE WIRING HARNESS KIT, AT THE ENGINE SIDE OF THE BULKHEAD, ADJACENT TO THE EXISTING RELAY. MOUNT THE NEW RELAY WITH SELF-DRILLING FASTENER, P/N 22510339. ROUTE AND SECURE THE RELAY WIRE HARNESS BEHIND THE RIGHT OXYGEN SENSOR HEAT SHIELD.

10. VERIFY SYSTEM OPERATION. WHEN SHIFTING THE TRANSFER CASE, YOU SHOULD HEAR THE ACTUATOR MOTOR OPERATE.

IMPORTANT: THIS RELAY INCORPORATES A 5 SECOND DELAY FOR THE FRONT AXLE TO ENGAGE IN ORDER TO ALLOW THE TRANSFER CASE SYNCHRONIZER TO ENERGIZE.

FOR 88-93 VEHICLES, IF THE AXLE HAS TO BE REPLACED, USE JUMPER HARNESS P/N 15313272. CKT 1695 (BLK/WHT) FITS INTO CAVITY A OF THE FAST ACTUATOR. THE CIRCUIT INCLUDES THE CABLE SEAL AND THE TERMINAL PIN. THIS CIRCUIT PLUGS INTO THE 5-PIN AXLE ACTUATOR CONNECTOR.

11. DO THE FOLLOWING STEPS IN ORDER TO INSTALL JUMPER HARNESS P/N 15313272:

1. LOCATE THE AXLE ACTUATOR 5-PIN CONNECTOR ON THE SERVICE ACTUATOR WIRING HARNESS AND REMOVE THE TPA. 2. REMOVE AND DISCARD THE CAVITY PLUG FROM CAVITY A. 3. INSTALL CKT 1695 LEAD (BLK/WHT) FROM THE JUMPER HARNESS THAT HAS THE CABLE SEAL AND TERMINAL INTO AXLE ACTUATOR CONNECTOR CAVITY A. 4. REINSTALL THE TPA ON THE 5-PIN CONNECTOR. 5. INSTALL THE SERVICE ACTUATOR HARNESS 5-PIN CONNECTOR INTO THE AXLE ACTUATOR. 6. CONNECT JUMPER HARNESS 2X2 CONNECTOR INTO THE EXISTING VEHICLE 4WD MATING CONNECTOR. 7. STRAP THE JUMPER HARNESS AND THE SERVICE HARNESS TO THE TAB ON THE AXLE TUBE.

PARTS INFORMATION:

P/N DESCRIPTION QTY --- ----------- ---

26060073 ACTUATOR ASM, FRT DRIVE AXLE 1 22510339 FASTENER 1 15313272 HARNESS, JUMPER (Z SPLICE)(88-93 K1-3) 1

AXLE CODE 12376316 KIT, ACTUATOR WIRING HARNESS (88-96I K1,2) ZLS, ZLT, ZLW ZLX, ZLY 12376317 KIT, ACTUATOR WIRING HARNESS (96I-97 K1,2) ZWA, ZWB, ZWD ZWF, ZWG 12376318 KIT, ACTUATOR WIRING HARNESS (94-96I K3) ZLX, ZLY, ZLZ 12376319 KIT, ACTUATOR WIRING HARNESS (96I-97 K3) ZWF, ZWG, ZWH

PARTS, EXCEPT P/N 15313272, ARE CURRENTLY AVAILABLE FROM GMSPO. P/N 15313272 IS EXPECTED TO BE AVAILABLE 9-21-98.

[Z15]

GM PART # 26060073
CATEGORY: All
PACK QTY: 1
CORE CHARGE: $0.00
GM LIST: $151.62
OUR PRICE: $89.88



DESCRIPTION: ACTUATOR when replacing your original unit you will need harness part number 88959465 for 1500 & 2500's or 12376318 on 3500's when replacing the original unit. New unit must be wired up using new harness kit.(please check with customer service before ordering to insure you get the correct harness as olders models may differ.)


PLEASE NOTE - THIS IS FOR INFORMATIONAL PURPOSES ONLY. PLEASE CHECK WITH A GM PARTS DEALER TO BE THE CORRECT PARTS FOR YOUR VEHICLE. THE VIN MAY BE THE ONLY WAY TO GET THE CORRECT PARTS.

[LovinMyTruck]

Thanks again....it looks like my 91 was excluded by the cold weather factor if i read it correctly...it'll be Thursday before i have a chance to call....thank you again.