4wheel drive not engaging replaced actuator on front dif.can hear it engaging and TCM is also making a noises when pushing shift buttons lights flash on buttons

There are two actuators. Likely ou're hearing the transfer case shift actuator (from driver seat). A common failure is ground to the front axle actuator. If you have helper select 4WD, find the front axle actuator behind front right wheel and see if it makes noise. If not, see following video.

See following video

https://m.youtube.com/watch?v=_09kPCh73OY

Most 4x4 systems require the trans to be in neutral to shift into or out of 4x4low.

There are 2 models here the push button will flash if the system is not engaging or disengaging properly . If front drive shaft is turning. That is with car raised and supported . if front drive axles do not turn then the axle actuator is not engaging axle shaft passenger side. Remove actuator and manually engage shifting collar with a screwdriver still does not turn then inner axle is twisted.

Dave,
The problem your are speaking about could be a few things. All things that are somewhat common to go bad on Chevys/GMCs. Each one of the cars I worked on had a different problem. I have changed the switches, the 4wd solenoid, and TCM on different trucks. IMO the TCM location in the passenger kick panel is a poor location allowing water and other passenger debris to get into it. Once water gets in that area you can imagine already what occurs. One of the cars the TCM bracket was rusted by the ground and eventually the weak ground fried it. The weird thing is the TCM would allow it to shift sometimes and not other times or partially engaging causing the wonderful light to blink rapidly. What I have found of some time with these trucks is pushing the button to change the truck to two wheel drive and driving a few feet in reverse helps ease the change.

So you can start with a new switch that pops in and out of the dash in a few mins. Can get one on ebay for under 25 dollars. Although, I personally would take off the kick panel and take a look at the TCM. If you see any rust around it, my money would be on that.

Good luck

On the full size, the front actuator is electric, not vacuum.

When in 4wd mode, a switch on top of the transfer case conducts 12 volts out to the actuator. Wire #50 (brown) is the 12v feed, and it conducts to the light blue wire (#900) to the actuator.
When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.

I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd.
The way this actuator works, is it is a sealed chamber that gets heated by voltage. When it heats, the pin in the end swells and pushes a shift fork in the front differential. The shift fork engages a spline on the passenger side of the differential, and boom! you have 4WD.

GM offered an upgrade to this actuator that is a motor instead of a heated device. However, it requires a small harness addition, a spacer, and a new actuator. It is about a $150 to $200 option.

Good luck. The actuator is usually the problem 90% of time but recheck all of the wire harness just to maker sure there is no short before replacing any parts. The actuator may not be fully engaged or disengaged and the fork to the spline may be what is causing the whining or grinding noise you hear.

88-UP C/K ACTUATOR UPGRADE
VEHICLE SERVICED: 1994 CHEVROLET FULL SIZE
PURPOSE: IMPROVE AXLE CONNECT ENGAGEMENT TIME AND
COMPONENT RELIABILITY.

SYMPTOMS: NO FRONT DRIVE AXLE ENGAGEMENT WHEN SHIFTED INTO 4X4.

Obtain the following GM part numbers:
(1) 26060073 Actuator
(1) 88959465 Harness/Spacer Kit

On the full size, the front actuator is electric, not vacuum.

When in 4wd mode, a switch on top of the transfer case conducts 12 volts out to the actuator. Wire #50 (brown) is the 12v feed, and it conducts to the light blue wire (#900) to the actuator.
When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.

Check voltage at the connector for the front actuator (at the front differential - it looks like a large bullet that threads into the front diff.) If it has 12 volts, the actuator is the problem. If it does not have 12 volts, check the transfer case switch and the power feed to the transfer case.

I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd.
The way this actuator works, is it is a sealed chamber that gets heated by voltage. When it heats, the pin in the end swells and pushes a shift fork in the front differential. The shift fork engages a spline on the passenger side of the differential, and boom! you have 4WD.

GM offered an upgrade to this actuator that is a motor instead of a heated device. However, it requires a small harness addition, a spacer, and a new actuator. It is about a $150 to $200 option.

If I were you, I would buy a new heated actuator. They are available at most auto parts stores, and are about $90. They are also on eBay for about $55 plus shipping. These are very easy to change - just thread out the old one, and thread in a new one.

Good luck, That actuator is usually the problem 90% of time.

if this is a push button 4 wheel drive you need to find out if the actuator on the transfer case is working, if not check the voltage to the actuator and make sure it is getting a signal if it is then change out the actuator, if it isn't then you need to case back to the fuse and relay make sure those are good and then last the button...
good luck

Check drive shafts are not damaged.if there ok you have a diff problem.

that vacume line goes back to the transfer case, the end that goes behind the motor hooks to a steel tube so it does not get hot from the exhaust., my guess it should be hooked up so it will feed vacume to the vacume ball so it can lock in the axels. if you start the car and shift into 4 wheel drive and listen under hood you should hear a hissing sound, that is vacume, if you can't hear it there, you may have to craw under the right side to hear it, probably came unhooked underneith the car

I just fixed a friend of mines 96 yukon...shift to neutral press 4H and u can hear the actuator make noise (we even replaced it with a new one his idea and the same thing happen as old one), so as he hit the switch for 4H i layed under it (on 4 jack stands) and I could hear the motor on the transfer case make a loud noise (well thats working) and before all this I asked him did u check all your fuses (he said guarnteed to be all good) one night it was bothering me so i looked through the owner manual for the yukon and in the fuse box on driver side by the door there are (2) fuse for the 4wheel drive unit,pull one of the fuses good...pulled the other one and it was blown put in a new fuse and it works like brand new..pull fuse for anything that has to do with 4 wheel drive componants,