I have a 97 4x4 4 door blazer that i have come to the conclusiun that there is something broken inside the front diff that is keeping it from engaging into 4 wheel. Along with bad gaskets and a recent vibrating noise,i have decided to hit the salvage yard and find a complete replacement.My question is once i get into this project is there anything i should replace while everything is apart.Seals, gaskets, ball joints.It is the GU6.Thank you

 

If you are going through all of that trouble, I sure hope you have made the proper conclusion. Since we are here to help, I just have to ask what you have tested that has lead you to this conclusion..?

Reason I ask, there is very little actually in the front diff that will cause the front axle not to engage that cannot be removed and inspected without dropping the complete front axle. It isn't the easiest thing to swap out...

#1- Have you made sure that vacuum is reaching the front axle actuator? - If not, check the vacuum lines to/from the vacuum switch on the transfer case.
#2- With vacuum, is the actuator pulling the engagement cable fully? - One way to check this is to pull the cable back by hand and hook a pair of vice grips up to the cable to hold it in place. You may want to use
#3- Is the cable moving freely? - Spray it with some WD40 to free it up if necessary.
#4- When you pull on the cable, does the front axle engage? - If not, then you must first check to make sure that the cable is properly connected inside the passenger side axle tube differential lock housing (held on by 3 bolts).

If it is inside the axle (shift fork), then you would atleast have to remove the passenger side axle tube for disassembly of the differential lock (as they call it) assembly.

I am writing all of this to make sure that you cover all of your bases before spending a ton of time and money on putting in a junkyard axle (and rebuilding it if you so choose). The front axles on these trucks are not user friendly when it comes to rebuilds. There are quite a few special tools required to complete the task.

 

thank you for replying.after reading through these forums and all of the great info that you have given out unforetunately i have gone through steps 1-4 and ruled them all out.I was leaning towards the shift forks when i started getting a wierd vibrating which stops when you put it into 4 hi.I think the gasket is gone on the drivers side so i had been driving it around with no fluid.So now i'm not really sure how much has to be replaced.I can buy the front diff with a small warranty for 175$ at my local salvage yard.From a 99 with 90k miles.I really dont want to pull the whole thing but i might have to anyway.I was looking on gmpartsdirect and i was thinking it might be cheaper just to replace it.I know either way its a lot of work.Please let me know what you think.Thank you

 

Ok, sounds like you've done your homework. I was just trying to cover the bases so that you didn't have to go through a ton of extra work to end up with the same problem after it was all said and done.

As far as the removal of the diff, you basically will end up popping the lower ball joints do disengage the CV shafts from the diff center section. Remove the front driveshaft, disconnect the diff lock cable, then remove the bolts holding the diff in. That is a general synopsis of the work necessary. I don't have my references in front of me to check the specifics. I'm just working from memory.