hi guys, i am having a similar problem, i have scoured the forum looking for answers, i think i understand the system and how it works, let me begin at the beginning.

i believe the transfer case vacuum switch went bad, it in turn took out the front diff....it howled like mad...i found an entire front end that the fella parting out told me was the same ratio s the one i had(i looked up mine, and asked him what his was..he did not know what mine was...) i finally got around to putting in the diff. the truck is quiet again...yaa..

i then replaced the vacuum actuator, and the diaphragm under the battery.

when i push the button, i can hear the transfer case engage, i also cannot turn the driveshaft, so...that part is working.

if i remove the battery while the truck is running and push the button, the diaphragm retracts., so that part works

today, i replaced the cable, and lifted the passenger side off the ground to check for engagement. i could pull the shaft with no cable and get the front wheel to not turn. so i installed the new cable, and pulled it by hand, the axle engaged.

i then hooked the cable up to the diaphragm, when i hand depressed the diaphragm, the axle engaged.

so put it all together, and drove it, the axle will not engage.

i verified this by lifting the pass side again...

i am planning on removing the battery again tomorrow to double check the diaphragm, but other than that, i am lost...

any ideas??

Edit, update,

today i removed the battery, and checked, the vacuum system does work, the axle does work, if i push the diaphragm in the axle engages, i first bent the bracket to give more throw gave an extra quarter inch, still no worky...so i zip tied the diaphragm, and it new works as it should....is there an adjustment on the cable??

 

Hi Matt,

Please read this (I know some of the images are no longer good). Not the same as your problem but it does describe how far the cable should pull and discusses general operation of the front axle locking in. There is also a blowup of the parts in the front axle mechanism. Take a look and then ask more questions. How much vacuum is actually reaching your diaphragm (gauge)?

https://blazerforum.com/forum/tech-a...4hi-4lo-41226/

 

Fixed the images. Photobucket went and screwed up all of their thumbnails. The images are all still there. If you see any other threads, feel free to send me a link and I'll get them fixed up.

 

Thanks! I will do that!

 

all that info is valid, however, as i stated, the vacuum diaphragm is pulling the cable, the vacuum diaphragm is compressing fully (you can manipulate it just a touch more, which engages the axle), the vacuum diaphragm when fully compressed is not engaging the front axle. when you move the cable say, 1\8 inch more, it engages the axle.

the vacuum actuator on the transfer case is new,
the diaphragm is new,
the cable is new

the axle engages when you pull the shaft on the axle.
the axle engages when the cable is pulled
the cable can be pulled 1/2 to 3/4 inch

in short everything works, but the diaphragm wont pull quite far enough..

when i zip tied the diaphragm, i have proper 4wd when i engage the transfer case.

is there an adjustment on the cable?? like the screw in portion on the plastic housing

i have read extensively on this issue, i am by far no expert, but i understand how it works, every part of the system works, but i need that small amount of pull

i do not have a vacuum tester


thank you for your help

 

This reinforces my belief that you need to get that vacuum gauge and test the amount of vacuum that you have there,

 

ok, thank you...i will let you know what i find.....may i ask what is normal vacuum?

 

Could you just leave the thing Zip Tied in the engaged position? This should produce a sort of "quick & dirty Bravada axle swap." I've been running the real solid right axle swap for a couple of years now and that part seems to have no problems. It's a little more noise and vibration above 60 mph but not annoying. No appreciable milage difference either.

 

Would be whatever you have at your intake manifold. Should be around 16-20 at idle I would think if it doesn't have a leak somewhere.

 

thank you sir..ill let you know