ok i did a little bit of research but couldn't come up with much so i figured id to go the source where people would know hands on...

its a 1990 Chevy Blazer 4wd 4.3L

problem #1 is with the 4wd

ok i put it in neutral and shift into 4 high or 4 low either one, and the light comes on saying the fronts are engaged, but as soon as i shift it into drive they go off and it is not in 4wd, and can do nothing to get it into 4wd, now i was told that the guy had to replace the vacuum lines for the 4wd system and i was thinking they could be on the wrong side, so maybe i could just switch them ( like ive had to do on a dakota before) and hopefully it would work, what is your opinion on what it could be?? and where in the world in the engine bay do the vacuum lines go to??


problem #2
ok this one is weird, get this when im driving at any speed below 50ish any rmp its fine no problems at all tranny shifts really good runs smooth ect ect... but when i start getting above 50's into the 60's and 70's it starts whining LOUD from what sounds like the rear end, but here is the catch, it only whines when your applyign throttle to it, as soon as you let off the gas the whining stops!! it does it in both Over drive and Drive, and another part of it is that when you are doing like 60-70 when you start to apply throttle a little bit it sounds like a bad medal grinding with shards coming from the same area but if you apply more throttle the grinding stops and it starts whining again, but doesnt get louder with the rpm's but does get louder with the speed as long as your pushing the gas....

i know im bad at runnon sentences but thats just how i am i guess and ANY insight on either problem is greatly appreciated!!!

 

For problem #1, check the actuator and the actuator cable for binding. It is possible that the actuator is fine, but the cable is bound up and not allowing the engagement collar to fully seat. It could also be a problem with the vacuum switch on the transfer case.

As far as problem #2 goes, are you sure it is coming from the back? If so, could it be a loose heat shield vibrating causing this noise?

Before we can really get into more specifics, it would help to know what you are working on.

 

sorry i forgot the most important part what kind of vehicle, but i edited it to show what it is a 1990 blazer 4wd 4.3l


and yes we are pretty positive its coming from the back and positive its not a heat shield cause it doesn't rattle, it whines and grinds.....

 

#1) I would hand trace the vacuum lines to the switch on the transfer case and see if some one didn't hook them up wrong if it's not the switch itself. These do go bad sometimes. The vacuum lines end at a tee in the engine compartment and one goes to the actuator. Sometimes the feel method is the best.
#2) Sounds like U-joint or rear end to me. I had a pinnion seal blow out on me before and had whining noise at high speed too. If it's the rear end, you need to find out like real quick 'cause it's not long for this world. These are the things I would check 1st

 

i have a queston for you jzoomer, do you even know where the actuator is on these trucks?.......it's under the battery tray, in case you didn't.

i'd check the bearings in the diff, sounds an awful lot like a diff in one of my full size p/u's. they'd start to howl on the highway-right around 80K (50MPH) just like your truck is.

as for the mention of "it sounds like a bad medal grinding with shards coming from the same area" that's a pretty definate statement. have you checked the fluid, and found metallic particles in it?

 

hey guys i have not been on here in a while just lurking from time to time figuring out things with my blazer as time has went by, thank you all for your input, i got the 4wd fixed and it works great now was just an unhooked vacuum line at the "T" near the throttle body.....


with my 2nd problem i am still having it but with some updates!

#1 it does not make the whining noise hardly at all if it is in 4 high (even going 60)
it only happens in 2wd

#2 i replaced the rear end fluid with 1/2 Lucas and 1/2 castrol, and thoroughly cleaned the inside before adding the new fluid, (the old fluid did have small shavings in it actually had quite alot of shavings but it was extremely fine shavings no big pieces at all)

#3 i put new tires on it this week hoping it was happening because the tires on the rear were a different size but that didnt help at all, although i can say i love the Falken Hi-country AT tires!!


so for those of you starting at this post ill recap below


the "whining" "grinding" noise is for sure coming from the rear!
ONLY WHEN ON THE THROTTLE (PUSHING THE GAS) does it make the noise
it will start making the noise lightly around 30mph and get progressively louder with the MPH but again ONLY WHEN YOUR (PUSHING THE GAS) I CAN BE DOING 80MPH AS LONG AS I AM NOT PUSHING THE GAS IT IS QUIET NO WHINE AT ALL, BUT AS SOON AS I HIT THE GAS SLIGHTLY EVEN THE WHINING STARTS!!!

i was told that i just need to get a new rear end, this problem is weird and at interstate speeds its unbearable!

if i was to need a new rear end how do i find out what gearing the existing one has so i can match it up??

thanks in advance!

 

You would rotate the driveshaft with the rear end jacked up. A 3.73 will have the shaft turn 3 and three quarters turns for ONE rotation of the wheels. 4.11 will have a little over 4 rotations for one rotation of the wheel.

You could also get that truck hopping on the interstate for a few minutes to build up some heat where that noise is coming from, then stop and get down under the truck and stick your hand on various places on the diff. The temp should be warm allover and really hot in the area you are getting the friction from. You said you had mis matched tires on the back, which is a serious no=no to do, so it might be worth popping the alxes out when you serviced the diff and having a look at the berring surface conditions on the axles. Any tiny little nicks and scratches will make a ton of noise the faster you turn them. A little silver shimmer in your old diff oil is normal from my experience, but if the magnet on the inside of the cover was thick with debris, its worth a closer look for the problem. The magnet will usually look 'fuzzy' but anything more than that is an indicator of something more severe going on in there. You may also want to check out the steady berring on the driveshaft, Im not sure if our blazers have them or not though, havent owned mine long enough to get a good memory of all the stuff it has.