Couple of weeks agoI was going to work and my blazer made a loud thud sound goin around a turn at a red light. Sounded to me like I had hit a chunk of ice that had fell off someones car. The sound came from the front right wheel like it had hit the lower control arm. So I pulled over no chunks in the road or nothing got back in my car and put it in 2wd thinkin maybe cause i went around the turn it may have just put it in a bid causing the hop and thud. Well at around 25-35 mph I can start to feel a vibration and a huming sound coming from the front (sounds like riding a quad on pavement the hum of the tires) which cont to get worse the faster you go. So I put it back in 4wd the sound stopped. But i dont think its in 4wd all the time. When turning left and gunnin it you can tell its in 4wd cause it will go and kinda understeer thru the turn. But turning right and doing the same it oversteers and the back wants to be up front. And just spins. I live in PA so there is plenty of snow when doin this. Also when going straight it doesnt seem likes it in either spining and wanting to fish tail. I did a visual inspect of the of the 4x4 everything looks well. I can also put it in 4 low and it gears down just not sure if its in 4wd. Does it gear down in the trans or the front dif?? when in 2wd i can turn the drv shft goin to the frnt dif but its kind of chopy. i got to turn in back then forward again and it will spin and when in 4wd there is some play in it about a1/8-1/16 of a turn b4 it stops.

I dont believe its an issue with the motor on the tc case do to been able to change it between all selections. Also i'm shyin away from vacuum do to experience on a blazer that had a bad vacuum issue and when tring to put it in 4wd the lights wld just flash and nothing would happen. I my self think it is sumin inside the front dif$$$$$ it seems as tho no power goes to the front right but seems to be goin to front left and when taking it out of 4wd the sound begins up frontand the choppy spin of the drv shft (like its hiting in the dif).If i was to guess i would think sumin broke in thedifnot allowing it to fully disengage and also not allowing power to the right wheel. but i also know nothing bout front dif or how this vaccuum set up works. I also have read a couple forums refering to a cable which i haveno idea where that is located to chck out. but im gunna go and unhook the vaccuum line that is on the firewall above the distributer. that is the line we replace on dudes to make his 4wd work. maybe this will at least narrow down the issue and hopefully get it out of 4wd cause its not like they are a low gas milage vehilce in 2wd.

Any info will help. I'm just hoping its not the dif it will be $$$$ and prob sumin i wont want to mess with.
*COMBINING CONSECUTIVE POSTS*
ok so the vaccuum lines on my blazer are not located in the same locations as the ones i fixed. Prob cause i dont have the auto 4x4 like the one i messed with does. Or maybe they had been messed with once before i looked at it. but it def isn't in 4wd drive we just got stuck in about a foot and half of snow and only the back wheels were spinin. it still is make the noise when in 2wd and now it doesnt seem like it gears down in 4 low but i does wine as if its in.

someone please have some info

 

ok so the vaccuum lines on my blazer are not located in the same locations as the ones i fixed. Prob cause i dont have the auto 4x4 like the one i messed with does. Or maybe they had been messed with once before i looked at it. but it def isn't in 4wd drive we just got stuck in about a foot and half of snow and only the back wheels were spinin. it still is make the noise when in 2wd and now it doesnt seem like it gears down in 4 low but i does wine as if its in.

someone please have some info

 

It sounds as though the front axle is acting up. When you put it in 4wd, the transfer case activates a vacuum switch which supplies vacuum to an actuator which pulls on a cable to engage the front axle. This engagement happens on the passenger side of the front diff, in the passenger side axle tube. If, for some reason, the collar inside the axle tube is not connecting or not disconnecting properly, it could cause the symptoms you are experiencing. It would not explain what you are describing while turning though, but worth an inspection.

The most common 4wd problem deals with the engagement of the front axle.

 

The turning thing must have been a flook. I dont think its in 4wd at all now but the indicator light says it is.i got it stuck on purpose to see if either front tire would spin and nothing. is it possible for the front diff to get caught between engagement and disengagement??the noise did come from the front passenger side and the vibration is more intense on the floor board onpassenger side when 2wd is selected. the lights also indicate that its goin in whatever i select. no continous flashing then switching back. i can hear it switching to all selections. also when put in 4 lo like i had said it wines but there is no hold back when you lift off the throttle. this may be a dumb question but does vaccuum hold it in 4wd and 2wd. if it was vaccuum related i would think that it would either be in or out and when changing it just wouldnt do anything and i would experience the cont flash. also i would think if the cable that does this was gunna get hung up it would happen when engaging or disengaging not while in use. it was in 4wd when this all started. which is leading me to believe that its catastrophic failure with in the front diff even tho im wishing that its the actuator or the cable. if one of those was to fail while in 4wd would it kick it out and get it stuck between.

 

No, vacuum only holds it in 4wd. You should start at the actuator which should be under your battery. You will want to check to make sure that the actuator is pulling in on the cable when the engine is running and a 4wd mode is selected.

If it does not pull in, disconnect the vacuum line and see if there is vacuum there. If not, then you either have a vacuum line problem or a vacuum switch problem.

If there is vacuum there, then it is possible that either the vacuum is not high enough (leaking vacuum line), the actuator has a leak, or the cable is froze up. If you cannot pull on the cable with a vise grip, the cable is bad.

 

will do. I'm headin to my parents house now to watch the steelers game so im gunna pull it in the garage let it thaw out. i'll check the cable out. i located it yesterday but its just to cold out to be workin in the weather. I'll jump on up there to update ya on the condition of the cable and vaccuum. do you know howmuch vaccuum should be at the actuator??? cause if its there i'll test it

 

how do you know if its moving the cable or not. does the diaphram on the actuator move. if so its not moving at all. gunna check and see if i got vaccuum now. but regarding the cable im not sure what i shouldbe lookin at to see if its moving it or not and i dont know where to unhook it to see if i can move it manually or not

 

The actuator pulls on the cable to engage the front axle. If it does not move, you either do not have vacuum, have a leaking actuator, or have a froze up cable.

You should be able to see it move.

You unhook it by disengaging the spring clip on at the actuator.

 

ok so i just poped the vaccuum line off the actuator and the diaphram on the actuator poped out so disregard the previous question. the cable moves pretty easily by hand just moving the actuator back and forth with little to noeffort. should it be really easy?? could the cable be broke?? also i did start it and watch the actuator had my girlfriend go from 4wd hi to 2wd and the actuator didnt move at allb i did this b4 disconnecting the vac line. im notretarded.so im guessing if i went out for a drive i could put it 2wd now with no noise cause the actuator is out. so thank good i dont think its failure in the front dif now. what controls vaccuum to the actuator. why wasnt it moving when switching between 2wd and 4wd?? where is the vaccuum switch located. o but wait if it was pulled to be in 4wd why isn't4wd working??

 

It may not be pulled enough?

The vacuum switch is on the transfer case. If you had vacuum when in 4wd, but not when in 2wd, then the switch is working. If you constantly had vacuum, then there is a problem with the vacuum lines or the switch itself.