i'm experiencing what appears to be a problem with my '97 blazer's 4wd system. when in 2-high and decelerating from highway speeds (65+ mph) it will sometimes begin to wail and drag like it's in 4wd (think of an air raid siren, the sound is very similiar and very loud. it sounds like 4high, but much louder - i think it's going into 4low.). at that point if i keep it moving above a few miles per hour, the 4wd seems to stay engaged. if i slow down far enough that the truck almost stops, the noise and drag disappear and everything seems normal.

also, when purposely switching to 4wd it sometimes will not disengage until i shut off the engine.

dont know about the wailing noise but the 4 wheel drive activator in the front diff tends 2 stick on mine 2, just stop and back up release the presser on it and i'm back in 2hi:cool2:

here's a noob question: if i yank fuse #19 will that disable 4wd for testing purposes?

don't know right off hand my truck is frozen up and i think its 10 below out side don't fill like freezing my nads off right now to see my be soom one else has so input on this prb good luck but like i said back up or it will take a while for the 4 wheel to disingage if u keep on running it and fills like sh....t coming out of 4wheel drive.

well, the main problem is that it seems to keep going into 4wd at 60mph on the highway when i'm decelerating. i can deal with it sticking, i cannot deal with 4low at 60mph.

i doubt its going into 4low at that speed from 4 high it would shattered the trans or the t case and if it did go into 4low your tack would red line with that muck speed (fill like hitting a brick wall) try disconecting the plug at the frout diff. that puts it into the in and out of 4 wheel drive first

here's some new information: if i hit the 4high button while it's making the noise, the 4wd engages and the noise stops. so apparently it's not going into 4wd while decelerating, but the noise has something to do with the 4wd system.

check the rear diff.

yea i was thinking the samething as smash when u put it in 4wheel it releves some of the presure on thr rear diff. if the ring and pinin are worn bad it well wine badly at higher speeds mine did this from a small oil leak in the cover had to replace the ring set

the thing is, it only happens under very specific conditions. it seems like i have to be going uphill in third, then let off on the accelerator before it starts making noise. i still haven't figured out how to make it happen at will.

Smash-K20 might have an idea, check the rear axel for bad gear wear, might be shot due to other owners, also check all u-joints. my 78 did the same thing sometimes and it was the u-joint coming off the t-case for the rear axel, dropped it going up a small hill, i was lucky it didnt drop at 65+mph or it might have done some real damage

my wife's 01 blazer had a similar problem. She said it just dropped into 4wd on the freeway at 65mph. It happened with out her touching anything. The next day it happened again. Took it to the dealer and they said it was a bad push button for the 4wd system. They replaced it under warrenty and never had a problem again.

is this a S/T blazer or full size Blazer the S/T blazer and trucks had a problem with soft spider gears in the frt diff and that would cause a howling noise at 35mph and up and it would go away when you shifted into 4wd that had a spider gear package to repair this problem but it never became a recall just a tsb

drnut:
i'll try disconnecting the pushbutton module, but i don't think that's the problem - seems like it's not actually going into 4wd, because when i engage 4high the noise goes away.

bronco75:
it's a 2-door. the noise only happens at 60+ mph under very specific conditions (so far it seems to be: decelerating while in third gear while going up a hill, possibly while turning right). engaging 4wd does make the howl/wail go away. can you point me toward the tsb? any idea how much the spider gear package costs?


edit:
blazer pictures: http://magtec.rvglug.org/misc/blazer/
bought the truck this past wednesday.

I haven't worked at a gm dealer for 2 years so I nolonger have access to their tsb's I have searched online but have found nothing
I am thinking the gm kit was like 350 to 400 and it was just a spider gear/side gear package I know of several people that have fixed it with aftermarket gears. What is happining is in the disconnect frt diff the spiders spin all the time and gm made some gears that where to soft and galled and cuased noise. when you engage frt diff it prevents the spiders spinning and the noise goes away