scopeface

93 S10 BLAZER 4DR, 4.3L TAHOE. ELECTRONIC 4WD. When I engage the 4HI it works fine for a few minutes and then, with a pop and an awfull WHIRRRR, it is out of gear, as in rolling in nuetral. I push the 4HI button, (still lit) again to disingage the 4HI it CLUNKS back into 2WD when the light goes out. This happens each time I haved used the 4HI. (Iv'e only had the truck for a few months.) The 4LO seems to be working perfectly. This is the first time I've had opportunity to try the 4WD. 5 inches of snow on 1inch of ice at 10-20 degrees F.

blazes9395

This sounds like a bad CV joint. If its broken, it will make this noise. Take a good look at your CV joints, by putting in 4x4 (hi or lo doesnt matter) raise the front end and spin the tire. The whole CV joint should spin, engaged to the front differential.

BlazerLT

No, it is not a bad CV joint, he is saying it is practically in neutral.

Scope, trace the vacuum line going to the vacuum actuator and look for cracks and replace it and the actuator just to be sure.

A loss of vacumm can have the 4x4 pop out.

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blazes9395

It could also easily be a vacuum problem too, yes, but I would take a look at the CV joints too.

BlazerLT

Yes, but that is not the problem here, you are side tracking him from what the real problem is.

A CV joint doesn't neutrailze the drive train like it is in neutral.

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scopeface

I had the ball joints and passenger side CV boot replaced when I bought the truck last march, so I'm reasonably certain the CV joints are O.K.. When it pops out of gear it is rolling freely and throttle has NO effect. Just coasting. When I push the button disingaging 4HI, 2WD resumes with a jolt. I'll inspect the vacuum lines thoroughly tommorrow morning and let you know what I find. Will a broken CV jiont still work in 4LO and not in 4HI?

BlazerLT

Nope, has nothing to do with your problem.

You either have a crappy vacuum line not allowing enough vacuum to get to the actuator for proper engagement or disengagement, or the actuator needs replacing, or your encoder motor is jammed.

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1995 Factory Blazer Service Manual for sale, PM if interested.

blazes9395

Actually that exactly what it does. I won't go into details as to why, but if you know how a differential works, you'll know why.

Have you ever seen a fwd car brake a C.V. joint, it doesn't go too far. The front differential on these trucks acts the same way, with the exception of it not directly being connected to the transmission. It will whine and make a whirring sound, especially when its coasting(off the throttle). This can particularly be seen in 4hi.

Technically its not working in either 4hi/lo. You may think its because of the gear reduction when you change to 4lo. You wont get no whining in 4lo because your not going fast enough. The clunk when you go back to 2wd is usually because the front differential is being unlocked, for this you need vacuum.

It could also be a vacuum problem, sure, its a very common problem too, from the actuator to the vacuum switch being bad, or maybe the lines too.

Not side tracking him or anyone here, providing my opinion, like you are.

Not claiming I am right, but given the information, I made my best guess. If I am wrong, I'm wrong, but please leave the b.s out LT.

BlazerLT

BS?

Comon man, how does a front CV joint gone bad kill the power going to the rear wheels?

No BS here, just fixing what he is claming is wrong. With improper disengagement and whirring, I would think a bad actuator would cause both.

Also, cut out the insults, I never said anything rude here so calling me advice BS is uncalled for and overreactive/immature.

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1995 Factory Blazer Service Manual for sale, PM if interested.