Hey guys, looking for some help here, could just be something simple i am missing.

We got a bad snow the other day and I had to put the blazer in 4wd for the first time in a year. My 4wd selector switch has always been kinda picky at times, but It finally went in and had no problems. Now two days later I am back in 2wd and when driving and when I am decelerating especially, I am hearing this low pitched grunty whine. It sounds like a drill battery dieing. Ive tried taking it in and out of 4wd a couple times to make sure it was slightly engaged, or the transfer case was still moving around but nothing. any help is greatly appreciated.

 

Check the 4x4 actuator operation. Jack up the front end and put it in 4x4 mode while running in park with e-brake on. Rotate 1 front wheel. If the other wheel turns the opposite direction then the 4x4 actuator is probably ok. If not, there is your problem. I dont know if the 98 has an electronic or vacuum actuated front axle lock, but if the other wheel isnt turning, the actuator is probably the problem. The 97 Blazer parts that I have use a vacuum actuated front axle lock and a problem of this sort can be a bad linkage cable, broken linkage retainer clip, leaking actuator, vacuum line to the actuator, vacuum switch on the transfer case, or vacuum supply line to vacuum switch. If you have the vacuum actuated one, I hope you have a garage to trace it down in. If you have the electronic actuator that should be simple :-) The way to tell the difference is if there is a cable linkage sticking out of the side of the front axle parallel to the passenger side cross shaft. If there is no cable and just a module with wires then it is electronic. The cable/vacuum actuated version also has wires for a little switch that monitors the position.

Since you hear a noise, it seems like it may be trying to engage but with a weak vacuum. I think the dog-tooth engagement mechanism might be skipping instead of engaging. I dont know enough about this xfer case to know if there is any way you could get a noticeable noise from the case when trying to engage 4x4 high.

Does your 4x4 switch have an "Auto 4x4" button?

 

no it is just the 3 button, heres something wierd, i pulled out the switch and put wd-40 on all the connectors and now the lights work all the time no problem however, if i am in 2hi and try to go to 4hi it will click but no engagement, however if i go from 2hi to 4lo i can def. feel it, and then i can go from 4lo to 4hi and feel it there too.

im still hearing the noise up front under acceleration (though harder to hear from exhaust) and especially when decelerating.

I think we are just going to take it to the guy who rebuilt my old transmission in my truck to have him do some "preventative maintenance" on my blazers transmission since it is getting up there in mileage: 150k. While he does that I'll have him check out and possibly change all the drive train fluids and go from there.

 

Good job on the switch. Going from 4lo to 4hi you will be able to feel even if the front axle isnt engaged. I have 240K miles on my original engine and trans and I beat the crap out of it. The only thing I have ever changed on the trans is the fluid and filter. If you ask for "preventative maintenance" at a shop, you will typically get a bill for the number of hours it sat on the lift without being touched. If you havent done a flush in a while, that would be good, along with a filter, but it shouldnt cost more than $250. It wont fix your front diff problem though.

I think the Tcase number in your car is 233 (without the auto-4wd), which means you should have the vacuum actuated front end cross shaft lock. There should be 3 vacuum lines going to a vacuum switch on the top of the Tcase. I cant remember which side it is on, but once you find the vacuum lines in that area it should be easy to trace (think it is on the driver side top of the case). You can pull the thing straight off the switch and hook a hand vac up to each port. IF you are doing this in the cold, be really careful not to twist or bend the hoses while pulling or you might break the plastic on the control valve. It isnt an expensive part, but its always annoying to replace something that didnt need fixing before.

One of the three ports on the connector you just pulled off goes to the front axle actuator and once you find it, you should see the vacuum increase as you pump. Pump it up to 20 inches of Hg on the gauge or around -10psi. If the front axle lock engages you should hear a click from the front end. Try rotating the tires and see if the other side rotates the opposite way. This will tell you if the vacuum lines, cable, actuator, and front diff are fine or not. Next is to test the control valve on the Tcase. If you put your hand vac line on each of the 3 ports you should find that 1 port is connected to a second port and the third port is blocked. If all 3 are connected, or blocked then this valve is your problem. Link will show what it looks like.
http://shop.advanceautoparts.com/web...8_369534718___

I have heard that when these valves go the can suck oil into the vacuum lines and they will not hold enough vacuum to engage the front diff. If you see oil in the lines when you pull the lines off this valve, then it is definitely the problem.

 

update: put it up on stands and checked the 4wd engagement everything there is working fine, my switch just needs replaced cause it has a mind of its own

i drove it up to my uncles who is a mechanic and lives about 2 hours away, it made the noise all the way up there and later that night i have him get in to go listen and what do you know it doesnt do it, we drove around for a good hour never could get it to make the noise, drive home the next day get halfway home and its doing it again, just cannot figure this one out

also sometimes when backing up it "jumps", kinda like turning on dry pavement in 4wd, it jumps and hops so i dont know what to think or where to start

 

The jumping and hopping could be due to making a minor turn when backing up in 4wd. Also, it could be due to your tires being a different size due to wear. In order for this to be the problem, the 4wd has to be engaged though. I just rebuilt my transfer case actuator and learned a bit more about the guts of the thing. It is set up almost exactly like an electric drill. A small DC brushed motor drives a planetary reduction gear set attached to the face of the motor. The output of the planetary set then drives one more set of reduction spur gears, which finally drives the actuator arm. A rotory sensor is attached to one of the spur gears for your transfer case. Since I have the NV136 case, the motor only comes on when I am laying into it on a slippery surface, so I cannot hear it actuate. But given the similarity to an electric drill, I would imagine that it would sound exactly like that if it was allowed to free spin without much engine noise. I wonder if the actuator might be your only problem. Maybe one of the spur gears is broken or stripped and the motor is free spinning trying to get in to or out of 4wd. Since the rotary position sensor feeds back info to the TCCM which controls the 4wd selector LEDs, that may be the root of your switch problem also. Thats all I can think of, sorry.
-William

 

tires are brand new so i dont think its wear, heading back up there for xmas today hopefully it makes the noise this time, thanks for the ideas though

 

my uncle the mechanic said it sounds like a normal vehicle slowing down , his hearing isnt the best so i dont think he was the best place to go.

could it be the input shaft wearing out? i know these were a huge flaw in design for the blazers, the griding in reverse it getting worse, its like a low grunting grind, don't know how to explain it really, im clueless here and trying to avoid taking it to a shop and avoid the big $$$

 

I have never heard of any problems with the input shafts on anything associated with these cars. Seriously, I am not exaggerating when I say that I beat the CRAP out of my Bravada. I am not saying that you should or anyone else should, but in terms of stress testing the OEM components, I am sure that I can take the gold medal and it has 242K miles now (original, un-rebuilt engine, trans and tcase). Granted you have a different tcase than I have so I am not an expert on your problem by any measure, but since nobody else has piped in on this thread its all you get .

The Tcase does not really have an input "shaft". It has an input splined hole. The transmission has a splined shaft that goes into the tcase. Usually a splined hole is stronger than the mating shaft since there is more metal at a distance farther from the center, so I would not worry about that. Also, if there were any hard problems (gears, bearings, shafts, engagement mechanisms, diffs, u-joints, etc.) this would not be an intermittent problem. This raises an important question. When you notice the problem at low speed is it all the time or only when it is acting up?

Honestly, knowing how the TCCM controls the lights on the switch and reading your problem over and over, makes me think the root cause of your problem is the encoder part of the tcase actuator. Basically the way that it works is that a motor turns a shaft that has several different positions that select internal "hard" connections. When you press the switch, the TCCM starts to turn the motor until a certain signal is received from the encoder that is part of the actuator assembly on the side of the tcase. Once the correct position is registered by the encoder, the TCCM maintains a small current to the motor to "lock" it in place and it illuminates the light solid on the dash switch. While it is waiting for the correct position to register it blinks the associated light (I think). If the motor was free wheeling or the TCCM was hunting for the correct position you might hear the actuator motor turning from the cabin. On stands I can hear mine from outside the car with the engine running, but not inside, so I'm not to sure on this one. It does sound like a pretty serious electric drill though. Looking at my "new" 233 tcase, with actuator, makes me think this encoder is on one of the two final gears that turn the shaft into the tcase. One of the old actuators for my 136 tcase that I took apart had a hole in the seal for this part of the actuator and it had water intrusion that corroded the gears. The 136 case does not have an encoder in the actuator, but if there was an optical or magnetic position sensor in this part of the actuator it's function would have been impaired.

Also, there is a single wire that goes from the TCCM to the OBD2 connector under that dash that is labeled as "Diag" in some of the wiring schematics that I have looked at. It is possible that a dealership has a tool to plug in that would talk to the TCCM directly to diagnose a problem. If the tool is advanced enough it should be able to identify a troubled encoder/actuator. DONT take it to anyone to have them do "exploratory" testing. If the problem cannot be diagnosed by the Diag connector or by an experienced mechanic's ear, then the only thing you can do is shotgun a new actuator/encoder assembly into the car (~$150). If the problem remains, I would trust your uncle that the noise is "normal" for an older car. If you live in New England, you are welcome to stop by my home sometime and we can put my encoder in there and see if the problem remains.

-William

 

alright took it to a local guy, and got it to make the horrible noise in reverse
his diagnosis is the faulty switch isn't sending the proper signals through the system keeping the 4x4 partially engaged, and this has worn out something in the t-case. so his recommendation, replace the switch and see if fully disengages the system. then if not have the t case rebuilt

my thoughts:
1.) could this be a faulty actuator?
2.) at this point the noise probably isn't going to go away, the damage to the t-case is done so why not just pull one from a junkyard that is good and swap them?

anyone ever pulled one and swapped them? how hard was it? what to look for at the junkyard? im guessing drain the fluid out if it has fluid and if no metal its pretty good right?