1996 S-10 Blazer
4600 Vortec
253,000 miles (I kid you not)

The other day I engaged my 4x4 HI on the fly at about 30mph. It locked right in and everything worked fine. 15 mins later I pressed the 2 HI button to diengage it. Nothing happened. No flashing lights, no clicking behind the dashboard, no nothing. Just simply like I'd never pressed the button.

I got it home, and after searching through here I gave the following a shot:

Started it up, put it in Neutral, put it in 2 LOW (which engaged), and then pressed 2 HI, and it disengaged. I then drove it up the street in a manner that I could confirm that I was out of 4 HI.

So NOW...here's what it will do and not do:

In Park: Pressing either 4x4 button does nothing.
In Drive: Pressing either 4x4 button does nothing.
In Neutral: Pressing the 4 HI does nothing. Pressing the 4 LOW engages it completely.

I can clearly head the 4x4 LOW engage when I press the button. It audibly disengages back to 2 HI. But if I even try to go from 4 LOW to 4 HI, it will do nothing. The lights flash and it stays in 4 LOW.

Last fall I had problems getting the front differential to engage. The transfer case worked fine. You could hear it very clearly. So I ended up replaced the 3 port contact vacum switch on the upper side of the transmission/txfr case area. It worked great all winter then.


So I'm lost. Are there TWO different motors that engage the 4 HI and 4 LOW? Since I'm hearing it go into 2 LOW, and confirmed that it was in fact IN 4x4 LOW, I know that part is working.

THOUGHTS??



Secondly, I know I'm about due for full blown tune up. I bought this bad boy with 189,000 miles on it, and I havn't done too much to the engine since. It was maintained impecibly. Original engine and transmission still. However I'm noticing a VERY STRONG gas smell anytime I'm around the outside of the truck. Never inside though. There are no visible signs of leakage either.

THOUGHTS??

 

well 1st off dont engage 4x4 while still moving stop then do it, you could have ****ed something up in the transfer case.
2nd it could be 02 sencer.

 

Am I mistaken that the 96 4x4 is shift on the fly????

 

Yours should be shift on the fly between 4hi and 2wdr.
In order to get from 2wdr/4hi into 4lo you must be in nuetral and almost stopped.

Driving in 4hi on dry roads could cause problems. What happens is while in 4wheel drive on dry roads, the drivetrain will get bound up. Even while driving in a straight line. It needs some slippage in the tires to prevent the binding. Most times if you accidently put it into 4hi on dry roads it will not disengage unless you provide relief for the binding. Just drive on gravel or dirt, or back up a little ways. Both methods relief the binding and then you can shift out of 4hi.

It is possible to screw up your 4x4 system, but not without a lot of complaining from your drivetrain first. My wife called my on 2 different occasions saying the truck was making strange noises. Yea, I had her pull of the interstate and drive on the grass on the off ramp, then pop it back into 2wdr. She wasn't even aware she popped it into 4hi. I have done it myself, my knuckle hits the button while shifting out of park.

 

Thanks for the advice. However it was positively pouring down rain when I went into 4Hi. So I knew I was ok when it came to the dry road issue. It still won't shift INTO 4Hi now. Only 4Low in Neutral.

 

Ok, I don't have any idea what could be causing your shifting problems or really the fuel smell (bad O2 as stated earlier or leaking injectors...).

Onto the going into 4hi on dry roads. This should apply to any high traction situation where no slip between the front and rear axles is permitted. This is because just about every true 4x4 (not AWD) has a slightly different ratio in the front diff than what's in the rear diff. The front is geared to slightly pull the truck/suv along when in 4wd so the front wheels are turning slightly faster than the rear wheels. This is why it is not recommended to drive in 4wd in high traction situations.

 

No, that is not true. The front and rear axles have the same gear ratio, plus a part time t-case (most 4x4 trucks use) locks the front and rear driveshafts together, they spin at the same speed. Since all four tires take a different path around turns you must have slippage. Turning is where you introduce the binding and thus the need for slippage. Even slight turns like on the interstate will cuase it to bind up. Usually the slippage comes at the expense of the tire. You will wear your tires out faster, not too mention the damage it's doing to the drivetrain, and jerky driveing conditions which can be dangerous.
Here is a link to How Stuff Works. They do a much better job explaining why and how the various 4wheel drive systems work. Even have little demonstration to explain the concepts visually.
http://auto.howstuffworks.com/four-wheel-drive.htm

 

It may not be true for the light trucks, but I know for a fact that my fathers older (mid 70's) chevy 3/4 & 1ton 4x4 pickups.

I realize that the front and rear driveshafts are turning at the same rate as wel l as the fact that the turning will induce wear on the tires and binding in the driveline. I just didn't know that the newer light trucks had the same ratio. I know for a fact that older trucks had different ratios in the front diff. We had problems with breaking ring gears in our '72 3/4 ton 4x4 Chevy and we thought it very weird that the front ring gear was a different ratio (when comparing the stampings on the ring gears).

I am by no means an expert in the 4x4 community and was only passing on what we were told for some older 4x4s when we were repairing them. Thanks for clearing it up on how the newer ones work.

 

Thanks for the thoughts....

I found the gas smell issue. MAJOR leak coming from the top of the tank. So I know where to investigate that at now.


However, would a good place to start be replacing the stepper motor for the 4x4?? I mean does it make any sense that the 2Low will engage, but not the 4Hi??

 

i am having the same problem with my 92 blazer 4x4 i can get it into 2 wheel drive and 4 lo but it will only occassionally go into 4 hi....which bothers me extremely because i dont want to drive around in 4 lo in snowy conditions at the expense of the transfer case....any ideas would be greatly appreciated....