98' 4x4 help...

I have read the How-to section above but I want to know anyone elses experiences.

I have a 98' Blazer with the 3 Button selector. When I click either button all I have is a click or clunk and the light blinks, it doesn't engage. I took the battery cover off and started it then removed the battery, looked at the vaccum switch under the battery plate, had a buddy press the buttons but nothing moved there.

I just had the intake gasket fixed and they said there were no vaccum leaks. So What could it be?

The mech. under the kick panel on the passenger side, that vaccum thing under the battery or the transfer case encoder, is there anything else im missing?

Thanks for the help in advance,
Justin Tidwell

Some of the blazers have a vacuum switch on the firewall just about dead center. Should have a 2 wire electrical connector and 2 vacuum lines. One line should have vacuum all the time the other will have vacuum when 4x4 is selected. Find out which one has vacuum all the time then select 4x4 and pull the other vacuum line off and check the nipple for vacuum on the switch. (Line that runs down to the vacuum diaphram under the battery). The computer is under the kick panel.

i had a problem with my 4x4 not engaging in my 96 blazer and my problem turned out to be the vacuum actuator under the battery, i went to salvage yard got a new one and 4-wheel works now. now i found out sumthin is screwed up with my differential it makes an aweful clunking sound when 4 wheel is engaged and driving dont have a clue wut it could be

This one does not have the switch on the firewall, I can't see one at all and thought I had read on where that was on 99' models and later, mines a 98'.

I can here the computer unit click, but thats it, just a light flash. The acuator under the battery compartment didnt move when we had the truck running and pressed either 4hi/lo.

Check your vacuum lines that run back to the top of the transfer case make sure they are good

Check your vacuum lines that run back to the top of the transfer case make sure they are good. Does the front dirve shaft turn when 4x4 is selected?

Negative, the front drive shaft doesn't turn, the 4x4 doesnt work. Like I mentioned, we looked at the acuator under the battery while it was running in nuetral, hit a 4x4 button, and nothing moved down there.

Could it be the TCCM? if its not, what are the other alternatives? vaccum lines or the acuator? If something is fubared in the tcase them will hooking up the computer tell me anything? no error lights on the dash..

This is where the vacuum line goes to the transfer case. It will be the top left line and will pass along the firewall near the distributor.
http://i48.photobucket.com/albums/f236/JaVeRo/Vacuum.jpg
It goes to a 3 port switch on the top of the transfer case near the front output shaft. When the transfer case goes to 4wd this switch will allow vacuum to the line that goes to the actuator beneath the battery. When you put it back in 2wd the switch removes vacuum to the actuator line and connects it to the third line which is a vent line probably tied to the transmission dipstick.

If your vacuum line is good, your problem MAY be this switch. you should be able to check for vacuum at the actuator when you push the 4wd button to see if this switch is working. If your transfer case is not engaging, the switch will never be activated so you still won't have vacuum.

If you replace the switch on top of the transfer case, make sure it has the o-ring on it. I had to take the old o-ring off to put on the new switch.
James

EDIT, I told you wrong, It's the bottom left in that picture.

i thought the transfer case engaged electrically and the differential used vacuum??

I have read the How-to section above but I want to know anyone elses experiences.

I have a 98' Blazer with the 3 Button selector. When I click either button all I have is a click or clunk and the light blinks, it doesn't engage. I took the battery cover off and started it then removed the battery, looked at the vaccum switch under the battery plate, had a buddy press the buttons but nothing moved there.

I just had the intake gasket fixed and they said there were no vaccum leaks. So What could it be?

The mech. under the kick panel on the passenger side, that vaccum thing under the battery or the transfer case encoder, is there anything else im missing?

and vacuum and electric both lock in the fron axel

Thanks for the help in advance,
Justin Tidwell


The how to should lead you in the right direction.
The transfer case is engaged by electric modules/pcm.
After it engages it switches both vacuum and electric to the front axe actuator to lock in front axle.
Check all fuses and power to transfer case and transfer case pcm first.
Does the transfer case switch ranges?
Shift buttons light up or flash?
Also we need to know which transfer case you have 233-236?
Check the tag on the back of it for ID.

i thought the transfer case engaged electrically and the differential used vacuum??
The transfer case does engage electronicly.

When it is physicaly engaged then something inside pushes the ball on the tip of the vacuum switch to allow vacuum to the front differential. If the transfer case fails to engage then the front differential will not get vacuum.

James

The transfer case does engage electronicly.

When it is physicaly engaged then something inside pushes the ball on the tip of the vacuum switch to allow vacuum to the front differential. If the transfer case fails to engage then the front differential will not get vacuum.

James

If it is a 233 the shifting is electronic controlled by the push buttons and pcm and TCM and electric encoded motor on the side of transfer case.
The only manual part is the encoder motor turning the transfer case shift shaft.
But the encoder motor is electronic controlled.

If it is a 233 the shifting is electronic controlled by the push buttons and pcm and TCM and electric encoded motor on the side of transfer case.
The only manual part is the encoder motor turning the transfer case shift shaft.
But the encoder motor is electronic controlled.

I understand that. I believe BB_Blazin was under the impression that I was claiming the vacuum controlled the transfer case. I was trying to explain that something inside the transfer case has to physicaly "push the button" on the vacuum switch...
http://i48.photobucket.com/albums/f236/JaVeRo/100_0131-1.jpg
for the front differential to get vacuum. I just don't explain things very well sometimes, at least that's what my wife keeps telling me. :)

I understand that. I believe BB_Blazin was under the impression that I was claiming the vacuum controlled the transfer case. I was trying to explain that something inside the transfer case has to physicaly "push the button" on the vacuum switch...
http://i48.photobucket.com/albums/f236/JaVeRo/100_0131-1.jpg
for the front differential to get vacuum. I just don't explain things very well sometimes, at least that's what my wife keeps telling me. :)

10-4
And sometimes I do not read thing real good or just right to.
The electronic shifting and then vacuum switching to the front axle electric and vacuum actuator does get confusing.
You are doing good on it. Carry on.
MT

1998 3 button has a NV233 tansfer case. The encoder/motor is electrically controlled by the TCCM. The front differential actuator is controlled by the vacuum switch on the transfer case. The encoder/motor must engage for the vacuum switch to supply the actuator with vacuum. There is a switch on the differential where the actuator cable goes in that tells the TCCM if the differential is locked. If it does not lock, the encoder/motor will put the transfer case back in 2WD, the 2HI light will blink telling you it is in 2WD. Check the vacuum switch, vacuum lines, and actuator. Manually operate the actuator to see if it locks the differential. Post back your results. Hope this helps.