2000 blazer No Transfer Case Vacuum Switch?

paulp64131 · 07-01-2009, 02:21 PM

2000 blazer No Transfer Case Vacuum Switch?
Can anybody verify this article. http://answers.yahoo.com/question/in...1200636AAictFZ I will put the quote in below.

from the article
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Your Blazer shouldn't have a vacuum switch.
In the passenger side kick panel there is a Transfer Case Control Module. (TCCM) You might have heard a clicking sound coming this area...

I've recently repaired two 2000 Chevy 4X4's with basically the same troubles (no 4 wheel drive).

This a known issue with these trucks, problems with corrosion built up on the pins (contacts).

You can clean the contacts of both the harness and the motor and apply die-electric grease to them and you should be good to go 4 wheelin... Hope this solves your problem!!

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I cannot find the Transfer Case Vac Switch. The Actuator under the battery leads right down into the Transfer case on the passenger side by front drive shaft. It does not go to a Vaccuum Switch as described elsewhere on this forum.

The prob I have is some times the Right front end will sound kind of like a roar when getting to about 30 mph. If I stop and put in to 4wd and back to 2wd it will stop doing that. So I think the 4wd is trying to engage partially at times.

Please advise. Thanks.

It is a 2000 Blazer with 3 button (no auto) Switch

MT-2500 · 07-02-2009, 11:46 AM

Which transfer case?
In the S-10 how to section muddog has a artical on the 233.

For repair on them.
Best to use a factory repair manual or a all data online sub.

http://www.alldata.com/products/diy/index.html

old_master · 07-03-2009, 09:39 PM

When the vacuum actuator has vacuum applied to it, it pulls a cable that engages the right front axle shaft. Follow the vacuum line from the actuator, it will take you right to the vacuum switch on the transfer case. There are 3 lines on the vacuum switch: One goes to engine manifold vacuum, one vents to atmosphere, and the third goes to the actuator under the battery.

paulp64131 · 07-06-2009, 08:07 AM

Quote:

Originally Posted by old_master

When the vacuum actuator has vacuum applied to it, it pulls a cable that engages the right front axle shaft. Follow the vacuum line from the actuator, it will take you right to the vacuum switch on the transfer case. There are 3 lines on the vacuum switch: One goes to engine manifold vacuum, one vents to atmosphere, and the third goes to the actuator under the battery.

I followed it, but it does not lead to a switch with 3 lines. It leads to a yoke on the tranfercase with driveshaft that runs the Passenger side front wheel. 1 line going into this case (straight in from the passenger side of the case.

old_master · 07-06-2009, 03:03 PM

That is the actuatoir cable that locks the right front axle to the front differential. Follow the rubber vacuum line from the actuator to the transfer case, (the transfer case is bolted to the rear of the transmission).

paulp64131 · 07-08-2009, 02:01 PM

Quote:

Originally Posted by old_master

That is the actuatoir cable that locks the right front axle to the front differential. Follow the rubber vacuum line from the actuator to the transfer case, (the transfer case is bolted to the rear of the transmission).

Thank you old_master!! I found it. Also found what I think is the problem.

There is a Vacuum line that is corroded (See Photo). I take it that it may go down to the switch on the transfer case. I can't tell because it goes back into the fender on the driver side. Can you offer any advice on switching that hose or repairing it?

There is a component that I am not familiar with (Amateur Mechanic) that sits between the fuse box under the hood and the firewall. Can that be unbolted easily for better access to the line or can I reroute that vacuum line to where ever it goes.

Thanks again to everyone for all the help!

Paul

old_master · 07-08-2009, 06:38 PM

The part that's "in the way" is the EBCM, (Electronic Brake Control Module), more commonly known as the antilock brake unit, and yes it can be unbolted and moved, gently, just don't remove the hydraulic lines. This will give you access to the reservoir. You don't need to remove the EBCM, (unless it's broken), to access the vacuum fitting on the reservoir.

Your "corroded" vacuum line goes to the vacuum reservoir inside the driver fender near the left hood hinge. The reservoir is for the HVAC system and the 4WD actuator. The three way connection is actually a vacuum check valve. The larger line comes from the intake manifold and supplies vacuum for the two systems while the engine is running. It connects to the black connection on the 3 way. The white connection that goes straight out of the check valve routes behind the engine to the transmission dipstick tube where it continues down to the vacuum switch on the transfer case. Also, attached to the dipstick tube you'll see a vacuum line with a cap-like fitting on the end. That is the vacuum vent for the 4WD actuator, and the line goes directly to the vacuum switch on the transfer case. The third fitting on the check valve has another vacuum tee a few inches away. One side of that tee goes to the reservoir, the other to the HVAC mode switch in the dash.

When you finally make it to the vacuum switch on the transfer case, the two lines that run along the trans dipstick tube, and the vacuum line that goes to the vacuum actuator under the battery tray, all connect to the vacuum switch.

In your original post the link you posted said the TCCM, (Transfer Case Control Module) does it all and no vacuum switch is used. As you can see, the link is incorrect. The TCCM does exactly as the name implies, it controls the transfer case. When the transfer case shifts into 4WD, internal mechanical linkage operates the vacuum switch and it applies vacuum to the actuator. The actuator engages a clutch on the right front axle shaft which connects both halves of the right front axle together making the front differential "live". When shifted back to 2WD, the vacuum switch routes the vacuum from the actuator to atmosphere and the axle disengages.

Anytime the vehicle is in motion, whether it's in 2WD or 4WD, the transfer case output shaft, and both front axle shafts are rotating. When in 2WD, there is no mechanical connection between the left and right axle shafts so the front differential is unable to apply power to the ground. With everything rotating while driving, you are able to "shift on the fly" without damaging anything.

paulp64131 · 07-09-2009, 03:33 PM

That appears to have been the problem. Was able to move the fuse panel, the EBCM, partially removed EBCM mounting bracket (Removed one bolt and loosened the other) on the inner fender for access to the vacuum hose connection. Pulled the old corroded hose and installed new one. Put it all back to together and tested 4wd (great) Drove it to about 35 miles around the city and highways at multiple speeds, Never had a problem. So... About $.50 worth of Vacuum hose, some help from some friends (you guys!) and a little time. Can't ask for better than that. I didn't use the Transfercase Vacuum switch yet. I will hold on to it for a few days then return it and order one from RockAuto. This one I got from Napa was about 3 to 4 times the price of the one online. I will go ahead and get one though since it is a high failure rate part and I have already had issues in that area.

Thanks again for all your help. Once again this forum saved me a ton of money and taught me how to do it myself!

paulp64131 · 07-09-2009, 03:34 PM

Just to clarify... Drove it approx 35 miles in 2WD NOT 4WD

old_master · 07-09-2009, 05:53 PM

Glad you found the problem. Thanks for posting back with the fix.

DukeOfEarl · 01-31-2015, 10:16 PM

I'd like to add some clarification as to the location of the vacuum actuator. There are actually two possibilities.

Do you have the 4 button switch (NP236 or NV236) on the dash or the 3 button switch (NP233 or NV233)?

If you have the 4 button switch on the dash with the "automatic 4-wheel" option, you will not have a mechanical vacuum switch on the transfer case, but rather, an electronic solenoid located near the center of the firewall above the engine. If this is the case, then engine vacuum will run to the solenoid, then from the solenoid down to the front axle actuator under the battery.

If you have the 3 button switch, you will have the mechanical vacuum switch on the transfer case. Engine vacuum will run down to the vacuum switch on the transfer case, then back up to the vacuum actuator under the battery.

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