4wd system operation 98up Blazers

[snorander]

Originally Posted by snorander

so I had the battery out and checke out my actuator. I can't pull the cable at all. The actuator will hods vacuum if remove the vacuum line & put my thumb on it so the actuator is good(I assume). Now for the million dollar question....How can I fige out if the cable is siezed of if the encoder motor is seized?

Thanks,

Steve

My typing is terrible this morning...let me try again...

so I had the battery out and checked out my actuator. I can't pull the cable at all. The actuator will hold vacuum if I remove the vacuum line & put my thumb on it so the actuator is good(I assume). Now for the million dollar question....How can I figure out if the cable is siezed or if the encoder motor is seized?

Steve

[snorander]

Turns out this was my problem all along fluid in the switch & lines. I wasteds so much time & money, 3 button switch, TCCM, etc. if I had only checked this first....

Originally Posted by JaVeRo

Another bit of information some might find necessary:



Since that document was released, the part has been redesigned. The old part was 15664811 and had a green stripe on it. The new part is 89059420 and has a blue stripe on it. You can find more information <a href="http://www.s-10crewcab.com/phpBB2/viewtopic.php?t=3197">here</a>

James

[snorander]

What I meant to say was, this was my problem all along....

Document ID# 1350749
2002 Chevrolet S10 Pickup - 4WD

HVAC Mode Switch Inoperative or Stuck in Vent Mode, Oil in HVAC Control Head and/or Vacuum Lines (Replace Transfer Case Vacuum Switch and Contaminated HVAC Components) #03-01-38-009 - (Jun 25, 2003)
HVAC Mode Switch Inoperative or Stuck in Vent Mode, Oil in HVAC Control Head and/or Vacuum Lines (Replace Transfer Case Vacuum Switch and Contaminated HVAC Components)
2001-2003 Chevrolet Blazer, S10
2001-2003 GMC Sonoma
2001 GMC Envoy, Jimmy
2001-2003 GMC Jimmy (Export Canada Only)
with 4WD and Two-Speed Electric Shift Transfer Case (RPO NP1)

Condition
Some customers may comment that the HVAC mode switch may be inoperative or stuck in the vent mode. After some diagnosis, oil in the HVAC control head and/or vacuum lines may be found.

Cause
When the transmission or transfer case heat up, the oil may expand and find its way into the transfer case vacuum switch. This oil expulsion may cause the vacuum switch seal to fail and allow transfer case oil to be drawn into the HVAC vacuum lines.

Correction
Replace the transfer case vacuum switch. Refer to the Transfer Case Vacuum Switch Replacement procedure in the Transfer Case sub-section of the Service Manual. Also, replace all contaminated parts in the HVAC system.

Parts Information
Part Number Description
15664811 Switch -Transfer Case Vacuum
Parts are currently available from GMSPO.

Warranty Information
For vehicles repaired under warranty, use:
Labor Operation Description Labor Time
K4120 Switch, Vacuum Control Transfer Case - Replace 0.6 hr
Add Diagnosis Time 0-0.3 hr
Add With Skid Plate 0.2 hr
Any additional time for replacement of HVAC components must be submitted as Other Labor Hours and requires appropriate authorization.

[bemcmullin]

Guys,

Here are the assembly drawings for the vacuum system control for the front diff.
NP1:
http://www.compnine.com/index.php?u=...06&grouptype=B

NP8:
http://www.compnine.com/index.php?u=...06&grouptype=B

This website has tons of GM assembly drawings!!!

Brendan

[7T9Shark]

OK, but what about us older Blazers?? I have a '96 that I am trying to troubleshoot for what appears to be an uncommanded engagement at highway speeds.

What happens is that while running at 55 mph, occasionally a high pitched whine starts and then gradually gets lower and loud as heck. I pull over down to 10 MPH, hear a loud clunk and all is well.

I pulled the battery, and checked the function of the vacuum actuator and when I start the motor and have someone switch the electrical switches in the cabin from 2wd to 4wd nothing changes. There seems to be vacuum at the actuator at all times. There is an electrical switch that is supposed to control the vacuum right behind the battery.

The question is, when is the switch supposed to supply vacuum to the actuator? in 2wd or 4wd? When choosing 4wd, is that switch supposed to have 12v applied to it? Maybe I'll apply 12v directly from the battery and see if it works.

I should also mention, that when driving in snow last weekend, the 4wd function DOES/DID work.

AJ

[snorander]

I would unplug the vacum line from the transfer case and see if fluid comes out of the line. If it does let it drain and replace the vacum switch on the transfer case. It fixed my problem.

[snorander]

In my truck, the vacum pulls the actuator to shift it into 4wd I'm pretty sure

[7T9Shark]

OK, I'll give that a try. I was under it this afternoon and it sure looks like it would take a contortionist to get the vacuum line off the transfer case, but I'll take another look tomorrow from the drivers side. Does the skid plate have to come off?

I see older posts do mention the perils of having fluid in the vacuum lines. That might explain why my heater won't blow on the florr anymore either.

Thanks for the tip. I'll be checking back in a day or two to follow up.

AJ

[snorander]

I was having probelms with the with it not changing between floor/dash/defrost for along time, but I never put two & two together. If I had payed attention to what I read on here I would have saved myself some money, grief, & time.

[7T9Shark]

I'm reading through all of you older posts and am getting some good info. However, this morning I lifted the right front tire and started the engine. I was able to rotate the tire freely, which means it is not in 4wd. That seems to contradict the fact that my vacuum actuator is pulled all the time the engine is running. (???) Maybe the actuator is NOT pulled in 2wd. More investigation needed, here.


Nevertheless, I'm going to heed your advice and remove the TC vacuum switch. If there's oil in the system, that's what I need to know.

I might even replace the thing, regardless. If it leaks vacuum, it would explain my heater issue.

On a side note, I saw that there is an electrical vacuum switch that controls the front axle actuator located between the battery and reservoir. I don't see where anyone in these forums say anything about that one. It's a puzzler to me to think there are TWO actuators controlling the front axle.

Your thoughts?

[old_master]

The vacuum switch on the transfer case is located on the driver side, inboard of the driveshaft yoke. In the image below, you can just barely see the three black ports of the switch behind the manual shift lever. If you have electric shift, the encoder motor takes the place of the shift lever and adds another obstacle when it comes time to replace the switch:



One vacuum line comes from the vacuum reservoir under the hood and should have manifold vacuum whenever the engine is running. The second vacuum line runs directly to the vacuum actuator under the battery tray. The third vacuum line tees into the transfer case vent directly above the vacuum switch and then runs up along side the transmission dipstick tube. There is a filter at the end of the line and it's zip tied to the dipstick tube. That line vents the vacuum actuator to atmosphere when 2WD is selected, (no vacuum to the actuator). When 4WD is selected, linkage within the transfer case actuates the vacuum switch. The vacuum switch connects manifold vacuum to the actuator under the battery. The actuator pulls a cable that operates a clutch on the right front axle shaft, just inside the axle tube. There is an electrical switch at the clutch that tells the transfer case control module when the axle is locked in and the 4WD light illuminates. If the vacuum switch binds and does not completely vent the axle actuator, a slight vacuum will still be applied to the actuator and cause it to partially engage the clutch on the axle. If/when this happens, you hear the noise you're hearing. If you select 4WD, and the switch is not totally seized, manifold vacuum will be applied to the actuator and the noise will stop. The switch is under $20 and the easiest way to get to it is reach over the frame crossmember from rear to front. IIRC a 7/8" deep socket and a 3/8" ratchet is the ticket. Gotta hold your tongue just right and cross your right eye, being a contortionist helps too

[7T9Shark]

Thanks for that complete description and photo. I have the electrically controlled device, so I suppose I'm in for a treat tomorrow when I replace it. Also, your "partial engagement" theory makes sense.

Next question - Then what does that electrical vacuum switch do that is in-line with the vacuum hose going from the actuator to the TC? It's located between the battery and reservoir on my '96.

Thanks.

[old_master]

Can you post a picture of it? Starting in, (I think) '99 there is an electrical vacuum switch on the 4 button systems mounted on the firewall above the distributor but I don't believe it was used on '96, unless someone added it for some reason. There might have been a factory TSB for it, not 100% certain of it though. Trace the vacuum line from the transfer case switch... IIRC the vacuum line to the actuator runs along the passenger side to the actuator under the battery.

[7T9Shark]

Eureka!! I just pulled the vacuum hose assembly from the TC switch and sure enough, my fingers were bathed in flluid!! Sure enough, the switch was stuck. Does the transfer case use ATF? Sure looks like it.

Next question - I plan to disconnect the vacuum ball and actuator from the system and blow out the lines. Will that damage any HVAC diaphrams? Do I need to blow the lines out at all?

I'd like to replace the whole hose assembly, but it seems to run along the top of the trans and I'm laying on my back in my garage floor, so am not keen on messing with it.

I'll send a picture of that switch we're talking about later. Right now, I'm off to the parts store to get a new switch.

[old_master]

The transfer case takes DexronIII. When you have fluid in the vacuum lines, it means vacuum is leaking past the seal in the vacuum switch. When this happens, it creates a negative pressure, (vacuum) inside the transfer case and ends up sucking transmission fluid past the seals lowering the transmission fluid level and drawing it into the transfer case, raising it's fluid level. When the transfer case fluid reaches the vacuum switch, it enters the vacuum lines. Every component in the vacuum system, including HVAC lines, actuators, reservoir, mode switch etc must at least be disconnected and checked for oil and cleaned out if necessary. Do not apply pressure to the HVAC actuators, it will rupture the diaphragms inside them. More than likely the output seal on the transmission will need to be replaced along with the input seal on the transfer case if they continue to leak externally after the vacuum switch repair. On a side note, fluid in the lines can cause the HVAC actuators to operate slowly and sometimes not at all. It can also cause slow operation of the 4WD actuator under the battery.