I noticed that. Crazy how they charge you more for the different packaging.They actually only have the Help! one in stock locally, But I can wait. I'm all for saving the green backs.

 

The GM part number for these switches is 89059420, which is supposedly a redesigned part after many of the originals failed and let t-case fluid into the vacuum lines. This happened on my '96 Sonoma and '04 Blazer. I went with the GM part on the Sonoma and Dorman on the Blazer. Not real impressed with the Dorman, for 3 reasons:

1. The 3 plastic tubes on the top of the switch were too small a diameter for the rubber cap/junction thing that plugs into the switch. I didn't get a good vacuum seal and 6 months later, when it snowed, I didn't have 4WD. The duct tape solution worked.
2. The plastic alignment pin thing (seen here, in line with the blue stripe; this is from the GM part, not Dorman) broke off when I had to deal with #1 above, making it difficult to put the rubber cap back on the right way.
3. The switch failed less than a year later, so badly that the vacuum reservoir was full of t-case fluid and was starting to leak fluid behind the HVAC dash controls and into the ash tray.

I put a GM part back in the Blazer.

 

Two things usually need to happen in conjunction to get transfer case fluid into the vacuum system; 1- failed input seal on the transfer case resulting in an over-full transfer case & 2 - failed lower o-ring on the 'valve' inside the switch. There just isn't enough fluid flying around in the transfer case to make for a huge problem in the vacuum system if the lower o-ring is failed with a properly filled transfer case.

Anyone that is having problems with transfer case fluid in the vacuum system, pull the fill plug on the back of the transfer case. If fluid pours out, you might as well fix the leaking input seal before making any attempts to fix the leaking vacuum switch.

 

Tranny fluid would indicate low when the input seal fails, correct?

 

Incorrect. A failed input seal would result in an over full condition inside the transfer case.

*EDIT to clarify* - Originally I read that to mean transfer case, not transmission. As such, 'incorrect' is not the proper term. 'Not always' would be more appropriate as I clarified in my response below.

 

Where does the fluid come from that causes the transfer case fluid level to increase?

 

I meant the transmission fluid level - i.e., would the reading on the dipstick indicate a low level.

(think me and the Capitain are asking the same question)

 

I originally read that to mean transfer case, that is my mistake. Trying to read & respond quickly on my phone doesn't always work out so well. The fluid does come out of the transmission. As far as whether you'll notice a difference (i.e. transmission fluid reading low), that depends (see below).
Yes, that is correct provided it loses a lot of fluid. The transfer case doesn't take a lot of fluid to get the level up to that of the vacuum switch. If your fluid level is in the middle of the range when hot, it might drop to near the bottom of the range but still show good while the level in the transfer case is high enough to cause a problem. It comes down to checking the transmission fluid as part of a preventative maintenance routine & recording the levels some how. Without that observation, you won't notice that there is a change in readings.

The best method is to pull the fill plug on the transfer case.

 

Thanks for all the response. I haven't purchased the Transfer Case Switch yet and will write the Delco Part number down for future reference. As of right now it seems to be a problem that occurred before my recent Transmission rebuild that was done last month. I removed and blew out all the vacuum lines and have only noticed fluid still in the A/C vacuum lines in the dash. I believe I will just order a new Vacuum Reservoir because I think it has fluid in it. But I may check the transfer case fluid levels first.

 

Hopefully you won't get this much excess fluid out of your transfer case:




I dunno, maybe a half gallon there....