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'03 Blazer Vacuum affecting Transmission??

Hey guys, i know this has been touched on in the forums, but I have a whole new slew of problems, hoping to get an answer.

I lost HVAC controls and 4x4 about 2 years back. Not until recently did I find out it could be my vacuum switch on the transfer case affecting both, or transmission fluid in the vac lines. I checked my actuator (good), ATF level in the transfer case (good), checked for leaks in the vac lines (good) and pretty much all I have left is replacing the switch, which I'm hesitant on if there actually is ATF in the lines and I'm missing it, hence having to replace it again.

Well, within the past week I started having problems with fluctuating RPMs at higher speeds, usually in 3rd or 4th gear. They started off around 100 RPM differences, then as of yesterday up to 1K. Today I lost 3rd gear, and can only drive in 1st or 2nd. If I leave the transmission in drive it will try to shift to 3rd, no longer propelling or accelerating the car, leaving me rolling and redlining.

I've read here and there that this could possibly be caused by ATF in the vac lines, although I don't quite understand why. I've singled out some common problems, and I'm hoping to find out if this is going to be an overhaul of my vacuum lines/transfer case alone, or transmission, transfer case and HVAC all separately, at which point this car will be seeing parts removed for cash. Any help at all is much appreciated.

Hi, how did you check the vaccum? At each vaccum actuator or at the vaccum switch?. Some times worn out lines doesn't allow to accumulate the need vaccum to actuate.
Particulary, the fron diff have also a internal gear that is actuated by a cable pullet by vaccum actuator. But it seams to be more like a "bad" vaccum line.

Regarding "loosing" gears and fluctuating rpm, it could be by a number of reasons, mainly related to worn out (splipping) clutches or solenoid valves or worn out speed sensor (tranny goes to "emergency mode") . Connect a scanner and take a look about PTC codes (cheap chinise bluetooth or USB OBD II connectors and a free software helps with this issue).

I don't have my repair manual here in my home, but i can get it in one days or two ir order to help you.

Best Regards

The only connection between ATF in the vacuum lines and transmission performance is if the input seal between the t-case and tranny is bad, and ATF is pushing its way into the t-case. If enough ATF leaves the tranny and enters the t-case, then transmission performance may suffer because of low ATF in the transmission. But it sounds like you checked the t-case fluid level and you didn't get a bunch of ATF pouring out when you removed the fill bolt (right?). Was the transmission fluid level ok?

I suspect the vacuum and transmission issues are separate. To properly diagnose the vacuum system, you also need to test all the lines and actuators in the dash. I use a MityVac for this. All it takes is one leak and you lose HVAC control and 4x4.

Quote:

Originally Posted by aqblazer (Post 547562)

hey guys, i know this has been touched on in the forums, but i have a whole new slew of problems, hoping to get an answer.

I lost hvac controls and 4x4 about 2 years back. Not until recently did i find out it could be my vacuum switch on the transfer case affecting both, or transmission fluid in the vac lines. I checked my actuator (good), atf level in the transfer case (good), checked for leaks in the vac lines (good) and pretty much all i have left is replacing the switch, which i'm hesitant on if there actually is atf in the lines and i'm missing it, hence having to replace it again.

Well, within the past week i started having problems with fluctuating rpms at higher speeds, usually in 3rd or 4th gear. They started off around 100 rpm differences, then as of yesterday up to 1k. Today i lost 3rd gear, and can only drive in 1st or 2nd. If i leave the transmission in drive it will try to shift to 3rd, no longer propelling or accelerating the car, leaving me rolling and redlining.

I've read here and there that this could possibly be caused by atf in the vac lines, although i don't quite understand why. I've singled out some common problems, and i'm hoping to find out if this is going to be an overhaul of my vacuum lines/transfer case alone, or transmission, transfer case and hvac all separately, at which point this car will be seeing parts removed for cash. Any help at all is much appreciated.

your shift censor b went it controls 2nd to 3rd shift and 3rd to 4th. When b sticks on you have no 3rd or 4th you have 1,2,and reverse easy fix drop pan filter and in front of valve body near backside of flywheel is censors they cost 18 dollars each at advance auto

No 3rd or 4th yor shift censor has failed you have 1,2,and reverse right? The b shift censor shifts 2nd into 3rd and 3rd into 4th when it goes mine stayed stuck on had exact same problem proof was when i took it out it was broken the copper windings. These shift censors are cheap and easily changed and they cost 18 dollars a piece at advance auto. If you need a diagram let me know ill post one of the valve body that shows where they are exactly in front of transmission pan after removal behind the flywheel boost va;lve right next to a censor. THE MOST COMMOM PROBLEM WITH 4L60E TRANNY IS SHIFT CENSORS,BECAUSE THEY DO NOT GET COVERED BY FLUID SO THEY OVERHEAT THEY SAY 45000 MILES IS THIER LIFE, AND THE BOOST VALVE AND IF YOUR REVERSE WORKS GOOD GOES RIGHT IN REVERSE AND GOES MORE THAN LIKELY ITS ONLY THE CENSORS

I'm having this same problem I think. Except I can't get a good reading on my tranny dipstick at all and seen there was tranny fluid all over the place, so I put in a bottle of sealer and some more ATF. The ATF smells really bad, but is red. I cleaned and dried everythinbg today to try and locate a leak, but I can't find it so maybe the sealer stuff is working now. Anyways, still having trouble shifting into third I have to pound it to high rpms and then it may shift or may not.

is it possible for a sensor to leak? and be really hard to find if you don't know where it is?

So I've dropped the pan today and replaced the filter and filled up with new ATF. The pan was clean, no debris. But I'm still having trouble shifting to 3rd. It WORKS, its just a pain to get it to shift...my dad thinks electrical. When I tried to order the b speed sensor they ordered me a speed sensor instead. Does anyone know the gm pn for this?? I have a 2000 ls 4WD. BTW, I topped up my transfer case (was very low) and replaced the 4x4 switch. 4WD still doesn't work either.
So, since there was no debris in the pan, should I assume the clutches are ok and it must be the shift sensor?? (which means I have to take the pan off again....F*&%)?