95 Blazer 4WD problems

I know Ive asked this question before but until today I havent been able to check things. My 4WD will engage but will not disengage. Old Master told me to check vacuum lines which today I did. I took out the battery box and put a line on the actuator and sucked on it and it seemed to hold vacuum the cable moved about half an inch like he said. I traced the vacuum lines back to the transfer case. There is a Y connector on the lines and one of the lines is burnt in two that comes off of it. But the one from the actuator to the transfer case is fine. Right out from the actuator there is a T connection and a larger vacuum hose goes to it and it has an electrical switch hooked to some kind of vacuum thing.
I have NO clue what to do now. I dont know where the burnt line goes to or anything. It was mentioned once that there was a line that came off and ran up beside the trans filler tube with some kind of filter on it but I dont see that at all.
Please help. And Im sorry if this is confusing I tried to word it best I could hopefully someone will be able to understand it. Im willing to give a phone number if someone can help me figure this out.

On the transfer case there is a vacuum switch with 3 vacuum lines connected to it.

One line runs to the actuator under the battery. If you put vacuum to it, it should operate the actuator and hold vacuum.

The second line is a vent to atmosphere with a filter on the end. Usually it runs up the transmission dipstick tube and is wire tied to it close to the top. That line should be clear and should not hold vacuum.

The third line should have manifold vacuum when the engine is at idle. It runs to a vacuum reservoir. On your 95 there is a black plastic ball mounted to the hood. There is most likely a vacuum tee and a smaller line that runs to the HVAC system, and then to manifold vacuum. If you pull the line off of the intake manifold, the line should hold vacuum.

To the best of my ability I have traced the vacuum lines from the vacuum switch on the transfer case. One to the actuator is good all the way. One up to the reservoir is good no holes.
The third line is the one that was burnt in two. Im assuming its the one thats supposed to run up beside the dipstick with the filter on the end. Where can I get a filter? I know I need to replace the hose but have no clue what type of filter its supposed to have.
Also that line has a Y connector on it. Is that from another vent? This thing is driving me crazy because I dont have a rack to put it on just laying out on the concrete.
I appreciate all the help ......Thanks

Just a followup to my previous post, the other line is coming from a vent on top of the transfer case into a Y and from then on is where it is burnt in two.
Would that hose and the absence of the filter on the end cause the 4WD to no disengage? As before I do appreciate all the help

The transfer case also has a vent and it's possible they're teed together. If the vent is plugged, the actuator under the battery can not vent the vacuum that was necessary to apply the actuator, and it will not disengage the right front axle from the differential. As far as a filter, the auto parts stores have fuel filters for small engines, lawn mowers etc. Get one that will fit into the vent line and you'll be good to go. Post your results.

Ok one more crazy question. The linkage from the cable that engages the 4WD is not connected. It had to have been in the past because Ive engaged it. I may have knocked it loose while having my hands all up in there. But the clip is missing. If its the same as the trans linkage theres a plastic bushing type of thing that holds it on. Where can I get one of those? Do they sell them at an auto parts store? I hope this is the last question and it will be all fixed and better once I do this (fingers and toes crossed). Thanks again.

Check the round tag on the rear of the transfer case, is the model number 231C? You can try an auto parts store. If they don't have it, you'll end up at the dealer or a bone yard.

Yep 231C for sure. Getting late so I will try to finish this tomorrow. Went to AutoZone they had a packet with a few bushings in it but none would work. Will try Napa tomorrow. Thanks for the help and I will post when I get done and hopefully this fixes the disengaging problem.

Ok here I am on day two. I cant find a bushing for the linkage on the transfer case anywhere Im supposing I will have to go to the dealer on that one.
Also broke a T vacuum connector on the line going to the actuator and NO one has it either, gee its becoming a nightmare. Any ideas other than the dealer on where to find these two things.

There's a Tee in the line going to the actuator???? Where does the other line go?
Is the vacuum Tee just a Tee, or does it have a check valve built into it? I'm surprised the auto parts store didn't have it... pretty common part. Might have to visit the local bone yard for both of the parts.

Ok, Ive tried everything so far and nothing has worked. Drove it this morning and the right front axle would not release. Im totally lost ....
I read a problem another member had and hers is EXACTLY as mine is. I have the problem with the air moving from vent to defrost when I accelerate going up a hill.......anything else I can check or do.

Two different problems. The 4WD actuator is not releasing vacuum, the HVAC system is not GETTING vacuum. Definitely a problem with vacuum going to the right place at the right time. Kinked line, missing line, line unplugged somewhere, restricted line, bad check valve, leaky reservoir, etc etc. Unplug the actuator under the battery and plug the line. Drive the vehicle, the right front axle must disengage, if not, the clutch mechanism on the axle has got a problem.

UPDATE: I was sitting around thinking about what you said about vacuum NOT getting where it needed to be and I thought I would cross the vacuum lines that come off of the transfer case. (I crossed the one from the actuator with the one going to the reservoir). As I told you I was having the same problem with another poster with the AC switching from vent to defrost on acceleration up a hill. After I switched them it does NOT do that anymore. I went up a hill at full acceleration and the air kept coming out of the vents. Is it possible that these crossed lines would also stop the axle from disengaging? I still have to get the bushing for the linkage before I can truly try this out for the 4WD but Im hopeful. Thanks.

"Is it possible that these crossed lines would also stop the axle from disengaging?" YES.

There is a tee/check valve in the engine compartment that looks like this: http://www.oreillyauto.com/site/c/detail/MUR0/74808.oap?tc=1&year=1989&make=Ford&model=Ranger&vi=1137631&pt=04109&ppt=C0328 Manifold vacuum goes to the black fitting. Typically, one of the white ones goes to the vacuum reservoir, the other white one goes to the HVAC system. The second fitting on the reservoir goes to the transfer case. The end result is that HVAC, transfer case and reservoir must be separated by the check valve.

The vacuum switch on the transfer case is a two position switch and looks like this: http://www.dormanproducts.com/p-32645-600-500.aspx Manifold vacuum goes to one port, the vent goes to another, and the actuator under the battery goes to the third port. In 2WD manifold vacuum is corked off in the switch and the actuator is connected to the vent. In 4WD manifold vacuum is applied to the actuator. With a little fooling around, you can figure out which port goes to what.

I will try to explain how this one is. The check valve you sent a pic of is connected like this. Black side is to the manifold vacuum. One white one goes to the reservoir, the other white one has a short hose and another T on it. The straight side of the T goes into a smaller line that goes into the firewall and the the other goes to the transfer case. Is that the right hookup??? I sure appreciate your help with this. All I know is when I crossed the lines coming off the transfer case the AC quit shifting itself to defrost on hard acceleration.

If the reservoir only has one fitting on it, the way you described is correct. The smaller line going into the firewall is for the HVAC. You can test the check valve very easily to make sure it's working correct, and not leaking. Remove the valve, you should be able to suck very easily on the black port, you should not be able to blow into it. Both white ports are connected to each other and you should be able to blow straight through them. Plug one white port and you should not be able to blow through the valve. Check out the vacuum switch on the transfer case and make sure it's connected correctly.

Once again I thought that switching the vacuum lines had fixed my problem. Well it did fix the problem with the air deflecting from vent to defrost when accelerating up a hill. But now it seems like it is NOT going into 4WD at all. I pulled it back into 4 wheel high and I thought it was going in but I got it into some wet grass and gunned it and only the right rear wheel spinned. I have no clue whats wrong with this thing anymore. Thanks

If the air distribution is ok while under acceleration, the HVAC is getting vacuum and the check valve is holding the vacuum in the system, that's good. The next step is make sure the actuator under the battery is getting vacuum when you select 4WD and the engine is idling. When you select 2WD while idling, the vacuum line on the actuator should not have vacuum applied to it: It should pass air in both directions freely, from the actuator to the vent on the trans dipstick tube. There might be a problem with the switch on the transfer case. If you want/need more help troubleshooting it, let me know and we can continue.....it's not difficult, just takes a little time.

If Im understanding what you are saying and please correct me if Im wrong. When I start it up and leave it in 2WD I should be able to blow through the hose that goes to the actuator and air should come out the vent tube. When I said that the air deflection was fixed I forgot to mention that it does seem to become a little less forceful coming out of the vent but does not totally deflect to the defrost. I truly need help figuring this out and I appreciate your help.

I just tried to blow through the actuator line and could not while running and in 2WD. I put it in 4WD idling and there is a very low volume of vacuum on the actuator line.
Before I switched the lines it would go into 4WD but would not release the right front axle. Now it appears its not even going in 4WD at all.

"When I start it up and leave it in 2WD I should be able to blow through the hose that goes to the actuator and air should come out the vent tube."

That is correct.


"I just tried to blow through the actuator line and could not while running and in 2WD. I put it in 4WD idling and there is a very low volume of vacuum on the actuator line."

The vacuum lines are still not quite right on the vacuum switch on the transfer case. You should have full manifold vacuum at the actuator when idling in 4WD.

You'll need to get at the vacuum lines at the switch to connect them correctly:

The first step will get manifold vacuum to the correct port on the switch.
At idle in 2WD, pull all 3 lines off the switch.
Connect the manifold vacuum line to one of the ports on the switch.
There should not be vacuum at either of the other ports.
Move the line to another port until there is no vacuum on any other port.

Next step is the line to the actuator:
At idle in 4WD, feel the two remaining ports on the vacuum switch, only one should have vacuum, connect the actuator line to that port.

Third step:
No brainer.... connect the vent line to the remaining port. ;)

Im not going to be able to check these lines till tomorrow hopefully. I have no way of getting it off the ground other than ramps. I will let you know what comes from it as soon as I can. Thanks again.

Any questions on what you need to do or how to do it?

Your explanation of how to get them right was very good. I think I can do it. Do you think that since the vacuum was so weak at the acutator line that its possible that the transfer case switch is bad? Would it be a good idea to replace it while fooling with these lines? Just curious because I thought of going ahead and replacing the check valve and the switch just to eliminate them as being a problem

The vacuum switch is not a real common problem but it does fail. Usually what happens to them is they leak internally and suck transfer case fluid into the vacuum system. Eventually it makes its way into the HVAC system and that's a REAL mess to clean up. The other problem is the switch can bind internally and get stuck between two positions. If that happens, the HVAC and the 4WD will work intermittently. Probably not a bad idea to replace it. They're not all that expensive and most auto parts stores stock the part in the Dorman "HELP" line. It comes on a card with a clear plastic cover over the switch.

http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_Transfer-Case-Switch-Dorman---Help_17190751-P_2315_R%7CGRP60008_369534718___

Ok thanks, I will post when I get the chance to check those lines out. Kinda not sure if Im going to replace the switch or not but will let ya know what I find out. Might be a couple days before I can get to it. Once again thanks a bunch.

Finally got a chance to work on this thing and done what you said. I checked hoses, took all of them off. Put the line with manifold vacuum on until I had no vacuum on the other two while idling in 2WD. I put it in 4WD and placed the line from the actuator on the port that had vacuum and naturally the other to vent. There still seems to be a low amount of vacuum on the line to the actuator. I didnt replace the vacuum switch like I had planned. Could that be the problem? Is there anything else that I can try??

The switch is not operating correctly and needs to be replaced. There should be full vacuum at the actuator in 4WD, and no vacuum at the actuator in 2WD.

Ok, I will have to do that when I get time and see what happens. Im just not sure how to get to it. Unless I drop the crossmember and I really dont wanna do that. Thanks for helping me I will post when I get a chance to replace the switch.

Another thing while its on my mind. I tried to blow through the vent hose again and if Im not mistaken you told me you should be able to blow through it freely. When I do blow into it I cannot and when I release it it blows back. Is that also showing that the switch is bad?

Depends what end you're blowing in ;) and what position the mode switch is in.

With the engine at idle:

In 2WD, if you remove the hose from the actuator and blow in that end of the hose, it should go through the hose and come out the filter/vent very freely.

If you remove the filter/vent and blow in the hose, (with the actuator attached) you shouldn't be able to blow into it, and it just might blow back when you try! The actuator, in this case, acts like a balloon, and you're trying to blow it up! It should hold vacuum if you suck on it, and the actuator should pull the cable in if you suck long enough.

In 4WD, the actuator should have full manifold vacuum to it. If you pull the filter/vent off of the vent hose, you should not be able to blow into the hose, and it should hold vacuum if you suck on it.

Bottom line, when in 2WD the actuator is connected to the vent and the diaphragm is relaxed, and the axle is NOT engaged.

When in 4WD, manifold vacuum is connected to the actuator and the actuator pulls, and holds, the cable in, and keeps the axle engaged.

LOL I suppose youre right about which end youre blowing in :rofl: I will try those things again tomorrow and see what happens. But like I said theres very little vacuum at the hose going to the acutator. Also the lights on the console beside the shifter handle do NOT light up anymore since I switched those hoses previously, Im assuming theres not enough vacuum to engage the 4WD thus no lights. They used to light up but wouldnt go off until the axle decided to disengage. Anyway Im going to replace the switch when I get a chance and will post and let you know. Thanks again. :smile:

It's possible the vacuum switch is leaking badly enough that it won't allow enough vacuum to get to the actuator. Something else to try, just to make sure the HOSES are intact and not kinked, cracked or leaking: (Don't need the engine running for this) check each hose separately, you'll need an assistant, try to blow and suck on each hose. Make sure you can blow through it AND that it holds vacuum with one end plugged.

The 4WD light is controlled by a switch on the right front axle. If the vacuum is released from the actuator slowly, it will take longer to disengage and turn the light off.

I have a question about the vacuum switch. Youve mentioned the Dorman brand to replace it with. Is that what you reccomend????? I called my local AutoZone but they have to order it. The Advance Auto close to where I work carries the Dorman brand, was just curious as to what you thought would be the better choice. Im also thinking of replacing ALL the vacuum lines going to it just to make sure theres no problems with them since they have been on there since manufacture other than the vent line that I replaced. I also want to ask about the acutator or more clearly the vacuum line going to it. right before the line goes under the battery box there is a "T" . There is a rather large line Im guessing about 3/8 that comes off that T . Its a short hose with an apparent electrical switch on it (It has an electrical connector on the end) I was just wondering what that is. I appreciate your help its been great and right on every time. :smile:

I've never had a problem with the Dorman 4WD switches, and the price beats the dealer by a long shot. Replacing all of the vacuum lines is probably a good idea! Not sure on the electrical part in the actuator line, where does the vacuum line go from the switch? Or does it dead end at the switch?

At long last I THINK I have it. I replaced the vacuum switch and STILL didnt have very much vacuum going to the actuator. I THOUGHT I had checked the vacuum lines thoroughly but alas I pulled the actuator hose completely off the vehicle and lo and behold there was a pinhole burnt in it about half way down the firewall. I replace the hose and now it shows its going in 4WD according to the lights on the console. Im not gonna truly road test it until I get the cable end fixed. It will be a couple days maybe but will post my results. It truly does make sense to be VERY thorough when checking the lines because I missed that one totally. Probably wasnt the switch at all but Im not taking it back out!!!!!. Thanks again for your help without it I would have NEVER figured it out. Ive got a few more problems but wont do that here will do another thread whenever I get a chance to do it. Once again a great BIG thanks :)

A thorough diagnosis is without a doubt, the most important part of the repair! Anybody can replace parts, the trick is knowing what part to replace. Let us know how the road test goes. Thanks for posting back the "fix".

Road test didnt go well. It does go in and out of 4WD great and the things you told me definately fixed that problem. Without your help I would have never figured it out and would have ended up with a HUGE garage bill. So for that I thank you very much. BUT!!!!! back to the road test like I said it goes in and out of 4WD wonderfully now IF I want to drive in a straight line. When I turn the wheels in 4WD Hi going foward OR backward there is a very loud thud coming from both front wheels like the CV joints are catching or something. Is there any other cause before I go and spend the money on the new axles????? Im about ready to give up on this thing and I hate to because the body and such is in great shape. If the axles are or could be the only cause I might go ahead and replace them otherwise I may just put a FOR SALE sign in the window. Again I wholeheartedly appreciate the help and your instructions and advice definately fixed the problem I had. NOW on to other things I suppose.

I dont know why my posts arent coming up. It wont let me do a quick reply anymore keeps telling me I need to register....sigh!! But if it does post I was wondering if it could be a differential problem instead of an axle problem since its doing it on both front wheels. Just a thought.

Not sure how familiar you are with 4WD operation, but you need to be aware of certain things...

When turning a corner, doesn't matter how gradual, or how tight the corner is, the inside tire turns slower than the outside tire. This difference in speed is what causes 4WD vehicles to "crow hop". The drivetrain binds and causes what you're describing. If the binding is severe enough, it can damage the transfer case gears and chain.

With that in mind, to help avoid crow hop, the circumference of all 4 tires needs to be equal. Here are the basics:
All 4 tires must be the same size, same manufacturer if at all possible.
All 4 must have the same amount of wear.
Tire pressure in all 4 must be equal.
When it needs new tires, get all 4 at the same time.

Do not operate the vehicle in 4WD on dry pavement. Part time 4WD, (what you have on your Blazer) is designed for use on snow, ice, mud, gravel etc, terrain where the wheels can not get 100% traction. If the wheels get good enough traction, the vehicle WILL crow hop and it WILL cause damage when it does.

I do understand how it works and what you mean about the hop. When I put it in 4WD and tried it I was just making a very slight turn in going up and down the driveway, not really enough to make much of a difference in direction. Im not sure whats going on but from my past problems Im afraid that I may have ruined the differential and possibly the transfer case from what you explain. I had to drive it for a while on dry pavement when it wouldnt come out of 4WD probably a distance of 30 plus miles........Im unsure what or how to check. Getting to be a pretty expensive fix and Im not sure its worth the time or money involved. Thanks again.

Are there any growling or grinding noises coming from the transfer case, when in 4WD, going in a straight line? Are you sure all the tires are the same size?

Honestly I didnt drive it far enough to see. I will try that tomorrow and see what happens. I only drove it down the driveway and reversed it back up. The tires are all the same size not the same brand but same size. Matching tires are on the same axle though. Front two match and rear two match but as I said they are the same size.

I got a chance to drive the Blazer today straight line to see what it did in 4WD. Sorry to say I think its shot. It has a VERY severe clanking catching type of problem. I cant tell if its from the transfer case or the differential. Dont know what to do now since I honestly dont have the funds nor know what it would cost to replace either or both.:frown: But one things for sure it definately goes in and out of 4WD just fine. :)

First thing is to narrow it down to transfer case, front differential or the clutch on the right front axle. Remove the vacuum line from the actuator under the battery and plug the vacuum line. Remove the front driveshaft from the vehicle and drive it in 4WD... if it still makes the noise, it's the transfer case. The noise might not be as noticeable with the driveshaft removed because there is no load on the transfer case front output shaft, but if there's a problem, you should hear still hear it. Also, grab the front yoke on the transfer case and see if you can wiggle it side to side, or in and out. Then try to rotate it by hand... should only turn about 1/8 turn in each direction.



FYI: Items 7 through 24 are all for the right axle clutch mechanism:

http://i561.photobucket.com/albums/ss58/cwhook/4X4Frontdifferential-Copy.jpg

Thanks for the exploded view. I have a question. What all years will fit a 95 as far as differential and transfer case? I know someone who has a 97 that he is gonna scrap, I havent seen it he just emailed me abou it.
Also I know this is off subject but what is the normal operating temp on the 4.3l engine? Mine is running around 200 degrees on an aftermarket gage. How accurate it is is another question. Thanks and I will update you when I get a chance to take out that front driveshaft. (Been working a lot of 12 hour days)

A boneyard will be able to tell you for sure which years will interchange. As far as operating temp... the stock thermostat starts to open at 192* and usually stabilizes around 198*.

He said his was pushbutton anyway. I dont think that would work. Thanks for the info on the temp. Mine seems to run around 200 and when idling will run up to around 220 just wasnt sure if that was good or not.

You might want to check with a 4WD specialty shop to see if the manual shifter can be fitted to the electric shift case. I have no idea, sorry.

As far as temp, 230* while at idle is too high. The thermostat might not be opening up all the way, the radiator & cooling system may need to be flushed, there might be debris partially blocking the radiator air flow, or the fan clutch may be defective. Also, there is a plastic shield with an access door for replacing the oil filter, if that shield is missing, or the door is open or missing, it will also cause the engine to overheat.

ARRGGGHHH....I havent had the time to work on the 4WD lately because of working so darn much, but all of a sudden the air stopped coming out of the vents. I have NO clue as to why. Ive traced the vacuum lines to make sure they are ok and they are. I took the check valve off and checked it again and it checks out ok. So now Im stumped again. Maybe just trading this thing off is my best option. :banghead:

A hand vacuum pump like this will make it much easier to find the leak:

http://www.harborfreight.com/brake-bleeder-and-vacuum-pump-kit-92474.html

If you can buy, rent or borrow one, let me know and I can walk you through the tests.

I told you in an earlier post that the air stopped coming out of the vents all of a sudden. I was looking under the hood and the vacuum line that comes off the manifold has oil on it and when I take it off there appears to be oil inside it. It looks like engine oil consistency wise. SIGH..........What could be the cause of that??? Getting ready to just give up on this thing its one thing after another. Thanks again for your help...

Put a drop on a piece of white paper, see if it has a red tint to it, (transmission fluid). If that's the case, the vacuum switch on the transfer case sucked fluid past the seal in the switch. Pull a couple of the lines in the HVAC and check them for oil. All fluid needs to be cleaned out of the HVAC lines, HVAC mode switch and actuators, transfer case lines, front axle actuator & the line to it, the vacuum supply lines, and the reservoir, or replace everything. Not a fun job, but it's got to be done if you want it to work properly.

Hey there old master. I want to thank you for ALL your help concerning the Blazer. I finally gave up and traded it the other day for a 02 Nissan pickup. Without your help I would have never figured out the things I did and would have spent a lot of money. I would give you a LOT more feedback if it would allow me to but it wont. Thanks again I totally appreciate it. :smile: