4x4 stopped engaging...im baffled

had a new engine installed in my car. not sure if the 4x4 was working properly before i took it to the garage, but it DID work in the past.

got it back and tried to shift into 4x4 and it didnt engage. it is a manual transfer case. it goes into 4hi fine but it does not engage the front axles. if i put it into 4lo, the gearing in the rear changes, but the front still will not engage. the tire indicator lights on the little display do not light up either. i checked the fuse box, and the 4WD fuse is fine, and there is +B across it. i took it back to the mechanic thinking they forgot to reattach something, but they didnt, and he is as baffled as i am. we checked some alldata circuit diagrams but it isnt too clear.

if anyone has any experience with this, or any thoughts, please let me know.

thanks in advance...

matt

Check your vaccum lines. I don't know what year your truck is because you didn't mention it. Just trace the vaccum linesj that go from your transfer case. In my 91 blazer there is an "actuator" underneath the battery tray. There will probaly be like 3 vaccum lines. Let us know if you get anywhere.

i will check it. its a 1995 LS btw.

check vacuum switch on the transfer case

Did you figure it out yet?

i have not yet. i plan to check it out tomorrow night when im able to get in a garage and jack it up. where exactly does this line go? a description or picture might help because i didnt see it. thanks

i checked it out and found that there is a vacuum line connected to the transfer case with a T-fitting right by it. not sure where the other end goes. was hard to see where the line traveled but behind the plenom i found a metal line that came up and was capped off for some reason. there was a vacuum line attached over top of it and it ran to an electronically controlled valve to the left side of the plenom. i just removed the cap so now there is control. i hope that was the right move. but i still dont have 4x4. any ideas appreciated.

matt

Don't aimlessly uncap and change things without knowing what you are doing.

Follow the vacuum lines going from the transfer case and vacuum switch and look for a line that is not attached.

well, if it isn't the vacuum that is the problem, what else could suddenly stop the 4wd from engaging?
matt

Vacuum actuator on the transfer case has failed.

Very common problem.

how expensive is this?

Call the parts dealer tomorrow and ask.

im talking about labor and what. is this something that the tranny needs to be dropped for?

No, the switch is 14 bux in the HELP section of your local auto parts store. Use a 7/8th's box wrench to remove it. Now before you start doing that, check the following.

1st: Pull up your battery tray (3 13mm bolts) and look at the vac servo under there. Is it torn? (If so replace it) If you squeeze it (carefully) is it pulling on the cable? (it should if the clip is seated properly). Is the vac hose attached?

2nd Follow the vac hose from that diaphram to the vac switch on the transfer case. Check for cracks, breaks, et-al. (If you've had the abs recall done it will go from the diaphram to a t connected to the moduylator attached to the water bottle then down to the transfer case)

3rd follow the other vac line from the switch to the main vac system. Again no cracks or breaks should be present.

Now if all this is good, now go change the switch on the vacume case.

If this doesn't solve it it's your encoder motor.

couple of things before i check all this tomorrow. is it a certain switch that i must buy, or do i need to remove the old one and take it in with me?

if the vac servo is cracked, where do i get one? again, if at a parts store, is it something i should take in?

and thank u for the help. all of u!!!

No, the switch is 14 bux in the HELP section of your local auto parts store. Use a 7/8th's box wrench to remove it. Now before you start doing that, check the following.

1st: Pull up your battery tray (3 13mm bolts) and look at the vac servo under there. Is it torn? (If so replace it) If you squeeze it (carefully) is it pulling on the cable? (it should if the clip is seated properly). Is the vac hose attached?

2nd Follow the vac hose from that diaphram to the vac switch on the transfer case. Check for cracks, breaks, et-al. (If you've had the abs recall done it will go from the diaphram to a t connected to the moduylator attached to the water bottle then down to the transfer case)

3rd follow the other vac line from the switch to the main vac system. Again no cracks or breaks should be present.

Now if all this is good, now go change the switch on the vacume case.

If this doesn't solve it it's your encoder motor.

Does the manual transfer case have an encoder?

Most part stores don't carry the servo (actually it looks much like the servo for your cruise control) So either get the replacement at the dealer or get it from a wreck.

The HELP part# for the vac switch on the transfer case is 49315. You will see that it's keyed so make sure you put the lines back on right.

Does the manual transfer case have an encoder?

After 94 they do.

ok, i pulled up the battery tray and there is no vac line connected to that diaphram. where should the line be connected to?

thanks!!!

i found the vac. line. put it back on and she runs great. thanks to those who helped. much appreciated!!! happy holidays

Excellent.

Maybe install a zip tie on it so it will hold better.

couple of things before i check all this tomorrow. is it a certain switch that i must buy, or do i need to remove the old one and take it in with me?

if the vac servo is cracked, where do i get one? again, if at a parts store, is it something i should take in?

and thank u for the help. all of u!!!


have you fixed the problem i like to know cuz my 95 LT is also having the same problem but it only shifts into 4lo i have already changed the switch on the transfer case and still nothing i disconected the battery to see if that helps will find out in the morn hope that helps if not then i have to try something else

have you fixed the problem i like to know cuz my 95 LT is also having the same problem but it only shifts into 4lo i have already changed the switch on the transfer case and still nothing i disconected the battery to see if that helps will find out in the morn hope that helps if not then i have to try something else


Did you check the vac actuator under the battery? Did you check the hoses leading to the switch on the transfercase? 1 goes to the vac actuator, 1 goes to the main vac system, 3rd is a vent hose. Did you check these for cracks/dryrot?

i will be tommorow i just learned about these vac lines now, but this could be the reason for the 4 hi not workin then how does the 4lo work then? i push the 4hi it blinks and goes back to 2hi i push 4lo it goes right in also i have to have the truck stop complety to even engage in 4lo i never had this problem before

the 4 lo goes in because of the transfercase motor. 4hi is actuated via locking the front diff. You may be going into 4 lo on the transfer case, but I doubt your front diff is engaged. To confirm this put the truck up on jack stands, run it through 4 lo, front tires should move. (or if you wanna do it on the ground, put it in 4lo and do a hard turn, you should feel hop. (don't do this for too long). If you don't feel the binding, you're front diff is not engaging and we need to go back to the vac system.

my 4lo works i knows this cuz i have use it in the recent snow storms so i can conferm the front tires are moving does this mean its not my vac sys!

my 4lo works i knows this cuz i have use it in the recent snow storms so i can conferm the front tires are moving does this mean its not my vac sys!


I would still check it for giggles. Take ya about 10 mins. Just pull the battery tray and check the vac actuator for tears/holes and the vac lines.

If in 4lo your front differential is engaging, then its not a vacuum problem because in 4lo the front differential is working. If the light is blinking in 4hi then throwing back to 2hi, then there is something wrong in the electrical of the system. It could be the encoder motor, the switch, or something between that.

ok i left my battery unhooked over nite hooked it up this morn and my 4hi works i have been pullin out my hair over this and found a simple fix thanx to this board! thanx

Sounds like you had logic lock.