4x4 trouble

Ok been doing a lot of work on this 1998 blazer

Yesterday I changed the tranny fluid and internal wire harness on the truck.
I had to lower the support a little for the transfer case to drop the pan.

I wanted to go for a test drive when I was done and all seemed well. I stopped for some gas after about 4 mile drive or so and when I started it back up it was stuck in 4lo.

Today I took a look and found that the actuator under the bat had a tear in it. I replaced that today and reconnected everything.

Now the thing is that if I turn the key to accessory I can get it to change two times and that is it. I can go from 2hi to 4hi. or 4lo to 4hi any combination:confused: works but if I try and push a third time I hear nothing. If I start the car I can not change it at all. Only when in accessory and not running.

What could this be?

Did I cause a wire to come loose when I lowered the transfer case a little?

Here are some things that I noticed. When to actuator was torn it leaked some liquid. That is how I noticed it. Second I checked the fluid level in the transfer case and it was well above the fill hole, about 2quarts over.

Third thing is that I k now the selector switch for the 4x4 is defective because the lights would not work before. If I squeezed the switch I could get the lights to go on and off but it always worked before I dropped the pan minus the lights. I could hear the 4x4 engage.

There is a vacuum switch on the transfer case, driver side, next to the front output shaft yoke. If it leaks, it will suck transfer case fluid into the vacuum lines for the front axle actuator and the HVAC system. In extreme cases, it will suck transmission fluid past the seals and into the transfer case causing the fluid level to rise, (check the transmission fluid, it's probably low). If/when this happens, the transmission and transfer case seals must be replaced. In either case, the fluid must be cleaned out of all of the lines. http://www.oreillyauto.com/site/c/detail/DOR6/600500.oap?year=1998&make=Chevrolet&model=Blazer&vi=1314133&ck=Search_600-500_1314133_3362&keyword=600-500

The transfer case being 2 qts overfull indicates a leaking front transfer case seal allowing transmission fluid into the transfer case. Over time it will get way overfull and start leaking out of the vent hose. The transfer case must be removed to chage this seal.

Can this be the cause of my P0740

Nope, P0740 is a problem with the torque converter clutch circuit.

Can someone show me a pic or a link to a pic of the seals that I need.

As mentioned in post #2, the root cause is a leaking vacuum switch on the transfer case. After the switch is replaced, the transmission and transfer case seals might not need replacement, (they might seal up on their own). Check the vacuum lines at the switch for the presence of fluid. If fluid is sucked into the lines it will cause slow engagement/disengagement of the front axle. The vacuum system is shared with the HVAC system which can cause the blend doors to operate slowly, or not at all, if they become contaminated with fluid. The lines must be cleaned out, along with the axle actuator under the battery tray.

The switch is located on the left side of the transfer case, slightly above and inboard of the front output shaft. Most auto parts stores stock it. http://www.oreillyauto.com/site/c/detail/DOR6/600500.oap?ck=Search_600-500_-1_3362&keyword=600-500

http://i561.photobucket.com/albums/ss58/cwhook/NV233selectable.jpg

Yes I did replace the actuator and it did have fluid in it. I will grab a new vacuum switch today.

Pick up a couple cans of carb or brake cleaner and clean out all of the fluid in the vacuum lines and actuator. Replacing just the switch will fix the problem, but it may not eliminate the symptoms, (gotta get that fluid out of the lines).

Most of the auto parts stores stock this one: http://www.oreillyauto.com/site/c/detail/DOR3/49315.oap?ck=Search_49315_-1_3362&keyword=49315 It's made by the same company, exactly the same part with different packaging and price tag ;)

Ok changed it out and cleaned the lines out. They did have fluid in them.
I will give it some time and check the fluid level on it.

Onn thing that I did notice is when I go to 4lo it kinda bucks into 4lo at like 1,200-1,500 rpm and if I go below 5mph it will do it again when I step on the gas. Almost like it takes it out of 4lo every time I go belpw 4mph. Is that normal

Shifting in and out of 4WD LO should only be done when the vehicle is stopped, or barely moving. If your speedometer says you're moving, you're going too fast. The gear ratio in 4WD LO is exactly that, LOW, lots of power & torque, not designed for speed ;) When accelerating, the transmission will shift into 3rd gear very quickly. The throttle is very "touchy" and the rule of thumb is "don't exceed 20mph in 4WD LO". Never operate the vehicle in 4WD HI or LO when on dry pavement: snow, ice, mud, sand, loose gravel etc, ONLY.

Ok well checked it out today and it seems that the fluid is still getting in some how. what do I have to do now.
Also the front diff leaks fluid out too. I know it is different fluid but wherewould it be leaking from there also.

If you replaced the vacuum switch and are still finding transmission fluid in the lines, either the switch is no good or you didn't get all of the fluid out of the lines.

Front differential leak could be most anything, cover gasket, case seal, axle seal, pinion seal etc etc. Clean it off and drive it a bit, then look for the leak. There is a chemical dye you can add to the differential fluid and check for leaks a with a black light... shows up florescent green, can't miss it. Most auto parts stores carry it.

cool I will clean it off and get some dye to see where it is getting out at. I didn't check the vac lines again I just took out the top fill screw on the transfer case and found 1qt-2qt of extra trans fluid.

Did you drain it down to the proper level after you replaced the vacuum switch?

Yeah I did but it seems to be pulling it from the tranny I am guessing. The tranny fluid level goes down and the transfer case fills all the way up

Double check vacuum at the actuator under the battery tray, (to make sure the vacuum switch is working correctly). Engine at idle, when 2WD is selected there should be zero vacuum at the actuator. When 4WD is selected there should be manifold vacuum present at the actuator.

In 2WD the vacuum switch connects the actuator to the vent line and it must be clear: no oil, no kinks, no leaks, and the filter at the end of the vent line, (on the transmission dipstick tube) must be clear. To test, pull the vacuum line off the actuator, engine at idle, 2WD selected, you should be able to blow/suck on the vacuum line with very little resistance, and hear the air flow at the filter.

I will have to wait till I get enough time to take out the battery and such. Is this the only possible way I can be getting the fluid in my transfer case?.

If so I may just replace the lines as I check them to make sure.

It seems to end up in there at a fast rate. After about 1 day the tranny is 2qts low and the transfer case is 2 qts overfull.

There's a seal at the transmission output shaft and one at the input shaft of the transfer case. Physically they are less than 4" apart. There's a fiber gasket between the two units where they bolt together. The purpose of the gasket is to keep dirt out, not to keep fluid in, (the seals do that). The only way the fluid can transfer from transmission to transfer case is if there is a negative pressure, (vacuum) in the transfer case strong enough to pull the fluid past the seals. The only way for vacuum to get into the transfer case, is if the vacuum switch is leaking vacuum past the seals inside the switch, or for some odd reason there is vacuum applied to the steel vent pipe on the top of the transfer case. I am not an artist, never claimed to be, bare with me on the rough, and I do mean rough, drawing:

http://i561.photobucket.com/albums/ss58/cwhook/VacuumSchematic.jpg

Thank you for doing that for me. I know for sure that vac line to HVAC looks dry rotted but have not seen any problems with my ac. I will dissconnect the lines and see what I find in them.

If I find fluid in them and clear them out do you think this can stop my transfer case overfilling? Granted the new switch I got is good?

If/when fluid gets in the HVAC lines, it will cause slow or no operation of the blend doors. It will not affect the 4WD system. The HVAC system has its own separate vent to atmosphere in the dash.

Ok, well I did not have time to disconnect and check all the lines today but I did go around and locate them so I can check them later. I'll keep you posted.

Got to check them and they seem to be free of fluid. I am not sure how it is getting in there.

One new thing happened to me. I got my truck stuck and I then put it in 4x4lo because my front tires where on good ground. My light said I was in 4x4lo and I heard the clunk under my seat near the transfer case but the front tires did not move at all. I tried 4hi and same thing.

I guess my question is was the 4x4 not engaging because the front tires where not rolling??

If so and I get it in 4x4lo can I come to a total stop and will it be in 4x4 right from take off or will it need to be rolling again to engage.

Right front axle shaft is not engaging to differential. Engine at idle, select 4WD, actuator under battery must have manifold vacuum and pull the cable ~1/2" to ~3/4".

Ok I will pull that batt and check..


If it does move what do I do next>]?

The light on the selector lights up solid and I hear the transfer case engage.

If I put the truck on jack stands and hit the 4hi button will I see the tires spin or do they have to be rolling on the ground to engage?

Here's an easy way to see if the right front is engaging:
Engine at idle, select 4WD, raise only the right front wheel off the ground, it should not turn by hand. Select 2WD and it should turn freely.

soon as I get the little ones down I check it out

Here are the findings. after I took out the battery I noticed that the actuiator and the cable where not connected. I took a look and it seems that the little lock spring that came with the actuator did not do a good job. After a little adjustment to the spring I was able to get it to lock on to the actuator and then tested if the wheel locked and I am back in business. Thank You.

Good job! Glad you found and fixed the problem. Thanks for posting back.

Hey I noticed that when I use the 4x4 the tranny fluid drops a lot faster. I think the transfer case heats up and dumps the fluid out the overflow line and then it draws it from the tranny again to refill. What is causing it to draw the fluid from the tranny??
I changed the vac switch and was able to blow through the vac line on actuator easy.

Have you replaced the front transfer case seal yet? It is not uncommon for them to leak. It is normal for trans fluid to be in the rear trans adapter between the transmission and transfer case on a 4WD. You know the transfer case vent is good because fluid comes out. Make sure the trans vent is open also.

I have not what is the gasket called so I can find it?

.... It is normal for trans fluid to be in the rear trans adapter between the transmission and transfer case on a 4WD...

If there's transmission output shaft seal and a transfer case input shaft seal, where does the fluid come from? Please explain

There is not a transmission output shaft seal on a 4WD GM truck. The adapter bolts to the back of the trans with a square cut seal around it's edge. (You can see it in reply #7) Fluid gets in the adapter. The gasket between the transfer case and transmission adapter (where the tailshaft would be on a 2WD truck), keeps the trans fluid in the transmission. The front transfer case seal where the transfer case input shaft comes out of the transfer case and splines to the transmission output shaft is essentially both the transmission rear seal and the transfer case front seal. Since it is removed from and installed into the transfer case it is called a transfer case front seal. The picture in reply #7 has the transmission adapter still attached to the transfer case so you can't see the seal. This is the seal you are after: The input bearing seal. Good luck.
http://i36.photobucket.com/albums/e50/twabelljr/tcaseseal.gif