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Is my transfer case toast?

clutch2k3

clutch2k3

1/2 ton status
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Could someone help diagnose whats wrong with my k5 or tell me what I did wrong? Short story is that during a test drive after manually locking the hubs and shifting the TC (Transfer Case) into 4H the wheels locked up. Here are the details of what happened:

- Back in December 2023 when I bought the k5 it had auto locking hubs and i test drove it with the TC in 2H, 4H & 4L and it was OK. In hindsight I'm not 100% sure if the hubs ever actually locked.
- In March of 2024 I finally finished rebuilding the front end. Part of the work I did was I replacing the auto locking hubs with brand new manual locking hubs (the popular Warn ones)
- I test drove it with the TC in 2H and the hubs unlocked up to 50 MPH and it drove (really) well.
- With the transmission in park and the TC still in 2H, I locked the hubs and drove slowly for a few hundred feet and it was OK.
- I shifted the transmission into neutral, left the hubs locked, shifted the TC into 4H and started driving very slowly. Within 30 feet I starting hearing a "ticking" sound from underneath the car (I assume the TC but I'm not 100% sure)
- I continued driving very slowly but the ticking sound got louder and then the car started to lock up.
- I continued driving very slowly but then the car completely locked up and the ticking was very loud.
- I put the transmission into park, shut off the car, and unlocked the hubs. I also visually inspected underneath the car and the engine bay and didn't see any problems.
- I started the car back up and the loud ticking immediately started again. After shifting the transmissionn into drive it was still locked up. When I pressed the gas harder the ticking got even louder and then I started hearing clunking and what sounded to me like gear grinding.
- I put the transmission into park, shut off the car, then put the transmission into neutral & the TC into neutral, got out of the car and tried pushing the car but it was still locked up. Just to be clear, at this point the hubs are unlocked, the transmission is in neutral and the TC is neutral but the car still won't roll.
- I took a breather and texted some car guys I know but they weren't available at the time. The blazer was in the middle of the road blocking the cul de sac (of course) so I jumped back in and shifted everything every which way (hail mary button mashing). The car started finally moving and the ticking went away. After it started moving the rear wheels were slipping on the pavement like the front tires were holding them up. I finally got it back into the garage and shut her down.
- My car buddy got back to me and said you have to go in reverse for some reason that I didn't understand but I started it back up, put it in reverse (hubs unlocked, TC in 2H) and went back and forth a few times in and out of the garage and the car appeared to be back to normal.
- I haven't moved it since.

any help is appreciated, TIA
 
Didn't touch the diffs except for changing the fluid in the front.

Would mismatched diff ratios explain the lock up when hubs are unlocked, trans is in neutral and TC is in neutral?
 
it could, driving on hard surface, if they close mismatch then it buck, fight and slip, but wouldn't lock up.
My suggestion is jack up rear and put on body stands. put t case in 4H hubs unlocked and get under there and turn the drive shafts by hand. See if you can narrow down where the ticking noise is coming from.
Is this an np203 t case ??
 
After seeing the pics in your other thread. It looks to be a np208 t case
 
Internet says it's an NP241 but how do I know for sure?

I'll try your recommendation. I might need 2 more 6 ton Jack stands first though
 
Could be they are very similar from the back, should red and silver round tag on front side. For sure it is not a np203 or 5
 
I took that pic when I checked the fluid level. It's a bit low but the fluid doesn't seem degraded to me. I couldn't believe how much greasy dirt was coming off of it so I took a pic
 
Maybe a messed up 4W drive selector ring, seen at 32:17 in this video, or this other part, seen at 9:16 in this video, maybe could keep the TC from switching into neutral.

Also, from looking at the goobered RTV job performed by someone in the past, they probably rebuilt it incorrectly and/or used the wrong parts.


blzr_20240305_234507.jpg
 
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Could someone provide the part number of a rebuild kit for an NP241 out of a 1989 Blazer? Do I want the Timken TCRK241?
 
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yes that looks like the one. Have you done any investigating is the t case making the noise ?
 
no but the only explanation I can think of for the TC not shifting into neutral is that there's an internal problem.
 
it happens a lot really. esp on hard pack. The 2 axles never really turn at the same speed. so there is tension on the drive shafts that hold things in the t case to bind and keep from moving. Many times it is necessary to reverse, like you did, to get things to unbind.
 
Just an added thought in your quest to find a solution to this situation - certain manual hubs ( like the OEM & WARN - BTW, the OEM’s are WARN hubs w/o the label on most of the 80’s GM trucks ) will allow the external dials to turn and indicate “lock” or “unlock” but the internal parts have not engaged yet.
As soon as the splines/teeth and resistance allows everything slides matching the dials indicated position mark. Most folks never even notice this happening.

The reason that I bring this up is that at some point in your description you said the hubs were unlocked but things were still in a bind but after the back and forth movement all was free - possibly the movement allowed the hub internals to do their thing and truly become free to match the dial position.

As far as the noises you described it was confusing as to if these were only under movement or also when stopped; and when you stated no movement was that the truck underway or the T-case lever resistance?


Like others have said up above engaging and disengaging your 4WD on pavement can be difficult on all parts involved - try doing these tests on a loose gravel road or soft grassy area especially when going back into 2WD ; this will help greatly in allowing internal parts to release with much more ease and effectiveness.


Maybe a video of these happenings will help make some clarity and help lead to pinpointing your problem.
 
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If your tires are different sizes, brands or wear, it's similar to mismatched gear ratios. In general, you're not supposed to use 4WD on pavement. It's not like a modern AWD system. What you describe could also be a problem with the front differential, like chipped gears or a bearing coming apart. A ticking sound can be as simple as a dry U-joint. It's very common for the front axleshaft joints to freeze up from lack of use, but the clunking and gear grinding has to be something more significant. There's some chance that as the driveline binds you're getting axle-wrap and that's making the CV joint bind or rub on something.

Even if you only have 1 set of jackstands, you can lift the front and spin the front axle and driveshaft to see if anything is going on up there.

Especially if you haven't done the maintenance lately, it would be helpful to drain the oil from the transfer case to see if there's metal in it (and prove there's oil in it!). Same goes for the front differential. It's more work, but also lets you verify the gear ratio. You can check the ratios at both ends by counting driveshaft and tire revolutions.
 
Thanks a lot for the responses everyone!

I'll be draining the TC and rear diff tonight

Just to clarify:
- 4 tires are the same size 32X11.5R15
- i was just trying to do a quick test on pavement
- the front differential was just serviced and spins fine, no chipped teeth
- the ticking occurred while the truck wasn't moving, with the front hubs locked and unlocked, so i don't think it could possibly be a u joint
- Ive already jacked up and spun the front end and all was fine
- the TC has oil in it
 
clutch2k3 said:
- the ticking occurred while the truck wasn't moving, with the front hubs locked and unlocked, so i don't think it could possibly be a u joint
Click to expand...
Are you saying the transmission was in gear, but something was slipping so the vehicle didn't move? That's an important piece of information. I guess it's possible you have a worn shift fork and the case is getting stuck between modes. You should verify that the shift linkage is adjusted correctly. https://ck5.com/forums/threads/208-linkage-adjustment.339528/. You can manually shift the case without the linkage for troubleshooting.

You might have better luck going all the way from 4LO to 2HI, rather than trying to shift 1 step at a time.
 
Are the tires the same brand? There can be wild variations in size between brands or if someone replaced two without doing the other two.
 
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