TH400 seems to be dragging

Vbb199

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TBH I did not know auto locking hubs was even an option in 83. I'm still new to sqaures / 4x4 in general.


If you mean they're not new enough to have auto locking hubs, i know where a 75 is right now with automatic lockouts.


100% original, my great grandfather bought it brand new
 

Bextreme04

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My truck is almost identical. 1980 K25 350/TH400/NP205 and like vince said, when in 2HI with hubs unlocked, I can freely spin the front driveshaft. I just did it last night to unhook the front driveshaft while pulling the whole drivetrain out. You should have a plug on top of the T-case to hook up your "4wd" light also. Mine stopped working and it turns out the plug had come off. I have 35's and 4.10 rear axle ratio and about 65mph is it for me. Its revved out pretty good at 65 but you can go to 70-75 if you need to, just not for any amount of time. It will be very obvious if you have a 205. Google what they look like, they don't really look like any other t-case, especially from the back.
 

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At 75, and with the aerodynamics of a barn door, I would think letting off the gas would tend to throw one thru the windshield?
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If you mean they're not new enough to have auto locking hubs, i know where a 75 is right now with automatic lockouts.


100% original, my great grandfather bought it brand new

Yeah...i thought auto locking hubs were a relatively new feature for trucks. (Like 2000s). Lol but....untill I bought this burb in Feb, I had never owned anything 4x4. I most def knew NOTHING about them.

Edit- lol now I know just enough to know that I knew nothing
 

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Based on the 2.61 ratio, I don’t believe it to be a 205.

edit: is the case aluminum or iron? Is it chain driven or not.

I’m thinking 208. Iirc all 205s were 2:1 low range...
 

Bextreme04

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Based on the 2.61 ratio, I don’t believe it to be a 205.

edit: is the case aluminum or iron? Is it chain driven or not.

I’m thinking 208. Iirc all 205s were 2:1 low range...

Yes, all iron case transfers had 1.96:1 including NP203 and NP205. The NP205 tag wont look like that either, it is a rectangular tag that is on the front of the transfer on the NP205. I'm betting on 208, although it should be 2.69 for a 208.
 

80BrownK10

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Yes, all iron case transfers had 1.96:1 including NP203 and NP205. The NP205 tag wont look like that either, it is a rectangular tag that is on the front of the transfer on the NP205. I'm betting on 208, although it should be 2.69 for a 208.
Yep your right. I didn't go look but I do remember my 205 has a rectangle tag.
 

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Yes, all iron case transfers had 1.96:1 including NP203 and NP205. The NP205 tag wont look like that either, it is a rectangular tag that is on the front of the transfer on the NP205. I'm betting on 208, although it should be 2.69 for a 208.
I’m almost positive the 208 ratio is 2.61. The tag on my CUCV states that, anyhow...
 

Old60Driver

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Welp, I haven't seen her yet since I started this post, but I'll be there tomorrow night. Sounds like I've got a 208! I'll double check everything when I get there and post pics. I've also ordered the Warn hubs. They should be waiting on me in Hutchinson!
 

Vbb199

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Yes, all iron case transfers had 1.96:1 including NP203 and NP205. The NP205 tag wont look like that either, it is a rectangular tag that is on the front of the transfer on the NP205. I'm betting on 208, although it should be 2.69 for a 208.


You're absolutely right, i got to thinking on it

In that pic, hes gotta have a np208.

The 2.61 is a 208.
Or a 241, but unlikely its a 241 since that was introduced a little later, and came with VSS in 90-91, but the "lore" is, out there exists a np208 with VSS also, should the purchaser have specified he wanted a np208 in his truck instead of a 241..... why? I dont know. I dont even know the difference....


I know for sure, the little later NP241's found in gmt400's has a backwards shift pattern from the 208.... (i have on retro fitted in my s10)

4Lo is all the way up on the shifter, vs all the way down like a 208.
 

Old60Driver

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Okay folks, I finally made it back to KS to give her some more TLC. :)

Looks like I've got an NP208. I'll post pics showing a better view of the tag, and another shot of the transfer case itself. Now, before any rags on me, yes, I know she's filthy. lol I haven't worked on cleaning anything yet. ;)

Update on the hubs. There's nothing wrong with them. I did some more testing on her, and they seem to be working as advertised, at least in my limited understanding of their operation. I could engage/disengage the transfer case, and the hubs disengaged as well. I do, however, have a set of Warns manual hubs and bearings for when I get more time, but at this point, considering I'm not planning on ANY 4 wheelin just getting her home to Texas, I think I'll just leave her be.

The drag that I mentioned? It seems to be engine braking. I hooked a tach up temporarily so I could watch RPM and get a better feel about what was happening on deceleration. Sure enough, at 60 mph, she's turning at about 2500. That sounds about right, yes? When I let off, the transmission doesn't disengage or slip or anything, the tranny and engine just wind down together. Almost like I'm driving a stick. It's been so long since I was in an early 80s era vehicle, I don't remember that as being something I noticed before. I mean it's not terrible, but it's noticeable. What do y'all think? Am I just spoiled by the newer technology, or could there be an issue with the drivetrain?

Thanks again for all y'alls replies, it's been a good damned bit of help!!!
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Frankenchevy

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Engine braking shouldn’t be anywhere as pronounced as a manual—as there’s no physical coupling, just a torque converter. I had a fairly low stall converter in my th400 before going manual and it seemed to coast comparably to my newer trucks with autos.

I don’t know the condition or history of the truck, but if you’re unsure of the condition of the atf it may be worth doing a fluid and filter change. Then again, some say that can be problematic in a trans with poor service history. What’s the fluid look like?
 

Old60Driver

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Engine braking shouldn’t be anywhere as pronounced as a manual—as there’s no physical coupling, just a torque converter. I had a fairly low stall converter in my th400 before going manual and it seemed to coast comparably to my newer trucks with autos.

I don’t know the condition or history of the truck, but if you’re unsure of the condition of the atf it may be worth doing a fluid and filter change. Then again, some say that can be problematic in a trans with poor service history. What’s the fluid look like?

Fluid was low (that pan gasket had given up the ghost a while back), but it looked and smelled good. I changed out the filter and gasket, and other than the 'dragging', the trans is perfect. Nice, solid gear engagement, no buzzing, no slippage felt, nada...

You hit it on the head though. Its the lack of coasting that weirds me out...
 

Vbb199

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On a fresh trans or newer more modern units with the tow/haul, overrun (engine braking) will be very much pronounced on engine speed, but as for something thats probably got age to it and a th400, its unlikely thats whats going on.
 

Frankenchevy

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Fluid was low (that pan gasket had given up the ghost a while back), but it looked and smelled good. I changed out the filter and gasket, and other than the 'dragging', the trans is perfect. Nice, solid gear engagement, no buzzing, no slippage felt, nada...

You hit it on the head though. Its the lack of coasting that weirds me out...
Are we talking about letting off in third gear at 65 or 70 miles an hour, or does it feel like it is dragging even at low RPM?

In a newer truck with a six, eight or 10 speed transmission they have double and triple overdrives. So even when you let off at freeway speed that top gear is only turning the engine at ~1300rpm or less...
 

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