TH400 seems to be dragging

Old60Driver

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So, I've been working on this stock 83 K20 that was driven very infrequently in the last 8-10 years. And none in the last 3 years. Got the fluids right, as she'd been leaking from....everywhere. Valve cover gaskets, trans pan, power steering, you name it. Installed new trans filter and fluid. She seems to engage very nice.

BUT, if I'm doing lets say 55 mph, and let off of her, she doesn't really coast. It's almost like the danged emergency brake is engaged. I can put her into neutral and notice a slight decrease in 'deceleration' but still, it doesn't feel right.

Granted, it's a 3/4 ton 4X4 so I expect some drag, and maybe I'm a bit spoiled with my late model truck. What's a good way to confirm that I'm sure I'm not in 4 wheel drive? I don't have a light, and everything is in the right position for rear wheel drive. I don't really want to chase my tail if this is normal.

Side question. What's a safe speed that I can drive her for extended periods of time. She's only a 3 speed, and I don't think 75 mph on the highway would be good for her. I'm thinking 60 mph for cruising. I'll be installing a temporary tach to check RPM before I get her on the road, so at least I'll have SOME data before I hit the road with her...

Thanks in advance y'all!
 

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It may be just as simple as you have a lockout on your front axle stuck? Maybe? :)

You said whats a good way to determine youre not in 4x4?

How many speeds does your transfer case have?
83, k20 i assume it to be a NP205.

Make sure its in 2hi. (If its a 205)

If its in that gear, and if its a NP205, your front driveshaft will be dead, should free wheel if you spin it.... if not...... you may wanna investigate your front diff.
Check your axle lockouts, make sure theyre "unlocked"

Couls be trans related?
a seal leaking on the clutch center support maybe.... 3rd can leak over into reverse, and it can cause drag on reverse at the same.... thats coming from my limited understanding of the hydraulic fluid passages.
 
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Old60Driver

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It may be just as simple as you have a lockout on your front axle stuck? Maybe? :)

You said whats a good way to determine youre not in 4x4?

How many speeds does your transfer case have?
83, k20 i assume it to be a NP205.

Make sure its in 2hi. (If its a 205)

If its in that gear, and if its a NP205, your front driveshaft will be dead, should free wheel if you spin it.... if not...... you may wanna investigate your front diff.
Check your axle lockouts, make sure theyre "unlocked"

Couls be trans related?
a seal leaking on the clutch center support maybe.... 3rd can leak over into reverse, and it can cause drag on reverse at the same.... thats coming from my limited understanding of the hydraulic fluid passages.


Thanks for the reply! And yep, it's an NP205, and I'm indicating 2HI from the cockpit. I'll double check the short shaft for free wheel. I should have thought of that yesterday, but, well, it was a long day, and I was just excited to have the motor runnin mostly like she should! lol

I'll double check the lockouts. It's bone stock on that regard, with auto hubs.

Thanks again, I'll update after I get things inspected!
 

Old60Driver

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Welp, I went and tried freewheeling the short shaft. Is it supposed to free-wheel 'freely'? This one doesn't. If I rotate the shaft (in either direction), she feels clunky, and doesn't make it a full turn before stopping. This is with the engine off, and the vehicle in park.

I'm guessing it should be moving freely, but I don't have any idea how the auto hubs work. How does the hub know when to engage or disengage? Looks like I've got some research to do. lol

I'd like to just keep the auto-hubs working, but if I have to move to manual, then so be it. I don't really plan on using her as an off road monster, but the occasional trip to the beach or off some dirt road at MOAB might be in her future. ;)

Thanks again
 
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Rickf

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Somebody please correct me if I'm wrong, I thought with the Tcase in 2wd the front auto hubs would disconnect when backing up for 10? feet or so,
then re-engage when in 4wd and going forward.
 

Old60Driver

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Somebody please correct me if I'm wrong, I thought with the Tcase in 2wd the front auto hubs would disconnect when backing up for 10? feet or so,
then re-engage when in 4wd and going forward.
I had an '86 S-10 Blazer that I seem to recall worked like that...

As an update, I put her in 4H and 4L, and it's definitely engaging in those modes. And definitely un-engaging when I pull her out of 4X4. That being said, the hubs are a different story right? I still need to pull them apart, inspect, and maybe replace with manuals.
 

Vbb199

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Somebody please correct me if I'm wrong, I thought with the Tcase in 2wd the front auto hubs would disconnect when backing up for 10? feet or so,
then re-engage when in 4wd and going forward.


This is correct i believe.... been a bit since ive had a np205 truck
 

Old60Driver

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Quick update. I'm not near the truck at the moment (I'll be driving up there Friday) so I can look at the transfer case, but I'm not sure now that she's an NP205. I found this pic while I was looking for something else. Is this an NP205 or something else? Not too familiar with the tags...
You must be registered for see images attach
 

Vbb199

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Quick update. I'm not near the truck at the moment (I'll be driving up there Friday) so I can look at the transfer case, but I'm not sure now that she's an NP205. I found this pic while I was looking for something else. Is this an NP205 or something else? Not too familiar with the tags...
You must be registered for see images attach


Sadly, the upper line thats been damaged is what we need to see.... send a pic of it, or tell us how many speeds the case has.


Someone else might know what theyre looking at with that. One of those numbers tells the gear ratio.
 

Old60Driver

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Sadly, the upper line thats been damaged is what we need to see.... send a pic of it, or tell us how many speeds the case has.


Someone else might know what theyre looking at with that. One of those numbers tells the gear ratio.

Roger that. I'll be up there tomorrow night, so I can get a better picture of the tag. I'll repost then.

Quick question. I've been looking into servicing or replacing the autolocking hubs. I would bet they've never been serviced. I don't plan on a ton of 4 wheelin', but I want to make sure it's available to me should I need it. I'm trying to keep her as stock as possible, but do most folks just replace the autohubs with manual hubs? Should I just go that route, or is there a chance I can service/rebuild the existing autohubs?

Thanks
 

Vbb199

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Roger that. I'll be up there tomorrow night, so I can get a better picture of the tag. I'll repost then.

Quick question. I've been looking into servicing or replacing the autolocking hubs. I would bet they've never been serviced. I don't plan on a ton of 4 wheelin', but I want to make sure it's available to me should I need it. I'm trying to keep her as stock as possible, but do most folks just replace the autohubs with manual hubs? Should I just go that route, or is there a chance I can service/rebuild the existing autohubs?

Thanks


I cannot confirm this, but i just recently was reading the damn things can come unlocked when backing down hills and such!


for me personlly, i'd be running strictly manual lockouts. But that's just my opinion. I assume the physical wheel hubs are the same, you just change lockouts
 

Vbb199

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Quick update. I'm not near the truck at the moment (I'll be driving up there Friday) so I can look at the transfer case, but I'm not sure now that she's an NP205. I found this pic while I was looking for something else. Is this an NP205 or something else? Not too familiar with the tags...
You must be registered for see images attach



I think it goes as follows:
2Hi, 4Hi, Neu, and 4 Lo. = np205 (cast iron)
Low lock, low, neu, high, high lock = np203 (cast iron)
2hi, 4hi, neutral, 4lo= np208/np241 (cast aluminum)

Been a little since ive actually had a 4x4 square and driven it. Ive had 2wd's for the past say, 5 years.
Ive got a big lifted s10 blazer on 1 tons i built, but its a frankenstein of parts lol
 

Old60Driver

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I think I'm going to get a set of manual Warns coming, just in case. I'll also get a service kit for the autohubs. I'm prepared both ways. ;) I like the idea of manual hubs, but really like the stock look of the autos... Well, my wife does. So that means I do too I guess. lol
 

83Burban

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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.

My 83 K10 burb has a 454 w/ TH400. I try to keep her just under 2500rpm, which is about 68mph with my 32s. She gets about 12mpg if im good at keeping steady speed and drive for highest vacuum.

But Tbh...she does not feel at all labored running 75 which puts me just a bit over 2500rpm. Its hard to say exactly but i would guess 75 falls somewhere around 2550rpm.

Now, when I let off the gas it def does NOT feel like I'm breaking. Does your truck make any odd sounds when "engine breaking"? Does it happen EVERY time you let off? Only at high speed?
 

Vbb199

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@Old60Driver

^^ What he just said got me to thinking,
Does the engine also "brake" (lug/decelerate) when you let off the gas? Or you just feel like truck overall slowing down like someone is pressing the brakes?
 

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