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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Austin4wd on May 31, 2016, 11:27:43 am

Title: 1980 K20 TH400 problem
Post by: Austin4wd on May 31, 2016, 11:27:43 am
So I got a K20 and its a TH400 truck. It runs like a top, just my trans doesn't seem to overly want to work. It drove forward about 50 feet and stopped. I put it in reverse and I got about 10 feet. Turned it off and let it sit a little bit and it does the exact same thing. Is my ATF to dirty and my filter is plugging up or is the trans gone?? I'm literally freaking out as I want to have it running before summer ends
Title: Re: 1980 K20 TH400 problem
Post by: LTZ C20 on May 31, 2016, 03:54:47 pm
Have you checked the fluid level and condition?
Title: Re: 1980 K20 TH400 problem
Post by: Austin4wd on June 11, 2016, 09:39:46 pm
I don't know if it's gone or not, but it does hold ATF. Is it a clogged filter maybe?
Title: Re: 1980 K20 TH400 problem
Post by: LTZ C20 on June 11, 2016, 10:39:39 pm
It's possible, you may have to drop the pan and examine and inspect the inside of filter and see if there are any obvious issue. Does fluid register anywhere on the dipstick?
Title: Re: 1980 K20 TH400 problem
Post by: Austin4wd on June 12, 2016, 12:15:38 am
It registers on the cold operating range when I don't have it running and on the warm/hot side after its idles for an hour, so I'd say healthy operating range
Title: Re: 1980 K20 TH400 problem
Post by: LTZ C20 on June 12, 2016, 10:55:57 am
Transmission fluid should always be checked with the engine idling in park on a flat and level surface.

So you go out when the truck is cold, start it, let the engine RPM drop to idle and then check the fluid level, if it registers in the cold area you are good, if it's over cold, it's over filled, if it's under cold, your low.

So once you check it cold, let the engine continue to idle for an hour or so and recheck it, it should now be in the hot range. Remember that compared to the engine temp, it takes transmissions longer to come to their full operating temperature, but once there, they should be close to the operating temp of the engine. If I remember correctly, 10-20° variance in temp between engine and transmission is good.

If your readings match cold to hot, then the fluid level is most likely not an issue. Meaning, it registers cold when cold and hot when hot. If it registers low when cold and low when hot then it's low for sure. If it measures over when cold and over when hot then it's over filled for sure. If the readings don't match, like low when cold and over when hot or cold when cold but under when hot, then fluid level needs to be investigated further.

I suggest a recheck of the fluid level just to be sure as you said you checked it cold with the engine off. Over filling a transmission is just as damaging as under filling one.

Report back with the results of the recheck.
Title: Re: 1980 K20 TH400 problem
Post by: Austin4wd on June 12, 2016, 11:39:14 am
I went and checked it did a cold reading and then waited for a while and did a hot reading, and the levels are where they're supposed to be. So my fluids are where they're supposed to be. I tried moving it and it only does the same thing. I'm reducing my problem to transmission is shot or the filter is clogged. Odd, a TH400 has never given me this amount of trouble
Title: Re: 1980 K20 TH400 problem
Post by: LTZ C20 on June 12, 2016, 12:19:31 pm
Ok, sounds like you got good results. How was the color, consistency and smell of the fluid? Did this issue suddenly just happen or did you the truck this way?
Title: Re: 1980 K20 TH400 problem
Post by: Austin4wd on June 12, 2016, 02:13:33 pm
The colour was the usual red, it didn't smell like burning kitty litter, and the consistency was the same as fresh ATF. Yes, I bought the truck like this, and I'm not complaining for what I got for $500, with this being the only problem with it
Title: Re: 1980 K20 TH400 problem
Post by: hatzie on June 12, 2016, 02:19:44 pm
Sounds like the PO burned it up and changed the fluid in an attempt to bring it back to life.
Title: Re: 1980 K20 TH400 problem
Post by: LTZ C20 on June 12, 2016, 03:05:14 pm
Quote from: hatzie on June 12, 2016, 02:19:44 pm
Sounds like the PO burned it up and changed the fluid in an attempt to bring it back to life.
I am believing that this probably the case. It would explain why it was sold so cheap if that's the only thing wrong with it. Luckily for you, it shouldn't be too terribly expensive to rebuilt depending on what parts have failed once it has been removed, disassembled and diagnosed.
Title: Re: 1980 K20 TH400 problem
Post by: Austin4wd on June 12, 2016, 06:51:48 pm
That's what I'm thinking, as my K10 also has a NP205 and that t-case has shredded 3-4 TH350s, so it makes sense it ate a TH400. I'll try replacing the filter, and if that doesn't work then I'll start hunting for a new trans
Title: Re: 1980 K20 TH400 problem
Post by: LTZ C20 on June 12, 2016, 07:59:43 pm
I highly doubt that the transfer case caused the failure of the transmission. A TH400 is far stronger than a TH350, even in stock form. So I would investigate further into the cause of the transmission not working properly instead of condoning the transfer case as the reason for the failure. It is most likely NOT related to the transfer case, but far more likely internal to the transmission.
Title: Re: 1980 K20 TH400 problem
Post by: Austin4wd on June 13, 2016, 12:23:25 am
I'm only placing my bet that the transfer case could have eaten the trans, but I'm not gonna quote on it. I'll do some more investigations once I get some other projects cleared up so I can drop the pan and check to see what's going on. I got a buddy who can help me rebuild it if I need too but it's still gonna run me up a couple hundred bucks. The guy I bought the truck from said it ran and drove fine then started acting up abou three years ago, and it was time to upgrade. On the plus side, I picked up a '90 Cavalier from the same guy cause he just wanted it out of his yard 😂😂😂
Title: Re: 1980 K20 TH400 problem
Post by: LTZ C20 on June 13, 2016, 02:32:26 am
Sounds like a plan. I really like the 400, it is an excellent transmission.
Title: Re: 1980 K20 TH400 problem
Post by: Austin4wd on June 13, 2016, 12:52:56 pm
I like the 400, it's a really tough trans and as I said earlier this is the first time one has given me problems, and I got one in an S10 (has a supercharged 383 in front of it) and not one problem
Title: Re: 1980 K20 TH400 problem
Post by: hatzie on June 14, 2016, 08:23:36 am
Might be an excuse to get a reman 4L80E...  Then again fixing the TH400 is probably cheaper. 

Putting a real filter in the cooler lines will keep things like 4L80E valve body screens clear of crud.   Even the TH400 will benefit.
Title: Re: 1980 K20 TH400 problem
Post by: Austin4wd on June 15, 2016, 03:33:03 pm
Lol I tried convincing my girlfriend to let me 4L80 the truck but she shoot me down (dang women lol) but yeah I got a buddy who's willing to rebuild the 400, just gotta bring him the trans
Title: Re: 1980 K20 TH400 problem
Post by: LTZ C20 on June 15, 2016, 11:20:51 pm
Does she own it? I usually just tell my girlfriend what I'm gonna do or after I've already done it. I usually just get an "ok whatever you want" or the "your stupid" look. Do what you want to it, it's your truck, right?
Title: Re: 1980 K20 TH400 problem
Post by: Irish_Alley on June 16, 2016, 07:03:48 am
usually they understand "but it will save gas money cause of the OD" price of a 4l80e and the stand alone tcu is maybe 500-1000 more than the th400 rebuild.
Title: Re: 1980 K20 TH400 problem
Post by: hatzie on June 16, 2016, 08:15:43 am
Quote from: Austin4wd on June 15, 2016, 03:33:03 pm
Lol I tried convincing my girlfriend to let me 4L80 the truck but she shoot me down (dang women lol) but yeah I got a buddy who's willing to rebuild the 400, just gotta bring him the trans

Girlfriend or wife?  My girlfriend has ZERO say in how I spend my money.  Don't like it?  There's the door.
Title: Re: 1980 K20 TH400 problem
Post by: Irish_Alley on June 16, 2016, 08:17:33 am
what about if your girlfriend says yes but the wife says no???
Title: Re: 1980 K20 TH400 problem
Post by: LTZ C20 on June 16, 2016, 04:58:10 pm
Quote from: Irish_Alley on June 16, 2016, 08:17:33 am
what about if your girlfriend says yes but the wife says no???
Well then it's the same as when mom said no and dad said yes. You do it anyway because one said yes. And if the other says "I said no" you say "but the girlfriend said yes" that will change the wife's mind lol.
Title: Re: 1980 K20 TH400 problem
Post by: Irish_Alley on June 17, 2016, 07:15:15 am
lol the subject will be changed in a second and she wont be thinking about the 4l80e. so lose/win ???
Title: Re: 1980 K20 TH400 problem
Post by: LTZ C20 on June 18, 2016, 03:04:44 am
I thought that was still a win/win? How could it not be? Lol
Title: Re: 1980 K20 TH400 problem
Post by: Irish_Alley on June 18, 2016, 07:09:11 am
cause the wife finds out about the girlfriend
Title: Re: 1980 K20 TH400 problem
Post by: hatzie on June 18, 2016, 07:25:46 am
Quote from: Irish_Alley on June 18, 2016, 07:09:11 am
cause the wife finds out about the girlfriend

And how is that not a win?  You get rid of both of them...
Title: Re: 1980 K20 TH400 problem
Post by: VileZambonie on June 18, 2016, 08:31:24 am
lol

Quote
girlfriend to let me

Something I will never understand. I have never had problems meeting women, having girlfriends and long term relationships etc but I would NEVER be with a girl who didn't want me to be happy. Part of my happiness includes doing whatever I want with my trucks and my life. How come so many guys have to ask permission from their girlfriends or wives to do things to their trucks? Time to trade in your pocket books for a wallet gentlemen!

I digress, did you drop the pan and check the filter/pickup tube assembly? check the valve body bolts too while you're under there (and don't ask for permission, ask for forgiveness instead)
Title: Re: 1980 K20 TH400 problem
Post by: Irish_Alley on June 18, 2016, 10:05:06 am
Quote from: hatzie on June 18, 2016, 07:25:46 am
Quote from: Irish_Alley on June 18, 2016, 07:09:11 am
cause the wife finds out about the girlfriend

And how is that not a win?  You get rid of both of them...
cause when she devorces you she will take the truck and the house lol.
Title: Re: 1980 K20 TH400 problem
Post by: LTZ C20 on June 18, 2016, 10:33:10 am
I think this has gone to far haha.
Title: Re: 1980 K20 TH400 problem
Post by: Irish_Alley on June 18, 2016, 11:22:55 am
Gone like a freight-train, gone like yesterday
Gone like a soldier in the civil war, bang bang
Gone like a '59 Cadillac
Like all the good things that ain't never coming back
She's gone (gone) gone (gone) gone (gone) gone, she's gone
(http://www.naioa.com/v2/modules/Forums/images/smiles/burnout1.gif)
Title: Re: 1980 K20 TH400 problem
Post by: hatzie on June 18, 2016, 06:29:06 pm
Quote from: Irish_Alley on June 18, 2016, 10:05:06 am
Quote from: hatzie on June 18, 2016, 07:25:46 am
Quote from: Irish_Alley on June 18, 2016, 07:09:11 am
cause the wife finds out about the girlfriend

And how is that not a win?  You get rid of both of them...
cause when she devorces you she will take the truck and the house lol.

Leykis 101.  Don't ever marry her and don't let her move in.  Nuff said.
Title: Re: 1980 K20 TH400 problem
Post by: LTZ C20 on June 18, 2016, 11:09:00 pm
I think that moving away from the girlfriend part, I'm sure it was a joke anyway, it's probably safe to say that your transmission requires more in depth diagnosis. Besides, I'm sure your girlfriend is a very nice girl.
Title: Re: 1980 K20 TH400 problem
Post by: RAD77C10 on June 19, 2016, 12:25:08 am
Could your K20 have different axle gears in & back?
Title: Re: 1980 K20 TH400 problem
Post by: Irish_Alley on June 19, 2016, 06:59:35 am
Quote from: LTZ C20 on June 18, 2016, 11:09:00 pm
I think that moving away from the girlfriend part, I'm sure it was a joke anyway, it's probably safe to say that your transmission requires more in depth diagnosis. Besides, I'm sure your girlfriend is a very nice girl.
this is very confusing first you say moving away from the girlfriend part then say youre sure shes a very nice girl.

but ok im done
(http://www.naioa.com/v2/modules/Forums/images/smiles/beatdeadhorse5.gif)
Title: Re: 1980 K20 TH400 problem
Post by: VileZambonie on June 19, 2016, 08:38:33 am
lol Yes it's humor. No one is picking on anyone's girlfriends.
Title: Re: 1980 K20 TH400 problem
Post by: LTZ C20 on June 19, 2016, 09:42:13 am
Quote from: Irish_Alley on June 19, 2016, 06:59:35 am
Quote from: LTZ C20 on June 18, 2016, 11:09:00 pm
I think that moving away from the girlfriend part, I'm sure it was a joke anyway, it's probably safe to say that your transmission requires more in depth diagnosis. Besides, I'm sure your girlfriend is a very nice girl.
this is very confusing first you say moving away from the girlfriend part then say youre sure shes a very nice girl.

but ok im done
(http://www.naioa.com/v2/modules/Forums/images/smiles/beatdeadhorse5.gif)
Now your just being a smart @$$ and you know your doing it. Lol
Title: Re: 1980 K20 TH400 problem
Post by: Austin4wd on July 11, 2016, 12:13:06 pm
Lol thanks guys but she went and left me as she hated it when I brought up trucks at the dinner table. Anyways away from women I don't have the cash for a 4L80 so I'm rebuilding the TH400 in the truck already. But I found an 83 TH400 4WD that's been rebuilt. So my thought is drop my transmission and t-case, break the two apart and slap the t-case to the 83, put back in the truck and drive away. But will my 80 t-case bolt to the back of the 83 trans or would I need a new t-case? Cause those 205's are heavy lol
Title: Re: 1980 K20 TH400 problem
Post by: Irish_Alley on July 13, 2016, 08:02:48 am
should of had a plan B lol. all transfer cases that come off a th400 are 32 spline. theres a long shaft and short and figure 8 pattern and round pattern. but if you have the adapter for that t case. it should be a simple swap. the 80 should have the figure 8 and the 83 should have the figure 8. you dont have to worry about the long shaft till 86 i think. so all should be good. you could even just take the trans out of the 83 and put that in your 80 with the t case from the 80
Title: Re: 1980 K20 TH400 problem
Post by: Austin4wd on July 19, 2016, 10:45:06 pm
The 83 trans is the transmission itself, not the t-case too as he's keeping it. But the trans itself, that's what I want. If it will work it's going on the 80 t-case and going in the truck. If I need too I'll keep the trans and swap the guts into mine lol
Title: Re: 1980 K20 TH400 problem
Post by: Irish_Alley on July 20, 2016, 12:26:34 pm
They should swap with no problems. You can swap the adapters if you want or leave them. Personally I would leave them alone and just swapping the transfer cases