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Old 01-25-2011, 11:58 PM
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T-400 Issues - Hunting gears and slipping?

My TH400 that I swapped into my 79 C-10 is giving me problems. There appears to be a loud whining noise, like a low power steering pump level but its not the power steering pump. The trans was low on fluid (it leaks out more than i realized when I had the speedo housing out changing the gear and housing) and it was run that way for a while. It wasnt low enough to cause issues but it was indeed low.

Now ive noticed that the transmission is either jumping in and out of 1st gear or jumping between 1st and 2nd. It does it 3 or 4 times and then finally stays in 2nd. I dont know if its slipping or shifting into neutral or what, maybe a little of both.

This is an old transmission, its originally from a 78 suburban and it sat outside of a truck for about 3 years before finally getting installed in this truck. It worked great for a year or so tho its not hardly ever driven. I have never changed the transmission filter or fluid and i've had possession of the transmission (and the original truck it came in) since 1999 or 2000.

Is it possible that the new fluid has cleaned up the gunk in the transmission and that it just needs a filter change (and changed again several more times after that to clean it all up) or does it sound like there is another problem?

I dont know if i could rebuild the transmission myself or not, i've never done transmissions or rearends before but i've done some engines. I am hoping its a clogged filter and not a clogged valve body or something. The fact that there is a whining sound bothers me tho. Either the transmission (pump?) isnt getting good flow of fluid due to a clogged filter or its going out. Hoping its just not getting good flow, lol. I dont have the money for a transmission right now.

Btw transmission has around 120,000 miles on it, most of which are all highway miles. Fluid smells fine and is red, not burned smelling or black.

Any ideas?

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Old 01-26-2011, 02:04 AM
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It doesn't sound good. You could change the filter to see if it helps and do a pressure check on it. That should tell you if it's going out. Normally once they start whining they don't stop.
Pressure Port is about middle of Pan, a few inches up on driver side.
Brake applied @1000rpm.
N @1000 = 55-70psi
D @Idle = 60-85
D @1000 = 60-90
2 @1000 = 135-160
R @1000 = 95-150
D @1000 w/Down Shift Solenoid On= 90-110
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Old 01-26-2011, 11:00 AM
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I though that the whining was from the pump working hard to pump fluid and that it would quieten down once fluid flow was restored. It would make alot of sense in this case - with the old transmission and new fluid put in it. That would clean it up and plug the filter, causing the problems I am having.

I am just trying to talk myself out of it being the transmission itself. lol.
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Old 01-26-2011, 06:50 PM
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I've got a new filter, dont know if i will make it to installing it tonite or not but i'm gonna try.
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Old 01-26-2011, 06:54 PM
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check for plugged filter first , that is a deep pan , there is a filter extension , umbrella seal at filter - o-ring in the case end if the o-ring is missing ,broke or just plain old and hard the trans will pull air and make the wining noise . old time trick was to double o-ring the case end.
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Old 01-26-2011, 07:31 PM
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Will check that, I dont think a new o-ring is included in the filter kit (its just a filter and pan gasket i think, but i didnt look for an O ring in the box. There is a seal on the filter tho for the extension.
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Old 01-26-2011, 09:08 PM
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Some Filter kits may not include the O-ring, but should.
This Wix kit does>> http://www.rockauto.com/catalog/moreinfo.php?pk=360724 and AC Delco does>> http://www.rockauto.com/catalog/moreinfo.php?pk=91765
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Old 01-26-2011, 09:13 PM
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I wanted a wix but the parts store didnt have it. They gave me a "Power Torque" brand filter. Looks like a nice filter but who knows. Ill find out how to get that extension tube off and check that o-ring. Ill probably need a new one for sure (the o-ring) if I mess with it. lol.
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Old 01-26-2011, 09:17 PM
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Yeah, they're usually hard/brittle from heat/time + stuck and come out in bits & pieces. LOL!
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Old 01-26-2011, 09:21 PM
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Yea if any transmission needs one from heat and age it'll be this one.

33 years old, behind a 454, and pulling trailers...lol.
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Old 01-26-2011, 09:23 PM
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Something shaped like this helps get them out>> http://www.makcotransmissionparts.com/T-1079.html
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Old 01-26-2011, 09:41 PM
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Ah, Ive got one of those. Use it to change the o-rings in my pressure washer quick connects.

Got one thats rounded like a hook on one end and slanted on the other end as well.
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Old 01-26-2011, 10:24 PM
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I think I found the problem. The bolt that holds the filter on was loose. I cant turn the bolt by hand but the filter flops around and fell off the extension tube without breaking that bolt loose.
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Old 01-26-2011, 10:36 PM
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Is the bolt Spacer there? Goes between the Filter & VBody.
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Old 01-26-2011, 10:53 PM
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Yes its there and was tight. Filter still flopped around tho. Is that right? The only thing holding it up and in place at all I guess is the pan. Filter element is black but doesn't look plugged up really. Still going to check that o-ring but i think I may let the trans drip all night and then tomorrow i'll wipe things off so i dont get drips all over me and then ill pull that tube and check it out. The fluid wasn't clear but it was still red. Some evidence of water in the pan at the very bottom, but not much. Didn't look like it was being pumped through the system. Some grey gritty stuff in the very bottom, some metal shaving it feels like but just some not much, i think its pretty normal especially for an old transmission. No chunks tho and the fluid smells fine.
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