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TH400 Tranny Help/Opinion

Melbatoast

Melbatoast

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Fort Collins, CO
So something is not working correctly in my transmission. I'm not sure what triggered it, when I parked it (after some wheeling) it worked fine... then wouldn't move the next morning. Park is the only gear that works, all other gears act like neutral (in every transfer case position). The linkages are working. I dropped the tranny pan, hoping that maybe somehow the pickup tube from the tranny filter might have come loose. It was still attached. I noticed some metal shavings in my pan (pictured). So what do you think I should do: A) button it back up with new tranny filter and fluid to see if maybe it'll work; B) Drop the tranny and put a new front pump on it; C) Drop the tranny and have it rebuilt; D) Any other recommendation you have for me.
This truck is a ex-military CUCV with 100,000 miles on it so I don't know the last time, if ever, the tranny was rebuilt. But the tranny has has never given me any trouble for the last 25,000 miles I've driven it. Anything look usual to you in the pics? Thanks for your help fellas... I need it.

P1010918.JPG

P1010920.JPG
 
Before you pulled the pan, did you check to see if you were simply just low on fluid? :dunno:
 
Yeah the fluid level was good, Shoulda put that in my post. It was two quarts low a few days before it stopped working and I filled it back up to spec before driving it again.
 
are those metal bits steel or aluminum...if steel take it apart. Are they clumped together or are they as big as they seem in the pic?
Some aluminum small bits or aluminum sand were common from some casting flash, but that should only be present if the pan has never been off.
Take off the bolt in the lower right corner of your pic, then see if you can move that shift valve in and out of the valve body smoothly.
 
Before you drop it out, ir may be worth it to drop the valve body and clean it really well. Even the slightest burr on one of the valves can make it stick in the bore.

Could do a shift kit while you're at it, since you'll want a new gasket anyway.
 
The metal bits in the pan are aluminum shavings, not chunks or anything. Really didn't look TOO significant, seems like every time I pull the pan to change the filter I find a few. But they could indicate an ongoing problem.
I tried disconnecting the linkage and the shift valve bolt and moving the shift valve manually. Couldn't really do it by hand. Though it seems to shift fine in the cab. Just when it's idling the engine doesn't lower rpm or sound like it's taking a load when I shift outta park.
I put it all back together with a new filter and filled it, no changes. Taking the valve body off isn't a bad idea. Shoulda done it when I had the pan off, but I'd rather drop the pan again than drop the tranny. It's gonna suck doing a tranny swap in my driveway when it starts snowing and getting cold again :doah: .
 
those little sand particle sized bits should only be present on older (T400//T350) trans, and should only be found on a first removal of the pan. At that time it should have been cleaned out. Those little sand sized particles were common to the era, and were casting flash particles. If any are "bits" or shavings, you have some problems going on....That manual valve in the valve body should move fairly easy, maybe a slight hangup a couple times in the stroke, but it should be moveable by hand all through the stroke...if not you may have dirt/particles in the valve body....Make SURE that you know the material....it can tell you where to look for problems in your parts.
Does the trans sound any different (like a pump whine has developed)
 
This probably won't be it, but it will save you headache if it is.

Make sure the linkage for the manual valve is adjusted correctly. The back of that valve should be just about flush with the end of its bore in the valve body when the detent is in the drive position.

You mentioned it was kind of stuck...there's a chance that the little clip that adjusts the location of the valve in relation to the rooster comb just got stretched/compressed and now it's not putting that valve in the right place.
 
If the linkage is connected, and you have full fluid, and you have no forward or reverse then you have either a pump failure or turbine spline failure in the converter in all likelihood. No stuck valve in the valve body can render a no forward or reverse condition in this trans. It sounds like this unit will need to be removed for some forensics.
 
Do you have a picture of all the sludge in the pan? From the looks of that corner, we are only seeing part of the sludge, and its starting to seem like quite a bit, meaning, you may have burned some some clutches up. The aluminum shavings are odd. I would expect them to be steel chunks, or larger aluminum chunks, or smaller particles, not aluminum shavings. Is your governor bore all scored and wore out? You can check that by removing the 4 bolts on the cover at the passenger side rear of the trans. What year is that trans, is it original to the truck?

A great source of info for that trans is the ron sessions book, tells you everything you would need to know to diagnose and/or rebuild it.
 
folkenheath said:
Do you have a picture of all the sludge in the pan? From the looks of that corner, we are only seeing part of the sludge, and its starting to seem like quite a bit, meaning, you may have burned some some clutches up. The aluminum shavings are odd. I would expect them to be steel chunks, or larger aluminum chunks, or smaller particles, not aluminum shavings. Is your governor bore all scored and wore out? You can check that by removing the 4 bolts on the cover at the passenger side rear of the trans. What year is that trans, is it original to the truck?

A great source of info for that trans is the ron sessions book, tells you everything you would need to know to diagnose and/or rebuild it.[/quote]

Great points Heath...

I have not been able to find one of these books either...unless you want to pay $75+ for it, I haven't been able to find one.
Click to expand...
 
76zimmer said:
Great points Heath...

I have not been able to find one of these books either...unless you want to pay $75+ for it, I haven't been able to find one.
Click to expand...

Holy crap, you are right, I bought one brand new just over 2 years ago for $30. I just looked, and now amazon has them listed used for $175, I better lock mine up! They must of stopped printing it, who knows, that is weird. It's just a paperback book.
 
I wonder if one of those metal bits got lodged in the pressure regulator valve or the screen in the passage leading to it might be clogged with them??..the valve body would need to come off to check both--I've seen tranny lose a check ball in the valve body or blow a valve body gasket and have no drive or reverse too....loose valve body bolts can cause troubles too by letting pressure escape instead of applying a clutch...
 
diesel4me said:
I wonder if one of those metal bits got lodged in the pressure regulator valve or the screen in the passage leading to it might be clogged with them??..the valve body would need to come off to check both
Click to expand...

Isn't the pressure regulator valve in the pump? If I am not mistaken you can get to that by removing the internal snap ring by removing the pan, and it's on the bottom of the pump in the front. The snap ring would be in the opening I circled in the picture below. However, I think you have worse problems than that. Although it can't hurt to check it to make sure it's clean and free to move.

case-PR.jpg
 
Seems pretty strange for it to work fine when parked,then "nothing" the next time he went to use it.to me..especially if it wasn't making noises or slipping,etc before!..

My neighbor had a Buick that did just that one morning--checked the fluid,full,clean,and the pan had been dropped and the filter changed a few months before,so I ruled out the usual suspects....I put it in "low" and heard a "thump" and it felt like it tried to engauge,so I kept doing it--after a few tries it did nothing,not even thump again....I decided to leave it in low and gave it a good rev,and it slammed into gear and lurched forward,after that it drove fine for about a week--then reverse wouldn't work!..if you left it in reverse and waited,sometimes as long as 15 minutes or more,it would suddenly go in and back up fine!..

He ended up driving it like that for months,then once he had the cash saved up to get it looked at by a tranny shop, they told him it probably had bad lip seals on the clutch pistons..or possibly the case was cracked internally where the "maize" of valve body passages were cast and letting pressure escape or pass into another passageway ,said it wasn't an uncommon thing to happen after high mileage..

He decided to sell it to a friend rather than fix it--he had a TH400 to toss in it--he took the old one apart and found valve body bolts loose and the gaskets had a peice blown out,a spring under a servo was broken,and the screen in the pressure regulator passage was almost completly clogged with varnish--said the clutch packs had suffered some as a result,but were still good enough to make it work OK....he rebuilt it and said it worked fine again after that..
 
I don't know how you found my original post gotblazers. I looked for it about 30 minutes before giving up and starting another thread. I actually just now started working on it. It has been so dang cold outside and school has been forcing me procrastinate on my truck.
So I broke down and found a reputable tranny shop in town who offered to tow it there for free. Turns out I need a new transmission case. I'm gonna go there in the morning to confirm. But when I got under there yesterday I noticed I'm missing one of the bolts that connects the transfercase (and transmission, I'm not sure the correct nomenclature) bracket to the crossmember. I guess this has been allowing the metal dowel (again probably wrong nomenclature) that helps line up the engine to the transmission to woller out the transmission case. Making everything a little cocked-eyed and causing premature wear on my front pump, torque converter, and flexplate, among other components I'm sure. The shop, Best Western in Fort Colins, CO, said they could probably find a donor tranny for the rebuild for $200-$300. Total will be around $1200 driving it out the door.
I'm not usually the type to go to a mechanic but I just sold my other vehicle (jeep) to finance fixing my beloved melba toast. So I had a little extra dough and am having a hard time finding time to do a tranny swap/rebuild with school.
Thanks for all the input, this board has SO many knowledgeable and helpful people :bow: .
 
Brought down by loose bolts! Damn the luck. It never fails to amaze me what i find loose or hanging on by a thread when i crawl under a truck.

Well, glad you got it figured out and its getting fixed. Don't worry about having it done. Just because you can do something yourself doesn't always mean in makes sense to at the time... I'm starting to feel this way about my next clutch job
 
Melbatoast;2871035[B said:
]I don't know how you found my original post gotblazers.[/B] I looked for it about 30 minutes before giving up and starting another thread. I actually just now started working on it. It has been so dang cold outside and school has been forcing me procrastinate on my truck.
So I broke down and found a reputable tranny shop in town who offered to tow it there for free. Turns out I need a new transmission case. I'm gonna go there in the morning to confirm. But when I got under there yesterday I noticed I'm missing one of the bolts that connects the transfercase (and transmission, I'm not sure the correct nomenclature) bracket to the crossmember. I guess this has been allowing the metal dowel (again probably wrong nomenclature) that helps line up the engine to the transmission to woller out the transmission case. Making everything a little cocked-eyed and causing premature wear on my front pump, torque converter, and flexplate, among other components I'm sure. The shop, Best Western in Fort Colins, CO, said they could probably find a donor tranny for the rebuild for $200-$300. Total will be around $1200 driving it out the door.
I'm not usually the type to go to a mechanic but I just sold my other vehicle (jeep) to finance fixing my beloved melba toast. So I had a little extra dough and am having a hard time finding time to do a tranny swap/rebuild with school.
Thanks for all the input, this board has SO many knowledgeable and helpful people :bow: .
Click to expand...

I recalled you posting this a long time ago so
1.I clicked on your avatar to go to your profile
2.i hit the tab that says statistics
3.I clicked threads started by you

I dont know about tranny rebuilds but that will save you 30 minutes next time :) .
 
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