Turbo 400 Build - Mega Carnage to Better than New.

[HotRodPC]

The 84 C20 I bought for $100 had a bad Turbo 400 in it. So here we go with some pics of the carnage and the rebuild. This was actually almost a FREE rebuild, but because I upgraded 1 paticular part. I have $25 in this trans. I'll explain as the thread progresses !!! So chill and watch it come together. Feel free to post or ask questions if you have any as I put this together. The pics are not alot in detail, but if someone gets some education out of it. It'll be worth it.

This trans had 173,000 miles on it when it went. The people I bought the truck from, were moving from Arkansas to Dyess, AFB in Abiliene, TX. They were towing a tandem axle enclosed U haul trailer, and the bed was full too. They made it 15 miles of Dyess, AFB when it blew.

Here is a pic of the trans out of the turck. You can see the color of the spilled trans fluid from the dipstick tube hole in the case. No, that is not motor oil. Certain to be some ugly stuff found inside this one with the fluid looking like that. You can only imagine the smell.

 

[HotRodPC]

Here are some pics of the trans on the trans table already partially disassembled. Again, the color of the parts and fluid make it obvious there is likely something catasrophic gone wrong inside this transmission. From this point right here is where all the hell starts. The intermediate drum is hung up, stuck, or welded somehow and I am having big problems getting the transmission any further apart from this point. Making it even more evident there is carnage inside somewhere. At this point I am assuming its an intermediate sprag failure.

 

[HotRodPC]

FINALLY !!! I was able to pry, pull, wedge and manipulate the input shaft assembly including the forward and direct clutch drums out of the case. I was able to do this, by removing the retaining bolt for the center support under the vavle body. This is what it looks like now. Notice its getting darker, more crispy, and that part of the Center Support came out with it, which isn't supposed to. Also see the tan fiber parts wrapped around the springs. Domino affect, one thing went wrong and destroyed other parts as well.

PIC#1 This is the center support. Hard to see if you don't know what you are at looking at, but look at the top of the of the apply piston and you see the fiberous part chewed up and stuck in there.


PIC#2Now the center support is out of the case. The center support is what gives a T400 alot of its strength also used in 4L80-E too. T350 and 700r4, 4L60-E DO NOT use a center support.
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[HotRodPC]

For the purpose of knowing what a center support is supposed to look like, here in first photo you see one in its normal condition. You can tell the color of the parts, which part with the springs have been destoyed by comparing the pics. And the 1 above of the center support still in the case.


There some of the destroyed pieces, and you can see some of the case lugs. Amazingly, none were broke or damaged. Probably the case saver with the help of the center support not being able to move save it. If this were a Turbo 350, I feel certain the case would have been trash or had to use aftermarket case savers which I refuse to use.

This is how a center support is supposed to look. A bit differant from the above huh??? CARNAGE !!! :head3:

 

[HotRodPC]

Here are all the assemblies removed the from the transmission. Now we get to start taking assemblies apart and find out what really went wrong. Notice the band is no longer round. I did that trying the get the trans apart when it was stuck, so that carnage don't count. However, it needed replaced anyway because of heat in this transmission, even though there was plenty of meat on the band, it was very brillte and the fibers were flaking off, so no harm done.

 

[HotRodPC]

Now with the trans case gutted, its ready to go to the local trans shop and put in the washer to be cleaned. I will be getting my money's worth out of this one. It pays at times to help people out. I did a process service for this guy who was a friend of a friend and was divorcing his wife for emptying out their bank account and he did not have $50 to serve her yet. She was trying to leave state with his kids and time was of the essence to get her served. So I served her for him and said we'd work out the payment details later, just take care of your kids. So that was done. He happened to have been a manager at a trans shop a mile away and I remembered that. Guess how much it cost to get cleaned??? You guessed it !! $0.



Pic #2 is the center support without the parts that were destroyed. Notice after all this damage, and 173,000 miles the center bushing is like new. Somewhat common in a 400. The center support keeps everything inline and gives no room for flex to either one side or the other, no matter how much torque is applied.

 

[HotRodPC]

Here is more carnage, why the trans would not come apart as it should have, and the actual failure that caused the domino affect for other damaged parts.

Here is the major initial problem in Pic #1` BROKEN SPAG !!! This gets beat on going from 1st to 2nd gear. This is why it needs to be upgraded for street/strip applications. Most hotrods, hit 2nd gear pretty hard with alot of torque, higher rpm, and alot of force especially if I built the trans, and especially with a full manual valve body. This was no hotrod truck though. Just a stock 454 carrying a good load and 173,000 miles of wear.

In Pic #2 You can see the sprag gear is wedged and cocked on the drum, which turned the steels and clutches sidways and started the overheating and burning from this point right here due to broken sprag. If it was not for being a tight fit, this gear would have came off, but it couldn't. I never did get the gear off. I trashed the whole drum. It was toast.

In Pic #3, this is the damaged, burnt and welded together intermediate clutch pack including clutches, steels and pressure plate that make up the intermediate clutch pack. The apply piston for this clutch pack is actually part of the center support assembly.

 

[HotRodPC]

OK, the case is now as clean as its gonna get. This thing ran 4 time thru the washer, still looked like hell, so I had to buy some commerical dereaser that eats skin to get it this clean. I had to call it good enough and live with it as is. Now that you seen all the fun stuff, and all the carnage. Its time for the boring stuff. The rebuild. Stay Tuned !!!

 

[HotRodPC]

Being that transmisison was going to need several hard parts replaced, I figured it would be best to find a donor trans for the hard parts. I got on CL and hit up all the Turbo 400 sellers that were $100-$150 and asked them for the code on the side of the trans. One Guy came back with a CE 69. That told me the trans was out of a 69 Chevelle Big Block SS Car. I was wanting a 69 or older transmission because 69 and older have the smooth race direct drum for use of the much stonger dogbone wedge element sprag instead of the weaker roller style that failed in this 84 truck transmission. The guy was wanting $150 for it, but when I asked for the code, he emailed me back with the code and said he needs it out of his way, he'd take $100. Guess he didn't know yet, I was buying it. So I got out there to look at it, knowing its a passenger car trans. I looked at the output shaft for threads, wo me saying a word, he says, I know, thats why I am selling it, it was for my rockcrawler build but it doesn't have a threaded shaft for the yoke, thats why I am selling it and everyone needs threaded shaft for trucks, so if you can use it, I'll throw in the Torque Converter too and take $50 to get it out my way. I never asked the guy to go down on the price, he was just desperate to get rid of it. He told me it worked fine, that it came from a buddy of his old car that was converted to a 700r4. It had been rebuilt before, I was just hoping it had the good sprag in it still and hadn't been swaped out in the recent rebuild. Many trans techs know the good stuff, and they will keep the good stuff for themselves or performance builds and rebuild yours with the inferior newer much more common type. But for the price regardless, I was buying it for sure and did. Cha Ching !!! Another CL Steal.

 

[HotRodPC]

Now the disassembly of the donor trans starts. Obviously it had been in sitting outside in wet grass for some time for the bottom of the pan to look the way it does. But it had a rag poked in the dipstick hole, and I was hoping that kept the majority of the water out of it. Pulled the pan, and did find some water in it. Not much but it had water in it, and I knew it was from sitting and the water had not been run through the trans. Looked very nice and clean inside. Pulled the valve body, nothing in there but pretty nice colored clean fluid. Awesome !!!

 

[HotRodPC]

Pic #1 Time to pull the front pump. Notice my homemade tools. I have used these forever and never ever had to use a pair of slide hammers yet. These made with a scrap piece of all thread I picked up at work, some wide shouldered jamb nuts, and I forget where I got those knobs, but you can also use more nuts and big washers which do the same thing, then use a pry bar off the bell housing.

Pic #2 Ahhhhhhhh, Looking very nice inside. Very Clean !!! Lovin It !!!

Pic #3 Very Clean. Obviously a little moisture or condesation did get in the trans by the looks of this drum. The rust part wiped right off like dust. No Harm whatsoever.

 

[HotRodPC]

Pic #1 And this one come apart just like it was supposed to. Simply held the input shaft and pulled the assembly out in one unit. Still looking nice and clean. Notice the Band is still in the case and its original location.
Pic #2 Showing a little sign of some wear finally. So yes, its a used trans, but still impecable condition. You can see darkness on the steel here. But its also possible that was left from the previous rebuild too. The discoloration is harmless in most cases as long as its not glazed and shiney, which sandpaper, or replacing the steel fixes that issue.
Pic #3 And moment I been waiting for. Hoping the direct drum is the smooth race type I bought this transmssion for. This one sure looks a bit differant than the other one. The sprag gear is pefect and nice sharp edges also very clean !!!

 

[HotRodPC]

Does this donor trans have the sprag drum I want that will allow updgrade to the 34 Element sprag for this transmission or not. We are one snap ring away from finding out.
Simple as removing the snap ring off the drum, pull the retainer off that the snap rings holds in place, and we will know.
WOO FRIGGIN HOO !!! Yippee !!! $100-$150 drum out of a $50 Trans. Lovin It !!! And its in perfect condition !!!

 

[HotRodPC]

So now its time for a little pause in the build and a short lesson in the Intermediate Sprag. Here is a pic of all 3 differant Intermediate Sprags to choose from for the THM400 in Pic #1. Notice the drum on the Left is notched to make way for the roller sprag. The roller sprag is used from 1970 and up applications. Its not a bad design, still works great and does have some strength. But, it is not near as strong as the drum on the right with the smooth race that accepts the 16 element dogbone sprag, aka wedge sprag. And naturally the 34 element sprag is even stronger yet. Why is it important to have this part beefed up? Because the sprag is overunning in 1st gear, or free wheeling for a better term. Then the second the trans hits 2nd gear, that sprag stops instantly and grabs the drum and starts spinning the direct clutch drum. Imagine how much force is put on that sprag when hauling a heavy load, or hitting 2nd gear at high rpm. And even more force if you have added a shift kit, and trans fluid pressure is raised for a firm instant shift. Picture something spinning at 3000-5000rpm and have to stop instantly with the wieght of a vehicle behind the force and then carry on with the weight of the drum and cluctches that outweight the sprag probably 10X. Sprags take alot of abuse. So its best if you can upgrade them if you expect to using high performance applications, or towing more weight than what a normal truck would be towing. I think the pictures show the obvious differance. So my upgade in this transmisison from from the roller sprag to the 16 element dogbone sprag and drum from the donor trans. Then, since the 34 element sprag fits the 16 element drum, I bought the 34 element sprag off of eBay for $25 which usually in itself is about a $70 part at trans shops.

The one on the left of Pic #1 is what was originally in my transmission and was destroyed. This is what its supposed to look like unharmed. Mine was far from this. So the drum on the left has a notched race for the roller sprag type. Then the drum on the right is a smoothe race for either of the 16 or the 34 element dogbone sprags. If I have not mentioned already, even the 16 element is stronger than the roller type sprag, so if you ever come across a 16 element sprag to use and don't have a 34 element, go for the 16 element over the roller type.

Pic #2, Here are both the 16 and 34 element sprags side by side. Even the 16 element is stronger than the above roller sprag. But the 34 is even much stronger. I would not have a problem running at least 600hp and slamming into 2nd gear with that 34 element sprag which is what I installed in my transmission.

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[HotRodPC]

While on the subject, of sprags and upgrades. I have found and robbed 2 pics for explanation purposes. First will be the spiral spring upgrade on the Intermediate Sprag of the Direct Drum. This spiral snap ring is sure not to come off and is much better at holding the sprag gear on the sprag to the drum. You can see the standard C snap ring above in previous pics. The differance is obvious. I advise using this snap ring even on a standard trans build with the roller sprag. It is possible that this trans failure of the broken sprag, is that this C snap ring popped off and that is what caused the sprag to break. If this spiral snap ring was used, that would not have happened. Just so happens, that this spiral snap ring is stock OEM equipment for a 4L80-E. So, where do you get one?? Call up the dealer or trans shop and tell them you need a snap ring for the intermediate sprag on a 4L80-E trans and this is what you get. They are about $13 at any GM dearlership. It doesn't do a bit of good to updrade to a 34 element sprag if this snap rings pops off, so best to be sure and insure it doesn't.