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End of last year I toasted the original 400 in my turbo truck, the converter in it was the wrong shaft length, it was junk yard pull. I didn't know what i was doing, still don't obviously...
Took it to a good transmission guy and had it rebuild and had him do the last few mods it needed like dual feeding the direct, drilling the necessary holes for more RPM, sprag upgrade, etc...Did about 200 miles on it last year with a stock converter and it worked well.
This winter i changed cams in the engine and put a 3400stall converter in that I ordered from one of the reputable recommended shops. Pulled forwards about 1/8th and used 1/8th washers to shim the rest since the engine has a 1/8" think conversion plate on it because its a buick th400. Transmission blows before i can tune the engine, 1/2 tank of gas about...
Fluid is nasty brown and has bits and flakes of clutch in it. It as still shifting and everything when i took it out but the reason i knew something went bad was because it started to whine like a supercharger like sound. It started off just lightly hearing it in when in 2nd gear and by the time I got home I could hear it in every gear except 3rd when at a low RPM cruise. It did not make the whine sound in park when revved up but it DID make it when in neutral when revved up. My transmission guy is taking it apart now.
The one thing i noticed when taking it out was about the converter to flexplate mating. The centering lug seemed to bottom out roughly 1/32" before contacting the shim washers. When i installed the thing new it has paint on it that i forgot to scotchbright off before sticking the engine back in. When I mated the converter to the flexplate, that paint made it really hard to pull the converter in by hand so i have to use the bolts to pull it in and did not see/notice this very small gap. This would essentially prevent the converter from flexing forwards towards the engine. But clutch flakes and this issue, I don't feel like they would be connected.
I don't run a kickdown switch, i have a transgo 1-2 kit and i just manually hold each gear or down shift too.
This is what I cant think of i did to it since it worked last year, did i **** up? I'll know more about exactly what went internally in a day or so. I'm pretty dumb when it comes to the transmission side hotrodding and I messed the spacing up last time.
But possibly a converter mismatch, a build or assembly error, or low fluid level.
So the converter was bottomed out in the centering lug before it made full contact with the face of the flexplate. It was 1/32" of a gap but that effectively prevented the flexplate from functioning as intended because the centering lug was pressed against the crank. So the bolts fastening the converter to the plate pulled the plate back to the converter by 1/32". It was little enough of a gap I couldn't tell because the paint on the new converter made it difficult to move the converter in and out of the centering hub. I assumed it was making contact on the faces of each but it was not, the centering lug bottomed out in the centering hub 1/32" before the mating faces of the plate and converter touched proper.
This would effectively prevent the converter from being able to push forward and flex the flexplate at all. To me this seems more and issue that would effect the engines thrust bearing more than the transmission but that's what I'm asking. If the converter not being able to push forwards at all would cause an issue with the transmission and not just adversely be effecting the crank thrust bearing.
Transmission guy seemed to lean towards me putting drag radials on it and not using the kick down switch and not down shifting by hand soon enough. The pump whine was because the filter was full of clutch flakes...
It ended up being the 2nd gear clutches. The whine was the filter getting clogged up with flakes of clutch. As to what caused it though the transmission guy couldn't really say. Both other clutch packs are perfect, both of those sets are the ones he replaced last year, the 2nd gear clutched were the Huges clutches I had in there from when I built it the first time before the pump went. They were red clutches from a kit rated for 600-800hp. Nothing was even burnt. You could see flakes of clutch probably a couple millimeters in size when I dumped the fluid out of the filter. The flex plate and converter issue were unrelated. I just need a washer about 1/16" thicker.
But all the hard parts are good. Has an upgraded sprag with the extra elements and the 4l80 drum, none of that had anything out of place. Could it just be a bad pack of clutches? Did going to a set of drag radials over stress it? I would get a smoke show going into 2nd last year on normal tires and it won't even chirp tires now and it has even more power without the tune even finished. He's going to drill the holes in the TB plate for shift firmness to the largest that trans-go recommends to see if that won't help. It was already on the larger size. He also found me a deep pan and lower oil pickup in his parts bin to throw on. He mentioned the possibility of the fluid being all forced to the back of the pan and into the tail shaft area on a really hard pull and said the larger pan would help with that. I know if I run under 1/4 tank of fuel that will happen with my gas tank and it has an EFI baffle and everything, still will do it.
Can anyone else think of a reason this happened outside of assembly error?
If we are talking a STOCK THM400 unit... Meaning no trans-brake or other significant hydraulic change... and was absolutely FULL of fluid...
90+ percent of the time I have opened a unit up with a burnt-up or wiped intermediate clutch assembly...
It was because who ever built the unit made one or more sealing errors during assembly.
They most likely thought to themselves: "I have built so many of these that I do not need to wet air check anything or double check my work".
Outside of that being the case...
From time to time I find after-market and/ or modified valve-body issues or center-support issues.
For the future; I would also highly recommend the use of an aluminum intermediate piston and 12 heavy-duty return springs (If not currently in use).
These are some photos from my shop... They are going into a book I am writing on the 3L80 and 4L80E.
Look at the aluminum piston that I use and the 12 release springs.
As far as the clutch plates go... Hughes Performance primarily use Alto Red-Eagle brand frictions and Kolene brand steels.
They are not terrible frictions in a THM400; However they are not better than the OEM Borg-Warner tan frictions either.
Really though... the builder probably nicked a seal. Sorry.
It is what it is. It has some modifications done. Dual fed direct, drilled back of the pump for constant oiling, tapped and inserted the set screw then drilled to help with converter thrust. Trans-go 1-2 kit. It has the aluminum piston. Nicked seal makes sense. He even said the stock 4l80e clutches were the best. That's what he put in the 1 and 3 last time. It's just the 2nd gear pack was fine at the time.
Last edited by LetsTurboSomething; May 2, 2020 at 11:02 PM.
Seen 2nd gear burn up because of a maladjusted or improperly installed shifter. Happened to my brothers th400 last season, our builder made us bring in his shifter so we could bench check it and sure as **** it was off, he's also seen many people install the shift arm and clips backwards on aftermarket shifters. Need to start with the shifter in low gear and make sure the cable comes in and out of the shift arm clean, then bump to second, and finally 3rd checking that it lines up with each gear detent as it should. His was wayyyy off, in every gear. Our builder said sometimes what happens is you'll adjust the cable and it then wont quite reach park so people will adjust for park, and then not have the other gears adjusted properly, but usually it will end up in an "over park" situation so you're good. The joys of making aftermarket stuff work together.
I have it back in and working now. Honestly after refilling it post install, I think it was my fault and I had a low fluid level. When i reinstalled it, it took 11 quarts before it was full while hot and running. When I swapped converters i poured about 2 quarts into the new 9" converter and shoved it on. I made a stupid mistake of not stopping to check it a couple times before i got further into the tune. It was pig rich and wouldn't even make boost until i got into the VE table twice then it hit hard and smoked the clutch in a single pull. I took real care this time and checked it 4-5 times and had to add nearly two more full quarts through those checks until it topped off at 11qt.
He could have fucked it up but I think i would have toasted it at the track last year if that was the case and not on the very first time out this year after changing converters. This one was on me I'm pretty sure. He only charged me $300 and threw in a deep pan and the pump pickup tube and stuff and said that would help keep the filter submerged if it was an issue with fluid moving around and into the tail shaft area or anything.
I've went out and abused it after reinstalling it and its solid now.
Still can't hurt to check shifter adjustment. My brothers 400 took a year to smoke 2nd gear, was driving home from the drag strip after he had done about 200 miles on the street the previous two days and finally let up the ghost 5 miles from home. The low fluid is very much a possibility as well. Also did you or your builder verify your dip stick, pretty much every aftermarket one me or my builder have come across is wrong, need to mark it at or just above the pan rail, my TH350 was a quart or so low before we double checked and corrected the stick.
Still can't hurt to check shifter adjustment. My brothers 400 took a year to smoke 2nd gear, was driving home from the drag strip after he had done about 200 miles on the street the previous two days and finally let up the ghost 5 miles from home. The low fluid is very much a possibility as well. Also did you or your builder verify your dip stick, pretty much every aftermarket one me or my builder have come across is wrong, need to mark it at or just above the pan rail, my TH350 was a quart or so low before we double checked and corrected the stick.
I did check the shift linkage when i put it back in. I made the dipstick as well and its still accurate.
Seen 2nd gear burn up because of a maladjusted or improperly installed shifter. Happened to my brothers th400 last season, our builder made us bring in his shifter so we could bench check it and sure as **** it was off, he's also seen many people install the shift arm and clips backwards on aftermarket shifters. Need to start with the shifter in low gear and make sure the cable comes in and out of the shift arm clean, then bump to second, and finally 3rd checking that it lines up with each gear detent as it should. His was wayyyy off, in every gear. Our builder said sometimes what happens is you'll adjust the cable and it then wont quite reach park so people will adjust for park, and then not have the other gears adjusted properly, but usually it will end up in an "over park" situation so you're good. The joys of making aftermarket stuff work together.
And doing this with 2 people is the way to do it. I had to crawl up under the car and back out about 10 times to adjust the shift cable on my ratchet pro and it sucked lol
Roach a Th400 in 200 miles, what did i screw up? 
