Rebuilding TH400, what parts do I need?

gbak

gbak

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Mar 24, 2008
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I think I have to rebuild the TH400 as there are more and more grey "mud" in the bottom of the pan after each year. I also got a feeling that it slips more and more. I also have leakage from the front of the TH400.

My motor is quite strong and I race once or twice each year, but just for fun.

Dont know anything about the converter except that it's painted dark green and it starts to grip around 2100 rpm, dont think it's a stock converter.

What parts should I replace?

Is any brand better/stronger then other?
 
Last time I worked on a auto trans was on my Z28, wasn't much real transmission work as I pulled the pan and replaced the filter and fluid but anyways.... I had a lot of grey gunk in the pan and I was very worried about the trans.... changed fluid and filter and put another 40000 miles on the car and this trans...... grey gunk is not necessarily a sign the trans is going bad... since yours is leaking and slippng, have a look in the tech section, there are a few rebuild threads:

http://vettemod.com/forum/showthread.php?t=1801
 
I have seen TimAT's exellent thread about rebuilding a TH400, that's why I now have been inspired to get the job done!

My Suzuki 75 hp outboard is rebuilt (bored/honed/new piston/rings new sealings ....) Must have something to do when it's cold and winter here in Sweden!
 
You'll want to get a seal and gasket kit, new faced clutch plates, front pump bushing, vacuum modulator, and a filter kit just for starters. The ATSG manual is really handy too.
Past that, it's just how "new" you want it. A new set of steel plates for all the clutch packs. But if you're going that far, I'd look at getting the faced and steel clutches for a 4L80- the fit is the same, but they are not as thick as the 400 parts so you can get more of them in- more surface area=more holding power.
It sounds like your convertor is working OK, and if the fluid looks decent the only reason to replace it is if the pump hub has a problem (wear) or you just feel the need to replace it.
And don't forget the shift kit-- Trans-Go or Gil Younger's "Mr. Transmission".
 
The Trans-Go kit is the one I use- They work really well .

Of the 3 rebuild kits, the only one that advertises Kolene Steels and Alto clutches is the Hughes kit. Without knowing what the others have in them for sure that one would be the pick. They advertise having bushings in them too, but 90% of the rebuilds the only bushing that ever needs changed is the front pump, so you m,ay end up with some that are not needed.

On the page that opened for me, they also list a 34 element sprag- that's the HD one. The only thing I've run into with that (and I don't recall if it was on a TH350 or a TH 400), is the intermediate drum that sprag fits on was changed about 1968, so the drum AND the sprag have to be replaced to use the HD one.

And I'd still look around for a 4L80 kit-
 
When I did my TH400 about 6 years ago, I used the B&M master overhaul kit, then bought a 69 TH400 drum and went the 36? element sprag I don't recall the # of the elements but it's the HP type. Why I did this I don't know other then to rebuild my own tranny for a change! I used the FORD ATF and a 2000 Stall B&M whole-shot TC. I only have 325 hp at most and really didn't need to do all the mods I did. I set it up according to the street/stripe settings. I can hold it in gear but the new pump spring increases the PSI and when idling the trans clunks which I don't like and don't feel like pulling the trans back out to replace those parts again. Otherwise it works great and normal driving you don't even know it's not a stock setup. I don't think I would use the FORD ATF again either, not a problem so far but the GM ATF would have worked fine. It wasn't bad to rebuild with the books and videos out on them and I'm not a automatic trans rebuilder. I did buy the plastic sleeves for the seals though, I made up a wire tool and tried the feeler gauge deal but didn't like the way they were going in. The sleeves work great but were expensive about $80 I think for plastic.
 
I know lots of guys that have used the Type "F" Ford ATF and had decent results. When I went to the GM Training center (a REALLY long time ago) I had a long discussion with the instructor about that. Turns out the Type F juice lacks some of the lubrication that GM specs call for. Not that it won't work, but the life may be cut short by lack of correct lube. If he was on the level or just pushing GM's stuff, I don't know. I do suspect that the 350/400 transmissions probably won't care as much as the later OD trannys will.
 
Looking at the list that Bulkparts has, you might be better off going thru them. One stop shopping and it looks like they have it all. Might save you on some shipping cost.
 
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