If it is cavitating because of that filter, not being a screen type filter, it will cause all of your problems. So it can be fixed in the vehicle. I wouldn’t pull the trans out until I put a Allison type filter, make sure there’s two of the right size O-rings on the pipe. Those cloth type filters do not work! And make sure the vent tube is clear.
You don't have to pay you, and you don't have to mark up parts for yourself. Get a few books, read through them, Grab a camera and get to it.
I screwed up the first one I did for a friend when I was 16, but after that they mostly all worked....
Here in Georgia, I just picked up my 400 that a great local shop rebuilt for me. Alto clutches, it already had a Transgo kit, 34 element sprag and nothing else too exotic for $1,200. $2,200 seems crazy for a regular 400.
@1pickup, don't be afraid to tackle the rebuild yourself. Get one of the books that Gimpy pictured (I personally like the Cliff Ruggles one) and look it over. I think you will find it pretty straight forward. If you just do a "refresh" build with just seals, gaskets, and clutches it is even easier, less costly, and requires fewer DIY tools.
I'm not sure if this makes a difference or if someone has already mentioned it. There are two different filters for a T400. An early one and a late one. I would be sure I had the right one for the year of the trans. Gene.
If it went into gear once without slippage, it probably isn't a pump problem. Either the pump is being starved for fluid, or you have a massive internal leak. You could put a pressure gage on the test port, but your description already points to a pressure problem. Sounds like it either has to come out and be repaired or replaced.
I am thinking something similar. In park, convertor hasn't filled up yet after leak down. Trans will engage a bit until convertor fills up but now there isn't enough fluid left in pump and cavitation occurs.
Just as an additional tip, when/if you pull the pan, get 4 of those large donut magnets at Home Depot and epoxy them in the corners of the pan. That will grab most of any metallic debris before it gets to the filter.
With a 30 year old automatic transmission you are just wasting time and money trying to fix it. Seals dry out and crack, clutches fall apart and loose the lining. Old fluid turns to mud. Just bite the bullet and rebuild it. I was there and am glad I went to the trouble to pull it and rebuild it.
Not sure what happened, but there is a ton of crap in the pan now. There was nothing there when I changed the filter, and it's got about 10 miles on it since then. I see the fluid has some metallic look to it, and the sludge looks like mud. It's coming out for a rebuild.
But it does require some specialty tools that might make the cost of doing one rebuild not all that affordable. And without the proper clamp tool to hang the trans tailshaft down it's a little more difficult to do it on a bench or the floor.
I use a short piece of pipe and some baling wire to hold the gear assembly when installing it, I put the case on a milk crate. The clutch spring compressor and bushing drivers are the only special tools I have, and they pay for themselves real quick.
I have made a spring compressor for the clutch drum spring with threaded rod, scrap steel and mig welder. A 25 gallon metal barrel with the round opening flattened on one side, will grab most transmission cases where the back of the pan bolts up. Makes a perfect height transmission stand to load all your rebuilt innards into trans case with tail shaft down..The thin metal tool snap on provided on their toolboxes to remove the drawers,worked perfectly with Vaseline to aid installing servo and drum lip seals. Threaded rod with a driver to make a slide hammer to remove the front pump. Cut the heads off the correct size and thread bolts, to align the front pump back into case on reassembly.If you take the front pump apart to clean or inspect gears,instead of buying a realignment band,with the pump halves loose carefully install pump upside down in empty trans case, tighten pump bolts,the halves are now aligned, remove and reinstall.
This? If so, it is $53.99, with free shipping. https://www.ebay.com/itm/2050611978...28&google_free_listing_action=view_item&gQT=1
And this is cheap enough to not bother a DIY: https://www.ebay.com/itm/356702408038?_skw=th400+clutch+spring+compressor&itmmeta=01JS2WY0SKHWDRM5YSHTY8RK03&hash=item530d1ecd66:g:JyIAAeSwVNBn4LIs&itmprp=enc:AQAKAAABAFkggFvd1GGDu0w3yXCmi1fSCd7Jl2Mm9gJUFhrgNYHP8LDpmiDqFbjVtYBolxHhnxA2lRfI+Gq9uw0nJp6maRMQT6yirvYSYb+cjmJoULyP96BfWLU7USsR4--x51WSyYhOYp18UCH/TjAhfvYcbtlm4gHutkHIa8JmhZ0+TtSWS3HfS/3BwgJBlnGOZDBl9XTafJ1I0BV83RrERtq3RCGmv2bdc2YafRXtFsOOoAXUkdpitq/qR2lL22P4iMCYwEcKN0iQrYLJpRZucYV0YBCcrJTXy1sm0v2YZho45VdcnKxfVjwnwSeMN0BLSFHgcK71PRupo6hFGIji2mO/wb8=|tkp:Bk9SR4qN-NzIZQ $24.00/free shipping. No press, no problem. $33.99/free shipping. https://www.ebay.com/itm/1557079692...lp:2332490&itmmeta=01JS2WY6C1MA5DXS0WZBQ3Y8ZT
I got one of these a long time ago, seems to do the job...but they are discontinued, and used ones cost money. Neat to see all the cheap new ones available these days.
The bench clamp is cheap enough that I bought a second one, to cut up and widen to hold a TH425. That has the lugs in the case, but they are out of range of a regular clamp.
It may still be out there, under a different brand: https://www.autotoolworld.com/Gearw...ePANypvWUpo-Hh9Axa6XNcIQiZiAhSF-2Ce2_N67avbbP
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