Stuffin' guts

CopperNick

Master Mechanic
Feb 20, 2018
456
63
Canada
So among the other items that I managed to salvage from the neighbour before the contractor turned the garage into a horror story I was able to score a THM400 from the old lean-to. It did not appear in the best of external condition but the ATF Oil was a deep red and right up with no smell to it so paid off the scrapper that had come to carry it off and drug it home to my shop.

One thing that makes this unit slightly unique is that it is the BOP or corporate version of the 400. This means it is meant to fit Pontiacs, Buicks and Oldsmobubbles but not Chebbies. Based on being able to score a useable Chev version 400 case in my travels, is it possible to remove the guts from the BOP 400 and transfer them to the Chevvie case??? I get that it would be a labor intensive exercise and probably a pain in the butt to execute but 400's of any ilk are not exactly plentiful on the ground around here and having one on hand to either use or swap for ??? could prove useful.

Thoughts and ideas???


Nick
 

lilbowtie

Comic Book Super Hero
Jan 7, 2006
3,320
113
Canton Mi
Very easy trans to work on and modify - Book " How to work with and modify the T 400 " is a great book.
 

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CopperNick

Master Mechanic
Thread starter
Feb 20, 2018
456
63
Canada
First, thanks for the replies. Good to know that the guts are universal and it is the cases that are specific. To answer one point, all I have at this point is the Corporate or BOP version of the 400, and an idea. Finding an empty Chev specific case that has not been damaged or raced to death would be the next step.

Yeah, yeah, overdrive blah blah. Understand that I am Not knocking 5 or 6 or more gears to make things smoother and faster. What is driving the agenda is space and architecture. The greater the number of gears in the case, the larger the case has to be accommodate all that stuff and the greater the need for computers and monitors to keep track of it all.

So the TH-400 is a woolly mammoth from the stone age of transmissions, so what? It was either a stone or a bone or a stick that Ugh the caveman first considered for use as a tool. That is about as basic as you can get and the 400 is about on the same par as all of them. What they also share in common is their durability and longevity. Consider, we still use rocks and sticks as tools today; bones not so much mostly because people are largely very attached to them and hate to give them up. The 400 is both durable and purpose specific, very strong. It all fits most transmission tunnels from the G-Body era without much by way of Sheetmetal modification, i.e. architecture.

The other argument also relates to space and architecture. As I just mentioned, the TH-400 takes up room but that room in the tunnel is pretty much already there. I have seen the elephants of the street, the 4L65's and the 4L85's and, like their earlier brethren the 4L60's and 80's, they take up space! Under a truck or van it is not an issue, but try stuffing a 4L85 under the floor of a G-Body and the first thing to go is a good chunk of the tunnel, all to get enough room to shoe horn the brute into position. Sure its a good thing but it is also muy mas $$$. And how many shade tree or lean to or one car shiplap garage occupants are set up to wrangle that large a swap? (For those of you sandie-bagging this thread that can and have done just this type of project while rolling around on a dirt garage floor or dodging the wife's Christmas decorations, major respect to you; my years of freezing my *ss off in a snow bank to crawl under a car to fix/replace some bit of mechanical kit that has gone the way of the edsel are long over and done with)

So me swapping the guts from one case to another is just me engaging in a learning process to keep my mind busy and my body from reminding me about its pains and hurts and damage. In the end I profit two ways; the exercise teaches me something I want to know and gives me a useable item at the end. Win-win.


Nick
 
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500/600

Royal Smart Person
Supporting Member
Nov 17, 2018
1,074
113
West Virginia
First, with enough low speed torque and reasonable gears, an overdrive isn’t a requirement.

Second, any engine that can’t use reasonable gears probably doesn’t require a TH400.

Third, BOP TH400s almost always come with extra clutches because those engines actually produced low speed torque in heavier cars.

Fourth, a BOP bell housing is stronger than the Chevy. I have seen many cracked and broken Chevy TH400 bell housings. The top two bolts on a BOP are brutally reinforced. Use an adapter instead of swapping cases.

Last, no overdrive made, including a 4L80, can be built to handle what a TH400 will for the same cost.
 

CopperNick

Master Mechanic
Thread starter
Feb 20, 2018
456
63
Canada
Had not given any consideration to an adaptor plate as BOP's aren't an area where I have lots of expertise or knowledge. That aside the 400 would have to come down for evaluation in any event for two reasons. First, being that it sat in a dirt floor lean to, semi-exposed to the elements for as many as several decades, even though the fluid appears clean and full, that is no indicator of what awaits inside. Second, if nothing else is bad, it still needs a front pump body and input shaft because both those items are toast from exposure to water and salt and snow and rust. The splining on both of them is done. I do know this box came out of a full size Pontiac station wagon from probably the early 70's pre gas crunch so the weight it would have had to deal with would have been there all right.

As for the Chev 400 case being lighter and more prone to break, I would think breakage would be inevitable given the way these transmissions got leaned on both on the street and at the strip. You can break stone given the correct tools or sufficient time. That aside, the idea of the adaptor is a good one; it would be a kit that consists of the plate and maybe some kind of spacer to put between the crank flange and the ring gear. Only drawback there is that moving the ring gear takes it out of correct alignment with the starter bendix gear. Might be some kind of spacers for the converter bolts and the knob on the front face to re-establish the relationship between it and the crank.

As I noted above, having the opportunity to take the 400 apart and learn about its internals is a valuable situation to pursue. Stuffing its guts into the Chev case, despite the loss of structural strength, is still a viable notion to me simply because I am not planning to race this t-mission and having access to the lighter case with the heavier clutches and internals on the street would be useful even if only dealing with commuter stop and go traffic. The econo-box squirrels around here should have wanted posters put out on them just for the level of stupidity they possess.


Nick
 

500/600

Royal Smart Person
Supporting Member
Nov 17, 2018
1,074
113
West Virginia
If it happens to be a Switch Pitch trans then it isn’t an easy swap without knowledge and correct converter. I have 2 and they only came BOP. They aren’t ridiculously uncommon especially laying around in old sheds rotting away.

I wouldn’t be using a TH400 myself if I didn’t need one behind my 500. I’d use a TH350.
 
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