Stuffin' guts

CopperNick

Master Mechanic
Thread starter
Feb 20, 2018
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Canada
All of which merely highlights my lack of knowledge about the peculiarities of BOP style 400's. I have heard of switch pitch but thought they appeared a lot further back in t-mission history, like the early to mid 60's and had long been discontinued as being too complex and persnickety.

As for the substitute bellhousing that, if memory serves, bolts to the pump body to case bolts, again not a bad idea. For me it would be the consequences of attempting to cut off the old bell section and botching the cut that would make me think twice about essaying the exercise.

For the sake of the knowledge itself, what makes moving the switch-pitch version of the BOP internals into a Chev version case more complicated than usual?


Nick
 

lilbowtie

Comic Book Super Hero
Jan 7, 2006
3,320
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Canton Mi
The switch pitch was made from 65 - 67. You need to identify each of the transmissions by the code tags riveted to the right side of the trans case. You can swap the guts into a chevy case, as long as it's an older case, like mid 70s or older. Newer cases don't have the passages cast in them. I run an Ultra Bell on mine not hard to do. I HIGHLY recommend the book I mentioned earlier by Ron Sessions - I'm not a trans guy but have built 5 400's (2 transbrake) and they are all still functioning.
 
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500/600

Royal Smart Person
Supporting Member
Nov 17, 2018
1,074
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West Virginia
The switch pitch was made from 65 - 67. You need to identify each of the transmissions by the code tags riveted to the right side of the trans case. You can swap the guts into a chevy case, as long as it's an older case, like mid 70s or older. Newer cases don't have the passages cast in them. I run an Ultra Bell on mine not hard to do. I HIGHLY recommend the book I mentioned earlier by Ron Sessions - I'm not a trans guy but have built 5 400's (2 transbrake) and they are all still functioning.
You are probably more of a trans guy than half the people who think they are a trans guy.
 
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CopperNick

Master Mechanic
Thread starter
Feb 20, 2018
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Canada
Appreciate the recommendation on tech text to read. Have to see if the local speed shop has it on order or if I have to deal with Chapters/Indigo on line.

As for the pedigree of the box that I have, any id tag that it may have been blessed with during production has long since disappeared. There is a small boss with a screw in it and the stump of a tag hanging off that but for id that is about as far as it goes. It is not a super duty case because there is no "K" casted into its body.

I would say tentatively that it came from the early 70's, say 70 to 73-75 because the engine that it had been mated to was likely a 400 or possibly a 455 Pontiac. This because my neighbor had a genuine jones for Pontiacs and ran them as his race motors in defiance of the SBC majority. At the time he gave up his garage he had around 1/2 dozen of them sitting on the floor. His kid got them and after that they were gone along with his pride and joy 70 GTO 4 speed that he had owned since new. I have never seen it on the street since and doubt it is any condition to be on the street as the kid never was all that mechanically inclined and Jack had no patience to try and educate him. (A lot of that going on back then)

Either way the donor car was, if I recall correctly, a station wagon. Jack ran 3-4 speeds on his late models so that would be the reason that the auto-stick got exiled to the lean to. The local track was short, maybe 3/8ths of a mile and auto-sticks had no real time to wind up before having to unwind for the corners; hence the manual with an in and out clutch. It was actually too bad in one sense since the donor car was actually in pretty good shape, just nothing that a young guy would drive in that era. Now it would be fitted with a set of 20's and murdered out to the limit.

So if I am understanding all that has been mentioned here, what I would be looking for is a Chev 400 case such as what came with a big block Chev like a Monte or Chevelle from the years just before the gas crunch, 70-73, and the bureaucraps stuck their slimy fingers into the situation and screwed a good thing up for all.

As it turns out I may have a source for that...…………………………..



Nick
 

500/600

Royal Smart Person
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Nov 17, 2018
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West Virginia
Then there was the TH375 which came in mid-70s Pontiacs. TH400 case, less clutches, smaller TH350 output shaft..............
 
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lilbowtie

Comic Book Super Hero
Jan 7, 2006
3,320
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Canton Mi
I was just looking on line and the price of that book is outrageous, amazon is selling used ones. I think I paid 14.95 back in the day. Here are the 400 codes so you know what your looking @

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CopperNick

Master Mechanic
Thread starter
Feb 20, 2018
456
63
Canada
Greatly appreciate the leg work and research, Lilbowtie. Had not gotten as far as trying to deal with Amazon. NOT a big fan of them due to their continuous demands to join their community when you log on to them for any reason. I have a supplier out in California who deals in used specialty texts; got all my vehicle/year specific OEM Factory service manuals from them. Will probably ask them first if they have this text. This week is a bust due to call in warnings already being posted so may be next week before I can move ahead on this. Also the 700R4 for the G-!0 has priority for buttoning up and the Van is waiting for it.

I did take the liberty of saving your pictures to an outside folder as they offer just too much information to try and read on a skinny screen. Printing them off to hard copy for ease of referral is on the agenda. Hope this is okay with you.

Thanks again for all the input.


Nick
 

CopperNick

Master Mechanic
Thread starter
Feb 20, 2018
456
63
Canada
Back again. Took a quick look at that BOP transmission but could not see enough of it to spot a tag. What it does not have is its as-issued torque converter. It was mentioned above that this era of t-mission could have come from the factory with what was termed a switch-pitch converter, even though I am reasonably certain that this model is post 70 and the sw-pi's seem to have been more prevalent before then.

So I guess the question of the moment becomes, does the replacement converter have to be specific, i.e. a switch pitch version, or can I pull a converter off the shelf for a Chev, like a TH350 for example, and plug it into place? Of course there would be the obvious problem of compatibility in terms of spline count and shaft diameter to complicate matters as I don't think they are so generic that you could merely plug and play one converter into another transmission unless the transmission converter came from the same class, eg 350 into 350 and similar.

Thoughts??
 

64nailhead

Goat Herder
Supporting Member
Dec 1, 2014
1,759
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Upstate NY
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.
Nick, what are the numbers on the tag and case? If it’s a switch pitch as mentioned above, then I’d reconsider treating it like TH400 Chebby.

TH400’s with aChevy pattern are cheap in mild above stock form with fresh rebuilds and a warranty. A genuine, functional THM400 from BOP is worth some $ to the right person .
 
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