Author Topic: TH400 case connector for kickdown wire  (Read 2500 times)

Offline Henry

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TH400 case connector for kickdown wire
« on: October 13, 2018, 11:29:01 AM »
Hi:
My truck is a 76 C-20 2wd with TH400 trans and 350 engine.

A rat chewed through the trans kickdown wire right next to the trans case connector. When I pulled the wire boot off the case connector for repair, I noticed that the case connector has two spade blades and one of them has been cut off. So only one spade is used to connect to my orange colored single wire that goes to the kickdown switch at the acc pedal. My overhaul manual for the trans shows that the connector should only be one spade and my wiring diagram shows that a single orange wire should be connected at the case connector. So can anyone explain what this two-spade connector is for that is in my trans? Should I be able to replace it with a single spade case connector that I see for sale on the internet?

Henry

Offline VileZambonie

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Re: TH400 case connector for kickdown wire
« Reply #1 on: October 13, 2018, 11:36:47 AM »
Google TH400 Switch pitch and enjoy endless reading.
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline Henry

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Re: TH400 case connector for kickdown wire
« Reply #2 on: October 16, 2018, 01:23:43 PM »
Hi Vile:
Thanks for the lead...actually all the info on the switch pitch (variable pitch) TH400 is very interesting. I dont think I have a SP TH400 in my truck though, because the SPs were originally made for CBOPs (Cadillac, Buick, Olds, Pontiac cars) for a few years in the mid-60s and I believe a TH400 for the CBOPs had a different bellhousing pattern to their engines from the Chevy engine. I do not have an adapter plate between my TH400 and 350 engine, so in my mind that indicates I do not have a SP. Furthermore, I have a ID plate on the pass side of the trans that has "78" for the bottom left stamping which indicates that it is a 1978 manufactured trans. So I do believe it came from a 78 model Chevy of some sort. I looked at the 77, 78, 79 truck wiring diagrams and do not see two wires coming out of the trans connector (only single wire) so I do not think it was a truck trans originally. Possibly it came from a large car. Wikipedia has a good write up on the TH400 (TURBO HYDRAMATIC) and they say that the second wire from the TH400 elect connector is for a trans signal to retard spark timing...so maybe this is why it is clipped off since my 76 has no such feature. Anyway, I have repaired my kickdown wire and reconnected it and will just leave the sleeping dog alone. Next time I have the trans pan off I will take a look and see where that second lead on the trans elec conn goes inside the trans.

BTW, does anyone know what the code of "CM" indicates on the TH400 trans ID plate?

Regards,
Henry 

Offline Henry

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Re: TH400 case connector for kickdown wire
« Reply #3 on: October 17, 2018, 02:38:54 PM »
Hi All:
I found a good website on the net that has a comprehensive listing of the transmission codes for GM products: http://www.teufert.net/trans/tranny.htm

According to this website the 1978 CM code on my TH400 trans means:
C=Chevrolet
M=series 20 and 30 motor home chassis

So the TH400 trans I had installed in my 76 truck actually came from a 1978 motorhome.

Regards,
Henry

Offline VileZambonie

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Re: TH400 case connector for kickdown wire
« Reply #4 on: October 17, 2018, 03:09:40 PM »
Makes sense. TCS and SPC are both ancient technology that belongs in the history books anyway.
,                           ___ 
                         /  _ _ _\_
              ⌠ŻŻŻŻŻ'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10