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I’ve got an ’86 GMC ¾ 2 wheel drive truck. Runs great, love the truck. I’m on my 2nd TH400 trans. (160K miles), and I’m starting to see signs of needing a 3rd trans. (Slipping, morning sickness). Here’s the question: Has anybody swapped a TH400 for a 700R4 in something like this? What will I have to contend with? I know the 700 is longer so I have to move the trans rear cross member and shorten my drive shaft. What about shift linkage, Speedo drive, vacuum for shifting, overdrive engagement? Any advice what be greatly appreciated.
 

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I think everything else is the same, you will need to ad a Throttle position sensor to the pump to control the torque convertor. That is just a bolt on item. linkage, and speedo will fit. There is no vacuum on a 700R4. You will need to get the proper torque convertor as well.


Can't remember if the 400 used the same kick down cable or not either. On the 700 it is called the TV cable, the adjustment is easy, but critical in making them shift right.


Pretty easy swap, especially on a 2 wheel drive. If you get a Haynes 6.2/6.5 service manual they have all the wiring diagrams for the throttle sensor, and I think they have the TV cable setup also.
 

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HAVE YOU CHECKED YOUR VAC PUMP TO SEE THAT IT IS WORKING?A BAD PUMP WILL KILL A 400 TURBO KWIK!
 
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