TH400 VSS swap to cable spedo.

[Mike1973]

1984 GMC 3/4 ton 2WD TH400 454 c.i.

I'm getting ready to rebuild a TH400.  I'm not rebuilding the 400 that is currently in my truck (which has a cable spedo.)  I ran across a TH400 HD and I'm planning on rebuilding it (I'm not sure what's so HD about it it still has the weak link intermediate sprag as opposed to the 34 element sprag.)  So...at the end of the day I would like to swap the VSS spedo for a cable that is currently in the truck.  Is this possible and what do I need to buy?  Any other tips?

Thanks,

Mike

[Irish_Alley]

not 100% sure but i would assume if the tail shafts were the same length then you can just swap the tail shaft housings

[Mike1973]

Do I need a spedo gear I'm asuming?  Anything else aside from the tail shaft?

[Irish_Alley]

grab your old gear cause it related to your axles

[Mike1973]

Let me ask this; With this swap I use a different trans. case of course is this as easy as removing the metal VSS "wheel" off the output shaft and replacing it with my original plastic cable spedo off my old trans?

[Irish_Alley]

Don't think it possible. Doubt the shafts are the same diameter

[jaredts]

I certainly could be wrong, but I believe this is an easy conversion.  I believe you just remove the reluctor wheel and place your drive gear on the output shaft.  Then just use your driven gear and housing in place of the sensor.  That is all that was required to change my 700R4 to cable driven, and since a quick search doesn't show th400 drive gears specific to different versions of th400's I believe this is also true for you.

[Mike1973]

OK thanks guys; I'm going to get into it in a couple days.  The advice was much appreciated and helpful.

[Engineer]

I certainly could be wrong, but I believe this is an easy conversion.  I believe you just remove the reluctor wheel and place your drive gear on the output shaft.  Then just use your driven gear and housing in place of the sensor.  That is all that was required to change my 700R4 to cable driven, and since a quick search doesn't show th400 drive gears specific to different versions of th400's I believe this is also true for you.

I "think" this is correct. I say "think" because I have not personally done it. I do know that every TH400 I have encountered has the governor gear machined onto the output. On the 2wds the speedo gear slips on behind that.

On the TH400 the VSS should be in the left rear of the case not in the tail housing.

What year is your TH400? I thought the late models had an intermediate one way clutch and not a sprag. When GM introduced the 4L80E they changed back to an intermediate sprag and made it either a 32, or 34 element.....34 is aftermarket don't remember what the GM piece is.

A direct clutch drum from a 4L80E will work in your TH400 so you can get a 6 disc direct clutch with the high load sprag if you need/want them.