i got a 87 6.9 that shifts very hard and it broke a brand new spedo cable. just wondering if the previous owner may have put a shift kit in it or am i looking at some trans trouble in the near future? if it's trouble i'm planning on doing a manual swap with an over and under drive but i'm hopeing it will last a while so i can get some money together.

 

Remove the pan and see how much crud is at the bottom. Previous owner may not have ever serviced it.

 

i also noticed that it doesn't want to shift till it tacks out or i let off the throttle. even when it tacks out it holds for a second or two before it slams both second and third.

 

Check the modualtor and vacumn lines that run to it. Little or no vacumn can cause late shifting. If you pull the hose off the modualtor and fluid comes out, replace the modualtor.

 

If it's an e40d tranny the reason it does that is because it is out of overdrive mode. try replacing the dome light fuse don't ask me why but mine did the same thing and so did a buddy of mine and it was because the dome light fuse were blown prolly cuz it feeds a module for the tranny. If that don't work try disconnecting the batteries that worked for a third buddy of mine.

 

i think you have a C-6 and if you have little vacuum it could be the vacuum pump , hows your brake pedal is it hard ?