I bought this car [87 iroc] a few months ago,its a 700r4 and who ever built the trans for it has it rigged where the converter will only lock up in 4th.It will lock up as soon as it goes into overdrive and will not unlock untill it down shifts to 3rd when braking for a stop or accelerating.Does anyone know how to correct this?I'm afraid to let my girlfriend drive it like this because you need to manually downshift it to 3rd when braking or it will make a pretty loud clunk noise.

 

Any tranny wizards here?

 

Have the computer controls been removed? I suspect so, which is why it is wired the way it is.

Assuming you don't have the computer working, your best bet would be to get a lock-up kit from Summit or Jegs. $75-125, if memory serves.

 

No the computer is there and working with no codes.It's a pretty stock l98 car.I hade an 86 a few years ago,had the trans rebuilt,and the shop did it that way on it too.But on the 86 the converter would unlock when you hit the brakes at least.I think you can just change something in the valve body to do this but I don't know what.

 

The computer is supposed to control the lock and unlock. It could be they unhooked the computer from the tranny and wired it directly--then changed the wiring in the tranny to only allow a 4th gear lock-up. I have a manual switch. When the switch is on, the tranny locks just like you are talking about--only in 4th gear, immediate unlock at downshift to 3rd. I have no clunking at all. It's in the on position 99 percent of the time--I really don't have a reason to have it not locked in 4th gear. The clunking makes me wonder if you don't have another problem. You need to trace the wires from the tranny and see where they go, and maybe check-out the internal wiring in the tranny if you want to change it back(if the wiring was modified to create the forced 4th gear lock-up)