I have a 1989 D100 with a 3.9L engine and a non-overdrive 3 speed automatic transmission with a locking torque converter. How can I check if my converter is locking up properly? I think I should be able to detect a small change in rpm when this happens but I don't have a tach in the truck and I can't tell by feel.

 

Have a scanner that can read engine RPM? It's only about a 200 RPM drop at 50mph.....

 

Are you sure it has a locking converter? I didn't think any of the 3 speed autos had one.

 

Thanks, I'll see what I can do about scrounging up a tach

 

According to my manual in this year the tranny is either an A727 or a A998, both have locking converters.

 

I've seen alot of 3.9 engines with a regular 904/998 3 speed trans, and many without lockup/ all the way into early 2000s vans. also possible trans has been replaced, being that any trans that bolts to a smallblock will bolt to a 3.9 who knows what may have been swapped in over the years/////