ACME Threaded Rods
 

The problem:

The threaded rod and threaded block that moves the power seat on my Expedition has issues. There is a fair amount of play that is a concern. From what I understand, the threaded rod is an 'ACME" thread (trapezoidal cut). My thought is that I can get a thread repair kit and just drill the block and install the inserts. What I do not know is how these threads work, how the kits work and what the sizes are. From what i can tell, until I get it completely apart, the outer diameter is about a 1/3 of an inch, and the inner diameter is about 1/4 of an inch. I think the rod is threaded at 13 threads per inch, but can only find a reference on the web to 12 per inch. It sucks measuring through the little slot.

If it were a finer thread, i would say helicoil. But these look special and I need a really coarse thread at a relatively small diameter.

This is also not something I know a damn thing about. Any machinists, machinery or mechanical engineers out there?

Thanks in advance.

BigCajun might be able to help.

Hey, sorry, had a busy afternoon.
I'm not familiar with acme threads.
The threads I make are usually measured in inches, like 8"or 10", not fractions.:)
Are you sure it's not metric?
Sounds like it could be 8mm-1.00.

Thanks for the response.

i actually got it apart and got more detail. The end result is that a stupid little plastic piece fell apart. I will post some pictures. There are 2 pieces of steel, one in a U, one that fits inside the U. The threaded piece is the ones inside the U. The whole assembly is only 2 inches long. There is a small piece of plastic that keeps the metal pieces from hitting each other. Well, that was a stupid choice of materials. With the plastic gone, the metal parts are free to move a bit and bang into each other. Good news is that it is safe, there is no danger of the seat moving more than 1/8 inch. Bad news is I have to fabricate a new plastic part.

Again, thanks for the response.