My 89 has (had) the famous sagging manual mirror, and since I was in the door replacing window motor and door lock actuator, I decided to take a stab at replacing it or fixing it. I came across a couple here and there for sale, but I was sure I would end up with the same problem. I searched, but I didn't see anyone post a possible fix for this, and this worked for me so I thought I would share. After finding a picture of the control ****, I realized I was missing the spring that holds tension on the wires going to the ****. Here it is with a zip tie trying to act like a spacer:



I went to my local hardware store to find some springs that may fit and I came up with these (after 2 trips):


Lighter Spring
Depending on how stretched your cables are this light spring may be enough. It was close to working for mine, but I forced myself to suffer through taking it back apart to test both springs.


Heavy Spring
The heavy spring is much more difficult to install as you have to install the cables on the adjustment ****, then the plate that the **** sits in. Slide the spring on, followed but the cable guide piece. You must compress the spring with the cable guide ALL THE WAY together to get the thicker part of the cable to set in the guide. Once you get one of the cables set in the guide, it's much easier to get the others set in the guide. But you will be compressing these little pieces together with the tips of your fingers as there's not much to hold on to. This is much easier to do with the lighter spring, but it may not provide enough tension. Remember, these are borderline antique pieces you're working with, so be gentle if you decide to use tools to assemble this stuff. I did send it flying halfway across the garage and thought I was doomed.


Back of adjuster plate and cable guide

I also took the smallest heat shrink tubing I had, cut a tiny piece and melted it onto each cable end. This helped them bite into the waller'd out holds in the control **** a little better. You do not need to remove the mirror like I did, but I'm fixing up the guts and the weather strip on the door and thought I would be replacing it anyway. I won't lie and tell you it's like new again, but the mirror has zero sag to it. It's very tight, but adjustment isn't 100%. You may have to help adjust it with a light thumb press on the mirror, but it holds the position you put it in. Has not seen the road yet, but 3 or 4 Third Gen door slams and it's holding!

If your cables are still too stretched, it may be possible to pull some slack and trim the wire shorter before doing the above repair. That was going to be my next step if this didn't work. The only hang up I had was what to use for the new ferrules on the cable ends.

Final Product:

 

Nice work. A friends car has the same issue. I tell him about this post.