Anybody have any info on replacing the brushes on a Ford positive engagement starter? I have the starter removed while replacing the engine, and thought I’d throw a set of brushes in there. I have had zero problems with this starter but figured it was time. It’s been on there since 1992 when I bought the truck, and I suspect it is original.

The factory manual talks about removing the through bolts and the end cap. I also removed the angled side cover over the pivoting pole shoe. However, when I tried removing the end cap, the main barrel also tries to separate from the drive end casting. The end cap only comes loose maybe an 1/8” and stops. I decided to stop, instead of turning a perfectly good starter into a paperweight.

Also, the manual talks about cutting then crimping and soldering the new brushes. The brushes I ordered have screw terminals, so are they even the correct ones?

 

All starter motors are extremely easy to rebuild. Just find a kit on Ebay for your year and model vehicle to obtain the brushes and springs. Make sure kit is for your particular engine. Once it’s apart spray out the carbon particles with electrical cleaner inside the casing and clean the armature with a very fine sand paper. No need to get carried away. You’re just lightly cleaning. That’s all there is involved in rebuilding a starter motor. Put, it back together. Once new brushes are installed. The starter will seem to be seized. It’s not, the brushes simply need worn in. A few revolutions of battery power will seat them.
The end caps are stopping because of magnetic force. You have to pull. And make sure all side casing screws/ bolts are removed. Don’t be intimidated. Take it apart. Pay attention to what goes where. Take pictures during disassemble.

 

It was a miserable job replacing the brushes. I do NOT recommend it, especially when you can get a quality Motorcraft reman for under $100. I had originally intended to take some pictures and show how to do it, but I have abandoned that approach. I have overhauled many motors, generators, etc. but have never met one so difficult. Replacement of the brushes didn't seem to be a prime consideration during the design phase.

I had previously mentioned the end plate (with the brushes) did not want to come loose. Turns out the brushes had worn into the commutator and left a ridge at the end. This was keeping the brushes locked in place. I had to resort to brute force and ignorance to get the plate free.

The brushes were not the typical carbon (or similar) you'd normally see. They were VERY hard and appeared to be bronze or some comparable alloy. I believe this starter was original (275k miles), and the brushes still had about 2/3 remaining. Unfortunately, they had worn down unevenly. And unlike the carbon dust you'd normally get everywhere from the brushes wearing, there was only a light copper sludge from wear on the commutator.

There are four brushes. two positive and (wait for it...) two negative. The negative brush leads had straight ring terminals on the end and were riveted to the case. The replacements had threaded terminals, but unfortunately were a flag style as seen in the previous picture. You drill out the rivets and insert screws to hold these flag terminals. The bad part was the flag terminals put the leads offset about 3/16" to the side. The brush holder was designed for the two leads to be directly in line with the holes in the case, and it couldn't be re-indexed. It may not seem like much, but having to joggle these negative leads put them very close to the positive brush leads.

The positive brush leads were downright miserable to replace. Originally they were spot welded to the heavy copper that formed the two field coils. This material was about .050" thick and maybe .300" wide, wrapped in a spiral. The free ends of the two coils were joined in the middle with a spotweld, also where the leads were attached. To replace these brushes, you were supposed to cut the leads flush at the spotweld. The new leads were a single piece with a small clip in the middle between the brushes. Somehow, you were supposed to crimp this undersized clip on the spotweld area, and then solder it in place. It was near impossible to get any sort of suitable pliers or crimpers into this tight area. In my overinflated opinion, you want a good mechanical connection BEFORE soldering. After several futile attempts, I ended up partially closing the clip first and then maneuvering it onto the edge of the spotweld area.

Once I got the clip more or less secured, that's when I discovered the copper had been been coated in insulating varnish. The clip had to come back off while I sanded away the varnish to expose bare metal. I had to use sandpaper wrapped around the tip of a screwdriver. I then tinned the area with solder, but all that copper makes a GREAT heat sink. The directions say to use a minimum 300W soldering gun. That ain't no pencil type, but one of those big pistol styles. I have one rated at 400W, but even that poor thing had a hard time heating all that copper.

After I reinstalled the pre-squeezed clip on the tinned copper, it was still a bear just to solder it. As careful as I was, I still managed to get some solder wicked into the flexible leads. AARGH! This of course makes the leads rigid and creates problems trying to route them into the correct locations with the brush holder.

This is when I discovered the length of the leads is very critical. The brush holder is plastic and has channels where the flexible leads are routed. An 1/8" too short and they will limit brush travel. An 1/8" too long and the extra material will bunch up around the corners and possibly touch where they shouldn't. (Think big bright sparks...) This was a very **** poor design.

Also, due to the hard material of the brushes, the commutator was heavily worn. You could not just slap new brushes in there (even if they went in easily) and call it good. I have a lathe and was able to clean up the commutator, but that's not an option for most of you.

To summarize Proust: Get a quality reman and save yourself the headache. I've ordered a Motorcraft replacement and it should be here tomorrow. Masochist that I am, I found a set of brushes with the correct straight terminals on the ground brush leads, and will try again. If this attempt works out better, I will keep it as a spare.