Howto: Starter Motor rebuild and replace brushes

[NoSlo]

You might be able to fix your own starter. You might even want to take it apart, maintain it, and check the condition so it doesn't leave you stranded!

- Remove starter from vehicle
- Clean starter externally, if it's nasty, you can pressure wash it at a u-spray car wash.

With a 13mm socket, remove the brush wiring from the external terminal of the solenoid:



With an 8mm wrench, remove the two long bolts that hold the motor together. Also break loose the 6mm black brush bolts a bit now:


You can now separate the motor body from the gearbox:


With T25 Torx head socket, remove the two bolts that hold the solenoid onto the front of the starter:


By tilting up while pulling the solenoid, you can remove it from the starter housing:


There's a black rubber doohickey that holds the solenoid fork in place:


Pull that out, and then the gearbox and fork can be removed:


Now, by pushing the shaft of the motor, we will remove the armature and brushes together as a unit. The permanent magnets of the housing will resist your pushing:


With the armature and brush assembly removed, we now remove the bolts that hold the brush assembly to the end plate:


It's free:


You can now simply pull the brush assembly off the armature. A little wiggling may help:


Now if you've actually done all these steps, you've noticed that your starter motor is nowhere near this clean - it's packed full of grease, gunk, and brush dust. Clean all the metal parts in gas or diesel (or some other parts cleaner that costs more and is less effective).

The copper commutator that the brushes contact will likely be pitted and scored if your motor is non-functioning. As the brushes lose contact, they start to arc. You can dip the commutator end in an inch of gas to get the cleaning started, and then a toothbrush under hot sink water with some soap can clean the rest off. Use a knife to clean the slots between the copper contacts.

You can further clean the copper commutator contact surfaces with fine grit sandpaper. You do not need to remove much material or turn until the pits are gone, just de-burr the surface so there is clean copper showing. Above is what the "after" looks like.

This motor failed because the brushes wore out and were no longer making good contact. The wires keep them from extending further. In an emergency, you might be able to flip some brushes 180 degrees so the backside is facing in, or cut away some of the wiring from the brush to get a few more starts out of it:


So we spend $21 on some new parts (5A1203 brush set):


Compare new to worn-out:


The new brush came with a round plastic insert holding the brushes in, but the center hole in this insert is too small to slip over the armature shaft, so we can't simply slide the new brushes off the insert onto the commutator. Instead, we discard the insert and push the brushes in one at a time and work them onto the commutator:


Now we start reassembling things, lining up the parts the way they were originally:


The shaft of the solenoid may also be contaminated. To clean it, I submerged the plunger end of the solenoid into an inch of gasoline, and compressed the plunger by pushing the solenoid down a few times. The cleaner works its way up into the piston and ejects oily contamination. You can follow by spraying electrical contact cleaner around the piston gap, working it in, and dumping it out. Let dry:


Test the solenoid coil with a multimeter, measuring the impedance between the small bolt on the end of the solenoid and the metal body of the solenoid. It measured about 0.8 ohms on mine. If it measures as an open circuit, the solenoid coil may have had a rare failure.

We can also test the solenoid switch contacts. Test between the big terminals. The back of the plunger should close a circuit between these two posts when it is pushed in. This passes battery power to the motor only when the solenoid has fully engaged the drive pinion via the fork lever. (.3 ohms on my multimeter = contacts are closed):

 

[NoSlo]

Now the gearbox can also use some cleaning. Remove the cover, and take out the little gears before they fall out and you lose them. There is also a ball bearing in the bushing end between the three gears - also good to remove yourself instead of it falling out and getting lost. You can pull out the whole gearbox and get in there with a brush and some gas and give it a good cleaning if needed, then lightly re-grease:


You can reinstall the armature and brushes the same way they were removed, but remember to reach through and hold both ends of the shaft. The magnets of the housing will want to pull it in.

The new brushes came with a non-molded rubber grommet, I decided to seal around that hole:


Somebody will probably have some contrary advice, but I decided to also seal up the ends of the housing with a bead of sealant, to keep water and oil out of the starter (especially the cascade of oil when changing the oil filter):


Put everything back together the way it came apart, applying new grease to the shaft ends and bushings, to the gear teeth, and the fork pivot and solenoid end.

The new brushes had a slightly different terminal shape, be sure this is on tight and doesn't touch the housing or any other contact point. Then you're done!

EDIT: This picture shows the solenoid installed 180 degrees from the correct position. The small bolt has to be on the "top" of the starter, otherwise the big battery wire wont clear.

 

[SHOdded]

Wow, nice writeup

 

[sperold]

This is why we keep coming back.

I had no idea you could buy the brush set up in that handy one piece configuration, nor did I know there was a gear reduction assembly in the starter.

Thanks for all this information, I would never have tried to rebuild one myself - but I would now!

 

[shaffer]

My starter just happens to be out, ill add the brushes to the to-get list. That was a great post.

 

[98SF19]

*WOW* Well done sir!
This is just what I was looking for a while back. I took a spare starter apart as described and after THOROUGH cleaning/oiling/greasing, it was still dead - no reaction at all to power input. I suspect the brushes are not making sufficient contact (didn't know that they wore down to the extent that the side-by-side comparison with new assembly revealed!) and/or the lubricant I used (INOX) affected the solenoid adversely. INOX is non-conductive.

This may get me to reopen the project - so to speak - as it seems a new brush assembly will be the key. I would imagine this write-up would benefit a multitude of DIYers across different makes and models as the fundamentals of operation are the same. I'll put a link in the Gen 3 section. THANKS AGAIN

 

[NoSlo]

And here we are again, brushes worn down. I'm sure they could make brushes that last 10 years like the original Motorcraft, but just don't. Same with remans including alternators, they just don't last like the $450 original.

 

[sperold]

Can this write-up be stickied, as I am pretty sure this is the best information available.

Could this short lifespan be due to a commutator issue rather than a poor brush material?

Thanks in Advance.

 

[itwonder]

Nice job. When rebuilding motors, I sometimes use dental floss to tie back brushes; just cut and pull it out once the brushes are started onto the commutator; may or may not help here. Keep in mind the solenoid contacts are another major wear point that can lead to a non-functioning starter.

To me, it's a cost trade-off between a new brush set plus new solenoid plus my labor vs. buying an all-new manufacture aftermarket starter (typically made in China). Probably worth it if you still have the original starter (not an AA or AZ rebuilt exchange).

I installed one of those Chinese made all-new starters in 2008. It gave good service until now; about 80K miles. It's near death (random slow cranking). Hopefully, NAPA will honor the LLT warranty on it.