Fixing a 12vdc brush motor that is a Rule 3700 gph pump

Thread Starter

sdowney717

Joined Jul 18, 2012
711
Pump leaked in bilgewater so it failed. I noticed 2 months later or so. Inside of pump not too bad, but the + wire was energized by a float switch and the positive brush lead disintegrated. I looked into getting a new brush but it's tough. Brush is 8.5mm by 9 mm by 20mm and lead comes out the side. I did find 8mm x 10mm side lead brushes 100 per pack for $26. 100pcs J432A Motor Carbon Brushes,Carbon Brushes Replacement Kits for Electric Vehicle DC Motor,8x10x20mm: Amazon.com: Industrial & Scientific
I decided to try to fix the old brush. I drilled hole right thru the side. Got some 16 gauge lamp cord and doubled it and soldered it into the brush.
Attached it to the positive wire. Brush spring is very strong, it will keep the brush in contact with commutator.
Question is how hot do brushes get when motor runs? Hot enough to melt solder?
This motor takes a 20 amp fuse

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I have to wrap a small paperclip wire around the connector as I used the tabs bent down to hold the brush lead, normally those 2 tabs fit into a socket hole and keep connection wire from pulling out the end plate.

I got silicone dielectric grease to lube the shaft seal and to help slide the pump wires thru its rubber seal grommet.

This is an expensive marine pump and actually is built good quality. It cracked years ago in shipping to me and the guy sent another, I fixed it and it worked for years till the fix failed, This fix I did a better job on the plastic motor housing, used Loctite marine epoxy to coat the motor housing.

Other negative original brush undamaged. Motor has a sealed ball bearing on impeller end and a bushing on the brush end, with permanent magnets.
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KeithWalker

Joined Jul 10, 2017
3,029
Over size carbon brushes are easy to file to the required sized (but messy!). I have done it a number of times for 12VDC 20A motors (electric flight). The brushes do get a bit hot but your fix will probable be alright.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
711
Here is the entire pump.
Outer case is PVC. The motor housing is different, a very hard plastic that does not yield and that is what severely cracked the first time, along with the pump top. I figure some guy at the post office dropped the box. Motor broke free inside the housing and broke 2 plastic parts.
The first time I used my solder gun to melt the cracked plastic together. This time I sanded it with 240 grit, then used Marine Epoxy. I tested it with water in a pot, and it does not appear to be leaking. The lower ball bearing support is a cheap pot metal, but it survived. I cleaned it and painted it and plan to use dielectric grease on various internal parts.

There are 2 shaft seals, the rubber faces the impellor. Dielectric grease seals the seals to the motor housing.
You wont find any info or parts for repairing Rule Pumps, meaning the insides of them.

No epoxy will stick to either plastic so I roughened every surface that was glued. The long bolt screws that hold motor together into the plastic housing, the attachment points had broke free, I used my solder gun to create furrows for the epoxy to hold onto to the plastic. Lining them up straight was the critical part to making this pump work again.

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Used the zinc diecast lower bearing housing to keep the bolts perpendicular and lined up
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Both of these were the damaged parts
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Thread Starter

sdowney717

Joined Jul 18, 2012
711
And this is what I found for dielectric silicone grease, 4 oz for $10, which is a good amount for a good price. That stuff is hard to find in larger containers. I figure this is what Rule used to lube the shaft seal. I was first thinking a lithium marine grease but switched to silicone grease when reading about its usefulness for repelling water. And it is a great high temp lube.
Amazon.com: Dielectric Silicone Grease - Waterproof and Non-Conductive Lubricant for Electrical and Automotive Applications - Easy Application 4oz Brush Top Can : Automotive

The grease I cleaned from the seal are was a translucent white, not a solid white, and it had stayed in place around the seals.

A big difference between an expensive Rule and a cheap Chinese bilge pump is the quality of the SS shaft, Rules do not crevice corrode the shafts. I had a cheap Chinese pump and it only lasted a year, the motor shaft rusted and it leaked in salty bilge water. Otherwise, the pump internals looked good quality. But if the shaft seal surfaces fail, the pump is dead and can't be fixed.
 
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Thread Starter

sdowney717

Joined Jul 18, 2012
711
Got it together and it works fine. I had to grind back the brush SS shaft end. The cap cover was depressed inward so also ground a spot on the inside there. It could be the motor housing is sitting up higher after fixing the mount points in the hard plastic housing. Only found that out when screwing the top cap back on, I heard a 'crunch', epoxy on cap cracked. That Loctite Marine Epoxy is very brittle. Ground down the crack and refilled. I also plan to put some fabric there with epoxy for more reinforcing. I forced motor to run to create a mark in the cracked cover to see where it needed to be ground for clearance.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
711
The silicone grease is real nice stuff. I lubed the 2 pump housing o-rings and filled in the 2 lower shaft seals. I also coated the repaired surface of the motor housing. From what I read, silicone grease repels water. Idea is the internals of the pump housing where water flows will stay cleaner. Bilges tend to be gunky sometimes. That dirty stuff floating in bilge water can stick and attract more dirt. It can build up on surfaces. The grease also made it easy to pull those 2 wires thru the rubber grommet. I first put the greased grommet into it's hole in the cap, then the wires get pulled thru the grommet wire holes.
 
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