Cooling fan problem

[mach2andy]

One of my cooling fans works fine the other does not. It turns slowly at best, sometimes not at all. I've taken it apart, and there is nothing obviously wrong with it. The brushes look OK and the little spring that tensions them is present. I've removed the armature, and cleaned up the commutator, but to no avail. There is no wear in the bearings. Any suggestions? Has anybody had one of these overhauled?
ATB
Andy

Addendum. I've found some pics on the internet that indicate that the surface of the brushes should be ridged, whereas mine are completely flat. So maybe my brushes are the issue?

[tim wood]

Took mine apart as I went through the cooling system. They are very simple. You’re correct the brushes are ridged. Mine were also flat and worn. Make sure that the insulation is present and the spring assembly that pulls the brushes inward.
If I recall you can buy an overhaul kit which includes new brushes, springs, and insulation.
Of course the armature must be free to spin without resistance.

[JerryL770]

You should measure the resistance of the stator coils. If you have an open circuit, then the motor is duff.

[mach2andy]

I changed the brushes [Lucas Part # 743171] on my fan motor and the fan was as recalcitrant as ever. I took the end casing off again and momentarily powered the motor and noticed that there was random sparking where the armature windings terminate at the commutator segments. I took the armature out yet again and found that 90% of these wires were loose. I re-soldered tham all, and hey presto the motor now works fine. So I guess I must have done the right thing? If anybody has to do this job, I found that an old fashioned soldering iron worked better than my mini gas powered soldering torch.
ATB
Andy

[johnetype]

Great that you fixed it. Just to add that the brushes are ridged to help them bed in. As they wear, they'll become flat. Likewise you can fit flat brushes from the get go and they'll work fine in my experience.