I'm a tinkerer, not and expert. I have a very old Hitachi cv2500 vacuum cleaner. I've managed to remove the carbon brushes which don't have identifying markings. I can determine the width and thickness but how do I get the length? I've checked various electrical spares suppliers who say they don't have these brushes any longer as they are obsolete. So, how do I guess the length? The brushes have just one wire attached. I'm sorry about the picture quality. I blame my wife.

If you can get brushes of the correct size to fit in the holders I would be looking at a length around 1.5 - 2.0 times what they are now in the worn state.

 

When installed there should still be some spring travel left so you can lift the brush away from the commutator. If they are a bit long you can just file the ends, don't worry too much about getting the curve on the end exact it will soon bed in once operating. 

 

Other than that, if the motor runs ok and doesn't spark excessively the job's a good un.

 

There are lots of motor repair place about that should be able to source brushes of the correct dimensions.

 

2 hours ago, Crossy said:

If you can get brushes of the correct size to fit in the holders I would be looking at a length around 1.5 - 2.0 times what they are now in the worn state.

 

When installed there should still be some spring travel left so you can lift the brush away from the commutator. If they are a bit long you can just file the ends, don't worry too much about getting the curve on the end exact it will soon bed in once operating. 

 

Other than that, if the motor runs ok and doesn't spark excessively the job's a good un.

 

There are lots of motor repair place about that should be able to source brushes of the correct dimensions.

 

Thanks. Just the advice I was looking for. 

Quote

I'm a tinkerer, not and expert. I have a very old Hitachi cv2500 vacuum cleaner. I've managed to remove the carbon brushes which don't have identifying markings. I can determine the width and thickness but how do I get the length? I've checked various electrical spares suppliers who say they don't have these brushes any longer as they are obsolete. So, how do I guess the length? The brushes have just one wire attached. I'm sorry about the picture quality. I blame my wife.

Take them to a decent mom and pop hardware store and show them. They may not have the "exact" size but will have something close. If they only have slightly larger one, buy a sheet of sand paper or try another store. They probably have bearing for the motor as well.

36 minutes ago, VocalNeal said:

Take them to a decent mom and pop hardware store and show them. They may not have the "exact" size but will have something close. If they only have slightly larger one, buy a sheet of sand paper or try another store. They probably have bearing for the motor as well.

Thanks for that.