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MG TD TF 1500 - Intermittent wiper
|I have been trying to solve my intermittent windscreen wiper problem. I dismantled the motor and found it to be clean and with reasonably fresh oil/grease, when it is running it runs smoothly. However, quite frequently it just fails to start, although acording to the ammeter it is still drawing current. It seems that when the motor stops in certain positions it can't get going again. I have taken the top of the motor, cleaned the commutator, checked the condition of tbe brushes (good), checked the tension of the brush springs (good). Any ideas what might be preventing the motor running sometimes? Thanks, Matt..|
|Matt, I'm guessing that your observation of the current being drawn indicates that the motor is running. I suspect that your shaft that is connected to the wiper blades is sticking and is not pushed in far enough to connect with the motor mechanism. I'm not sure to phrase this. On the back of the wiper motor is the chrome handle that you use to park the wipers. Make certain that it moves freely in an axial mode. Push it in if you have to. Good luck. Bud|
|Bud Krueger (TD10855)|
|No, the motor is only running sometimes. When it does run it operates the wipers correctly. When it does not run it still draws current, but fails to spin. Matt..|
|matt, have you ruleed out mechanical binding? old grease or worn gears etc.? if so...if the 60 year old insulation breaks down in an armature or filed coil between the windings...not to ground, wouldn't that effectively give you fewer windings and therefore less horse power? regards, tom|
|I have a question for Bud. In your response you stated "the chrome handle that you use to park the wipers." What do you mean by "park"? I assume that means you manually turn the chrome handle to move the wipers out of your face when not in use? If that is the case then is it normal for the chrome handle not to mount back into the on off chrome handle? I would assume you could adjust your wipers in the off position, so that they would close properly on the on/off switch. I hope this doesn's sound stupid, maybe I am thinking of something else?|
|Not sure if I'm answering your question, but --- Yes, you can flip the on/off handle to the off position when the wipers are at the end of their sweep. Then you just put the pin into the handle. You can also turn the switch off at some other time and use the handle to park the wipers. Bud|
|Bud Krueger (TD10855)|
|Thanks for the suggestions, Bud and Tom. I've now stripped the motor down and removed the gears. These were covered in grease, but it had not dried, suggesting either the motor is newer than 60 years, or has been rebuilt in the recent past. I have checked all the windings and they all appear to be OK, each pair of armature windings has a resistance of 4 ohms and the field windings have a resistance of 17 ohms (these are wired in series).|
I have now tried running the motor without the gears attached (ie very little work to do), and I have the same problem, in certain positions the motor fails to spin, although it is still drawing current. I just have to move it on a little by hand and off it goes. I don't think it can be a poor connection, because of that were the case, there would be no current draw.
Any other ideas?
|I think you have some open windings in the rotor, or bad contact with some commutator segments. Check the resistance at the place where it stalls|
Sounds like a rebuild to me.
|Matt, another fix type of operation is to take a small, hard tool and scrape clean the area between the armature segments. Bud|
|Bud Krueger (TD10855)|
|I've checked the resistance at the point of stall - same as elsewhere (4 ohms). Cleaned the commutator and scaped out between the segments. Still fails to run! I've found that a sharp tap on the casing sets it going, so there must be some mechanical resistance preventing rotation. I'm going to clean off all the oil and grease and try a light machine oil on the bearing. I'll let you know if this works. Matt|
|Are the brushes long enough to firmly ride on the armature? Make sure they're free to move in the brush holders and have good connection to the wiring. |
Brush springs are still strong?
|Cleaning out the grooves in the armature worked for me....|
|Check that the brushes meet squarely with the commutator. They are only held in position by a rather flimsy brass and phenolic brush holder. When I rebuild these things, I often find that the brush holder is bent. Also, be sure that the brushes are properly arched and not dirty on the ends that meet the commutator. Any dirt can be cleaned off the brush tips with some fine wet-or-dry sandpaper. If each pair of commutator segments measure 4 ohms, try also measuring THROUGH the brushes. I think you'll find some high resistance one one or more of the segment pairs. Also inspect the shunt windings on the armature. This should be a cotton covered winding over each pole. This winding is designed to increase the current flow and provide a little more power. Often, a stalled motor will cause these to burn. If the shunt winding is broken, it can cause the motor to stall in one position.|
|I have a YA that has the same installation as the TF (or vice versa as the Y is older..). I had some intermittent trouble with it that I traced to the back bearing.|
Under load the whole armature was drawn against the housing, jamming it solid. It drew lots of current when jammed and ran like (noisy) clockwork on the bench with out load.
So even if it is not the same motor, please check the rear bearing for too much play.
|Willem vd Veer|
|Reactivating to get easy access to the good specs that are in it. Bud|
|I wonder if Matt found the problem and if the shunt winding was indeed at fault?|
|J E Carroll|
|My reverse engineering says that the second winding is for inductive 'kick' suppression. The motor should run fine without it ( but the inductive kick will soon damage the windings).|
My notes say you should get 4.8 ohms segment to segment of the commutator. Field coils should 8.3 - 8.6 ohms each depending on the ohmmeter used.
|Thanks for that Bob|
|J E Carroll|
|You don't say which motor you have. |
I have a CR (mgtf) wiper and had a similar problem.
The rotor has self aligning bearings which can be adjusted by means of a thrust screw on the end bearing. My motor also locked up for no apparent reason. I traced my start-stop problem to the setting on the thrust screw at the end of the rotor spindle. I found that an incorrect setting would cause a slight mis-alignment of the gears at the other end of the motor when it stopped thereby locking it up. A sharp tap would start it off. It took me an age to get the thrust screw set up correctly so the gears didn't mis-align when you stopped the motor. Hope that helps.
|A R Jones|
This thread was discussed between 14/08/2011 and 14/01/2013
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