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Failing starter solenoid?

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NutmegCT

NutmegCT

Great Pumpkin
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Seems that the more I fix things, the more I discover more things that need fixing.

I'm sure that never happens to anyone else.

1953 MGTD. Battery fully charged at 13.1 volts.

I've got ignition disconnected while I do compression tests; plugs removed, engine is easy to turn.

This morning I tested all four cylinders. No problems with starter at all. Battery had gone from 13.1 volts to 12.6 volts during the test.

But this afternoon, after recharging the battery back to 13.1, I tried the tests again. First cylinder, starter spun nice and strong, no problems. But second cylnder, I hit the starter button, starter immediately spins nice and strong for about one second - but then immediately slows and turns very slowly.

Release starter button, starter stops turning. Battery has gone from 13.1 to 12.8 volts.

Repeat - same thing.

Is this a failing solenoid? failing starter? failing battery?

I even tried this with a second battery in parallel. Same result.

Thanks.
Tom M.
 
Check the voltage at the starter when the problem is happening. If it is dropping way down, you got a bad connection or the solenoid has gone south.
But if the starter is turning slow with at least 10 volts applied, the problem is inside the starter. Might just need new bushings, or brushes, so I'd have a peek inside.
 
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Keep in mind that the battery will give you a false high reading immediately after charging. It may show 13.1V right after you disconnect the charger. However, if you let it rest or put a light draw on it, after a few minutes it should drop down to about 12.5V if the battery is healthy.

A test you can carry out in addition to those recommended by Randal is to bridge the large cable terminals on the solenoid with an old screwdriver or pair of pliers. There will be sparks when you bridge the threaded posts so don't let that spook you. If the starter runs at speed when the solenoid is jumpered, it suggests a problem with the contacts in the solenoid. If the starter is slow when the solenoid is bridged it could be bad connections or a bad/tired starter.
 
Thanks gentlemen.

Question: if battery has been on charger all night, and charger shows "fully charged" in the morning at 13.10 volts ... and I crank the starter four times (ignition off) for four seconds each time - should the battery then be down to 12.5? Seems like a fast drop to me.

And a related question: should the starter slow and stop when voltage drops to 12.5?

Tom M.
 
12.6 is 'nominal' for a fully charged battery. So, 12.5 is probably OK, given that your voltmeter might not be right on the money (and I don't know what temps are running in Conn, been a bit of a cold snap here). That drop is exactly what Doug was talking about, and I think I mentioned before as "surface charge".

No, the starter should run full speed on 12.5. Generally they are rated around 9 volts anyway, to account for the drop in the cables, etc in cold weather.
 
Tom, If it spun up fine before it is not likely bushes -

1. check the ground - battery and engine - and then the terminal connections. Sounds very much like something is partly loose (the most annoying kind)

2. Check with another known good battery. Eliminate the simple things first.

I think it is highly unlikely the starter is the problem - unless it just needs a good clean and lube (dry lube!)
 
Another possibility is bad ignition timing. If the timing is too far advanced for some reason, the engine can fight the starter.

I've had several starter failures where the starter would only turn very slowly and often draw way too much current. Most impressive one was where one of the brush leads got out of place and was dragging on the armature. I thought the car was on fire, but it was just the smoke from the battery cable.
 
What do you think of the possibility that the brushes are very worn, and/or no longer able to slide in their holders?

Before I head off to work, I'm going to try the starter again. If it spins fast, then slows down and stops, I'm going to tap the starter head with a hammer to see if that improves the situation. Hammer tap might loosen up sticking brushes - at least as a test.

TM
 
As Randall said, high compression and advanced timing can make it hard for the starter to turn over, however, I believe you said this happened to you during compression tests while the plugs were out. Is that correct?

I cannot tell you what the symptoms are for worn, or dirty brushes. I have had one starter where the brush springs broke and therefore all the brushes did not make contact. However, I don't remember what happened except it was an obvious failure and would not turn the engine over. That is not consistent with your description of the starter slowing down.

If you don't want to try my test to jumper the solenoid with a screwdriver, try jumper cables. Use the cable from the battery hot terminal directly to the starter. If the starter still slows and stops you can feel confident the problem is in the starter. If it operates normally, the problem is in the connections (cables, cable terminals, solenoid contacts, etc).
 
Yes - all plugs are out, so starter has an easier time of it. By the way, there's no traditional "solenoid" with exposed terminals on the car. Just a pull cable to close a mechanical switch to complete the starter circuit.

This morning same symptoms, but I tried something new. I just kept the starter circuit closed even after the starter slowed and stopped.

Starter actually came back to life on its own - but again very slowly. Kept the starter circuit still closed, and the starter would seem to "catch" and turn fast, then slow again, then fast again.

I did use the "battery direct to starter" test (omitting that starter switch), and same result. Fast at first, then slow, then stop, then fast, then slow again, all the time the cable was directly connected to the starter.

The plot thickens.
Thanks.
Tom M.
 
If you bypassed your starter switch (solenoid) with jumper cables and the starter behaved the same, the problem is most likely associated with the starter itself. I would remove the starter, inspect, and clean it to see what you find.
 
Sorry, I forgot about the compression test. Maybe it's different on a TD, but on an MGA, that switch still has posts sticking out. But I've never been fond of shorting them out anyway, as a bad connection can instantly damage the post.

Pretty clearly a starter problem, not much point in theorizing about it. But, they are usually a 4 pole design, meaning that if one brush quits making contact, the motor still turns just slowly. So I expect you'll find some combination of a sticking brush and/or wear making the armature not run true (so the brushes have to move to follow it).

If you don't want to disassemble it yourself, I'd say you have enough evidence to buy a new one.
 
I can handle checking and replacing brushes and brush springs if needed - I just don't look forward to removing the starter! You have to drop the entire exhaust line to get the starter out.

There a guy in town who's good at rebuilding starters and generators, if needed.

Today I'll try to check the brushes in situ, and maybe blow compressed air in there to see if that helps.

Thanks.
TM
 
Ground problem!

I ran a heavy cable from battery positive (ground) post straight down to chassis near starter.

Pulled starter knob, starter ran perfectly. Never slowed or stopped until I released starter knob.

To me that's a ground problem. According to Moss TD catalogue, there's supposed to be a ground cable (part #31) from chassis to gearbox, but I can't find one down there. Once I figure out if the cable is really missing and where exactly where it should be connected at each end, I'll get one from Moss.

Thanks all for the suggestions.

Ground problem it was indeed.
Tom M.
 
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glad you found it - always the easy things first!
 
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