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MG MGB Technical - Am I on my 4th starter since summer?

This is a follow up to my electrical gremlins posting.

Well I have three starters on the garage floor right now and it looks like there will be a fourth. But before I go and waste good money I am on a fact finding mission to get as much info as possible. I sometimes wonder if I am doing something basically wrong. The latest starter was brand new and was installed less than a month ago and I donít think Iíve put a 100 miles on it.

I had the car in the garage for a about 4 days last week before starting up on a cold morning. As I cranked it sounded like a weak battery on a cold winters morning. Eventually it started and was ok from there. I left it standing again for a day and tested the voltage and was about 12.15V. When I went to start up again the battery sound very very weak, and at times I could hear a faint clinking noise coming from the starter when I cranked the engine, not the solenoid though, so I stopped and put it on charge. Tested the battery again and it was about 12.6v. Again when I went to crank it sounded very weak and wouldnít fire, so I left it again and put the charger on. Later battery read 12.7V. Went to crank and all I got was the CLONK coming from the solenoid.

Am a doing something basically wrong?

GG Ginty

its your battery. Voltage can be OK, but its got high internal resistance and won't deliver the required current. Check the voltage while cranking. Should be > 10V
Art Pearse

Can't check the voltage when I can't crank!
GG Ginty

"Am a doing something basically wrong?"
>>>I think that sums it up pretty well.

By your posts, You have a constant stream of Gremlii, and they all live on bad connections that leak electrons out, and they reproduce evermore Gremlii. Eventually they cause electron leaks, and eat enough electrons that the starters are starving to death! On a good diet, it is likely that enough starters will recover that you can be the starter store.

On the face of it, the battery is not getting charged (12.15V is effectively a dead battery) and when it is charged it is not delivering power when needed in large doses, ie, starting. = CLONK

Most common cause of all this is bad connections, in this case in the battery cables, at the ends and/or in the wire itself.

Little Gremlin offspring are responsible for your TS/Brake light problems too. They are exactly like their parents, living on smaller bad connections.

"I am on a fact finding mission to get as much info as possible. I"
>>>Email me and ask for "Electrobabble".

Where in RI? I have a friend in Providence, and might visit the area over Christmas.

FR Millmore

Sorting out electrical problems is tough enough even when you're under the hood with all the tools. At best, we can only offer some suggestions to you from experience. First, I don't know your car's year, but regardless of year, there is an important grounding strap between the drivetrain and the chassis. Prior to about 1974, it was at the driver side motor mount and later, it was at the rear of the transmission. I had a similar problem with a 70 MGB and discovered the gremlin while cranking with the hood up and noticed smoke coming from the throttle cable just prior to it burning in two. Without the ground strap connected (had managed to work loose), the DC circuit could only be completed by the throttle cable.
Rick Penland

It doesn't need to be actually turning over the engine, just trying to! 12.15v is very low for no load, and 12.6v and 12.7v just removed from the charger is also very low, let alone if that was measured *while* it was charging. Depending on the charger it should be around 13v-15v charging and just removed, settling to about 12.8v. Low voltage can be due to a knackered battery, incorrect charge (should be around 14-14.5v at about 2k) or drains causing the battery to discharge when parked up.

The important thing is to put load on the battery when testing the voltage. If you only get the clonk it's quite possible the battery voltage has dropped so low there is only enough to hold the solenoid in but not make any progress in turning the engine. When voltage drops even lower the load of the motor can cause battery voltage to drop so low it won't even hold the solenoid in, and that is when you get the chattering.

The voltage should be measured directly on the battery posts, then compared with the voltage between the brown at the fusebox and a good earth on the engine. As you drop below 10v at the battery posts that is showing a weak battery. The difference between those two voltages is how much you are losing in any bad connections i.e. at battery, solenoid or engine/gearbox earth strap. If you have twin 6v batteries measure the voltage between the posts the link cable is attached to as well. Total losses can be got down to 0.2v in each 'leg', anything more than 0.5v is worth investigating. I've seen 3v lost in the past, and it still cranked - just about - but was a difficult starter as coil voltage was pulled so low as well.

Drains can be checked by removing the battery earth strap and connecting a voltmeter on its 12v scale in its place. Note analogue instruments are best here, digital may give variable results. With everything off, on a dynamo car, the meter should show nothing. An alternator car will usually show a few volts from the reverse leakage current of the alternator diodes which can be ignored. With the alternator unplugged it should drop to zero. If it shows 12v with the alternator plugged in but zero with it unplugged the alternator is faulty. If it shows 12v with the alternator unplugged you have a drain. Note any clocks, radios, alarms etc. should be disconnected to check the remainder of the cars systems for a drain. With clocks, radios and alarms measure the current as well, you shouldn't see more than about 30mA, but even that is enough to flatten a battery over a couple of weeks and knacker it in a couple of years.
P Hunt

And yes I do have some electrical issues going on and it is only through experience and positive responses that one can learn more

FRM I live in Newport and I have a 74.

Pual thanks for you detailed reply I will take a look this week when I have a chance

GG Ginty

Gerry. If I remember correctly, you have a 1970 vehicle which would have the pre-engaged starter. Quite easy to run a jumper lead to the large terminal of the starter and back into the passenger compartment. This allows you to hook up your volt meter to the jumper lead and ground while you turn the ignition switch to the start position. I have seen good batteries which showed only 4.0 volts at the starter due to bad connections or bad cables. I agree with the rest, I would gather more information before installing another starter. Did you have any of the previous three starters tested for basic function before deciding to replace them? Might be something worth doing.

Les Bengtson

When your car failed to start did you try jumping it with cables from another vehicle?
By the way, I am close to you. I have a house in Swansea, MA and spend most days in Tiverton, RI
Good luck,
Dana Wilson


My car is a 74.


No I didn't try jumping. At the moment this is my daily driver and did not have access to another car at the time.

As soon as I can get a window of oportunity this week I will start to take a much closer look. Test from battery all the way to the starter, check grounds, clean them up etc

Thanks everyone
GG Ginty

Gerry. Same starter from 68-74 1/2. For the 75 models, they added a second spade terminal that provides 12V input to the 6V coil when the starter is engaged. Both starters will work with the pre-75 cars and can be tested in the same manner.

Les Bengtson

Do you know the age of the battery? RAY
rjm RAY

Have you had any if the starters tested. Usaully Auto Zone or Advance Auto will test them for free.

SK DeGroat

I think I agree with the "it's the battery" answers. I've had similar symptoms on both my MGBGT and at least one other vehicle. A bad cell in the battery can still give you a 12+ volt reading, but not deliver the juice needed to turn the starter/engine. Just had it occur in a relatively new battery in a Honda. Got it started by jumping, but it would not hold a charge once the engine was turned off.
I think I would take the battery somewhere to have it bench tested before removing the starter again (having had to do that routine before, as well).

Patrick Callan

Had this problem with a customers car years ago. Turned out to be a shot earth lead on the battery. Grabbed hold of it whilst turning over the motor - it got VERY hot. It was one of the old braided type on a 70 GT.
Garth Bagnall

hi try fitting new earth leads ie . short leads from engine to chassis i have had this sort of trouble in the past hope this helps..paul..
p phillips

This thread was discussed between 14/12/2009 and 29/12/2009

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