MTFCA Forum

A set of six coils I rebuilt 26 years ago came back to be adjusted.. in checking the secondaries, all passed, but on two coils capacitor leakage was indicated. All six of these coils had the orange drop capacitor installed on that first rebuild.. replaced those two with new stock orange drops and they just work fine right now. What would cause the leakage in those capacitors that needed to be replaced?.. manufacturing problem? Model T owner problem ?.... Thoughts and comments appreciated ..... Thanks.

26 years is a likely factor. Improper coil adjustment may subject the capacitors to extreme operating conditions, resulting in early breakdown.

Only 26 years?? I'd say that's a decent run. How long should they last?

It depends on which cap you used. There were some used years ago that were not the right material (if I recall correctly).
There were some later ones that were correct only a little larger. Dan

I can only assume that all of those capacitors used in the the six coils were from the same batch, only two that had leaked.

Other than testing with "leakage", Is there a negative effect in the operation of a coil? Do the points burn up sooner?
Does the leakage matter during the speedy operation of a coil? Will the condenser/coil fail soon? Does testing on an ECCT show a "fail"?
Overall does it matter?

The degree of leakage would affect how much effect the problem had on the other parts of the system. Both performance and durability of the system of system components such as points and timer is degraded by a leaky or off-spec capacitor. No leakage is ideal, and if any is present, the less the better. Abnormal leakage probably indicates that failure is in progress, and that the capacitor's electrical value is off-spec. For best results, I suggest replacing all the old capacitors with new ones of the correct type, then readjusting the coils.

TXGOAT2 wrote: ↑

Wed Jun 18, 2025 12:29 pm

The degree of leakage would affect how much effect the problem had on the other parts of the system. Both performance and durability of the system of system components such as points and timer is degraded by a leaky or off-spec capacitor. No leakage is ideal, and if any is present, the less the better. Abnormal leakage probably indicates that failure is in progress, and that the capacitor's electrical value is off-spec. For best results, I suggest replacing all the old capacitors with new ones of the correct type, then readjusting the coils.

I was looking for real model T experience with such coils, not theory.

Bad capacitors give bad performance.

A bright blue spark is a happy cap.

An orange spark indicates a bad cap.

A bad cap causes increase in point wear, as it prevents flash over on points.

It also degrades secondary voltage,as the cap increases primary voltage.

Here is link to old forum. There is a lot of good info on there.
https://www.mtfca.com/discus/messages/1 ... 1322781074

Thanks Dan and Big2bird !.,.,. I can account for the changes in my two previous posts, it was a six coil order, not five.

Hey Speedytinc ..... Used both analog meter and ECCT to check capacitors.... Both testing methods showed failed capacitors on the same two coils.

Big2Bird ..... Your strictly visual results are important indicators of a coil problem without using electronic methods. Thank you. Hopefully those who read your post will look to have their coils checked/ rebuilt.

Moxie26 wrote: ↑

Fri Jun 20, 2025 9:21 am

Hey Speedytinc ..... Used both analog meter and ECCT to check capacitors.... Both testing methods showed failed capacitors on the same two coils.

I suspected as much.
My question was referring to how important is your detecting leakage. The ECCT will show a bad cap but still be a functioning coil.
Does the cap really need re-replacing? In discussing with my local coil expert, I got my answers.

Regarding leakage - It depends. If bad enough there will be much sparking @ the coil points but no spark to the plug.
It goes back to visual cues as BigBird says.
The ECCT will show during testing. The output spark will be a strong blue clack with little to no spark @ the coil points ideally.
Sparking @ the points with a strong output spark will work for a time, but will burn the points faster.
With that information, cap replacement necessity can be determined. I would be very unhappy to find the caps needed to be replaced again.

Speedytinc.... For my standard it's either a "go or no-go" test basis result.