34 Coil Carbon Brush

Steve Staysko

Steve Staysko

Senior Member
Yesterday I took my 34 out for a drive and it ran great until I stopped. About 20 minutes later I started it to drive home and I could only accelerate to about 35 mph with the engine stumbling. The coil was rebuilt by Skip and I have a new condenser built by Third Gen.

I took the coil off and 90% of the carbon brush had broke off. Any ideas as to why it would break, has it happened to others? I removed the distributor to investigate and didn't see anything unusual.

I have a distributor that was rebuilt by Bubba, which I installed and put everything back together. It started up and idled nicely but I have very little acceleration. Because I drove it home running very poorly could it have damaged the coil or condenser?
 
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You can buy another carbon brush and spring. Just pull the broken one out and clean the brass tube then insert the new spring and brush and Guide the new spring into the tube then push the brush with your finger until it bottoms out.

Suggest you clean the center of the rotor where the brush rides make sure all is smooth.

I would be surprised if you damaged anything driving with a broken brush.
 
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Check with a timing light that shows degrees of advance and see how much advance you're getting. If the advance mechanism isn't supplying enough advance, that will kill your power.

You may not have a timing pointer, but all you need to do is mark the front pulley, pick something to reference the mark too (I bolt on a bent piece of welding rod to the timing cover). Then you can rev the engine to say about 2200 RPM and then use an adjustable timing light to "dial back" the mark/reference to where you started at idle. You can then determine the total mechanical advance. You need to know where you are at to start with.

Where do you have the vacuum retard set at (the adjuster on top of the plunger)? Maybe you have it too tight and it is preventing the mechanical advance mechanism from delivering full advance. Do you have any idea as to if your Bubba distributor has the 11A advance mechanism in it . . . or the early 34 type (which delivers a lot less advance).

To test this theory, back-off the adjuster on the distributor until you don't feel the spring tension on it, then turn it back in until you just feel the spring - then see if your total timing amount increases/moves. Again, using an adjustable timing light to dial back to your idle point.

As a rough guesstimate, about 3/8" of movement on the OD of the crank pulley is about 10 degrees of crankshaft timing.
 
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Steve Staysko said:
Yes but Bubba set up the rebuilt distributor that i just installed yesterday and he would have had that all set up!
Click to expand...

I would return all back to how it was running initially prior to breakage of carbon brush. Test drive in this condition with your original distributor and see how it performs speed wise. Then you may see that the "upset" could be the Bubba distributor???
Phil NZ
 
Steve Staysko said:
Yes but Bubba set up the rebuilt distributor that i just installed yesterday and he would have had that all set up!
Click to expand...

I know that Michael does offer rebuild of the 34 distributor with 37 internals.
In my case offered a noticeable increase in pick up and pep over the standard set up -Maybe you had one of his with the later internals -Karl
 
It is possible the mechanical advance weights are stuck or the vacuum brake piston. Yes Bubba checks them but if put on a shelf for a while it is possible they will start to stick in one position. Consider checking as Bored&Stroked suggest.
 
Terry, I removed the rebuilt Bubba's distributor and the mechanical advance weights were not stuck but when I compared the tension on the vacuum brake piston compared to my original distributor it was about twice the tension. Does that matter and how do I determine the correct adjustment? I'm now going to reinstall my original distributor after replacing the rotor and a new carbon brush in the coil....
 
Steve with modern gas I think you need very little tension on the vacuum brake . I seem to remember Michael telling me when he sent me mine that he sets the vacuum brake very lightly and if it pinked to tighten it up a bit-It never did -Karl
 
By hand screw the adjustment out all the way and then screw in in about 1-1/2 turns. Ford says spring for the brake 18-12225-B is 0.875" long. Just in case someone tried to modify it over the years.
 
If the vacuum brake is too tight, then your advance will be limited. As I wrote up above, you can try all sorts of things, but unless you put a timing light on it, you really have no idea as to what is going on and why the engine performs as it does.

Heck, you may have different initial advances and different total advances (between the two). You can at least compare the two distributors with a timing light.
 
You should run a little hand reamer in the hole in the coil
to clean the hole and and round it up so the brush makes
good contact and slides nice. G.M.
 
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