My '67 has developed a rattling noise that I've determined is coming from the distributor.

I first noticed the noise earlier this summer. It was intermittent then, mostly noticeable at idle. It seemed to be coming from the right side of the instrument cluster, or from behind the console. At first I thought it was the tachometer because the needle would sometimes act erratically (bounce) or get stuck at 2,000rpm. Reaching in behind the cluster and tightening the knurled coupling restored the tach operation, so I thought nothing more of it.

But lately this noise is happening more often, and is louder. It’s a rattling, metallic clattering noise - sort of like ball bearings bouncing around. The noise follows the engine speed.

Yesterday I removed the tach cable from the distributor and drove the car. The noise was still there. While I had the cable out I lubricated it with graphite as per instructions on other posts here. I was careful to avoid getting any lube on the last 5-6 inches of the cable where it connects to the tach in the cluster. I reconnected the cable. The lubrication seemed to 'smooth' out the action of the tach needle, and it appeared to read the engine rpm's properly - at least it seemed to during my brief test drive.

However, the mystery noise emanating from the console was still there. I crawled around the inside of the car in an effort to determine the origin of the rattling noise. From the inside of the car the noise seemed to be coming from behind the radio.

I then listened under the hood with the engine idling and the top ignition shield removed. Among the usual mechanical engine noises, I detected the clattering noise as being more pronounced at the rear of the engine. So, I reached for my long-handled screwdriver (i.e. poor man's engine stethoscope) and proceeded to place it at various places as I put my ear to the end of the plastic handle, finding source of the noise to be the distributor itself. The noise was loudest when I put the screwdriver tip on the tach drive connection - the threaded fitting where the tach cable connects to the distributor. Note the tach cable itself was not connected to the distributor at this point.

I then drove the car again. It performed normally, except for that rattling noise. The noise seems less pronounced as rpm increases. But, it could be that the distributor noise is being masked by other engine sounds that become louder as rpm goes up. The distributor rattle seems to get fainter around 2,000rpm, only to return at around 2,200rpm. But the noise is now more or less constant, regardless of rpm.

My question is - what's wrong with my distributor that is causing this noise?

Is it the distributor, or something else? Is there a bearing or bushing inside the distributor that's failing? Or is it something inside the engine where the cam connects to the distributor shaft?

Is this noise critical?

Lastly, is there danger in driving the car for any distance? My mechanic of choice lives about 30 miles away. Will it be safe to drive the car at highway speeds for that distance?

Thanks for sharing your tips and experience.

 

Yes, don't drive the car. The dist is driven off the cam, and also drives the oil pump.

You need to pull the dist out and disassemble it and find your problem, or iliminate the dist itself as the problem.

Lars Grimsrud use to do dist work (C3 guy here on the forum) not sure if he still does, if you are uncomfortable doing it yourself.

 

Have you removed the distributor cap and had a look around inside? Could be something very simple like a rotor screw coming loose. Pretty quick and simple check

 

Likely the tach drive gear in the distributor starting to dig a hole in the distributor housing. If not corrected the drive gear & shaft gear will misalign and you will have to replace both the mainshaft and drive gear.

Remove the cable from in back of the distributor amd with a wide blade tool remove the tach coupling. Inspect the drive gear end for wear. If worn you need to remove the distributor to inspect the mainshaft gear.

The fix is to install a nylon bushing on to the housing opposite the drive gear to correct the alignment. Also a good time to lube the grease well and clean the weights and springs.

 

Good advise. Here is what he is referring to.
Joe

 

UPDATE.

First, thanks guys for your advice on my distributor noise.

Last night I removed the distributor and took the tach drive worm gear out. The teeth are obviously cut in way that indicates abnormal wear:



I didn't disassemble the distributor further, figuring I'd found the source of the rattling noise. But I did take this photo of the mainshaft inside the distributor housing. It doesn’t look chewed up, but are those metal filings in with the blackened grease? Not sure.



So, what causied the tach gear to be eaten up? Is the tach gear made from softer metal?

And, could the filings from the tach gear get into the engine? If so, what should I do?

I'm looking to buy a rebuilt distributor from a forum member to get back up and running, with the idea to rebuild my old (worn) distributor later. I figured that would be better than simply replacing the chewed-up tach gear to only have the problem repeat itself sooner than later.

Alex

 

You are correct in not simply replacing the gear. The gear you took out has been rubbing on the inside of the distributor housing which is made of cast iron. The gear is a high carbon steel much the same as the material used for making drill bits. It will wear but not as much as the distributor housing. I had the same problem with my '67 327/300. The fix I implemented was to mill the flat portion of the distributor housing with a 3/4" end mill to restore the chewed up distributor housing surface inside. Then I determined how deep I could drill a 1/8" hole in the housing (inside) without drilling all the way through to the outside. This allowed me to use a brass button available in kits to repair just this issue. The 1/8" hole locates the button and keeps it in place. I used a new tach gear with a brass button in the end of it, lubricated the surfaces, and put it back together. Now I have a brass on brass wear point and have had no further issues. Other remedies include drilling and tapping a hole in the distributor housing to accommodate a set screw to push against the end of the tach gear. The only problem with this is if you wish to maintain the originality of your distributor, you wind up with a set screw visible from the outside of the distributor. You will need to replace the gear and I have heard of some who had problems with meshing correctly with the distributor shaft. I didn't have that problem. The kit I got ahold of had a new coupler as well as the steel flat washer and new gear with a brass button. If you replace the gear without dealing with the chewed up surface of the inside of the distributor, your repair will probably fail as the distributor surface will cause the same wear problem that occurred the first time. Just out of curiosity, how many miles does your car have if I'm not to nosy to ask. Mine had just around 40,000 original.
Good luck with whatever method you choose. It would have been nice if GM would have figured out an assembly that wouldn't be prone to failure as this is not an uncommon problem.

Steve

 

Hi Steve,

Thanks for sharing your knowledge on the issue, and how you went about fixing your distributor.

My car has 85,000 original miles. I think this is the actual mileage because although I’ve owned the car for 3 only years, it came with paperwork confirming the mileage going back to the early 1980’s.

My challenge is that I don’t have machining skills or equipment, so must find someone who can rebuild my distributor. Two names came up in my research as being reputable distributor rebuilders/tuners: Don Baker and Lars Grimsrud. I was able to reach Lars by phone this morning. He was very helpful, and confirmed much of what you wrote about the cause of the distributor tach gear wear. Lars recommends replacing the main shaft as well, because in his experience this inevitably gets damaged when the tach gear gets chewed up. Another side-effect is that metal filings get down the main shaft and ruin the bottom bushing, so it should also be replaced.

Unfortunately, Lars isn’t taking any work right now because his ‘Sun’ distributor machine is down while he searches for parts to fix it. He suggested I call back towards the end of the year when he hopes to be back up and able to take new work.

In the meantime, I’ve left a message for Don Baker, so we’ll see what he has to say.

My other option is to buy a complete 111194 distributor from forum member Howard Nardick. He’s got several different tach drive part number distributors for sale and I’m waiting to hear back from him on availability.

How long have you owned your ’67, and are you brave enough to post a photo of your car?

Gotta love those mid-years! And the ’67 is of course, the best!

 

I have had the car going on 6 years. It is a June 23rd coupe. Marlboro Maroon with black standard interior. It had 33,094 miles on it when we got it. It has a little over 41000 now. The previous owner had it for around 20 years and only put about 2000 miles on it. He should have driven it a bit more. It would have been better for the car in the long run. It was a top flight regional in '89 and again in '91 although it would take a bit to get it there now. It has been a lot of fun, and I have enjoyed working on it. A lot of the car is typical Chevrolet which I was already familiar with but there is still a lot of things that are only Corvette that have been entertaining.

 

As an afterthought, your gear wear is substantially more severe than mine was. My distributor only took a hit on the end of the cross gear and the inside of the distributor housing. Not much in the way of loose particles but a fair amount of galling which necessitated the need for repairing the surface on the inside of the distributor. The distributor shaft gear came out unscathed. With the amount of damage you show in the pictures I think you are right to replace the cross gear, distributor shaft and bushings. You can also adjust the endplay of the distributor shaft while it is apart.
Hope everything works out for you.

Steve

 

Hi Steve,

Yes, you're right - my distributor has chewed up the cross gear pretty good, so it'll need a fullsome rebuild.

In the meantime I'm buying a refurbished 111194 distributor (correct for '67 327/300hp) from forum member Howard Nardick. The price seems right, so I can get back on the road and rebuild my original distributor at a later date.

Your car is beautiful, by the way! Thanks for posting a photo. And, such low miles! I had a 41,000 original mile '65 coupe many years ago, and I know what you mean about using the car. Stuff goes bad from just sitting. These cars want to run, and it's good for them (and us too!)

Cheers,

Alex

 

Hi Steve,

Just wondering - are you located in the Pacific Northwest? I ask because I recognize the red cedar and other familiar trees in behind your Corvette in the photo. I live in Vancouver, BC. so the this vegetation is very familiar. If you'd rather keep your location private I understand (you haven't listed in your profile or avatar). Or, you could PM me instead if you want.

Cheers,
Alex