Tach gear failure prevention

[Timothy B.]

As part of my latest project, I pulled my distributor for inspection and to fix a couple of things I didn't know to do when I rebuilt it about a year ago. One of those things is one of the "preventative measures" that are discussed in this forum for tach gear failure. The thing is, when I took it apart again and inspected the bottom of the cast iron housing where the tach cross gear rides, I see no significant wear. It has been described that the cross gear wears into the housing, creating a cavity the can be seen and felt as a circular indentation. As the attached photo shows, there is only a circular contact pattern visible but no detectable depth to it. When the cross gear is installed, there is some, but not much, endplay in the cross gear.

So, my dilemma is this: Should I just leave well enough alone and reassemble knowing that the car sees maybe 1000 miles a year, or try to install one of the "fixes". I don't think there is room for either the plastic or metal buttons without machining out the back of the housing for clearance. I could however drill a hole and install a set screw (technique Paragon endorses) to take out the small amount of endplay that is there. What should the maximum endplay be I wonder?

[Brian Monticello]

Re: Tach gear failure prevention

I'd leave it alone. No sense in fixing it if it isn't worn. FYI here's what mine looked like.

[Timothy B.]

Re: Tach gear failure prevention

Wow, excellent photo Brian! How many miles were on your car at the time of the photo? Was it well lubed at the time, or do you think your wear was caused by lack of lube?

[Brian Monticello]

Re: Tach gear failure prevention

Have no idea how many miles were on this distributor. The upper oil well was dried and caked, the tach gear cavity was full of grease, and the mainshaft and bushings were in great shape. Most of the the components on this car were somewhat maintained but not rebuilt. ..... kinda like how someone would treat a daily driver.

I pulled it to change the vacuum advance and decided to check everything out - glad I did! I suspect I would have had failure had I waited too much longer.

Brian

[Randy S.]

Re: Tach gear failure prevention

Tim,

I have also seen a tach gear with a brass/bronze button on the end. Sold by Greenwood Chevy on ebay. Haven't seen it at any traditional corvette vendors.
Seems like an alternative to nylon buttons and set screws.

Maybe others have experience with it.

Randy

[Brian Monticello]

Re: Tach gear failure prevention

I went with the bronze button. IMO, the set screw is a better solution because it is adjustable. This bushing that I used was originally too thick and I had to dress it down until the proper cross-gear end play was acheived. Works fine but once it wears I'll be in the same boat again.

One word of caution though about the set screw - it has to be right on and rest in the "dimple" at the end of the tach gear. If you look closely at my installation of the brozne button you'll see that it is not centered. This was one of my first real projects on the car and the hole I drilled wasn't centered. In other words, the button solution is a little bit more forgiving!

Brian

[Justin N.]

Re: Tach gear rebuild

Tim,

My 67 dist. had a hole through the assembly that isn't supposed to be there. Bubba had screwed a bolt into the hole that stuck out looking like Frankenstein's neck! I had placed a bronze button like Randy talked about, but this isn't correct for my year, I think 68 or 69, but not sure. After rebuilding it myself, I got scared about the work because it still seemed wonky. I sent the whole thing off to 'TI Specialty' and had Dave Fielder weld up the hole and complete the assembly. Here's a shot of my shotty work before the rebuild!

Justin #41362

[Gerard F.]

Grease Fitting instead of a set screw

On my 67, I replaced the set screw with a grease fitting on a replacement tach drive distributor. It works just fine and you can put grease in where it is needed the most. Of course, as you probably know, the original tach drive distributor didn't have a hole for the set screw. My original is sitting in a labelled box with the tag in place waiting for some future restoration.

See you at Golden Gate.

Jerry Fuccillo
#42179

[Wayne K.]

Question, what is the best kind of lube to use ? *NM*

[John H.]

Re: Question, what is the best kind of lube to use

I slather my gears and cavity with gray moly lube (ARP Assembly Lube); same stuff used OEM on the clutch fork and throwout bearing groove.

[Wayne K.]

Thanks John. Slather, now thats a word...

I haven't heard for sometime. I think the last reference I can remember was when I was slathering the little woman with BS about something and she told me to stop as it was getting hard to breathe.

[Gerard F.]

Must have been quick Wayne

Slather means "to cover up or spread quickly" or "to use in a lavish or wasteful way". I'll defer to John on the type of grease. I think I used a green, light lithium grease about a year and a half ago.

Jerry Fuccillo
#42179

[John H.]

Re: Thanks John. Slather, now thats a word...

Wayne -

"Slather" is the only word that fits! That cavity gets NO lubrication from anywhere else, and the only lube those gears will ever see is what you put in it when you assemble it; in this case, "more is better"