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Tach Drive distributor

Subfixer

Well-known member
Joined
Jan 28, 2002
Messages
634
Location
Groton, CT. USA
Corvette
1964 White Roadster
The Tach on my 64 quit working the other day. I checked the cable, and it was OK. If I spin the drive cable, the tach seems to work (no binding). Then I took the drive gear assembly out of the distributor and found that the teeth were sheared off. The teeth on the distributor shaft were stripped also. I have purchased a new distributor shaft and tach drive assembly (with needle bearings). My question is... what is the lubrication requirement for the tach drive gear. The 63/64 shop manual does not cover this (nor does my new assembly).
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
I've found gray moly grease to be excellent for this application, as it doesn't break down or dry out; I use ARP Assembly Lubricant (from the ARP bolt people, available at any speed shop), but I'm sure there are other brands of gray moly lube that would work equally well.
 

Subfixer

Well-known member
Joined
Jan 28, 2002
Messages
634
Location
Groton, CT. USA
Corvette
1964 White Roadster
Thanks. The repair was really simple, Swapped out the main shaft and the drive gears in about an hour (removal from car, cleaning, reinstallation, startup). I love old simple cars!!
 

Subfixer

Well-known member
Joined
Jan 28, 2002
Messages
634
Location
Groton, CT. USA
Corvette
1964 White Roadster
Well, the repair only lasted a week. Stripped the gears again yesterday. Anyone know what I am doing wrong? Tach is free spinning, new tach cable, new main distributor shaft, new tach drive gear assbly (with needle bearings). Did I forget anything?
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
There's a fit spec (for end play) for the gear/shaft assembly in the housing; there should be a thrust button in the end of the cavity for the gear to keep it from "walking" back and forth. If it has excessive end play, it will do as you describe. Most of the resto parts houses have the "buttons", and some folks drill and tap a hole in the end of the housing and use a setscrew to set the end play instead of the "button".
 

Subfixer

Well-known member
Joined
Jan 28, 2002
Messages
634
Location
Groton, CT. USA
Corvette
1964 White Roadster
Boy, do I feel stupid. :/
Took everything apart yesterday just to discover the gears were good, but my new tach cable broke. It made the same sound as when the original gears let go. Anyway, turns out that the new tach cable was about 4" longer than the original, so when I installed it, I must have exceeded the bend radius. Put the original tach cable back in and all works fine again. :)
Thanks for all the suggestions and help.
 
R

ralc

Guest
cORVETTE TACH DRIVE REPAIR

Well, the repair only lasted a week. Stripped the gears again yesterday. Anyone know what I am doing wrong? Tach is free spinning, new tach cable, new main distributor shaft, new tach drive gear assbly (with needle bearings). Did I forget anything?

had the same problem Turns out that the old gear had bored into the case. Took it to Nelson Specialties and they made it better than new their # 800-494-7532 They do most of the NASCAR stuff
 
R

ralc

Guest
Tach drive Corvette distributor

Sounds similar to that part of the repair they did for me. They installed a custom made piece to repair the damaged housing and supply the proper end play on the gear.
They also cleaned the housing in an acid bath, installed new oilite bushings and new heat treated weight pins for the advance. The mag pulse coil was replaced. I had to fill out a spec sheet on the car and engine so they could set the proper vacuum and mechanical advance. The car accelerates better, no ping or stumble and I can use 89 octane gas

You can't just install a new mainshaft and crossgear in a distributor with stripped gears. The gears strip because the crossgear eats itself into a self-produced counterbore in the distributor housing, and once the bore gets deep enough, the crossgear locks up and trashes everything. You have to fabicate a steel insert to fill the counterbore correctly and restore the crossgear thrust surface at the correct location. I fabricate the new thrust surfaces on a lathe and custom fit each one to the defective housing. Making the surface from steel (rather than cast iron) produces excellent durability.

Don't use the brass thrust buttons sold by some vendors - they will trash out almost immediately, and will pollute the entire inside of your distributor with brass shavings.

Lars
 

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