cable driven tach not working
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,364
From: At my Bar drinking and wrenching in Lafayette Colorado
You have to machine the inside of your distributor housing to accept the brass button. Some later tach drive distributors used a nylon thrust button, and these distributors have a hole in them to hold the nylon piece in place. The brass buttons have a stem that is larger than the hole for the nylon piece, so you have to open the hole up. The diameter of the brass button is also too big to fit in place of the nylon part, so you have to turn it down. On the distributors without the nylon button and hole, you first have to machine out the damaged area on the thrust surface and create a couterbore for the new thrust button to seat into.
By the way - I have had poor luck with the brass buttons - they get chewed up pretty quick. I've been machining steel inserts for the thrust surfaces, and that holds up much better.
By the way - I have had poor luck with the brass buttons - they get chewed up pretty quick. I've been machining steel inserts for the thrust surfaces, and that holds up much better.
Thread Starter
Burning Brakes
Joined: Dec 2005
Posts: 1,179
Likes: 100
From: cranford nj
Lars, thanks for the info I think I'll order the nylon button and try that. It's a 71 and acording to the paper work I found the tach hasn't worked since 72. I did get it to work for about 2 days so I know I missing something.
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,364
From: At my Bar drinking and wrenching in Lafayette Colorado
If the tach is not working, the thrust button will not fix it. You either have stripped teeth on the crossgear and mainshaft or a broken cable. If the teeth are stripped, you need to replace the mainshaft, crossgear, crossgear bushing, and you need to repair the thrust surface wear inside the distributor housing (or else the gears will lock and strip again).
Thread Starter
Burning Brakes
Joined: Dec 2005
Posts: 1,179
Likes: 100
From: cranford nj
Lars, does the plastic button pop into the hole in the dist housing, I think the problem is that I had a brass button and I just put it in not realizeing how it all worked. I'll order a plastic one and look at the teeth in the dist.It hasn't worked since 72 only being 1 year old do you think the teeth could be shot?
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,364
From: At my Bar drinking and wrenching in Lafayette Colorado
The thrust button has no effect on whether or not the tach works - it only provides a thrust surface for the crossgear. If you have a brass one in there now, the nylon one will not change things. If the tach is not working, you have a broken cable or stripped gears.
Tech Contributor
Joined: Aug 1999
Posts: 15,135
Likes: 3,939
From: Connecticut, USA
I too had the same problem with the gears and shafts on the market. Bought from several vendors got the same crappy part from each one. The ones I got were not machined correctly to mesh with the shaft. I even went as far as machining the brass plug out and installing a new one that I faced off a few thousands at a time - still ng. I returned them all and not one supplier could offer me an explanation- because they didn't know either. I found a goo dGM gear and it's working to this day. The only gear I'd trust is from Hy Tech in FL if they're still in business?? I heard the owner passed away unfortunately.
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