Distributor tach drive cross gear issues
#1
Burning Brakes
Thread Starter
Distributor tach drive cross gear issues
It seems that the 1110984 (1962 250hp single point) distributor doesnt have a set screw to adjust the tach drive cross gear, so cannot install a plastic or brass button. Is this correct?
Without the set screw, which cross gear do I buy? There are ones that have a steel end, ones with a steel end and bore to allow a button, and ones where the button appears to be pre-installed.
Any help would be appreciated.
Without the set screw, which cross gear do I buy? There are ones that have a steel end, ones with a steel end and bore to allow a button, and ones where the button appears to be pre-installed.
Any help would be appreciated.
#2
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It seems that the 1110984 (1962 250hp single point) distributor doesnt have a set screw to adjust the tach drive cross gear, so cannot install a plastic or brass button. Is this correct?
Without the set screw, which cross gear do I buy? There are ones that have a steel end, ones with a steel end and bore to allow a button, and ones where the button appears to be pre-installed.
Any help would be appreciated.
Without the set screw, which cross gear do I buy? There are ones that have a steel end, ones with a steel end and bore to allow a button, and ones where the button appears to be pre-installed.
Any help would be appreciated.
#3
Burning Brakes
Thread Starter
i.e. This:
vs this:
Last edited by sprinter; 11-23-2014 at 10:18 PM.
#4
Most times you can drill/tap for a set screw through the distributor housing or install a bronz bushing inside the distributor housing. What you don't want to do is not repair the housing if it's wore because the main shaft and cross gears will mis-align and strip causing replacement.
#5
Race Director
GM used a plastic button somewhere around 1969-1970, I never saw a factory installed set screw and have owned quite a few tach drive distributors, send yours out to Lars in CO, he will repair the housing and set the thrust, for a nominal fee.
#6
Burning Brakes
Thread Starter
The cross gear thrust is inward, the hardened washer is simply there to protect the brass bushing from the gear teeth.
Most times you can drill/tap for a set screw through the distributor housing or install a bronze bushing inside the distributor housing. What you don't want to do is not repair the housing if it's wore because the main shaft and cross gears will mis-align and strip causing replacement.
Most times you can drill/tap for a set screw through the distributor housing or install a bronze bushing inside the distributor housing. What you don't want to do is not repair the housing if it's wore because the main shaft and cross gears will mis-align and strip causing replacement.
http://65corvette.nonethewiser.net/m...inter03-04.htm
#7
Tech Contributor
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I wouldn't recommend it. The brass will get chewed up very quickly, and it will send metal fragments down into the lower shaft bushing, destroying the bushing and the mainshaft. There is a good reason the factory never used brass thrust buttons. I charge people quite a bit of money to fix what you're planning on doing...
Lars
Lars
#8
Burning Brakes
Thread Starter
I wouldn't recommend it. The brass will get chewed up very quickly, and it will send metal fragments down into the lower shaft bushing, destroying the bushing and the mainshaft. There is a good reason the factory never used brass thrust buttons. I charge people quite a bit of money to fix what you're planning on doing... Lars
#9
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Some people have used a set screw with a hardened steel ball bearing soldered on the end to adjust the cross gear end play and prevent wear.
#10
Burning Brakes
Thread Starter
Thanks for the advice. I would rather not drill the housing if I dont have to. Is end-play really an issue? If so, maybe I can machine a custom thickness thrust washer to take up the play?
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#12
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Thanks Lars, the housing is not damaged, so it looks like I will just use the steel-end one I have. One more question for you - as I rotate the mainshaft back and forth, the tach gear can slide in and out by about 0.040" as it is thrust forward and backward. Is this normal?
Lars
#13
Burning Brakes
Thread Starter
#14
I wouldn't recommend it. The brass will get chewed up very quickly, and it will send metal fragments down into the lower shaft bushing, destroying the bushing and the mainshaft. There is a good reason the factory never used brass thrust buttons. I charge people quite a bit of money to fix what you're planning on doing...
Lars
Lars
I had installed a set screw that had a plastic tip but it looked terrible as it stuck out of the rear housing. I think most of the vendors sell these brass buttons, can you provide a picture of the damage you have seen regarding this button.
How do you repair these in the shop, I guess you could have one made from steel easy enough. It's hard to see in my picture but I recess the housing .060 so it sits flush and the hardened washer can be used on the gear to protect the brass bushing plus the gear sits centered.
Last edited by tbarb; 11-27-2014 at 05:26 AM.
#15
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I have never heard of the damage you are referring to with the installation of the brass button. I installed one on my 1967 Corvette distributor and inspected it some time ago only to find what looked to me like a little scratch. I think most of the vendors sell these brass buttons, can you provide a picture of the damage you have seen regarding this button.
Here is one that I received just this week: This is from a Forum Member who rebuilt this distributor just a few hundred miles ago, but he was not happy with the advance curve, so he sent it to me for checkout and curve. The crossgear and the thrust surface had plenty of lube. The crossgear end surface was not scored up, yet the brass button is clearly headed for early failure. It's hard to get a 3-dimensional view from this 2-dimensional photo, but the thrust surface is worn almost halfway through. This is one of the better brass buttons I have seen after use:
The brass shavings had scored up the lower bushing pretty bad, but the mainshaft was still in serviceable condition. I replaced the lower bushing, polished up the shaft, fabricated a good, mild steel insert, and got this one set up and tested at a nominal cost.
When I first started rebuilding tach drive distributors about 10 years ago, I thought the brass buttons would be great: I used them in several of my early builds. I received every single one of those distributors back in less than a year with complete thrust button surface failure, and I lost my butt on the work. Needless to say, I don't use them any longer, and I haven't had a failure since.
Lars
Last edited by lars; 11-28-2014 at 12:15 PM.
#16
Lars,
Thanks for that picture, the next time I have mine out it will be addressed. It's always something..
Thanks for that picture, the next time I have mine out it will be addressed. It's always something..