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I replaced my tach cross-gear, as the tach. no longer worked, and the part showed an extensive concave wear in the gear teeth. The new cross-gear part worked for about 1 hour's drive, then no more. To my surprise, it was also worn out the same way! The bronze button on the end also showed wear around the exterior face. Am I installing this part incorrectly? Is the button supposed to come off and be inserted from the outside of the distributor shaft? It's costing me $30 a shot to trouble-shoot this. Thanks for your help.
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Re: C3 - tach cross-gear chewing problem
Seb-----
I've seen these replacement cross gears with a brass button on the end. However, I wouldn't use that type. Check the inside of the distributor housing for wear (where the cross gear end bears on the housing). If it's worn, but not too bad, then I recommend installing one of the brass buttons available from Hi-Tech Innovations. Installing this button will require drilling a hole in the end of the housing on center with the cross gear. If you don't want an external hole, you can either attempt to drill the hole only partially through the housing or, simply, fill the external hole after drilling and installing the button. I recommend the latter.
If the housing is badly worn, then you will need to repair it. You can fill the worn area with an epoxy like JB Weld, grind it smooth after curing, and then install the button, as above.
If you still have problems with the cross gear after doing this, then it means that your mainshaft is out of alignment for one of several reasons. It may have been marginal from the day it was manufactured or the bushings may be very worn. In either case, I'd recommend sending the housing off to Hi-Tech Innovations to have new bushings installed and jig-bored. This will result in perfect alignment of the shaft.In Appreciation of John Hinckley -
Re: C3 - tach cross-gear chewing problem
Thanks for the response.
The replacement cross-gear I bought did have an attached brass button but with no hole. The original had a small hole on the end? I believe there is already a very small hole on right through the housing. This made me wonder if there was supposed to be a pin or something that goes through the housing to the cross-gear, but by your response, I don't think so, must be just a vent hole?
Although I didn't try really hard, it is very difficult to get a good look inside the cross-gear housing while the distributor is installed. I was really hoping I wouldn't have to pull it off.Comment
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Re: C3 - tach cross-gear chewing problem
You have to replace the main shaft at the same time or it will eat the cross gear up like popcorn. These gears are case hardned. If one it broken the other is too.Comment
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Re: C3 - tach cross-gear chewing problem
Seb,
I restored my distributor myself about 7 years ago (~15000 miles ago). I did have to remove the distributor and you will too. When I removed mine, I inpspected the mainshaft and found that the area where the lower bushing is was very worn. There were gouges in this area. I replaced the loser bushing and installed a new main shaft and new cross gear. I lubed the cross gear interface with high pressure lithium based grease. I recently removed the distributor for inpspection and new points and found this grease to have done an excellent job in this service. Both gears looked as when new. The tachometer is steady as can be. I suspect you will find a similar experience. If you have to replace the upper bushing, you may require special tooling. The surface of the main shaft should give you insight as to a failure mechanism.TonyComment
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Re: C3 - tach cross-gear chewing problem
You didn't mention the year of the C-3, but there were two different designs, one where the crossgear rides directly on the inside of the crossgear cavity, and one where there is a small hole drilled into the bottom of the cavity and a plastic bushing is snapped into the hole to provide a wear bearing surface for the crossgear. I forget the changeover but I think it was about 72 or 73. I agree with Wayne, I have never seen one where the crossgear was eaten up without taking at least a tooth off the mainshaft. If you buy a repro mainshaft, you will need to have the distributor advance curve recalibrated by someone with a distributor machine.Bill Clupper #618Comment
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Re: C3 - tach cross-gear chewing problem
1972 350 coupe. Mine does not use the plastic clip.
All roads seem to lead to pulling the distributor out. I guess I found another winter projectComment
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Re: C3 - tach cross-gear chewing problem
Seb-----
The hole in the housing indicates that either the distributor originally had the nylon thrust button or someone added the hole later. Sometimes, a set screw is installed in these when certain retrofit cross gears are also installed.
I recommend the brass button installed in the hole from the inside. You won't need to drill the hole since it's already there.
As others have commented and I should have in my original repsonse, you MUST change the mainshaft whenever the cross shaft gear is removed damaged. I always consider that a "given" and, perhaps, that's why I forgot to mention it in my original repsonse. If the cross gear is damaged, then the main gear will also be damaged. Without fail. So, you really need to remove the distributor to rebuild it. No sense in just replacing the main shaft and cross gear; it's time to attend to the whole unit and there's no better time than when it's out for this repair. After all, you don't want to pull it out again, do you?
By the way, Hi-Tech Innovations can not only install new distributor bushings for you and jig bore them, they can also transfer the auto cam from the top of your old mainnshaft to a new mainshaft. That way, you will retain the same mechanical advance curve that you have now, assuming that you also re-install the same springs and weights.In Appreciation of John HinckleyComment
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Re: C3 - tach cross-gear chewing problem *TL*
The addition of the drilled hole to locate a plastic thrust button was late 1970 model year (around and after s/n 12,000). About the same time changes were made to the configuration of the ignition shielding and the addition of the RFI shield for those distributors with points type ignition.
TerryComment
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Re: C3 - tach cross-gear chewing problem
Seb:
The last time I replaced that gear on my 69 I ordered a kit from Paragon that included a set screw, a drill guide, a bushing installation tool, and a tap guide tool. These are used to drill a 1/4-28 hole in the back of the distributor housing, tap it, and install a set screw. This does not allow the cross gear to move forward causing the breakage at the end of the gear. Mine has been there for about 10 years without problems.
Hope this helps.Comment
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