Help! need to replace tach cross grear

[jswope]

I need to replace the tach cross gear in my '74 350. I have the new gear, high tech bushing (with needle bearings) and a brass button. The old gear has a round spot eaten out of the edge. It looks like it slipped in too far, got stuck and got chewed on long enough to cut a nice crescent into the teeth.

I had this gear and dist. shaft replaced about a year ago. (twice) The second time after only two days of use. First time only replaced cross gear, second time replaced gear, dist shaft, and plastic button. All of this done by others last time. This time I think I want to try it myself.

Now for the questions:

Can the button be installed without removing the Distributor?

If so, is it advisable to do this repair without inspecting the shaft gear?

If I remove the dist., can it be removed and replaced without having to reset points and timing, etc?

Any other words of wisdom before I dive in?

 

[JohnZ]

If I remove the dist., can it be removed and replaced without having to reset points and timing, etc?

Any other words of wisdom before I dive in?

Yes, the distributor needs to come out, and is easy to re-install; mark the housing where the rotor tip is, mark the housing clamping flange and the intake, and don't turn the engine over while you have the distributor out.

Suggest you use the link below to Dave Fiedler's site, which has an excellent article on problems, solutions, and how to rebuild a Corvette tach-drive distributor:

www.tispecialty.com

 

[jswope]

Wow! Dave's site scares me. All I want to do fix my tach drive. Dave's site said that the 74 should have a through hole for the plastic button. Is he saying that I should see a hole on the case opposite the opening for the bushing and cross gear? If so, I do not see this. Does this mean that I do not have the correct distributor? Sorry if I sound dense but, I thought this repair should be simple other than the possible need to remove and reinstall the distributor and possible need to replace the main shaft. Hopefully, with all the repair kits being sold for this on the web, the kind of adjustments Dave's site talks about (milling etc.) are not normally needed.

If it is likely to take that kind of effort, I think I will upgrade to a new HEI dist. with a mach. drive and install the high tech bushing and gear in it. Has anyone out there done this?

 

[petes74ttop]

Great Article

Thanks for posting such a great indept article, I'll keep that one for the future. PG.

 

[73shark]

Is he saying that I should see a hole on the case opposite the opening for the bushing and cross gear? If so, I do not see this.

The hole is small and hard to see w/ the distributor in the car. It's opposite the tach shaft output end. When you have the dist. out of the car, you use the hole to punch out the plastic button.

 

[jswope]

Thanks. I found the hole (before I removed the dist.) I guess I will go ahead and remove the dist. and inspect the tach gear on the main shaft before I try anything else. Thanks again.

 

[73shark]

While you have it out, check the side play between the main shaft and the bushings. Any slop here causes erratic spark timing at higher rpms. Also check the end play which is controlled by the shim washers between the gear and the lower end of the housing.

 

[6880 Mike]

...I guess I will go ahead and remove the dist. and inspect the tach gear on the main shaft before I try anything else....

If the cross gear is chewed up, it usually takes the shaft with it when it fails.

 

[GTR1999]

Also check the new gears for fit. I haven't had a distributor to rebuild in a few years now but the last 2-3 I found the new side gears and main shafts were not machined correctly. I played with several and returned them all. I was told by a supplier the brass button on the end had to be fit to engage the mesh, well that sure wasn't the answer. I machine off 001 at a time and even fit a new brass plug oversize to machine, the gear mesh was bad. Hopefully that is corrected. After getting the same crap from 3 vendors I used an old GM gear I had and it fit perfect.

 

[jswope]

Thanks for all the input. I have been thinking about replacing this distributor with a new HEI w/tach drive. There is one being sold by dependonauto in Martin TN. Do an any of you have any experience with thier distributors? Opinons about this kind of "upgrade"?