Distributor Main Shaft Drive Gear(s)

**Timothy B.** · January 13, 2015, 03:41 PM

Re: Distributor Main Shaft Drive Gear(s)

HI Stu,

Pick it up and walk it clockwise completely around and try it one tooth counter clockwise compared to where it was. Just pick it up enough to move the gear, the oil pump drive will follow.

You will get a feel for this and if the oil pump drive will not allow the distributor to drop back down it only takes a few seconds to walk it completely around and somewhere in that 360* you will find the oil pump drive again and it will walk around as you move the distributor one tooth at a time to get where you want to be.

**Larry M.** · January 13, 2015, 04:47 PM

**Stuart F.** · January 13, 2015, 04:55 PM

Re: Distributor Main Shaft Drive Gear(s)

Thanks Tim. You and I are on the same page with that method. I think I've done that since my first Chevy V8 back in 1956, but it was not as easy with the old style (small rotor) distributors.

This one has me fooled because I was so sure I hit my marks. BTW, I found I could walk the distributor even with the tach drive cable connected as well as the primary lead (cap off of course). But, unless I hear otherwise about the drive gear, I'll do as you say and try one more tooth clockwise. It is hard to admit, but maybe I'm just loosing my touch due to old age I guess. However, I did have success yesterday tweaking my son's 69 L-89 tri-power (Holley's).

Stu Fox

**Stuart F.** · January 13, 2015, 05:06 PM

Re: Distributor Main Shaft Drive Gear(s)

Thanks Larry for the reply. I'm with you on the indexing. My engine is all GM original 63 L-76 that's never been apart. My dimple is correct to the rotor. I even pulled the distributor out again to check it as sometimes these old cataract eyes can play tricks on me. It's right, and as noted I barred the engine over to TDC before I dropped it so I have arrived at: What now? Were there more than one gear?

I will do as TIM suggested and go one more tooth tomorrow. I just don't like flames through my expensive 3461s Carburetor, if you know what I mean.

Stu Fox

**Larry M.** · January 13, 2015, 05:24 PM

Re: Distributor Main Shaft Drive Gear(s)

Originally posted by Stuart Fox (28060)

Thanks Larry for the reply. I'm with you on the indexing. My engine is all GM original 63 L-76 that's never been apart. My dimple is correct to the rotor. I even pulled the distributor out again to check it as sometimes these old cataract eyes can play tricks on me. It's right, and as noted I barred the engine over to TDC before I dropped it so I have arrived at: What now? Were there more than one gear?

I will do as TIM suggested and go one more tooth tomorrow. I just don't like flames through my expensive 3461s Carburetor, if you know what I mean.

Stu Fox

Stu:

If one tooth as Tim suggests works, that is great. If however, you only need 1/2 tooth, then what I said will work for you (rotate the gear 180 degrees). It is possible that the gear you purchased is different than the original factory GM gears, and thus requires this 180 degrees out installation.

Is the new gear from GM/Chevrolet or from another place like Jegs, Summit, Crane, Isky etc etc???

Good luck to you.

Larry

**Ken A.** · January 13, 2015, 05:35 PM

Re: Distributor Main Shaft Drive Gear(s)

There are 2 gears. One, for HEI, measures .500 inside. The other, for your app, measures .491; easy to mix up.

**Stuart F.** · January 13, 2015, 06:23 PM

Re: Distributor Main Shaft Drive Gear(s)

Larry and Ken;

Thanks for your input. The gear I put on was from a rebuilt unit that bought for why I don't know other than to keep around as a spare. It appears correct and fits the shaft perfectly.

I will give the "one tooth" move a try tomorrow and, if it fails, will go back to my original gear which wasn't all that bad. I just wanted to tighten the unit up where ever possible.

Thanks again.

Stu Fox

**Joe L.** · January 13, 2015, 10:54 PM

Re: Distributor Main Shaft Drive Gear(s)

Originally posted by Stuart Fox (28060)

Were there ever more than one drive gear for GM Chevrolet distributors?

I put a new one that I've had for many years on my distributor rebuild. I am having trouble getting it to time up properly, and yes, the dimple is oriented correctly with the rotor. I set up my installation by barring my engine over to TDC (I have a timing tape on my dynamic balancer).The only mark I can see with my timing light close to the timing tab is the 10 degree mark, I.e. It is too far advanced and can not retard the distributor any more. It is against the coil bracket. It seems to run ok, but it starts like it's too far advanced.

I've never had any trouble dropping a distributor like this before.

Any thoughts?

Stu Fox

Stu------

From 1965 to 1985 GM cataloged only one distributor drive gear for ALL Corvette applications-----GM #1958599. Presumably, this was the gear also used in PRODUCTION. This gear was also SERVICE for 1955-64 Corvettes.

**Jim T.** · January 14, 2015, 11:09 AM

Re: Distributor Main Shaft Drive Gear(s)

Stuart if your original distributor gear was running with the original camshaft gear all these years, why did you want to change it?

**Duke W.** · January 14, 2015, 02:16 PM

Re: Distributor Main Shaft Drive Gear(s)

Good question for Stu.

Duke

**Stuart F.** · January 14, 2015, 07:41 PM

Re: Distributor Main Shaft Drive Gear(s)

OK, Gentlemen. I get it. I will probably change it back tomorrow. I was just a little concerned about the wear pattern on the gear, both on the gear teeth and the top face bearing on the main housing (with shims). As it stands now, my distributor rehab project has diminished down to only adding the set screw bearing on the old steel cross shaft. I could not use ANY buttons, bushings, or shafts in the process. They are all going back tomorrow. Now I can't even change the gear!

Thanks, as always, for your welcomed advice.

P.S. I spent the day ferrying my son's Covetttes to the Mecum Auction.

Stu Fox

**Joe C.** · January 15, 2015, 11:09 AM

Re: Distributor Main Shaft Drive Gear(s)

Stu,

The steel gear available from GM is clocked differently than the original type iron gear.

**Gene M.** · January 15, 2015, 01:31 PM

Re: Distributor Main Shaft Drive Gear(s)

I can not imagine any wear of any concern even with 100,000 miles. The gears have so much contact area and the load to drive the distributor and the oil pump is low for those type gearing. Only if one were using a special high output oil pump with 50 weight oil would any issue be of concern.

**Joe C.** · January 15, 2015, 01:53 PM

Re: Distributor Main Shaft Drive Gear(s)

Gene,
I put a Comp solid roller cam in my engine and it chewed the shlt out of the stock, iron gear. The cam is made of iron, but is nitrided, so I didn't think there should be a problem. Timing moved about 10 degrees over time so, sure enough the gear was chewed up on the driven side. I installed a GM STEEL gear and now they make nicey-nice together.

Oil pump is standard volume pump with 58# (HP) relief spring. It is NOT a high volume pump.

Distributor Main Shaft Drive Gear(s)

Distributor Main Shaft Drive Gear(s)

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