1969 distributor tach gear L36

[Joe T.]

Hi guys: My distributor (GM:111926) seems to have a lot of end play (1/8" or a little more) in the tach drive gear assembly. This car has a history of eating tach drive gears (and distributor main gear tach drives). I wondered about the end play being a culprit in this problem. I have seen buttons and thrust washers in catalogs , but do not have those parts when I diassembled this distributor. I don't see room inside the tach drive "hole" for more parts than I have. The Chevy overhaul and service manuals don't have any reference to this drive assembly.
Now for the questions: Is there a "button" that lives inside this thing? Is this end play normal? I don't know where else to look in my references. Thanks and regards...joe

[William C.]

Re: 1969 distributor tach gear L36

Originally there is no button, but there is a small washer between the gear and the brass coupler. Usually, over time, the crossgear will "eat" it's way into the cast iron at the end of the cavity away from the coupler, and then a thrust washer may be retrofitted, Chevy started using one in the 70's, but they drilled a hole thru the housing to retain the washer, and it is very visible. There are other approaches that take a little more time to accomplish, but first I would chack to see it you have the spacer between the cross-gear and the coupler, second, check the distributor housing for wear opposite the end where the coupler screws in, and if wear decide which repair option you need. Also, if the car is a "serial eater" I'd look real hard to make sure the cable isn't too long, putting foreword pressure on the cross gear resulting in the gear eating itself into the housing.

[Joe T.]

Re: 1969 distributor tach gear L36

Bill: Thanks for the info and insight. The car is indeed a "serial eater" and I don't know why. That doesn't sound normal. I didn't, but now do have the washer between the coupler and the driven gear. I also have a 90 degree coupler to add if this continues. I also checked several times to see if the tach cable was binding and causing extra stress and wear on the gear train, but that seems to be OK. Rebuilding this distributor has become something of a habit (3 new driven gears and two mainshafts) so its not a mystery or strange undertaking, but it seems a waste of money unless I can fix this problem. How would I check to see if there is wear in the "well"? It looks like a good machined surface in there, with a small protusion that fits into the end of the driven gear. Looks ok, but I don't know what its supposed to look like. Stay tuned?
Again, thanks for the information and I will try as you recommended. Regards...joe

[Jim T.]

Re: 1969 distributor tach gear L36

Joe I recommend you visit www.tispecialty.com/articles/article6.htm and learn how to work on your distributor. Very good article by a specialist. You mentioned end play I believe that the tach gear has. How much clearance does your distributor shaft have at the distributor shaft gear end that drives off the engine camshaft? My factory set up distributor had to much on my 68 and my 70. Purchased a box of shims from GM and set them up. Check out the refurbishing of the upper bearing oil cavity. My 68 had only hardened crud in this cavity. Distributors are one of the most unmaintained part on a Corvette and I am guilty, the maint should of been in the owners manual and service manual.

[Timothy B.]

Re: 1969 distributor tach gear L36

Joe,

The machined surface and small protusion you are seeing inside the distributor is caused by the gear wearing on the distributor. The inside wall of the distributor should be flat and when this wear occures the alignment changes between the gears and you know the rest.

[William C.]

Tim has the correct problem Identification! *NM*

[Joe T.]

Re: 1969 distributor tach gear L36

Thanks guys. I was afraid someone was going to say that.

Now that I know that the wear is there and significant by my view, what is the corrective action? I don't want to replace the distributor, since I believe it is original with the car. I don't think putting a loose washer back there is a sound idea, since there is the opportunity for it to wind up in the mainshaft housing or worse. I see that the tach (driven) gear has a shouder between the gear and rear of its shaft. Is there a washer or thrust bushing that will ride in this shoulder and keep the driven shaft off the housing? Do I drill out the rear of the housing and put one of those "buttons" in there? (Does anyone have a picture of one of these distributors with that button)? I have rebuilt this distributor more than once, so it should be fine as far as the mainshaft goes, but I will certainly break it down again, clean it up and bring it up to spces. Thanks again....Its a good thing I like doing this...it never ENDS!

[Joe T.]

Re: 1969 distributor tach gear L36

Jim:
Thank you for the direction to that site! It is a WEALTH of information and describes my problem(s) EXACTLY! Now all I have to do is figure out what I am going to do. I MAY braze (brass) the end of the driven shaft and grind it to fit and give me the end play (.010) that is required. I haven't read all the options yet, but most of them do not sound easy. My other option seems to be to drill the distributor to accept this button. Does anyone know why some distributors had the button and some did not?
Thanks again...stay tuned for progress in case anyone else has this problem? Its amazing it hadn't surfaced here before, but I found nothing in the archives.

Thanks agains and regards...Joe

[William C.]

Re: 1969 distributor tach gear L36

It is possible to drill partway into the housing from inside the tach gear cavity, and then drop one of the brass thrust washers available from Corvette vendors into the hole, and wind up with a repair that is not detectable from the outside. Usually this will require the deletion of the washer between the crossgear and the retainer that holds the crossgear, depending on the thickness of the added thrust washer. That should end the Hunger your distributor has for mainshafts and crossgears.

[Terry M.]

Re: 1969 distributor tach gear L36

Joe the addition of the nylon button, and the accompanying through-hole to locate it, was an effort (too little, too late) to minimize the tendency of the tach drive gear to eat itself and the main shaft gear. As Bill points out a shallow hole can be drilled in the inside to locate the button without altering the external appearance of the housing.
As someone mentioned that hole came about during 1970 model year, so if you ever intend to have your 1969 judged you want to avoid it.

[Joe L.]

Re: 1969 distributor tach gear L36

Joe-----

The installation of the thrust button will likely be the end to your problems. The reason that Chevrolet added the button about 1970? Very simple; to correct EXACTLY the problem that you've had and that MANY, MANY others had. My original 1969 distributor, manufactured without the button, lasted about 40,000 miles before the tach gears failed. I bought a new SERVICE distributor at that time of the same part number but which, by then, had the button installed. It lasted for 160,000 miles and was still fine when I took it out. That's the difference that the button makes. And, we're talking about the stock, NYLON button here. I think that the bronze button will be even more durable.

As others have suggested, you can attempt to drill the hole for the "pin" on the button without drilling through. However, if you do drill through, it's no problem. After installing the button, simply fill the external hole with epoxy, sand to surrounding contour after curing, and paint. No one will know the difference.

One note of caution: while the button will usually solve the tach gear problems, sometimes the problem is due to improper alignment of the centerline of the mainshaft with the centerline of the cross gear. This problem is created at the time that the distributor housing was originally machined. The only way that I know of to correct it is to install new bushings and jig-bore them to proper alignment. However, the only vendor that I know of that offered this service was Hi-Tech Innovations in Florida and I understand that they've gone out of business. I know that Dave Fiedler at TI Specialties, as well as many others, can install new bushings and ream them for proper sizing. However, I don't know that he has the capability to jig-bore the bushings.

[Clem Z.]

also shim the main shaft vertical play to

.005/.007 to help prevent chewing up the gears

[Jeffrey S.]

Re: 1969 distributor tach gear L36

Joe:
I had this problem on my '69 and I purchased a kit from Paragon that included some guides and a set screw. The guides let you drill into the back of the distributor, tap the hole and insert the set screw. Very easy fix and never had the problem again. In my experience, the problem was that the natural action of the brass gear was to move to the other side of the housing and the back end of the gear was eaten up. This set screw prevented that movement forward and the center of the gear was in the center of the mainshaft gear. Paragon still sells the entire kit including the tack gear for $55 or you can buy the installation tools seperatly.
Jeff