L-72 distributor questions

[William C.]

Re: L-72 distributor questions

As I recall, 1971MY was the first year for the nylon button and it did fix the problem with distributor shaft wear, at least in my last 20 years of working on distributors I've never had to repair the housing on one with the factory button.

[Joe L.]

Re: L-72 distributor questions

As I recall, 1971MY was the first year for the nylon button and it did fix the problem with distributor shaft wear, at least in my last 20 years of working on distributors I've never had to repair the housing on one with the factory button.

Bill-----


Yes, the cross gear and mainshaft gear on my 1969 distributor failed right after the warranty on the car expired at about 40,000 miles. The rear of the cross shaft bore on the housing was significantly galled. I replaced the original distributor with a brand new SERVICE distributor of the original part number. However, by that time all of the SERVICE distributors had been modified with the nylon thrust button. My replacement distributor was still going strong at about 160,000 miles when I temporarily retired it.

[Glen C.]

Re: L-72 distributor questions

Glen,

The brass button is a aftermarket fix. I believe in 1970-71 GM started using a nylon button and the distributor housing has a small hole drilled completely through the distributor where the cross gear rides for the nylon button to clip in.

If you have the brass button and want to install it, locate the hole to be drilled be installing the screw in bushing and get a 5/16" (I think) drill bit that fits snug in the bushing hole and use it as a pilot to give a drill start for the hole. This will locate the center where the gear rides. Check the brass button shaft for the hole size and stay just under so it's a press fit. Make sure you drill through straight but it's not rocket science :-)

After you drill the pilot hole have the distributor milled 1/2" diameter 1/16" deep (I forget the name of the drill bit for this) so the button sits flat inside the housing. This is necessary for the gear alignment to the main shaft.. Cut approx. 1/8" of the brass button shaft so it does not stick through the distributor and fill this small hole with JB weld. Let it harden and get a razor blade and shave it flat. Paint and you will never know it's there... Also, if you have to reduce the diameter of the brass button to fit inside the 1/2 hole you milled just chuck it in a drill and spin it against a file to reduce it a bit..

Thanks to everyone who provided feedback on this procedure. My 64 SB has been running for 25 years (that I have owned it) and has had no problem in the distributor area. Except for points. So, I think the oil and gauze procedure will work just fine for now, and I'll re-read the "two inch rule" and select, hopefully, a more compitable vac can.

[Glen C.]

Re: L-72 distributor questions

The parts house is wrong. The 201 was OE on all '63 engines and L-71, but not the others you listed.

If you don't convert to full time vacuum advance - but why on earth would anyone not do this given the benefits - you can use just about any VAC with 16 deg. or less advance because the Two-Inch Rule doesn't apply since there is no vacuum advance at idle, which is why such engines will run hot and get lousy intown fuel economy.

Regarding Joe's post, I've got the "B10" penciled into Lars Grimsrud's list - 0 @ 7" , 12 @ 12", so this may be an exact replacement for the L-72 OE 360 VAC.

My hand hand written notes that show a NAPA part number of VC-1765SP, but I don't know the source of this data.

On a note of caution, some specs list distributor degrees and some crank degrees. In not sure if the "12" is dist or crank. If it's distributor, the crank advance is 24 deg., which is way too much. Someone is going to have to buy one and test it.

All of the specs in Lar's list are DISTRIBUTOR degrees.

Duke, I just bought the B-26 aka. VC-1765 from NAPA. I tested it with my minivac, It starts to pull in @ 5, all in @ 12. I won't be able to test it on the engine for a while.

[Duke W.]

Re: L-72 distributor questions

That's within range of acceptable tolerance. It should add a maximum of 16 degree at the crankshaft.

To be sure you are measuring added vacuum advance correctly, I recommend you tie up the centrifugal advance with a stiff rubber band when testing to ensure that the centrifugal doesn't start until well above normal idle speed.

Duke

[Glen C.]

Re: L-72 distributor questions

That's within range of acceptable tolerance. It should add a maximum of 16 degree at the crankshaft.

To be sure you are measuring added vacuum advance correctly, I recommend you tie up the centrifugal advance with a stiff rubber band when testing to ensure that the centrifugal doesn't start until well above normal idle speed.

Duke

Thanks for the tip.

[Glen C.]

Re: L-72 distributor questions

No, the 201 requires 15-16" to pull for the limit, so it doen't meet the Two-Inch Rule for an engine that idles at 14". To meet the rule you need a 12" or less VAC.

The 201 15 is okay for a 327/300 with a manual transmission.

It may not meet the Two-Inch rule with Powerglide idling in Drive at 450-475.

So how about checking idling in Drive vacuum - or anyone with a base engine/Powerglide.

For '66 the 327/300 VAC was the 355, which is 16 @ 12". Maybe there's is a message in that change.

Duke

Duke, After rebuilding my 3460S (early production) AFB, carb on my 327/300 Powerglide 64 Vette, I checked the vac can and found that it is not working at all. I am reading ~15" at idle in drive from the original non-ported carb vacuum source. This reading may be affected by the lower than stock compression & the milder than stock 327/300 cam ??? I will follow your suggestion above and get the #355 or equivelant vac can and make no change to the vacuum source. Thanks again for your help.

[Terry M.]

Re: L-72 distributor questions

As I recall, 1971MY was the first year for the nylon button and it did fix the problem with distributor shaft wear, at least in my last 20 years of working on distributors I've never had to repair the housing on one with the factory button.

Nylon button started mid-1970 based on the hole in the distributor housing. 1971 was the first full year for it.