1970 Clutch Cross Shaft Zerk Fitting Thread Size?

[Mark E.]

The thread size of the hole for the zerk in my clutch cross shaft is 3/8"-16. Yet I can't find a zerk with that thread size. The 3/8" zerks for sale I found are 18 or 24 thread pitch.

Do 3/8"-16 size zerks exist? Or has the cross shaft been improperly rethreaded?

[Joe L.]

Re: 1970 Clutch Cross Shaft Zerk Fitting Thread Size?

The thread size of the hole for the zerk in my clutch cross shaft is 3/8"-16. Yet I can't find a zerk with that thread size. The 3/8" zerks for sale I found are 18 or 24 thread pitch.

Do 3/8"-16 size zerks exist? Or has the cross shaft been improperly rethreaded?

Mark------

No zerk fitting ever used ANYWHERE on a Corvette was ever 3/8" of any thread pitch. So, yours has been modified.

SEE CORRECTION BELOW

[Mark E.]

Re: 1970 Clutch Cross Shaft Zerk Fitting Thread Size?

Mark------

No zerk fitting ever used ANYWHERE on a Corvette was ever 3/8" of any thread pitch. So, yours has been modified.

Bummer. But thanks Joe.

[Joe L.]

Re: 1970 Clutch Cross Shaft Zerk Fitting Thread Size?

Bummer. But thanks Joe.

Mark-------

My apologies. I was INCORRECT. The threads for the cross shaft grease fittings are 3/8". I believe they are UNF 3/8-24 but I am not 100% certain of that.

Notwithstanding this, I can't think of any other zerk fitting on a Corvette that is this large.

By the way, I cannot find that GM ever supplied this size zerk fitting in either PRODUCTION or SERVICE. The cross shafts installed in the cars were not fitted with a zerk fitting. Instead, a plastic plug filled the zerk fitting orifice with the zerk to be field installed.

[Mark E.]

Re: 1970 Clutch Cross Shaft Zerk Fitting Thread Size?

Thanks Joe. I couldn't find a 3/8"-16, so I ordered 3/8"-24 and will hope for the best.

From what I've read, grease should be added until the shaft is full and it oozes out the ends.
Is this correct? I ask because it will take most of a tube to do this. In the past, I removed the shaft and lubed up the ends by hand.

[Chris H.]

[Keith M.]

Re: 1970 Clutch Cross Shaft Zerk Fitting Thread Size?

I would not fill the shaft. It works. But think about it. What is the service interval? If you keep filling the shaft the grease that reaches the ends..which is the only place it needed.... will be what...10...15 years old? probably more. Grease does not technically go bad I suppose...but. Just a thought.

[Barry H.]

Re: 1970 Clutch Cross Shaft Zerk Fitting Thread Size?

Mark & Joe, I was under the impression that Zerk Grease fitings were tapered Pipe threads. I found 2 taperd Pipe taps, 1/16"-27 threads
& 1/8"-27 threads they are both listed as American Standard Dryseal Pipe Threads in the "Machinist's Practical Guide".
Barry Holmes

[Joe L.]

Re: 1970 Clutch Cross Shaft Zerk Fitting Thread Size?

Mark & Joe, I was under the impression that Zerk Grease fitings were tapered Pipe threads

Barry------


I used to think so, too. I always thought that all zerk fitting threads were NPT or some special, self-tapping thread. But, I was wrong. While most zerk fittings are so, some are UNF. As it turns out and to my surprise, the clutch cross shaft zerk is among the UNF fittings.

[Joe L.]

Re: 1970 Clutch Cross Shaft Zerk Fitting Thread Size?

Thanks Joe. I couldn't find a 3/8"-16, so I ordered 3/8"-24 and will hope for the best.

From what I've read, grease should be added until the shaft is full and it oozes out the ends.
Is this correct? I ask because it will take most of a tube to do this. In the past, I removed the shaft and lubed up the ends by hand.

Mark------


I'm virtually certain now that the threads are 3/8-24.

Yes, the purpose of the fitting is to allow the cross shaft tube to be filled with grease and, thereby, grease the ball studs and seats at each end which are the only things that need lubrication.

However, that's not how the factory did it. They applied grease to each of the ball studs prior to the installation of the cross shaft. That was deemed adequate and I'm sure it was. As a matter of fact and as I mentioned previously, no zerk fitting was even factory installed in the cross shaft. Instead, the drilled and tapped orifice was fitted with a plastic plug and that's how the cars were delivered.

Zerk fittings were installed in SERVICE. This allows the cross shaft ball studs to be lubricated without removal of the cross shaft. No harm is done by filling the cross shaft. It's just that a lot of grease is wasted when this is done but it's easier than removing the cross shaft. However, if one has the cross shaft out of the vehicle for some other reason, the ball studs can be properly lubricated just as the factory did and, then, it's not necessary to inject grease at a zerk fitting. Given the rather limited operation that the VAST majority of these cars get in today's world, the ball studs can be considered "lubed-for-life". As a matter of fact, GM service instructions never called for the cross shaft to be lubed through a grease fitting or for the ball studs to be serviced at any particular or regular interval.

So, if you wish to remove the cross shaft and lubricate the ball studs, that's fine. If you wish to lubricate them by filling the cross shaft with grease via the zerk fitting, that's fine, too.

[Mark E.]

Re: 1970 Clutch Cross Shaft Zerk Fitting Thread Size?

Joe,

As always, I appreciate your help and thorough reply. Thank you.

[Mark E.]

Re: 1970 Clutch Cross Shaft Zerk Fitting Thread Size?

I would not fill the shaft. It works. But think about it. What is the service interval? If you keep filling the shaft the grease that reaches the ends..which is the only place it needed.... will be what...10...15 years old? probably more. Grease does not technically go bad I suppose...but. Just a thought.

Think about how old wheel bearing grease gets in a much more demanding application.

[Ron G.]

Re: 1970 Clutch Cross Shaft Zerk Fitting Thread Size?

Just my two cents worth. Like everyone else replied, absolutely no Zirk fitting.

[Joe L.]

Re: 1970 Clutch Cross Shaft Zerk Fitting Thread Size?

Just my two cents worth. Like everyone else replied, absolutely no Zirk fitting.

Ron------


By the way, the original plastic plug was never available in SERVICE but I suppose it's probably available in reproduction.

[Ray K.]

Re: 1970 Clutch Cross Shaft Zerk Fitting Thread Size?

Mark, Joe, others--

I finally got curious enough to go take a look at the cross shaft on my 1965. After a bit of a search, I located the grease zerk that was once installed in the cross shaft. Removed the plastic plug and screwed in the zerk fitting. There may be some zerk fittings with a 3/8 X 24 thread but my car is not one of them. I then tried a couple of other fittings from my brass assortment that matched the zerk threads and all were the correct thread size. A bolt with a 3/8 X 24 thread will screw into the threads on the cross shaft but gets tight after a couple of turns. Using a tap from my Craftsman set to verify the threads - the tap is clearly stamped as ( 1/8 PIPE ). My guess is that the cross shafts would have had a pipe thread to easily accept a standard grease zerk fitting.

Ray