C3 Rag Joint Restoration

[Tom K.]

Hi All,

Tom K is back and looking for still more advice. I am really grateful for all the help so far. Having an authoritative source of info is the absolute best!

This time I'm in the midst of restoring my 1973 Corvette steering coupler. The AIM only lists a P/N for the upper flange on the steering shaft - I guess since the rest of the joint was supplied to the assembly plant as part of the steering box assembly. I did a lot of digging through the NCRS archives and found a P/N of 7818568 for the service replacement steering coupler assembly. I looked online and found an NOS coupler, but I imagine it will be really expensive (the ad said 'call for price' ) and most likely not an exact replacement. Can someone confirm that 7818568 P/N for a 1973?

Anyway, my preference is to purchase and / or make the correct parts to restore the original rag joint correctly. So...
I removed the original shoulder bolts and rivets. The rag is toast as it has broken at one of the bolt holes. I bought a Borgeson rebuild kit and the rag appears pretty good, it does have seven layers - the hardware is not worth using for a restoration, and from what I have read on the forums here the hardware may not even be safe. Also, the Borgeson rag does not have the grounding screen. My thoughts are to get all high-tech with some wire cloth and a wooden fixture that I can drill through to make the holes and then turn the OD to get the overall size right. When I look closely at my original rag joint, the wire screen does not seem to have been molded into the rubber - is that true? My thought is if it was molded on, how did they insure there would be steel exposed to complete the ground? It seems like even an adhesive might have interfered with the electrical function - any thoughts on how to attach the wire mesh piece to the Borgeson rag, or should I just assemble it under the bolts and rivets?

In my search through the NCRS archives I found drawings of the C2 steering coupler shoulder screws, but nothing on the C3 screws, so I think I will just re-plate mine. I'm wondering how close zinc plating will match the original cad plating? The copper plating should be easy enough there were several threads here with some hints and I'm pretty sure I can figure it out.

Of course I ground the heads off the rivets and knocked them out of the joint so they need to be replaced or re-made. I cannot yet find a source for the proper rivets, but I have access to a lathe and will make up a couple - unless someone knows of a source???
For dimensions of the rivets, I can measure what I've got to get most of the dimensions, except the length of the part that is peened over. I measured the upset part of the rivet heads before grinding and I will make up a tool to get the same size and shape when the new ones are heated up and peened. I am assuming the rivets would have originally been made from a low carbon steel like 1045 without any heat treatment - can someone confirm? Can someone provide the length of the rivets past the shoulder? I should be able to figure it out if necessary through trail and error - I'm pretty good at errors! But hopefully, I learn from them...

My capture strap is pretty rusty, but again I'm thinking If I sandblast and re-plate it in zinc it should be ok. The stamped bowtie shaped center thingie looks like it will clean up ok and be re-plated too. I did find the pinch bolts online, so I will buy those.

One last thing - I noticed one of the rivets is worn where it was rubbing on the upper flange, there must have been a fairly large mis-alignment between the steering box input and the steering shaft. I don't know how to prevent this after I restore the coupling - any ideas there would be appreciated too.

Has anyone gone this route to restore their original rag joint?
Am I just way over-thinking this?

Again, I really appreciate the knowledge you guys have and your willingness to help with my project


Tom Krause

[Joe L.]

Re: C3 Rag Joint Restoration

Hi All,

Tom K is back and looking for still more advice. I am really grateful for all the help so far. Having an authoritative source of info is the absolute best!

This time I'm in the midst of restoring my 1973 Corvette steering coupler. The AIM only lists a P/N for the upper flange on the steering shaft - I guess since the rest of the joint was supplied to the assembly plant as part of the steering box assembly. I did a lot of digging through the NCRS archives and found a P/N of 7818568 for the service replacement steering coupler assembly. I looked online and found an NOS coupler, but I imagine it will be really expensive (the ad said 'call for price' ) and most likely not an exact replacement. Can someone confirm that 7818568 P/N for a 1973?

Anyway, my preference is to purchase and / or make the correct parts to restore the original rag joint correctly. So...
I removed the original shoulder bolts and rivets. The rag is toast as it has broken at one of the bolt holes. I bought a Borgeson rebuild kit and the rag appears pretty good, it does have seven layers - the hardware is not worth using for a restoration, and from what I have read on the forums here the hardware may not even be safe. Also, the Borgeson rag does not have the grounding screen. My thoughts are to get all high-tech with some wire cloth and a wooden fixture that I can drill through to make the holes and then turn the OD to get the overall size right. When I look closely at my original rag joint, the wire screen does not seem to have been molded into the rubber - is that true? My thought is if it was molded on, how did they insure there would be steel exposed to complete the ground? It seems like even an adhesive might have interfered with the electrical function - any thoughts on how to attach the wire mesh piece to the Borgeson rag, or should I just assemble it under the bolts and rivets?

In my search through the NCRS archives I found drawings of the C2 steering coupler shoulder screws, but nothing on the C3 screws, so I think I will just re-plate mine. I'm wondering how close zinc plating will match the original cad plating? The copper plating should be easy enough there were several threads here with some hints and I'm pretty sure I can figure it out.

Of course I ground the heads off the rivets and knocked them out of the joint so they need to be replaced or re-made. I cannot yet find a source for the proper rivets, but I have access to a lathe and will make up a couple - unless someone knows of a source???
For dimensions of the rivets, I can measure what I've got to get most of the dimensions, except the length of the part that is peened over. I measured the upset part of the rivet heads before grinding and I will make up a tool to get the same size and shape when the new ones are heated up and peened. I am assuming the rivets would have originally been made from a low carbon steel like 1045 without any heat treatment - can someone confirm? Can someone provide the length of the rivets past the shoulder? I should be able to figure it out if necessary through trail and error - I'm pretty good at errors! But hopefully, I learn from them...

My capture strap is pretty rusty, but again I'm thinking If I sandblast and re-plate it in zinc it should be ok. The stamped bowtie shaped center thingie looks like it will clean up ok and be re-plated too. I did find the pinch bolts online, so I will buy those.

One last thing - I noticed one of the rivets is worn where it was rubbing on the upper flange, there must have been a fairly large mis-alignment between the steering box input and the steering shaft. I don't know how to prevent this after I restore the coupling - any ideas there would be appreciated too.

Has anyone gone this route to restore their original rag joint?
Am I just way over-thinking this?

Again, I really appreciate the knowledge you guys have and your willingness to help with my project


Tom Krause

Tom------



GM #7818568 is the correct SERVICE part number for the L69-82 Corvette steering coupling. Of course, it's long-since GM-discontinued. This was a very high quality part and unlike any aftermarket replacement I'm aware of.

I know of no current coupling component kits that contain parts equivalent to the original components. But, I suppose that also means that if one is to rebuild an original coupling, one has no choice but to use what's available. In case you're wondering, GM never supplied component parts of the couplings.

I believe that Jim Shea, a retired Saginaw engineer, that posts here has posted blueprints of the Corvette steering couplings. You might review his past posts in the archives for some of the information you seek.

I'd be very careful about replating any of the fasteners. Any plating performed has to include post-plating treatment to prevent hydrogen embrittlement. Also, I highly doubt that the plating that you characterize as "cadmium" is actually cadmium. Most likely, it was zinc to begin with.

[Tom K.]

Re: C3 Rag Joint Restoration

Hi Joe,

Thanks for your reply, I knew cad plating was widely used at the time and from some other experience I assumed it was more likely to be the plating on these parts. I did go through the archives pretty thoroughly and I saw many posts from Jim Shea, but none with the drawings for the rivets or screws for the later (C3) couplings (unless they are the same as the earlier couplings). As the 7818568 coupling is the service part, I would expect it is not a really good match for what was originally on my car, which is why I'm interested in restoring my original part.
I will research hydrogen embrittlement and see if this is something I can deal with and produce safe and reliable bolts. If that turns out to be the Achilles heel of my plan, do you know of a source for the bolts? Thanks in advance.

Tom Krause

[Timothy B.]

Re: C3 Rag Joint Restoration

Tom,

If you search the archives for 67-early 69 steering couplers there are pictures from me showing the service replacement Saginaw part.

I don't know off hand the differences or if the service part shown will work for you, if you think it will send me a private message as i still have a few left.

[Tom K.]

Re: C3 Rag Joint Restoration

Hello Tim,

Thank you for the kind offer, but the differences between the 67-69 early and 69 late - 82 couplers are significant. I am having the box re-done and it may turn out that I need to replace the gears. If that happens and it turns out I do need to swap to the early style coupler, I will certainly get a hold of you.

Tom Krause

[Joe L.]

Re: C3 Rag Joint Restoration

Hello Tim,

Thank you for the kind offer, but the differences between the 67-69 early and 69 late - 82 couplers are significant. I am having the box re-done and it may turn out that I need to replace the gears. If that happens and it turns out I do need to swap to the early style coupler, I will certainly get a hold of you.

Tom Krause

Tom------


The 67-E69 and L69-82 are definitely not interchangeable.

[Robert R.]

Re: C3 Rag Joint Restoration

Guys,

The following photos show at least one difference between an original rag joint (part no. 7813351) from my 19,000 mile '74 and the SERVICE replacement (part no. 7818568) that I bought over the counter in 1991 for my restored '74. You can see that the casting of the replacement part has a raised area next to the pinch bolt on the lower flange whereas the original part does not. There may be other differences that are not easily detectable when the couplings are installed.



Bob

[Joe L.]

Re: C3 Rag Joint Restoration

Guys,

The following photos show at least one difference between an original rag joint (part no. 7813351) from my 19,000 mile '74 and the SERVICE replacement (part no. 7818568) that I bought over the counter in 1991 for my restored '74. You can see that the casting of the replacement part has a raised area next to the pinch bolt on the lower flange whereas the original part does not. There may be other differences that are not easily detectable when the couplings are installed.



Bob

Bob-------


There were actually 3 different couplings used in PRODUCTION over the L69-82 period and each was supersessive to the former for SERVICE. For L69 through about 1971 the coupling was GM #7808553. From about 1971 through about 1974 the coupling was GM #7813351. Finally, from about 1975 through 1982 the coupling was GM #7818568.

I believe that at some point in this series, the wire mesh grounding feature was deleted and this was likely with the introduction of the 7818568. There may also have been other minor changes between part numbers or, even, within part numbers.

Nevertheless, my first choice for replacement over any other option absent an NOS 7808553 or 7813351 would be to use an NOS GM #7818568 if I could obtain one. In fact, that's why I acquired several of these before they were GM-discontinued [none for sale].

[Robert R.]

Re: C3 Rag Joint Restoration

Thanks Joe,
I agree with your observations. The point I wanted to make is that there was a visual difference between the original '74 production part and part number 7818568. My January 1975 "1953-1975 Corvette Parts Catalog" lists part no. 7813351 for '69-'74 and part no. 7818568 for 1975.

Looking at Tom's pictures I believe his coupling is identical to my original coupling. That would make sense for his 1973 car.

Bob

[James B.]

Re: C3 Rag Joint Restoration

Upon inspection, my service coupling (7818568) appears to have the wire mesh ground. I can feel the wires at the edge of the coupling. Do we know why the part number had changed three times between L69 - 82?

[Tom K.]

Re: C3 Rag Joint Restoration

Hello James,

Can you tell me how the wire mesh appears to be assembled to the actual rag joint disc?
I got some wire cloth that looks pretty close top that used on my original coupling, but Im not sure if I should try and find a way to heat it up and attach it to to the rag joint disc, or just assemble it beneath the bolts and rivets. My original wire mesh appears not to have been joined to the rag joint disc, but its 45 years old so Im not sure. Can you see the wire mesh in your 7818568 coupler?

Thanks in advance

Tom Krause

[James B.]

Re: C3 Rag Joint Restoration

Tom,
The wire mesh appears to be bonded to the first layer of the red speckled surface cushion. I can see and feel the wires poking out all around the edge of the cushion at that first layer.

[Gary R.]

Re: C3 Rag Joint Restoration

Tom
Maybe this will help, this is the last GM service rag I have. These pic's were taken years ago for my photo file.

[Tom K.]

Re: C3 Rag Joint Restoration

Thanks Gary, Thanks James!

I remember reading in one of the posts from Jim Shea that they used different color inks for the different applications 4-layer, 7-layer and with or without wire grounding plates. Im thinking that he was referring to service applications and my original probably didnt have a colored ink. But I may need to figure out a way to bond the wire mesh to the Borgeson rag...

The hunt continues


Tom Krause

[Tom K.]

Re: C3 Rag Joint Restoration

Well - I got this far...

I made the new rivets and made a tool to flatten them. I made four rivets thinking I will need a couple of tries to get the length right. Hopefully, my map gas torch will provide enough heat to make them form correctly.

The original parts have been tumbled and they are ready for plating.

I made the wire cloth disc for the horn ground. I will try again for a better wire cloth disc - the edges of the one I made on my 5th attempt are still kind of raggedy. As often happens in a project like this, the part I thought would be the toughest turned out to be no problem - the OD of the disc is easily cut accurately enough by marking the outline and cutting by hand with snips! I have been using a gasket punch and driving it into a 2x4 to cut the holes. Sometimes it cuts pretty cleanly and other times it doesn't. Does anyone have an idea on how to make this part more accurately? Maybe something tougher than wood would help the punch cut better - maybe a piece of nylon?

I also need to decide on a glue for attaching the wire cloth disc to the rag joint. I dont know what the original rag disc looked like, did they have a colored ink like the service replacement rag joints, or should I use a black glue and assemble it without other colors? The new 3rd edition of the 73-74 JG only has a picture from the edge of the rag joint I cant see the face of the rag so I'm not sure what should be there. Any one out there know how this should look?

Thanks again everyone!


Tom Krause