SAE or Metric

[Greg S.]

I need to remove the bolt that holds the steering shaft to the cloth coupler on my 75. It is a 12 point bolt. Is it SAE or Metric size? I need to buy a socket set and don't want to buy the wrong type. When if ever did GM switch to metric size? Any recommendations on sources for 12 point sockets?

[Patrick H.]

Re: SAE or Metric

SAE.

I just use the 12 point socket that comes in the standard tool kit, nothing special.
Look at your sockets - some have 6 points and some 12. I use the 12 and have never had a problem.

Patrick

[Edward J.]

Re: SAE or Metric

I need to remove the bolt that holds the steering shaft to the cloth coupler on my 75. It is a 12 point bolt. Is it SAE or Metric size? I need to buy a socket set and don't want to buy the wrong type. When if ever did GM switch to metric size? Any recommendations on sources for 12 point sockets?

Greg, Those bolts should a 7/16 12pt. Gm starting using metric bolts around 78/79 What I remember is the bolt and nuts in the beginning where plated with a blue finish, this was a easy way for the tech to identify them. this was a tuff time for mechanics as there were still a lot of SAE nuts and bolts mixed in.at some point the metric was in full swing 81/82?? Tuff to remember that far back.

[Joe L.]

Re: SAE or Metric

I need to remove the bolt that holds the steering shaft to the cloth coupler on my 75. It is a 12 point bolt. Is it SAE or Metric size? I need to buy a socket set and don't want to buy the wrong type. When if ever did GM switch to metric size? Any recommendations on sources for 12 point sockets?

Greg------


As Patrick and Edward advised, an SAE 7/16" 12 point socket is all you need. You most likely have one of these in your tool box.

So, when did GM change to metric? Well, as Edward mentions, the "phase-in" started about 1978. However, not too many components of even later C3 were actually metric.

The C4 Corvette was hailed as the first "all metric" Corvette. But, it really was not. That's because the Gen I and Gen II small blocks powering most C4's (except ZR-1) used a core engine that was still all SAE. Peripherals were metric but the core engine was still SAE.

The C5 Corvette was really the first "all metric" Corvette.

[Terry M.]

Re: SAE or Metric

Greg------


As Patrick and Edward advised, an SAE 7/16" 12 point socket is all you need. You most likely have one of these in your tool box.

So, when did GM change to metric? Well, as Edward mentions, the "phase-in" started about 1978. However, not too many components of even later C3 were actually metric.

The C4 Corvette was hailed as the first "all metric" Corvette. But, it really was not. That's because the Gen I and Gen II small blocks powering most C4's (except ZR-1) used a core engine that was still all SAE. Peripherals were metric but the core engine was still SAE.

The C5 Corvette was really the first "all metric" Corvette.

One might have to define 'all metric,' and obviously GM has a different attitude toward its meaning than we do. I believe air conditioning fittings remained SAE well into the 1990s for most GM vehicles. I have not had the pleasure of putting a wrench to many C5s so I cannot cite specific examples; however other GM cars up to the end of the C4 era retained SAE air conditioning and some other tubular fittings.

[Edward J.]

Re: SAE or Metric

Terry , The A/C brackets where the first to see the metric fasteners, along with the alternators.

[Terry M.]

Re: SAE or Metric

Terry , The A/C brackets where the first to see the metric fasteners, along with the alternators.

I wasn't thinking of brackets. I was thinking of the nuts on the aluminum tubing connections.

[Tom R.]

Re: SAE or Metric

Gm starting using metric bolts around 78/79 What I remember is the bolt and nuts in the beginning where plated with a blue finish, this was a easy way for the tech to identify them. this was a tuff time for mechanics as there were still a lot of SAE nuts and bolts mixed in. At some point the metric was in full swing 81/82?? Tuff to remember that far back.

I have seen the chassis of many 78s with those powder blue nuts/bolts. From my observations, I have seen them used to secure the transmission to the tranny mount, rear portion of the frame to secure tank straps, steering linkage.

[Michael G.]

Re: SAE or Metric

In general, metric conversion was done only when a particular component redesign took place. Because there were no direct conversions from english to metric, internal threads in such things as engines and transmissions could not be easily changed to metric without revalidation, an expensive and time consuming process. As such, many fasteners on carry-over components remained english into the 90's long after the majority of the attachments on the vehicle were metric.

Some threaded parts never really did get converted. Spaced-thread tapping screws and tapered thread plugs were examples of this. An M4.2 x 1.41 metric tapping screw was really an unchanged #8 (10?) thread, "soft" converted from english to metic. On such a screw, you actually find an english thread with a 7mm metric hex head.