Name that bolt!?
Drifting
Joined: Jul 2002
Posts: 1,995
Likes: 110
From: Garland Texas
The changeover to metric started in 78 but only on newly designed parts. When the Malibu changed in 78 it was a completely different car except for engine and trans and related parts. So all the body bolts were metric and the engine bolts were SAE. R4 air compressors were assembled and adjusted with metric but mounted to the engine with SAE.
There was nothing new on the 78 and 79 so no metric bolts. In 80 they went with the new Dana diff. New spring mounting design so it got metric bolts even though the Dana internal bolts were still SAE. 84 was a new car but, same as the Malibu, only the engine had SAE.
The blue color designated metric threads so they could be easily identified. The metric changover cost us(mechanics) thousands of dollars in new tool purchases. American metric bolts are not the same size as Japanese metric. We use 5.5, 8, 10, 13, 15, 18, 21, 23. They use 6, 8, 10, 12, 14, 17, 19 mm.
Mike
There was nothing new on the 78 and 79 so no metric bolts. In 80 they went with the new Dana diff. New spring mounting design so it got metric bolts even though the Dana internal bolts were still SAE. 84 was a new car but, same as the Malibu, only the engine had SAE.
The blue color designated metric threads so they could be easily identified. The metric changover cost us(mechanics) thousands of dollars in new tool purchases. American metric bolts are not the same size as Japanese metric. We use 5.5, 8, 10, 13, 15, 18, 21, 23. They use 6, 8, 10, 12, 14, 17, 19 mm.
Mike
Racer
Joined: Sep 2009
Posts: 437
Likes: 3
From: Alvin Texas
Trackdogg is right on. anything new was coded blue for the metric, to aide in the assembly. Going through the change as a mechanic then was an adventure having to deal with the two systems. I still have new blue bolts removed from cars of that era when we changed or added accessories; been a long time.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 98
From: Ontario
The changeover to metric started in 78 but only on newly designed parts. When the Malibu changed in 78 it was a completely different car except for engine and trans and related parts. So all the body bolts were metric and the engine bolts were SAE. R4 air compressors were assembled and adjusted with metric but mounted to the engine with SAE.
There was nothing new on the 78 and 79 so no metric bolts. In 80 they went with the new Dana diff. New spring mounting design so it got metric bolts even though the Dana internal bolts were still SAE. 84 was a new car but, same as the Malibu, only the engine had SAE.
The blue color designated metric threads so they could be easily identified. The metric changover cost us(mechanics) thousands of dollars in new tool purchases. American metric bolts are not the same size as Japanese metric. We use 5.5, 8, 10, 13, 15, 18, 21, 23. They use 6, 8, 10, 12, 14, 17, 19 mm.
Mike
There was nothing new on the 78 and 79 so no metric bolts. In 80 they went with the new Dana diff. New spring mounting design so it got metric bolts even though the Dana internal bolts were still SAE. 84 was a new car but, same as the Malibu, only the engine had SAE.
The blue color designated metric threads so they could be easily identified. The metric changover cost us(mechanics) thousands of dollars in new tool purchases. American metric bolts are not the same size as Japanese metric. We use 5.5, 8, 10, 13, 15, 18, 21, 23. They use 6, 8, 10, 12, 14, 17, 19 mm.
Mike
Burning Brakes
Joined: Dec 2011
Posts: 844
Likes: 6
From: Fort Wayne, IN
a friend of mine was driving his 79 Vette last thursday and the driver's side trailing arm failed....bolt that attaches the spring to the trailing arm pulled straight through the t/a...twisted and torn metal. Luckily he was a few feet from his parking space...still had to get a town, but he wasn't charged for it since it wasn't very far.
Le Mans Master
Joined: Jul 2000
Posts: 6,001
Likes: 112
From: Saginaw Michigan
For several years while GM was converting a lot of their nuts and bolts to metric, suppliers were instructed to use a blue dye on the metric fasteners.
I think that the blue dye requirement was buried in a purchase specification so that the dye requirement could be eliminated by updating the spec and not having to change a million nut and bolt drawings.
Interesting fact, the Saginaw power gear housing had tapped bosses for the mounting bolts to screw into. Whatever the metric equivalent for the mounting bolts, the metric bolt would strip out a gear housing pad that was a conventional thread. I don't remember what the exact sizes were. But Saginaw never converted the gear housing to metric in fear that using the wrong bolts could cause a safety problem.
Jim
I think that the blue dye requirement was buried in a purchase specification so that the dye requirement could be eliminated by updating the spec and not having to change a million nut and bolt drawings.
Interesting fact, the Saginaw power gear housing had tapped bosses for the mounting bolts to screw into. Whatever the metric equivalent for the mounting bolts, the metric bolt would strip out a gear housing pad that was a conventional thread. I don't remember what the exact sizes were. But Saginaw never converted the gear housing to metric in fear that using the wrong bolts could cause a safety problem.
Jim
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Melting Slicks
Joined: Aug 2001
Posts: 3,046
Likes: 124
From: Wichita KS
Years ago I asked Dave McLellan about the blue finish on some of the fasteners on my 1980. I thought it was some sort of protective covering. He related the blue finish was to id the fastener as metric.
Melting Slicks
Joined: Aug 2001
Posts: 3,046
Likes: 124
From: Wichita KS
The three rear bolts retaining the rear spring to the differential carrier are metric. The longer two bolts are Hex M12 x 1.75 x 90 (10.9 PC). The shorter bolt is Hex M12 x 1.75 x 30.
BTW the driver's side bolt on my 1980 was also broken off. I removed the entire batwing and had a machinist remove the remaining bolt shaft. The machinist then installed heli-coils in all three bolt holes (I personally don't like the idea of tightening steel bolts into aluminum threads).
BTW the driver's side bolt on my 1980 was also broken off. I removed the entire batwing and had a machinist remove the remaining bolt shaft. The machinist then installed heli-coils in all three bolt holes (I personally don't like the idea of tightening steel bolts into aluminum threads).
Thread Starter
Advanced
Joined: Aug 2011
Posts: 75
Likes: 0
From: Calgary Alberta
Hopefully not over $5 a piece.
http://parts.nalleygmc.com/products/.../11514112.html
http://parts.nalleygmc.com/products/.../11514112.html