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My son and I are working on his RX-7 again and discovered it is a 78 not a 79 as we thought. Anyway, we are doing suspension, steering and brakes all at once.
The problem we now have is that the car fights us at every turn. We are mostly dealing with rusted bolts and nuts that haven't been apart since 78. We finally managed to get all of them apart with heat, brute force and other means of "persuasion".
The two bolts that are not giving up are the ones that link the control arm to the crossmember / axle carrier. The nut is off but we cannot drive the bolt out of the bushing. Before we go at it with a Sawzall we want to make sure we have replacements first.
To determine the thread size and length isn't a problem but do any of you know what strength class these bolts are? Probably not simple 8.8 class bolts. 10.9 maybe or even 12.9?
Initial cars were constructed beginning in 1978, but the factory only recognizes 79 as the first model year of production. Un-officially, the prototypes, pre-production or "early build" cars were constructed from Feb - Aug 78. "Mid production" 79's from Sept - Dec 78 and "late production" 79's from Jan -Jun of 79.
During this time, many detail changes happened that first year, not all fully documented. They changed the hood prop rod location and actuation a couple times, added a passenger door mirror, changed the A/C control, phased out the speaker dash ect...but they are all 79 models.
Hardness specs for bolts are controlled be engineering specs. Basically a bunch of engineers using mechanical and chemical properties of materials to "standardize" the tensile strength and other properties of grade 5 vs grade 8 and the other hardnesses. Fasteners for suspension assemblies usually require a higher strength than those used to say attach a cover or oil pan. Your existing head (regardless of imperial or metric) should already be marked with the appropriate hardness marking.
as mentioned, the Model Year and when the car was built have nothing to do with each other. Mazda quite often builds cars outside of what one would consider normal, the fun example is the 1993 Rx7, not a single one was built in the calendar year of 1993...
