Brake master cylinder bore differs on std vs. HD brakes for 1990???

[HallenTi]

I am in need of a rebuilt brake master cylinder for my 1990 coupe, with the Z51 and FE3 options (one of the two includes HD brakes - I can't remember right off!). I know for sure that it has the 13" directional front rotors (have had to replace them in the past). My question: Some parts stores show a difference between the bore size on the brake master cylinder, depending on "standard" or "HD" brakes. Is there actually a difference in bore size? One parts man speculated that the difference might just be the size of the fittings, but newer reman people may include adapters so one brake master cylinder fits either. Does anyone know for sure? Thanks, Tim

 

[HallenTi]

I did some checking and found a remanufacturer - Pacific Brake Bond (PBB) - that appears to have the answer, so thought I'd include it here in case anyone else had the same question. I saw a 1984 master cylinder for sale on eBay so asked how it compared to the 1990 w/HD brakes master cylinder. Warren at PBB said: "The 84' master has a 13/16" bore with 3 inlets & the 90' master has a 15/16" bore with 2 inlets plus a built in proportion valve." Tim

 

[HallenTi]

Not wanting to be dishing out false information, I wanted to add that after my post and update, the rebuilder replied back to me, correcting himself, saying that all 1990's had the 7/8" bore cylinder whether it has standard or HD brakes. Just thought I'd better pass that along as well.