Hey guys, I just bought a Mack RD688SX with a allison 5 speed automatic trans and a 672 rear end. Max hwy speed is 53 mph. I'm a scrap iron dealer located in the Houston, Tx. area. I need to get this old ride running at least 70 mph. I have contacted the local Mack dealership and they tell me there are no parts available for re-gearing the chunks. Their solution to my problem was to replace the 65000 lb rears to 44,000lb with a 520's ? something rears. They also said that I could leave everything like it is and add a 2 speed aux. gear. Anybody have any experience with this problem ??
