I have had BW overdrives for 45 years. The T86 will handle a 350. The T85 and T89 will handle big engines. Olds used them behind their big blocks. Overdrive is usable in all 3 gears, but it is not practical. Overdrives do become free wheeling at under 28 mph which is awkward. However, the overdrive can be locked out with a cable operated lever. The governor is what senses the 28 miles per hour. I drive mine around with the overdrive locked out around town and use the overdrive on the highway. I like 3.89 and 4.11 rears. It gives you plenty of acceleration in town. A .70 overdrive gives me an effective rear ratio of 2.73 and 2.88 which gives excellent fuel economy. Back when I ran on quarters marked off on country roads, I used 2nd over which gave me just the right gear to finish the quarter. Overdrives were never very popular with GM big they were big with Ford, and there is much parts interchangeability. Few people use them because they don't know how to drive them to get the most out of them. My first overdrive was in a 56 Ford I bought over 45 years ago. I have always had overdrives, and I am strongly thinking of putting one behind a 302 GMC and use the factory 56 GMC 3.90 rear. An overdrive is not free wheeling at speeds over 28 mph.
Last edited by crenwelge; 09/26/2008 6:19 PM.
