Triumph Stag - Borg Warner Gearbox Tips 

Good transmission. If it won't go in reverse and you've checked the linkage it's probably either the clutch or the rear band. If it'll go to top gear it's the rear band. They were better in Volvo's. I still prefer a manual transmission in these older machines.

Unfortunately the technical analysis was extremely light weight. Yes lots of talk about fluid but not the various options available for the improved friction materials available for the clutches and bands. Nor was there any discussion regarding the various torque convertors (3 sizes depending upon torque capacity) sprags (a stronger BW51 sprag is a direct fit) valve body options and throttle cams, various sized front servos or range control valves that can be fitted to these transmissions to improve shift performance and durability. The BW35 was a versatile light weight world transmission built to suit engine capacities from 1.5 litres to 4.4 litres (Leyland P76 V8). Even Ford in their 289ci Falcons used a BW35 during the mid 1960s. In OZ they were upgraded to BW40 and BW51 status in Fords big six Efi engines into the 1980s. Many components can be upgraded using the later version BW40/51, even the entire geartrain from a BW40 will fit into an early UK case BW35. As for ATF several types of fluid are available depending upon the frictions and bands used in the transmission for firmer or softer shift quality. Type F generally for the early model BW35 using the original friction specifications and Dexron for later spec frictions within these transmission generally after a rebuild.

Great video thanks. I’ve just bought a stag and the auto box kept dropping out of gear. Had it looked at and it had been overfilled. Would have never known without these experts to help.

Makes a lot of sense. Never heard of dipping the stick while engine running, thats a great tip. Not knocking his skill but would have thought that if asked to diagnose reason for failure and one if the main reasons is either too much or too little oil, i would have drained all fluid and checked against factory reccomend volume. And also considered having the oil checked for type. Just for the sake of determining what actually caused the plates to deteriorate. Could the plates of actually been ok at purchase time, and be damaged by friction heat build up on the trip home due to low oil level? Cheers

Very informational this has been. Does this suggest if the gear box has been sat a long time (27 years) and we top it up after all this time we are fine or is it wise to actuallly get the auto box looked at? Or will it be fine long as we refilled it before use?