I assume you guys use a "one - pause - one" method of shifting rather than just trying to pull it straight thru... and that you aren't loading the box up while cold.
It is possible that switching to Royal Purple trans oil might help - it'd be worth a try.
Barry, I have switched to Redline D4 ATF and have ZERO grinding when it is 20-30 degrees outside. It just goes right in like when it is 90 degrees outside. Bobby Archer uses it in all the cars that run at the track and has had zero failures. Bobby sells all the redline oils.
I believe the castrol syntorq stuff is thicker to minimize neutral gear rattle. It would only make sense it is a tad thick on the cold days until it is warm.
Red Line Synthetic Oil Corporation has the most complete line of automotive lubricants available. Red Line realizes that reducing friction is necessary in a rear differential,
but that friction is actually necessary in a transmission so that synchronization may occur. No lubricant can do a perfect job for both. The same is true for engines. Reducing friction is a goal of engine lubricants, but the detergents used in most motor oils compete with the friction reducers for the metal surface. So if you want the lowest friction, use an oil formulated for the lowest friction. Red Line manufactures Racing Oils which contain few detergents, so no compromise has to be made.
RED LINE MTL and MT-90 are designed to provide excellent protection and improved shiftability for manual transmissions and transaxles. MTL and MT-90 have cured the problem of hard shifting in numerous transmissions which have notoriously difficult shifting. The secret to their success is two-fold.
First, they have the appropriate coefficient of friction for most manual transmission synchronizers. Many gear oils, engine oils, and ATFs are too slippery for proper synchro engagement.
Secondly, the viscosity characteristics of MTL and MT-90 allow proper shifting over the entire temperature range which the transmission will experience...... The synthetic base oils used have a very high viscosity index which provides relatively constant viscosity as temperature changes.
BENEFIT SUMMARY
Eliminates notchy shifting
Designed for manual transmissions and transaxles
Perfect synchronizer coefficient of friction
Enables high-speed downshifting
Excellent shifting even when cold
High-performance gear protection
Non-corrosive toward synchronizers
Satisfies manual transmissions and transaxles requiring motor oils or GL-1, GL-3, or GL-4 gear oils.
IMPROVES SHIFTING
Red Line MTL and MT-90 are able to improve shifting in most manual transmissions and transaxles. They provide a relatively constant viscosity as temperature changes and provides the proper coefficient of friction to allow synchronizer engagement.
Most gear oils are very viscous at lower temperatures. This higher viscosity requires increased shift effort to move the synchronizer gears with the shift fork and to squeeze the oil from between the synchronizer cone and the mating surface attached to the gear .
Without contact of these two surfaces, the gear speeds will not be synchronized and locking of the synchromesh gears will not occur. Excessive viscosity results in a longer time required to synchronize before locking occurs.
Viscosity of common lubricants at 0°C (32°F) is compared with Red Line MTL in the chart below. Note that the viscosity of ATF and 10W30 motor oil seems to be adequate. These lubricants are not well suited for transmission use because of two factors - shear stability and improper coefficient of friction - which will be discussed in more detail later. At even lower temperatures such as -17.7°C (0°F), the differences between conventional lubricants and Red Line MTL are even more dramatic. At such a temperature many of these lubricants would prevent shifting into certain gears, depending on the design of the transmission.
All oils are slippery, and with most lubricated components, the slipperier the better, but this is not so with manual transmissions.
The synchronization of shifting gears requires friction to transfer energy from the synchronizer, which is locked to the input shaft, to its mating surface attached to the gear to be locked in as the drive gear. Few modern transmissions use sliding gears to change gearing other than for reverse gearing.
Synchromesh transmissions have the gear pairs constantly in mesh. The drive gear is selected by using the shift forks to slide a synchronizer ring, which rotates at the same speed as the input shaft, in contact with the selected drive gear. Once the drive gear is brought to the same speed as the input shaft, the locking ring on the synchro assembly is allowed to slide over and lock into the drive gear.
Sorry for the long winded response, but this is from the Redline website.
I know it is talking about the MTL and MT-90, but Bobby Archer says use the D4 ATF which works great. THe MTL/MT-90 just explains the characteristics of what the manual transmissions need.
