Automatic Transmission / LSD Information

By Antony Lawrence

There has been an ongoing discussion about which G20's had LSD's (well, ongoing about 1.5 years ago anyway) It was always my private suspicion that the Canadian cars came with the LSD due to the weather up here. I spoke with Clark Steppler at JWT and he confirmed that was what he has found looking at the fiche So if you are buying a Cdn. G20 it will most likely come with LSD, for all years produced. This might be something to consider for you folks buying G20's in the Northern US, especially considering our terrible Cdn. dollar. My car, a 93.5 has LSD (as confirmed by the tranny ID# on the engine plaque on the firewall) no 93.5 G20's came with LSD in the US. If you want to know how to tell if your car has the LSD the last letter (or is it the second last) on the transmission code will be an A or V, A is no LSD, V is LSD. This code can be found on the silver plaque on the firewall.

Clark also gave me a little info on the automatic transmissions used with the SR20DE. Nissan uses a clutch material that tends to disintegrate in largish chunks, this is the normal wear pattern. What can happen over time is that these largish chunks can clog the oil filter in the transmission pan, causing low oil pressure and the tranny to run hot. He recommends dropping the pan once every year when you change the tranny oil and cleaning out all this junk, this seems to be a main area of failure on these transmissions.

The other problem is that the torque converter lock-up clutch uses the same material, the clutch is the last component in the tranny oil cycle before it flows to the radiator cooler. Over time these pieces can clog the radiator cooler, once again lowering oil pressure. The problem is that the most delicate components of the tranny (I forget what they are) are right after the oil inlet, thus they take the brunt of abuse from this problem. He recommends checking the flow through the radiator cooler annually to make sure it is not becoming clogged.

On the later model Q45s they installed an in-line filter after the oil outlet to catch this material. This filter is available but it is apparently fairly expensive. I'm sure there must be another, after market filter that could be used for this purpose. Perhaps finding one would be a good project for someone with an automatic, I know I will be looking into it.

Finally, Clark feels that with little in the way of modifications the auto trannys can handle about 200hp, he indicated that internally they are very strong. The big problem is the length of the shifts. Most modern automatic transmissions lengthen the shift as it makes the transition seem smoother and more luxurious. The problem is that the long shifts mean the clutches are rubbing away and creating lots of heat. With a lot more power the clutch material can wear away very quickly. It is difficult to reprogram the electronically controlled transmissions to shorten the shifts as it is largely a function of the valve body. Also the auto. transmission computers control shift length based on throttle position, the computer is preprogrammed with a shift map that assumes stock horsepower. For example lets say at half throttle the computer calls for a shift to last .5 seconds, in a stock car that may mean only 70-80 foot/pounds of torque are being transmitted, what if you have a turbo, it could mean 140 foot/pounds of torque, obviously a big difference.

A cheap way of getting around this problem, without revalving the valve body might be to trick the transmission into thinking the car is always at full throttle when it shifts. That might be another interesting project for someone with an automatic car to take on.