The Ultimate Guide to Nissan Automatic Transmissions

By:Moyea

History: Did you say I have a Skyline transmission?

Jatco being a leader in import transmissions for years, have made transmission for about every Nissan (and other JDM) cars on the market today. The links explain it better than I can:

http://en.wikipedia.org/wiki/A…ssion
http://en.wikipedia.org/wiki/L…sions

Let’s get to the technical: http://auto.howstuffworks.com/…n.htm
http://auto.howstuffworks.com/torqueconverter.htm

Mechanically speaking the M/T is the better of the two. A/T uses several smaller clutches, gear sets, bands, and other crap to work. Very heavy and very complicated. As opposed to the beefy, manly M/T gears and clutch. M/T’s can take a hell of a beating under load but to a point. In this respect your A/T will most likely not outlast the M/T but even the stock M/T is not built for the stress we put on our cars. OEM A/Ts and M/Ts are built for the daily drivers often using modulators, resistors, or boosters to ease the shifting of gears. A/Ts are especially victim to this due to the torque converter, Transmission Control Unit (TCU the A/T brain), Valve body, solenoids, resistors, etc. The factory didn’t even come close to the potential of quality components and as you can see their are many things you need to upgrade. The cost of these upgrades are easily twice of M/T upgrades. Don’t be discouraged because the results can be twice that of an M/T.

The Slowmatic: Did you know the fastest 300zx in the country is an A/T?

The perceived slowness of the A/T is mainly due to a few culprits:
– Mechanical > Torque converter (TC) and valve body (VB)
– Electrical > Transmission computer (TCU)
– FLUID!!!!!!!!!!

There are other things but these are the easiest and cheapest to upgrade.

OEM TCs are the weak point.Replacing this unit with one built right and with a higher stall speed is common. This is a matter of preference and application though.

http://www.converter.com/q1.htm and

http://www.importperformancetr…shtml

…are both good sources. Simply stated, aftermarket TCs provide better acceleration and higher power to ground output.

The Valve body is basically the heart, not the brain as some people call it, responsible for the hydraulic systems of the A/T. This is a very complicated system dealing with pumps, valves, fluid pressure, etc. In short, OEM A/T VBs don’t do their job as efficiently as an aftermarket unit. A good unit can improve shifts, durability, and fluid transfer to name a few things.

The TCU is the brain of your A/T! The TCU is essentially the same as the ECU/ECM for your car. It takes in various inputs ranging from vehicle speed/rpm to fluid temp. The OEM TCU is usually set to allow comfortable shifts and low torque output (compared to what it can do). This is where the A/T beats out the M/T. For me to make an adjustment to the vehicles transmission on an M/T, would require mechanical changes usually involving removing the tranny and adjusting gear ratios. A/T requires much less work for adjustment. With an aftermarket TCU I can adjust every aspect of my transmission all on a laptop. I can change shift points, line pressure, coolers, trans brakes, lockup, etc.This provides infinite possibilities for transmission control. And when I say total tranny control I mean everything, even manual shifting. This by far the best reason to stick with automatics. It’s also the second most expensive thing to upgrade.

Fluid is by far the most important thing in the A/T. Just like oil is the life blood of your engine, ATF is the same for your tranny. ATF is needed for everything your A/T operates, low ATF or oxidization means no line pressure and no lubrication. This means your clutches won’t lock up right or worse yet break. This is the first thing and cheapest to upgrade on an A/T. Just like motor oil, not all ATF is created equal. Synthetic is they way to go here because it provides a much higher resistance to oxidization and heat.

http://www.amsoil.com/StoreFront/atf.aspx

Tips and facts: Did you know 4RE401A is the most widely used transmission in the Nissan line up?

Where to start?

Change the fluid, gasket, and filter. Some times the filter cannot be replaced, usually not the case, but with a good cleaning (parts cleaner) and having the fluid flushed (twice) it’s a good start. Check or ask to inspect the fluid and filter removed from the car. This is a good indication to mechanical problems. Metal parts, shavings are signs that the transmission will need to be rebuilt in the future, for now keep on trucking.

Next step is to get a temp gauge.

http://www.autometer.com/cat_g…sid=4

Being able to monitor the abuse you’re putting on the A/T is crucial, I would never race a car without some sort of monitoring device. (Tip: You can use an oil pressure gauge to monitor ATF pressure too/ not needed if you have an aftermarket TCU which has an output for it).

Then get a tranny cooler, preferably one with a fan mounted to it, I found this out after I had already bought one without. After some hard runs or drifting ATF heats up, the fan allows you to maintain temps at low speeds or idle. But any cooler is better than nothing, the stock cooler is mounted on or in the radiator which doesn’t help to bring temps down. The best place to put the aftermarket cooler is in front of the radiator. (or on the hood ).

Shifter is next. I have yet to find aftermarket shifters for the 4RE401A but if you own a domestic your in heaven.

http://www.bmracing.com/index….cat=2

Three types to work with ratchet, gate, detent. The type in the 4RE401A is a detent but don’t quote me on that. The key thing to look for is reverse lock out, preventing you from killing yourself. I prefer a ratchet style because it works like a sequential shifter on M/Ts, every pull of the shifter changes gears then returns the shifter back up. This is very sick! Once again you have now taken away one of the main reason people switch to M/Ts. And yes…..you can downshift.

Tip: You can use your stock stick to shift but become very familiar with the gears and the rpm in which you can upshift and downshift (it’s in the FSM). 1=1st, 2=2nd, D w/o OD= 3rd, OD=4th. Don’t be confused with M/Ts 5th is like OD for them. DO NOT hold your finger on the shift button you may push it into neutral or reverse!!! Only press the shift release when downshifting, it will slide freely when shifting up to Drive.

After that it’s really up to you. I think aftermarket VBs and then a tranny build should be done in that order. The reasoning behind this is if you do blow your tranny it will most likely be one of the clutches or bands so you can salvage your aftermarket VB and put it in another A/T. Then when you get the money for a bulletproof A/T rebuild your all set. Transbrakes are also something to consider.

I threw the torque converter last because selecting a TC is matched with the output of the engine (amongst other things). If you plan on putting out 400lbs/tq you don’t want to buy a TC that’s built for 250. So you can wait until your finished with the power adders or just get a slightly higher stall TC (500 1000 more rpm over stock).

Mind over Matter: TCU vs. Man

http://www.visualexpert.com/Re….html

(Do NOT Try This) How many times have you been laying down rubber with your boys and every run you do you best them? I hear all kinds of excuses like “I missed a gear” or “You got lucky off the line”. The truth is this; a comparable M/T cannot shift as fast as the A/T. I know some M/T guys can relate to this fact. Driver reaction time and accuracy is something that plagues the M/T world, footwork is a desirable and valuable skill. A/Ts do not face this problem because of the TCU taken’ only a fraction of a second to change gears.

DVD Extras and Theory: “If you’re just going to swap it, can I have it”?

The 4R01 is hands down the most available import tranny out there. Just think back at all the time you went to the Pick N’ Pull. So what does this mean for you? Options!!! If you burn out your tranny who cares?! There’s like 600 of them at the yard going for as low as $300. There is always somebody trying to get rid of them for swaps.And you can just swap aftermarket parts to another tranny.

Here’s some theory for you: Did you know your A/T is in the SR20DET? In fact, the Silvia A/Ts are actually beefier than yours because of additional clutch plates and higher stall to accommodate the turbo. In fact, it’s in the 300zx too, wake up!

Can these be interchanged or their parts? Domestics can why not imports?

With simple modification (crossmember, drive shaft) I think 240’s can see a whole new light. Now this is just speculation because I can’t find a tranny guy who knows what I’m talking about. Also, in theory, since you share the same A/T as a Silvia engine swaps can be easier and cheaper. You can chose one of two things keep your tranny and replace the engine or swap for a beefy SR20DET A/T, either way an aftermarket TCU can adjust for any tranny change.

Motorsports: Drag! And that’s it? NO!

I’m not going to make a long spiel about this because I think the point is made. A/Ts can do ANYTHING an M/T can! This means drift, drag, road, circle, and rally. Did you know Formula 1 uses a semi automatic? The gearing and clutch (no clutch pedal) are similar to an M/T but the TCU and hydraulics are like an A/T. It is the perfect fusion of transmissions. Truth of the matter is transmissions are evolving all the time eventually the traditional M/T will be completely outdated and the A/T is not far behind. SM/T is the future!

http://www.autoracing1.com/Mar…1.htm

http://www.drifting.com/forums…pp=15

A/Ts have all the potential of an M/T at twice the cost. That’s it!