In my opinion, there are 5 things that need to be done with the Patrol 4 speed (RE4R03A) auto transmission.
1 - Trans fluid temperature gauge. Heat is the No.1 trans killer.
2 - Synthetic trans fluid. There are several choices now depending on your budget. I currently use Castrol TransmaxZ but will switch to Nulon after my rebuild because of cost.
3 - Larger trans cooler. I use a Davies Craig in series with the original TB45E cooler. The ZD30 trans cooler is twice the size of the TB45E unit but the ZD30 has a higher stall TC which generates more heat.
Here's the Davies Craig with the original TB45E unit:
4 - Increase the trans fluid line pressure. There are several shift kits or changeover valve bodies available again, depending on your budget.
I fitted a TransGo shift kit to mine. Cost $135 at the time. The replacement Castrol fluid cost me more than that!
I'm currently overhauling a Nomad valve body I bought secondhand from a friend who moved to the Extreme version so I'll swap that in place of the TransGo.
5 - Fit a manual torque convertor lockup system BUT learn how and when to use it. The factory settings switch it off at the slightest sign from the TPS that you're about to accelerate because it isn't built for heavy torque load. Used wisely, it will help keep your trans cooler and last longer.
There are those who leave it switched on during gear changes which is a recipe for premature wear.
I did my initial TC lockup install using Chaz's original circuit diagram but I added a security from pin 36 to eliminate all risk of engaging it in Park or Neutral.
Here's the circuit with the Park/Neutral security included:
I have long since modified my system and now control it with a Jaycar frequency switch that can buy in kit form.
It cannot be activated under 60 kph so no longer needs the Park/Neutral security. I have it wired to my rear demister switch (which I never used) which has a small amber light that comes on over 60 to tell me it's armed.
I also have a small flashing LED in my pillar pod that tells me it's activated. Also have another LED there that tells me when the TCU has locked the TC.
Here's what I currently use:
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