Keas Jatco 4n71b automatic transmission build info.

[jeffer949]

Hello everyone.  

I am building a 1984 Maxima wagon (not a Z but has the same basic drivetrain.)  I have turbo'ed the stock L24e and have a L28et sitting on the stand to put in.  My car is auto and has the L4n71b transmission.  I am in the process of rebuilding a 1984 300zx Turbo auto transmission for the car which is a 4n71b.  

 

Firstly there is very little info on the internet about these transmissions and half of it is wrong.   In my searching for info on how to build the 300zx transmission up to handle power the name KEAS from Australia keeps popping up.  They seem to have done alot with the jatco transmissions in the performance world.  Well I emailed them and asked for pricing on a valve body   This is where I was shocked. They sent me the instructions on where to drill the separator plate and then he sent me the info on building up the transmission itself and how to address the weak points.  I asked if I could share and he said yes so putting the info on here to help future builders.  

 

What is interesting is that they don't modify any of the springs per the level 10 info and the shift kit the guy from austraila sells. See details in the thread below.  Little hard to follow but i think you can understand. 

 

Jeff,

 

The only Valve that could use a slightly Stronger Spring is the Pressure Modifier Valve. 

Over-do the strength of the Spring and extremely late or nil WOT Shifting will occur.

 

The Weak Areas in order of Failure are:

Intermediate Shaft

Input Shaft

Over Drive Sprag.

 

We have Billet Piston/ Servo Sets but your not there yet.

 

See attached PDF for transmission upgrades.

 

Have fun.

 

Paul.

 

Wow thank you so much for that info. I have the stock modulator from the turbo 300zx.  And I have  ATP nx-2 modulator. Thats adjustable that is listed for the turbo cars. Not sure about the diaphragm thickness.  

 

With the separator plate do I need to do anything with the valves? The info I've seen online say to shim the  pressure regulating valve 2.54mm and the pressure modifier valve the same or install a stiffer spring.(or pin it for very firm shifts. From the link below. 

 

https://www.mygen.com/users/dbruce/myz31/LevelTen_Performance_Automatic_Transmission_Install.htm

At what point are the cast band pistons not viable and billet ones are needed?  

 

And yes the engine is a l28et from a 280zx turbo. Not sure if you ever got those in Australia but its the same l6 platform as the L24 from the 240zed etc. 

Jeff,

I'll assume your Engine is Turbo Charged.

The Valve Body (If it was from a Turbo Charged Vehicle) runs into Shifting issues around 13psi.

And you cannot buy the Turbo Specific Modulator anymore. It contained a thicker diagram that lasted longer the NA items.

I would fit a Full Manual Valve Body that has fixed Line Pressure.

As a starting point- try modifying your Separator Plate as shown on the PDF

 

Building a 1984 Maxima Wagon in the USA. Has a L28et from a 280zx turbo with a 4n71b from a 84 300zx turbo behind it. Planning on around 300 hp to the wheels Just replaced all the gaskets, seals, o-rings, clutches, steels, and bands set all clearances to factory spec. What valve body mods do you offer? Finding info in the states is hard and your name keeps popping up so I thought I would see what you offer and pricing. Thanks

 

 

 

JATCO 4N71B Rebuild Modifications.pdf