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DIY Stage III Shift Kit Installation for S30 and S130 Jatco Autos


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I have been contacted by a few people regarding a shift kit that I was involved in developing a few years ago. We actually developed this shift kit for the 4 speed Jatco 4N71B but recently adapted it to suit the S30 and S130 3 speed Jatco 3N71B. The kit is especially effective in turbo cars which soon destroy the standard auto after winding up the boost.


The installation can be complex for some, but easy for others.


It can be a great modification for those who have an auto S30 or S130 but don't want to go through the hassle or cost of converting to a manual.


I have included some info below from my development (which may be different to others) so people can read up and understand the process involved, and find out what a shift kit does if they didn't already know.


This shift kit was developed to reduce the sloppy, soft gear changes during acceleration in older cars with hydraulically controlled auto transmissions. This improves acceleration and reduces wear or damage caused to the transmission, espcially when the engine is producing more horsepower than standard. This kit allows safe operation of the standard auto with up to 14 psi boost pressure on turbo engines (calculated on the 4N71B 4 speed only).




1 x DVD containing an electronic document with all the developed information including detailed photos and diagrams required for you to remove the valve body from your transmission and perform this shift kit modification yourself, as well as templates to show you which existing holes in your valve body require enlarging.


1 x Spring, to replace the existing pressure modifier spring inside your transmission’s valve body which will increase fluid pressure.


All you need, is to have a small amount of mechanical know-how to perform this modification yourself. If you do not feel confident, you can always take the contents of this shift kit to an Auto Transmission service center and they can install it for you.


An automatic transmission's main focus is smooth shifting between gears. To accomplish this it often goes into two gears at once while shifting up, which is known as a shift overlap. By installing a shift kit you are increasing the speed at which these gears are changed. It will also reduce wear because the transmission won't be taking as long to slip from one gear to the next, similar to riding or slipping the clutch in a manual gearbox. Increasing engine horsepower in automatic cars can also speed up the damage and wear caused inside the auto transmission because the automatic is trying to smooth out gear changes as it was designed, with only the factory levels of horsepower. This is especially the case with turbo engines where it is very easy to achieve up to 50% more horsepower with little modifications to the engine.




An automatic transmission has bands and clutches that are actuated by hydraulic servos controlled by the valve body to change gears. It is this hydraulic control center or valve body that receives pressurised fluid from a main pump operated by the fluid coupling/torque converter. The pressure coming from the pump is increased by replacing a spring in the valve body so the regulated pressure is higher and as a result, pushes a network of spring-loaded valves, check balls and servo pistons much faster. The fluid ‘pressure’ is not only increased to speed up the gear change, but the fluid ‘volume’ as well. The valve body is contains a separator plate consisting of many holes which let fluid pass from one side of the valve body to the other. Enlarging particular holes allow a larger volume of the higher pressure fluid through.


Turbo cars also make use of the existing vacuum line which runs to the auto transmission from the engine inlet manifold. This vacuum line initially uses the engine vacuum to control shift points. During acceleration when the engine is producing boost, this shift kit allows the positive pressure from the turbo in the intake manifold (boost) to increase the firmness of the gear changes as well.


Installing a shift kit will not correct or eliminate symptoms of a previously faulty transmission.

The auto gets signals to change gears from both vacuum from the engine inlet manifold and electronic signals from the accelerator pedal or throttle position sensor depending on year model. This shift kit will rely more heavily on the vacuum modulator on the side of your auto to control gear changes rather than electronic signals so if your vacuum modulator (small round thing your vacuum line hooks up to) is 40 years old it may require replacing to get the full benefits of this modification.



Ok. So to perform this modification to your valve body you need to do the following.


- Pick up a service kit which includes a new bottle of trans fluid, a new filter and pan gasket (usually pretty cheap). I also recommend running an external trans fluid cooler if you live where it gets hot as this will generally help your auto last longer regardless of your modifications.


- Jack the car up, handbrake on and shifter in neutral.


- Have a container ready to catch the fluid. Unfortunately there is no drain plug for this so it gets messy.



1. Undo the 10mm headed pan bolts starting from the lowest point of the pan. Oil will begin leaking from here first so keep drip tray handy. Take note of how easy the bolts come undone. This is how tight they should go back on.


2. As fluid draining slows down, support pan with one hand as you remove the last bolt. Lower pan away.


*Note: How does your trans fluid look? Are there bits and pieces of fibrous material floating around in it, or is it dark in colour indicating high metal content? Does it smell burnt? These can be signs of how healthy your auto may be.


3. You should be able to see your valve body.




4. Take note of how the gear selector linkage is sitting in the rod on the RH of the valve body (red arrow in pic below).




5. Also take note of how the pins/rods from the solenoids on the LH side sit inside the valve body (yellow arrows in pic above). Note: depending on your auto you may have two electrical terminals to disconnect from the valve body as well.


6. Remove the following 10mm headed bolts (yellow arrows below) and providing you’ve left your trans in Neutral, you should be able to drop the drivers side down and slide it off the pins on the LH side. The vacuum rod can fall out, while the electrical solenoid rod will stay in there. Do not undo the nuts where the red arrows point to, you will undo these later.




7. Drain remaining fluid from valve body.

*3N71B valve body pictured below.




8. On a clean surface, undo the 8mm headed bolts (and one 10mm) that hold the trans fluid filter to the valve body. Take note of the torque required to loosen.




9. Remove the remaining bolts, working from the outside towards the centre (this includes the second 10mm headed nut and bolt) As the very last bolt is loosened in the centre the valve body will begin separating. Hold it together with one hand as you

remove the last bolt completely. With two hands holding it together like a burger, flip it over and lower it down on the surface where the filter was attached.








10. Remove the top half of the valve body ensuring the separator plate remains on top of the lower section.






11. Lift off the separator plate carefully and you will see a ball bearing sitting on a strong spring. There will also be one or two small cups sitting on very weak springs. It is important you remember where these go. 4N71B Valve bodies will have one black cup without a spring underneath.

*3N71B shown here.




12. Remove the loose springs, cups and ball, and clean all the parts with petrol or Brakleen. There will be a lot of fine build-up in the small chambers and channels of the valve body.




13. Identify side plate A (as shown below) and carefully remove the three 8mm headed bolts. Take note of bolt torque. Valves inside are spring loaded so the plate will eject itself.


*4N71B shown.










14. Remove the pressure modifying valve and the spring. Replace the existing spring with the red ‘higher pressure’ spring (supplied with shift kit), reinsert valve. The stronger red spring will increase fluid pressure.






15. Compress the three valves against their springs so the plate can be reinstalled. This can be tricky. Try compressing the valve with the red spring first, then sliding the plate over it, then compressing the other two.






*Red spring installed




16. With a clean separator plate, mark the holes to be drilled out using the template provided.


(template included as part of shift kit, if I included the rest of the photos and diagrams, it wouldn't be fair so its words only from here)


17. Some holes just require enlarging to the diameter (mm) in the picture, others will need enlarging and elongating or extending. This can be done by drilling a second hole next to the existing hole, and using the drill or a dremil, port out the small gap between the holes. Ensure you do not go outside the stain on the separator plate that shows where the channels are. Drills holes out accurately and sand off burred edges of hole with emery tape. If this step is not followed, fluid may pass through where the separator plate does not seal.


18. Clean separator plate once again.


19. Reinstall springs and cups or balls in their original position.


20. Sit separator plate on top of lower half of valve body, ensuring cups and ball sit under original holes.


21. Rest top half of valve body on the separator plate, ensuring it stays straight. Compress slowly so cups and ball rest on their springs in the appropriate valley.


22. Flip valve body over as before, and with one hand keeping valve body compressed together, wind a couple of 8mm headed bolts in finger tight.


23. Install short 8mm headed bolts and the one 10mm to secure the valve body together finger tight at first so you ensure the valve body halves and separator plate all line up well, then tighten. Remember the initial torque required to loosen them. These are aluminum threads so we don’t want to strip them by over tightening.


24. Install new fluid filter with the remaining 8mm headed bolts and one 10mm headed bolt and nut.


25. Check all bolts have been tightened.


26. Slide valve body back up inside auto, ensuring solenoid pins line up again, as well as the gear selector rod.


27. Install bolts in correct order, note the different lengths.


28. Clean off old gasket from pan (cork gasket in this case)


29. Depending on what your replacement gasket is made of, apply gasket sealer etc and reinstall pan.


32. Add approx 3L of new trans fluid through your filler point.


28. Start the engine and with foot on the brake, test that the engine revs drop when auto is placed into Drive and Reverse indicating the auto is working as normal.


29. Drive car off car ramps or lower as required.


30. Trans fluid level should be checked again with the engine running at operating temp and the auto in Neutral or Park. Top up fluid as required by dip stick level.


31. Take car for drive and enjoy.


Hopefully this little tutorial will help you guys understand a little bit more about how your auto works and what exactly a shift kit does.

Edited by RB30X
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Interesting, but there seems to be little interest in performance autos in AU except for drag racing. Some of the Z32 blokes are a bit more adventurous, the shift at will kit available has attracted some. I was considering using a four speed Jatco in my competition Z but it all seems to involve a lot of pioneering work and dealing with people who are not familiar with circuit car requirements, which I have done enough of.

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Yes auto's do limit the use of the vehicle in any racing forms except drag as you mentioned. There are the cruisers out there that have squeezed a little more horsepower from their L series and its the sloppy auto shifts letting them down. A shift kit would suit those people.

There is a famous VL turbo track car in New Zealand with a Jatco auto. Smashing down gears coming up to corners in an auto does not offer the engine braking that a manual gearbox does though.

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  • 2 months later...

Will installing this kit actually raise the rpm shift points or just make the shifts crisper?


Just letting the trans shift by itself under hard acceleration I noticed it shifts way early-like 4300rpm. The car is much quicker shifting manually. Love to install a jatco 4n for the overdrive and use this kit-would that work also?

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Yes this kit suits both 3N71b three speed and 4N71b four speed jatco autos. How high rpm the auto holds gears for is related to your throttle position aka lack of vacuum in the inlet manifold so that could be an issue with your vacuum modulator. Although I know exactly what you mean about the early shift when in drive and I can say this kit did rectify that issue in one of my old cars. It speeds up the time between gear changes as well as mentioned above.

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Am I correct in assuming that this modification is compatible with the 84-89 Z31 E4N71B? If so I would like to pick up a few sets.


Apparently so, but I would like to confirm first.


One member is getting a kit me to try in an 84 300zx, although I'm not sure if his is an L or an E (4N71B).


I'd say the pressure increasing would be the same but the seperator plate may be different.


If you have a spare valve body it would be worth trying if you knew what you were doing.

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  • 4 weeks later...
  • 1 month later...

I seem to remember that 1984 4n71b are L4n71b meaning they are not electronic.


Thanks, either way the shift kit still decreases shift times and increases pressure.

The 4N71B's over here are electronic and they work fine.


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  • 4 months later...
  • 5 weeks later...

FYI, after a couple of requests, I've found a supplier of a softer spring that can be used as a stage II shift kit (for those too scared of the stage III) :D

PM me if interested.



hows it going i know this threads old but do you still have these kits stage 3 ? for a 3n71b out of a 1981 280zx turbo i contacted you before but i have been away for awile can you pleses email me back at pinoybg1572@yahoo.com thank you

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  • 1 month later...

Hi There from Arizona. I am trying to find a shift kit that will allow me to use the 3n71b or 4n71b for a road race (circuit racing) application. Will your kit work for that? Sounds like it will from what I read if I use a cooler. Look forward to your response. Also what would the shipping be to Phoenix AZ USA? Thanks.

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Certainly mate. I sent you a PM.


I dont have a link for you, but google or youtube HSVSUX.


Its a New Zealand based circuit racing sedan (Holden VL Commdore) with a tricked up Jatco behind an RB30ET.



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  • 1 month later...

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