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S30 and S130 Automatic transmission performance.....the JATCO 3N71B


A to Z

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Since my car is a 1972 240Z with the Automatic transmission, I have developed a keen interest in how to increase performance using or rather keeping this transmission.

 

The JATCO 3N71B.  Used by both Datsun and Mazda in the early days.....early 1970's.  While Datsun owners have done next to nothing with them, Mazda owners HAVE.  In fact they are still used in Mazda Drag racing circles, and Australia seems to be the place where all levels of performance upgrades are to be found.  

 

Being a street car, I was interested in a shift kit to get rid of sloppy shifts and the possibility of a higher stall torque converter to get the car accelerating off the line comparable with a manual trans car fitted with 3:54 gears.

 

So, the Automatic cars in 1972 came with 3:54 gears, and "drive" is a 1:1 ratio, so in Drive it is the same as a manual car in 4th on the interstate.

 

"RB30X, a member on here I found, has been making and selling a "Stgae III shift kit" for these transmissions.  You get a heaver duty spring to go inside the valve body and a CD with instructions on the modifications that are necessary to make it work like it really should.  He does however note, that he also sells a Stage II kit with a tad bit weaker spring, for those who don't want it to shift "too hard".  Hestates that teh modifications actually INCREASE the life of the transmission, as there is less drag!

 

The next point in street car JATCO performance seemed to be Torque Converters.  Even in Australia, that is a bit of a challenge.  I found a shop, called TCE in Victoria, Australia that will custom make torque converters for our transmission.  When I contacted them, they sent me a PDF file fo me to fill out and return to them, so they could look into what I would need for my individual setup.

 

My thought process as of right now, is to use the 3:54 gears in the rear, because If I go with a lower gear set such as 3:90 or 4:11, the cruising RPM's in Drive are going to be awful.  The one option is to find the rare 1984 year model only MAXIMA Automatic the "4"N71B.  The trans is the same but has an overdrive for the highway.  1985 and onward, are electronic, not old school juice box controlled, and for an old Z car, you can't use the electronic ones, so, you have to find the trans, and also use the engine flex plate for that transmission and the crankshaft spacers.  In short, A LOT of work and money.  The 240Z at least is light enough, that 3:54's I believe will work, and acceleration with the shfit kit and torque converter may be the way to go.

 

TCE asks for information on the car.  One of the things they need are the came specs.

 

Stock cam spec's?  Welll they change from car to car 1970-1973 used a Nissan A cam.  A google search got me this cool page that breaks it down and compares to aftermarket grinds:

 

www.atlanticz.ca/zclub/techtips/cam/index.htm

 

1970-1973 "A" cam= .409 lift, 248 Duration, 109 degrees lobe separation, BTW. :)

 

I will get a quote back from TCE I hope soon, and will add that to this writeup.  You CAN make the auto work with the L series engine without going to a Chevy Turbo 350 with the adaptor kit!  I will post a copy of the sheet I filled out which gives some of the critical info ont he car they ask for.

 

Here is a link to get the shift kit if needed.  If it doesn't work, go find him, "BR30X" on HybridZ.

 

VL Turbo Commodore Nissan Datsun Jatco Automatic Shift Kit Servic | Engine, Engine Parts & Transmission | Gumtree Australia Gladstone City - Gladstone | 1021151782

 

Also, I have attached some relevant pics.  The torque curves are useful in that TCE and the owner need to be able to see where is the optimum RPM for stall speeds etc.  These are for my car, a stock L24 Automatic, in a 1972 240Z.  To check your cars torque curve, if still stock, go to Google, type in your car, i.e. "1972 240Z Automatic Torque Curve" and the first site, it's the one to select ..."Automobile-Catalog".

 

Cheers!

 

A.jpg

b.jpg

c.jpg

d.jpg

e.jpg

Torque Curve 1.jpg

Torque Curve 2.jpg

TCE Hi Stall Specification sheet 2020.pdf

Edited by A to Z
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Ok, well, I have found more information to post.  Comes fromt eh Ratsun forum, in particular the Admin over there, "datzunmike".  cool info:

 

Quote: "JATCOs were installed on April '71 and on 510s at about the time they switch from column to floor shift so you're ok there.

 

The Z and ZX did use the same converter and it's a different part number than the 510 but also used in most 4 cylinder 710/610 A10 S10 even the 620 truck so probably all the same. The biggest difference would be the number of clutches and plates inside.

 

However!!! The 280zx turbo automatic was much different. It had extra plates and clutches and a modified vacuum diaphragm for firmer shifts to contain the turbo power. (I think the internal line pressure relief spring was also stiffer for higher pressure) The internal first and second gears were also different and lower.

 

Regular 3N71B

2.456

1.458

1.000

 

280zx turbo 3N71B

2.841

1.542

1.000.... this gets the engine and turbo spooling faster.

 

Here's the kicker. The stall speeds is increased on the zx converter from 2,200-2,300 to 2,400- 2,700. Again to spool the turbo faster at a lower vehicle speed." /UNQOUTE

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I did some part number cross referencing.

 

The part number for a PL510 torque converter is 31100-X0301

The part number for 240Z torque converter is 31100-X0500

 

So, there IS a difference!  That means that a PL510 torque converter will flare higher, or stall quite a bit higher than the stock 6 cylinder one.

 

The part number for the Z is 1970-1978.  So 240, 260, 280 used the same one.  The big differnce is in the 1981-1983 TURBO cars.  They stall a bit higher than the naturally aspirated ZX cars.  Naturally aspirated 2200 RPM or so, Turbo 2700 RPM or so.  

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From the reading I have been doing, it appears that given a certain torque converter, that if you put it into a more powerful engine, that torque converter will actually stall HIGHER.  Not sure how that works, but if that holds to be true....then a stall converter from a 510 that had the factory stall of 2200 RPM, will stall about 2500 or more approximately in a L24/240Z !  I was able to get a used converter today form a guy who pulled it from a 1972 510 wagon for a good deal.  I will clean it up and see what happens.  Of course the Stage III shifter will go in as before.  Results to follow! :)

 

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Today the 510 converter arrived, and by making some calls, I found a shop in Denver that rebuilds converters.  A quick call told me for around 100 bucks they will cut the converter open, rebuild it....bearings and stuff I imagine and seal it back up all nice and clean.  When I asked about adjustments for raising the stall, he told me "yes, we can tweak the plates a bit"....so I could also have them add a hair to the 510 converter as well! With any luck we're talking 2800 to 3000 RPM....which would put it right in the torque sweet spot.  The main question is, what would a Z drive like around town, and cruising with a 2800-3000 stall?  Would it create more friction and wear just cruising, would it be kinda like driving around slipping the clutch all the time?  Comments welcome.  The address to the converter shop is:

 

Branting Industries

5280 W. 56th Ave.

Arvada, Colorado 

(303)425-9004

 

Seems to be a fairly quick turn around, although he did tell me he was swamped with business.

 

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