Building the Bulletproof Transmission, Secrets of the Pros

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Phantom grip LSD
Phantom Grip Differential intalled
The Phantom Grip limited slip differential is a very simple unit using spring tension to force the hardened steel blocks into the sides of the pinion gears.  The competition spring and shim kit shown here allow adjustment of the differential’s action.  We recommend shimming the differential as hard as possible.  The lower picture shows the Phantom Grip in place.  If there is no limited slip available for your car, chances are Phantom Grip makes an application for you.

The above tricks will help the Nissan FWD transmission live forever with a modified naturally aspirated engine, even under road racing conditions and will withstand use in a turbocharged car up to 300 hp with occasional blast at high boost levels to 350 whp or so.
To go beyond this as a seriously turbocharged car will, it is recommended to swap the stock transmission to one from an Infiniti P11 G20 1999-2002 or a B15 Sentra 2000-2002 model year.  The P11 transmission is harder to adapt because it has a hydraulic clutch but the smooth operation of a hydraulic clutch is probably worth the hassle.  The 1999 P11 transmission has a higher first gear and closer 1-3 gear ratios which is probably better suited for turbo cars and road racing.  The B15 Sentra transmission and the later P11 tranny has a lower 1st and is probably better suited for street driving and off the line acceleration with a NA motor.

This transmission known as the B15 tranny is much stronger.  The B15 tranny has a thicker more heavily ribbed case and slightly beefier gear stacks particularly third gear. Most importantly it has features designed to keep the shafts from flexing and gears from spreading under load.  The B15 tranny has beefy shift shafts and forks that are supported by heavy twin spring loaded detents that bolt directly to a ridged part of the case.  The shift forks ride on the gear stack shaft supporting it and they are in turn supported directly to the case by the detents.  On an older Sentra tranny the shift forks only lightly touch the gears and are moved by thin unsupported shift shafts.

On the B15 transmission, the reverse idler gear stays meshed with the main shaft and rides in bearings on a thick shaft supported on both ends.  The gear helps prevent the main shaft from moving.  On an older Sentra tranny the reverse gear idler is not engaged unless the car is in reverse and has no support function at all.  On the B15 tranny it looks like Nissan took a serious look at the problems of the old gear box and addressed them.  The LSD diff and axles from the older transmission will work and the transmission goes in with a swap to the old speed sensor and some minor fabrication.

The B15 gear box is still not all that strong and can benefit from the shockproof heavy, deburring and polishing of the gears, cyro, shotpeening and WPC prepwork.  With our tricks applied it reportedly can withstand a Honda like 500 plus hp for a time.  I wish that these tricks were known back in the FWD compact car’s heyday, Nissan might have ended up on the podium more and the market might have become more diverse and longer lasting.

Lastly it is important to only use as much clutch as necessary to contain the power of your engine.  The heavier duty a clutch is, the more shock it will transfer to the rest of the drivetrain by default.  Heavy pressure plates, solid hubs, metal pucks and other power containing tricks all put more stress on the transmission.  Our thinking is to have the clutch be the safety valve of the drivetrain that will slip before the transmission breaks.  So don’t use that tire chirping solid hub 3 puck clutch disc with the double diaphragm pressure plate unless you really need it, and if you use one, realize that it will help contribute to transmission failure.

Really heavy duty clutch
This Unorthodox Racing clutch has metal pucks and a solid hub, ideal for handling a lot of power while being easy on syncros.  This clutch can hold about 500 hp but it is pretty hard on the transmission.  Use a clutch like this only if you really have that much power!
JWT clutch disc
This JWT clutch disc has metal pucks and can hold over 450 hp while the sprung hub helps cushion the transmission from shock.  It is a good compromise between a full race clutch and a stock type disc that probably can’t take the load.
JWT HD clutch disc
JWT makes this semi-metallic disc with a marcel spring and a sprung hub. This disc can hold up to 300 hp and is almost as easy on the transmission as the stock clutch.

For owners of other Nissans and in fact any other car, your transmission can and will withstand substantially more power with this level of prep.  Readers owning DSM’s, GT-R’s, Subaru’s and EVO’s take note.  Shockproof Heavy, Deburring, Cryo treatment, Hardpeening and WPC treatment of the gears, shafts, case and other internals will substantially improve the performance and service life of your transmission.

Hopefully you will have found this article to be informative and can apply these techniques to your transmission build no matter what sort of car you have.
 

Sources

Technosquare Mechanical work, fabrication, welding

Jim Wolf Technology Motor mounts, clutch

WPC Treatment High tech metal treatment

Phantom Grip Universal LSD diff

Nukabe/Cusco Nissan FF mechanical LSD

Energy Suspension Motor mounts

Redline Shockproof Heavy gear oil

Cryo Science Cyrogenic metal treatment

6 comments

  1. What would you do for a VX transmission going behind a turbo’d engine? Any other recommendations for the project would be welcomed

    1. It depends, you can use these tricks to make the stock transmission last longer, mean I could say get a Quaife dogbox or a ppg gearset but I need to know about your budget and end use.

  2. The amsoil severe gear 250 oil doesn’t effect the synchros? I was going to get the synchro mesh one which is 75 90 weight but I’m running about 300wheel in a 70 series p11 tranny. Rather get the heavier oil. I’ve used shock proof heavy gear oil forever but wanted to use amsoil because I’ve heard good things. Let me know. Thanks

    1. Its almost like who cares if it affects the synchros or not because this transmission is so fragile. I have been running this gear oil in my race car for years with no damage to the synchros so far. The transmission has not blown up either!

  3. Hi, I built a trans for the Grand Prix of Lemons in NZ, it has a PAR syncro gearset
    We have a U13 Blobbird with tuned GTIR engine and trans, we had to lengthen the driveshafts about 20mm each to fit it
    We lasted about 6hrs before the stock 3-4 selector broke, PAR and PPG are out of stock, 10 days wait for PAR. The gearset looks stressed on 2nd gear and has worn the teeth, plus what looks like slight breaking through the hardening in the centreline of each tooth on the drive side
    We started with GL5 oil and changed to GL4 Castrol 5 speed to try and help the 3-4 syncro, it spat the pusher springs out in the end.
    What should I do to this thing, a later box? Ours has double syncro on 2nd and it works great, and looks like double syncro on 5th, but the book says its got a cone for rev which I doubt as rev is on a sliding idler
    I have used redline shockproof oil in my Rocket 3 BSA gearbox and our rally Capri 9″ diff, but wondered if it would upset the syncro engagement on this thing
    Regards
    Nelson

    1. I have used Shockproof heavy on Syncro boxes for years with no ill effect. It works pretty well for keeping weak gearboxes together longer.

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