Datsun Fairlady Parts from Rallye Enterprises, Ltd.

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MAINSHAFT 5th GEAR #323-03

Splined and Unsplined Versions

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Nissan left out a step in the manufacture of the 5th Gear. This extra step was to insure the two pieces that make up the gear didn't separate from each other. Gears 1-4 have their two pieces both pressed together and splined together. Apparently Nissan figured the U20 would not develop sufficient torque to require the two pieces be splined, so they skipped that procedure. Sadly, as so many 2000 owners have discovered, the U20 CAN spin the two gear components apart from each other which gives an EXTRA neutral position, a trashed 5th gear and sometimes other damage as the two pieces kiss and make up while spinning.

Nissan started adding the splines to the 5th gears beginning with SRL311-14141, September 30, 1969 production. Arrows in pic above show the area in question. If you have your transmission out and it has the old style, it is recommended you replace it with the new style; or a used one that has been modified. You can of course just install another old style 5th gear and hope it survives as it. Many of them did.

If you decide to not do this; remember that if you ever think the car is slipping in 5th gear that you stop using 5th immediately. This assumes of course it isn't the clutch; which would also slip in 4th under load. The increased cost of repairing the transmission if you let it run in this situation can be high. The strain will be reduced if you at least do not use 5th until you can get the car apart.

There are other problems that can develop in that area of the transmission; most notably in the transmissions before the mainshaft was redesigned; and in the later transmissions due to the improved shaft being assembled improperly.

As of 6/1/15 this gear was not available or just about not available. We typically have used ones of both types. If yours is not torn up otherwise; you can have a precision welder bond the two pieces together. It takes a talented guy to do it as the thrust faces and fitment specs must be left intact.

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