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71B reverse idler gear and forks

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#1 ppeters914


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Posted 29 June 2018 - 06:35 AM

Wish I could post pics, but seems like all image hosting sites require money these days. Besides, DatzenMike probably has these images burned into his brain.  :lol:


I have two FS5W71 5-speed transmissions. One came with my '67 1600 roadster. History on this is unknown. I believe this transmission originally came in a '79 620 diesel pickup because:

  • Shorter shifter ears
  • Speedo drive retaining screw at 12 o'clock
  • Steel forks
  • Servo 5th gear
  • Main nut is left-hand thread (DQ Vol 11 Issue 2 states nut changed from RH to LH in 4/79).
  • Starter housing on left side. AFAIK, only roadsters and diesels had them on the left.


I bought the other 71B at Canby 2009. It came out of an '83 280ZX:

  • Tall shifter ears
  • Speedo drive retaining screw at 6 o'clock.


The earlier trans is completely dismantled for a rebuild; the later trans mostly apart. Questions:


1. The earlier trans forks are steel (cast?); the latter aluminum.

  • Are they interchangeable?
  • Any advantage of one over the other?
  • Anyone have good part numbers that aren't NLA, or know where to buy new 1-2 and 3-4 forks?


2. The earlier trans has a 23-tooth reverse idler key with a chipped tooth. Found a thread from 2008 in the Nissan Diesels forum that mentions the reverse idler gear came in 21T, 22T, and 23T.




Haven't contacted the various transmission parts sellers (Transmission Exchange, Drivetrain.com, Cobra, etc.) yet. Googling finds 21T and 22T, but no 23T. CarPartsManual Online for the 620 shows one part number (32282-E9000) without tooth count, and it's NLA.


Can you substitute the easily found 21T or 22T for the 23T?





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#2 DanielC


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Posted 29 June 2018 - 07:14 AM

I would think you cannot substitute an idler gear with a different number of teeth, because a different tooth count usually means a different diameter too.  The mating gear diameter is also changed, and that gears tooth count may also change. 

It is also hard to measure a gear diameter because the actual diameter of the circle the gear teeth makes theoretical contact with the mating gear teeth is somewhere between the top and root of the gear teeth, on both gears. 

A smaller gear may work, but it will usually have more free play.  The gears may also not be engaged as close together as the correct gear would be.  This would mean both gears are engaging farther out on the teeth, and will be weaker, and more prone to breaking off. 

#3 datzenmike



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Posted 02 July 2018 - 06:24 PM

Welcome back Mr. Peters.



Only the 720 had a diesel option, there were no 620 diesels. Maybe someone already put an SD front case on an older 5 speed?


I could also not find anything about 21, 22 and 23 tooth reverse idles gear you mentioned. You would need a matching reverse gear and the reverse counter gear. Seems like a lot of bother for reverse which is hardly used.... mileage wise. Myself I would run with the chipped tooth and make sure I didn't wheel hop, which is probably what caused the chip.


Do you remember the '85 SD bellhousing I brought down to Canby?


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