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  • Namerow

    By Namerow

    Namerow

    By Namerow •

    'A' Transmission vs 'B' Transmission

    We all know that Nissan decided to replace the Z's 'A' transmission with the 'B' version.  However, I don't think I've ever read anything that discusses why this was done.  We all just assume that the 'B' was "better".  But, how so?  This was an expensive decision, so: 'Why?'.  What, exactly, was so wrong with the 'A' unit?  Did customer sentiment demand a replacement?  Or was it a reliability/warranty issue?

    I'll  also be interested to hear the opinions of those who have had a chance to drive Z's equipped with both the 'A' and the 'B' transmissions.  Back-to-back, is there a noticeable difference?  Noise?  Vibration?  Shift quality?

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    jfa.series1
    5 hours ago, Mark Maras said:

     When did they change from the A to B transmission?

    Pretty sure it was with the '72 models, consistent with the change in the console design.

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    HS30-H
    • Popular Comment

    I think this all boils down to natural evolutionary progress. Nissan's 'A' type transmissions were products of the 1960s whereas the 'B' type were products of the 1970s, able to benefit from several years of feedback as well as improvements in metallurgy, bearings and heat treatments along with new technology in machine tooling (AMADA gear-cutting machines in particular) acquired by Nissan and their suppliers. 

    Regarding changeover dates, I think you need to go with production date rather than the often nebulous interpretations of 'Model Year', but the topic is far wider than one series and one market anyway and that's because the different variants of 'A' and 'B' type transmissions were used across a wide range of models and a whole world full of markets, not least of them Japan's own domestic market.

    On North American market Zs the changeover from F4W71-A to F4W71-B is stated as being end of August 1971, whereas for Europe, Australia and UK Export markets there was a changeover date of end December 1971 for the FS5C71-A to FS5C71-B Servo-synchroed 5-speeds. In Japan the factory gave firm chassis numbers for the applied changeovers and variants with 4 and 5-speeds were sold alongside each other. 

    I've driven Zs with F4W71-A, FS5C71-A, F4W71-B, FS5C71-B and FS5W71-B transmissions and I'd say the biggest factor is condition. The Servo-synchroed transmissions are (in my opinion) really satisfying to use when they are still in good condition, but those steel synchros wear out faster than the brass Warner type and they become baulky. Linkages on the 'A' type had a reputation for becoming sloppy and a little bit of attention/blueprinting there can make a big difference. Warner-synchroed versions are easier to use but (again, in my opinion) perhaps less 'sporty' in shift feel. We can throw gearing combinations (including diff ratios) into the mix here too, as a closely-spaced set of ratios driving a higher numerical diff ratio will always feel intrinsically more sporty than the opposite.

    My favourites would be a nicely run-in but not too tired FS5C71-A or an FS5C71-B, but the next generation 'C' type transmissions are one step better - especially in shift feel - and that's another evolutionary improvement. 

     

       

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    Namerow

    @HS30-H Great insights.  Thanks. 

    Interesting that the steel synchro rings wear faster than their brass counterparts.  I would have expected the opposite.  Is it, perhaps, a case of the steel synchros being more sensitive to wear? 

    And what exactly causes a synchro ring to lose its effectiveness?  Wear on the conical face (does it somehow lose its profile, or does it it get etched)?  Wear on the teeth?  All of the above?

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    HS30-H
    24 minutes ago, Namerow said:

    @HS30-H Great insights.  Thanks. 

    Interesting that the steel synchro rings wear faster than their brass counterparts.  I would have expected the opposite.  Is it, perhaps, a case of the steel synchros being more sensitive to wear? 

    And what exactly causes a synchro ring to lose its effectiveness?  Wear on the conical face (does it somehow lose its profile, or does it it get etched)?  Wear on the teeth?  All of the above?

    I think one of the key points is the nature of the synchro engagement itself, which is a clue to why Nissan chose not to use the Porsche-patent Servo steel synchro 5-speeds as standard equipment on the North American market Z variants.

    Different people interpret this in different ways, but I find the steel synchro action to be quite 'metallic' in feel - kind of like a rifle bolt action - and you can feel that through the gear lever. The synchros almost seem to suck the gears into hard engagement when you get it 'right' and I think this can feel disconcerting to some, almost as though the synchros are not doing their job. I think these characteristics are more suited to what we might call 'spirited' driving and they are comparable to the type of shift feel in sporting cars from other contemporary manufacturers like ALFA Romeo, Lancia and - of course - Porsche themselves. They can be very satisfying to use, but their very nature means they wear more rapidly in their contact areas.

    The Warner-patent brass synchros on the other hand seem to me to be very benign and forgiving. In good condition they give a very smooth change and you don't need to be so conscientious about rev-matching. Despite the material itself being softer, the nature of their engagement means they wear less rapidly. They don't live forever of course, but they seem very durable. A lot of people prefer their feel. 

    The above differences are certainly exacerbated by the gear ratio sets that they were usually paired with. A long time ago I picked up the useful mnemonic that the Servo-signifying 'C' in FS5C71-A and FS5C71-B can remind us of 'Close' ratios and the Warner-signifying 'W' in F4W71-A, F4W71-B and FS5W71-B can remind us of 'Wide' ratios. It is generally true. A close ratio transmission with overall 'short' gearing is much more likely to be worked hard than a wider ratio trans with 'tall' overall gearing. More shifts means more wear to synchros.       

     

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