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C71-B or W71-B? And how is each to drive?


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Hi all

below are pics of my 71B gearbox (not the best photos sorry). 

1D67E8F1-4D27-4186-B19C-6F62DF14B62B.thumb.jpeg.dee62b209120ca868cf5d6aaf12acfe8.jpegC6A90912-A960-482C-BE67-243196479FF6.thumb.jpeg.b39f8b4aac152b01e418feb63017263d.jpeg

Few questions:

1. Is it a C or a W and is it even possible to tell without opening it up? 

2. What’s with the double slip yoke? So there is what I believe to be a slip yoke going into the gearbox however it won’t budge from the gearbox, isn’t it meant to slide out? Then a uni joint then another slip yoke. Then my driveshaft which has a spline and then a flange to the diff. If I’m not mistaken this is a modified set up by P.O. to make the 71B fit the 240z?

3. I know the C71-B is meant to be the more desirable box, Porsche servo synchros and sportier feel. But what does that translate to in real life driving? Is the C71-B way better to drive? And if so worth finding one and paying a premium for it? I know this will be a little subjective and also difficult as not sure how many people have driven both boxes?! 

Ryan 

 

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3 hours ago, 240ZBUILTBYME said:

1. Is it a C or a W and is it even possible to tell without opening it up? 

An original Australian market car would be more likely to have an FS5C71-B than an FS5W71-B, as the Servo-patent synchro type 'box was standard equipment in Australian market Zs, superseding the FS5C71-A in January 1972. The only way to tell for sure is to split the case and inspect the internals. Note that gear ratios between the Servo and Warner synchros are different too.  

4 hours ago, 240ZBUILTBYME said:

2. What’s with the double slip yoke? So there is what I believe to be a slip yoke going into the gearbox however it won’t budge from the gearbox, isn’t it meant to slide out? Then a uni joint then another slip yoke. Then my driveshaft which has a spline and then a flange to the diff. If I’m not mistaken this is a modified set up by P.O. to make the 71B fit the 240z?

It looks to me as though the still-attached propshaft stump is the front half of an earlier FS5C71-A propshaft which has been modified to fit the slip yoke output of a 'B' type 'box. What's the production date of your car? If it was built before January 1972 it would have had an FS5C71-A transmission with a flanged output and a matching flanged, two-piece propshaft with a sliding joint in the middle. It looks to me as though this type of flanged prop - with the output end modified by attaching a slip yoke to the U/J - is what is 'stuck' on the output end of your 'box. Some heat and a few carefully aimed whacks ought to free it.

4 hours ago, 240ZBUILTBYME said:

3. I know the C71-B is meant to be the more desirable box, Porsche servo synchros and sportier feel. But what does that translate to in real life driving? Is the C71-B way better to drive? And if so worth finding one and paying a premium for it? I know this will be a little subjective and also difficult as not sure how many people have driven both boxes?! 

As mentioned before, the ratios are different (a useful mnemonic: 'C' type synchros = 'Close' gear ratios, 'W' type synchros = 'Wide' gear ratios) but the shift 'feel' is all about positivity of engagement. Generally speaking, the Porsche Servo-patent steel synchros were developed for sports cars where the driver was expected to be more positive/deliberate in changing gear, and the Servo-patent type allows for that (although they wear out faster than the softer Warner-patent type). The Warner-patent type was expected to be used more smoothly and sedately, and perhaps we could say it doesn't really like to be rushed. Personally, I like the Servo-patent synchro feel and enjoy that positive-engagement feel (it's as though the synchro 'sucks' the gears into engagement when pressing on) but with the caveat that the Servo type is at its best when it is 'run-in' after a few hundred miles, and after maybe something like 20k to 30k miles they start to wear noticeably and gradually become more baulky. The light that burns twice as bright burns half as long. This is particularly true with the FS5C71-A in my experience.

Anecdote: The north American market cars were fitted with Warner synchro transmissions (Japan and the rest of the world got Servo synchros as stock equipment) because it was felt that the average buyer in the north American market was not sophisticated enough as a manual transmission sports car driver to enjoy the Servo type synchros and the more closely spaced gears that they were usually paired with. In which case I think it is a cool part of an Australian market car's identity, and cool to stick with Servo type synchro 'boxes where possible.     

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2 hours ago, HS30-H said:

An original Australian market car would be more likely to have an FS5C71-B

Firstly, thanks @HS30-H for the amazingly detailed reply.

Interesting, I didn’t know the C71-B was the only one supplied to the Australian market. I will crack it open and do my research on telling the difference.

2 hours ago, HS30-H said:

What's the production date of your car?

Mine is a 1971 but is a bit of a Frankenstein. Bought it with a L20 installed and the 71B. Gear lever was impacting on the trans tunnel. I have a spare 71A which came with the car and may or may not be it’s original gearbox. 

2 hours ago, HS30-H said:

Personally, I like the Servo-patent synchro feel and enjoy that positive-engagement feel

2 hours ago, HS30-H said:

I think it is a cool part of an Australian market car's identity, and cool to stick with Servo type synchro 'boxes where possible.     

Thanks for your opinion, I also think it is cool. And I’m crossing my fingers it is a servo syncro box. Otherwise I will have to source one. 

2 hours ago, HS30-H said:

the caveat that the Servo type is at its best when it is 'run-in' after a few hundred miles, and after maybe something like 20k to 30k miles they start to wear noticeably and gradually become more baulky. The light that burns twice as bright burns half as long.

Hahaha I like the metaphor. This is great info to consider. 

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2 hours ago, 240ZBUILTBYME said:

Mine is a 1971 but is a bit of a Frankenstein. Bought it with a L20 installed and the 71B. Gear lever was impacting on the trans tunnel. I have a spare 71A which came with the car and may or may not be it’s original gearbox. 

If the car is a 1971 production year Australian market model then its original transmission would have been the FS5C71-A. Honestly, I'd go with that. They are lovely to use when in good nick, and the straight stick will fit your console and trans tunnel like it was made for it (er, it was....). The ratios are great with the 3.9:1 rear end, and you get the steel Servo-patent synchro shift into the bargain.

 

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Alan is correct - your Z would have been fitted with the '71A' box from the factory. Hence the interesting mod to the tail-shaft you have discovered,
and the leaver hitting the front of the tunnel.

I have to disagree slightly with Alan on the 71A units, as they are quite a bit slower in shifting and less accurate in action then a B or C box.
Also the cost to rebuild the 'Monkey Motion' shift mechanism to an acceptable standard is eyewatering - nearly $1000 to make it serviceable. 
Not only that, the bulk-ring synchro's are expensive to buy and they are not fast to engage (compared to the brass warner style), hence a slower shifting gearbox...
Other 71A parts are also somewhat harder to acquire (read expensive) here in Australia too.
To fully rebuild one you are looking at around $3500 (including labour).

Of course the decision is yours Ryan about what you use and how original you want to make your Z.
If you are aiming for an original restoration, use the 71A box you have.
If not, use a late model S13/S14 Silvia 71C box as this will bring the shifter up in the correct position.

Finally, the gearbox in your photo is most likely a wide ratio 71B box with brass synchro's on 1st through 4th, and a steel bulk ring on 5th. 
In other words it's a 240K gearbox and it worth about $200

HTH

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6 hours ago, C.A.F. said:

Of course the decision is yours Ryan about what you use and how original you want to make your Z.
If you are aiming for an original restoration, use the 71A box you have.
If not, use a late model S13/S14 Silvia 71C box as this will bring the shifter up in the correct position.

Thanks Lurch. My car is not matching numbers so I see no point making originality my goal. I do want there to be a certain degree of originality to the car though. 

So it’s funny I was set on keeping the 71B I have as I felt it more original than upgrading to a 71C. But as you guys have said my car would have come with the 71A. So 71C is just as original as 71B, to my car anyway. 

So now I’m leaning toward the 71C option if my 71B box is the less desirable/enjoyable wide ratio.

Lurch is there a specific code for the S13/S14 71C? 

Decisions, decisions.... 

thanks all for you input and knowledge!

Edited by 240ZBUILTBYME
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11 hours ago, C.A.F. said:

I have to disagree slightly with Alan on the 71A units, as they are quite a bit slower in shifting and less accurate in action then a B or C box.

 I feel it unwise to abbreviate the identification codes to an extent that confuses the sub-variants. For example '71A' units could be 4-speed (Warner synchro) or 5-speed (Servo synchro), and there are many 'B' box sub-variants that can be both Warner and Servo synchro type. The Japanese market B-types usually had flange type outputs too, so it becomes increasingly complicated. 

I don't know where the poor reputation for the FS5C71-A comes from, except to guess that it might be tainted by worn out examples long after the fact. Over here in the UK many a tired FS5C71-A was replaced with a newer FS5C71-B or FS5W71-B simply because they were plentiful from breakers. Gradually the easy way out became an 'upgrade' in local lore.  

About synchro types: If the Warner-patent type is "faster shifting" in comparison to the steel Servo-patent type, you'd have to wonder why Nissan chose to fit their Sports Option/Race Option 'Competition' versions of these transmissions with the steel Servo-patent type? The factory certainly never used Warner-patent servo transmissions in their Works race and rally Zs. Doesn't seem to add up, does it?

11 hours ago, C.A.F. said:

Also the cost to rebuild the 'Monkey Motion' shift mechanism to an acceptable standard is eyewatering - nearly $1000 to make it serviceable.

"Serviceable"? Are you talking about blueprinting here? They worked perfectly well off-the-shelf (ie, new) and - as mentioned - they eventually wear out.

I think this "monkey motion" term comes - along with a lot of other nonsense - from the USA. Perhaps an engineers opinion of a slightly fangled linkage arrangement, but there are design problems with the B-series 'boxes which don't seem to get mentioned because their reputation as 'the' upgrade in period was cemented long ago.

I always take the all-pervasive American lore with a very large pinch of salt. I tip my hat to Australian lore, but hope it hasn't been tainted by USA Uber Alles syndrome. 

 

TLDR: FS5C71-C with the Kameari Engine Works 'Cross' (tr: 'Close') Gear Kit is a wonderful thing. Recommended.  

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