RC I think the later C boxes had dual synchros on 2nd to avoid these issues

One other thing to do every time you replace a synchro cone make sure you tape up the gear leaving just the mating cone section exposed and then get it glass bead blasted for after a while they polish up and the friction required for good synchro operation is lacking.

This makes a vast improvement in synchro operation, Even works when you don't replace the Brass synchro cone on the other gears so when the box is apart glass bead all the synchro cone mating surfaces on the gears.

Just a note; on my 56 series box I had a similar issue, the syncro looked fine but after measuring the cone very carefully it turned out the cone was ever so slightly worn. I put a brand one in and the problem went away.

Tom

Same. 71B was used circa 1975-1985. Then the 71C revision came out. Since they use the same synchros, it's not clear why the 71C is a better shifting gearbox. Maybe because they have less miles on them.

Many RB used the 71 box. The biggest RBs used the FS5R30A gearbox, it's heavier and larger around

Then there is the FS5R90A which many say shifts worse than a 71B box. Maybe you could take its removable bellhousing and put it on a World Class box

I would just fix the Stumpy that has the shift problem

Are fj20 boxes the same? Just change the bell or d21 like fattos?
Could just bite bullet and go rb long box, make a custom shifter?

wow, thanks, maybe it is worth pulling the box apart and checking

especially if there is no other options available

New syncro is $44 list price (buy one for 2nd gear, no need to buy a whole set). I think it is Nissan part number 32604-P0100? which sells for $32 online

New synchros have made crunchy gearboxes better. But not always, apparently the tolerances are more than the factory replacment measurement, so look at the dog keys/synchro teeth alignment too (visually compare the "bad" one to the other synchros in the gearbox)

Some have reported cracked shift forks cause shifting problem (still shift, but not very well)

Others report the same issues in high-mileage 71C gearboxes (poor shift at high RPM)

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  71B_71C Synchros.jpg (54.85 KB)

Several have mentioned problems shifting at RPMs above 5000. 2nd gear wasn't mentioned.

Now of course this wasn't a problem with a new box as they were fitted to engines with a 7000 RPM redline. And not specific to the stumpy, but to all 71B series (280ZX, etc). The newer 71C has improvements. The 71B took more time to shift (needed more time to synchronize)

Quote:So apparently it did shift, but "crunched", which sounds like a synchro problem.

General factors affecting syncros:
* Incorrect gearbox fluid. Using 10W40 not recommended. Using ATF not recommended. Synchro depends on friction, so use the recommended 75-140 weight oil
* Worn synchros
* Corroded synchros. Using GL-5 lube can do this. Use the recommend GL-4 "safe for yellow brass" oil

I'm quite happy with my R30 skyline stumpy behind CA18DET
And i really like the shifter being in the correct spot

but - one issue - can't shift into 2nd (down or up) at high rpm. This is apparently a typical trait of the R30 gearbox.

Has anyone any knowledge of an upgrade to synchro's or any possible other changes which help with this issue?

I feel like i read something about it once, but searching google hasn't revealed anything for me