So I took my one buddy out for a drive today and he said my 56-series 'box is on its way out. Now he does work for a gearbox rebuilding center, but how could he know from driving with me? Are there telltales I could listen or feel for?

I was considering an automatic for a replacement to deal with the A15 a bit better (and because I read of a guy who got 17km/liter of fuel with an automatic), and I came across an article on swapping L4N71B gears and overdrive into the 3N71B on a 510 forum. Is this for real? And is it a good idea?

Or should I consider another automatic gearbox and just have an adaptor plate made?

I don't mind modifying the tunnel.

Quote:By sound. Howling, grinding while shifting, indicates problems, though they are unlikely to "go out" as long as the oil level is full in the box. They won't get quieter by themselves but probably won't get any worse.

Just about the only "going out" symptom is a severe chattering/ticking - which disappears in fourth gear (4th bypasses the cluster gear). This is usually worst in 1st gear due to worn bearings. A similar but more constant ticking is caused by a broken gear tooth.

Another severe problem is a vibration from worn output shaft. But 1) it is unusual and 2) probably caused by propshaft issues rather than gearbox issues.

Quote:Fantastic idea. Swap the 4N71B in (I doubt if swapping gears into a 3N71B is agreat idea, as the 4N71B already has the right parts, depending on which one you get). But it has only been done a few times and there is no detailed walk-through. There is an overview in our Datsun 1200 club article L4N71B Swap.

Regarding fuel economy, since this is a lockup overdrive automatic, you could easily get just as good of highway (high speed) fuel economy as with a stock 4-speed. But the around-town (low speed) fuel economy will be worse. It won't get as a good of economy as with a 5-speed manual.

Thank You ddgonzal.
When I got the GX, I had the prop' shaft's yoke machined down and an output shaft bush made to accomodate this, and had the porpshaft balanced. I also replaced the universal joints after which there was NO vibration or abstract noise. All I hear when driving is that 'straight-cut gearbox' whine. However, my father informed me that that's almost a trademark of that era. =/ I'll have one more thorough listen next time I visit the dyno.

As for the automatic gearbox route, I am very pleased to hear your opinion! Although, I was under the impression that the 3N71B transmission was somewhat lighter and more compact than the L4N71. Is this true? Or should I have started looking for an L4N by now?

Yes the 3N is lighter and more compact than the 4N ... but so is a 4-speed manual lighter and more compact than a 5-speed manual.

Get the short 4N and it's a pretty good fit.

A very good point! Might I ask if you would know of any sources of information on the JATCo transmissions? I seem to be limited to wikipedia and one or two other forums. To be honest, I didn't even know there were more versions of the 4N other than the E4N that my R31 has and the newer RL4's. So I suppose you're refering to the 4N that was built shortly after the 3N?

I really appreciate your knowledge on this!

These gearboxes don't have straight cut gears in forward gears. Single helix is the right term I think. I doubt the reverse is straight cut either, member revhead would know, he posted a rebuild on one of these boxes. My 60 series dogleg certainly doesn't make any straight cut gear noises.

I wonder if the whine could in fact be your diff...........

The whine is mostly the differential, which does not have straight-cut gears either. But the gearbox whines a little bit. I think new cars make the same sound, but are more insulated, thus you never hear the sound.

JATCO transmissions are used by many makes of cars. Just search for JATCO on the web.

I think the gearbox rebuild centre friend might have heard a diff whine and declared a gearbox rebuild.