Tc Lock?

[Peter I]

G'day folks,

I don't own a Skyline.

I just thought I should make that clear from the start.

I've recently grafted a 4N71B from an '85 R30 into my '81 Datsun 280zx.

It's a job that took forever (because I'm slack), but now that it's in and running, it's different to what I expected.

I'm hoping that someone who drives a 4 speed auto R30 could tell me if I'm imagining things.

The internet tells me that these autos didn't have a locking torque converter (TC). It's not the electronically controlled box and it doesn't have the TC locking solenoid on the bell housing.

But … if I'm cruising on the motorway about 90kph / 2000rpm in 4th, the revs suddenly drop a couple of hundred rpm's, without any drop in speed … just like a "modern" 4 speed does when locking the TC.

Is this just something that was always there with the three speed, but I didn't notice due to turning much higher rpms at motorway speed?

Is this just an effect of the tall gearing and TC stall speed?

I wouldn't even consider the possibility of a locking TC except …what is that oil line that runs from the bell housing (just where a locking solenoid would be) to the rear of the box and why is the TC itself so much bigger (and heavier) in the 4 speed than the 3 speed if neither one locks?

Tell me if I'm dreaming, I can take it (sniff).

Pete.

[Socrates]

The Series 2 R30s were 4 speed
where as the earlier ones weren't

http://en.wikipedia.org/wiki/Jatco_4N71_transmission

From what I understand the torque converter doesn't change that it has 4 gears, it just changes how it would shift into them.

The 4N71 was a 4-speed automatic transmission from Nissan Motors. It was available as either a light-duty ("L4N71B") or medium-duty ("E4N71B") unit for rear wheel drive vehicles with longitudinal engines. The latter used an electronically controlled lock up torque converter.

Edited April 27, 2013 by Socrates

[steve200b]

I have one that has a manual valve body etc with the lockup removed and a 3000 converter I sit on around 2500 at 100

[Peter I]

Unfortunately, Wikipedia isn't very reliable for accurate information.

As you can see below, different pages tell you different things (I hadn't looked at this particular page before).

That's why I was interested in hearing from guys who actually use this box.

http://en.wikipedia.org/wiki/Jatco_3N71_transmission

"In 1982, it gained a locking torque converter (L3N71b) for greater efficiency, and gained an overdrive section in 1983 (L4N71b), culminating with preliminary electronic sensors and control functions being added in 1985 (E4N71b)."

[Peter I]

In regards to the speed/revs I mentioned, I'm still using the original 3.54:1 R180 diff.

A guy who's done this conversion (posting on Zcar.com) recommended keeping this diff.

After using it for a couple of weeks, I find it a bit too tall for my driving (I live in the Blue Mountains - lots of climbing hills).

I have a 3.9:1 diff I can try as time permits.

[Peter I]

OK, after lots of googling, I came across this automatic section from a 1984 RX-7 manual.

http://foxed.ca/rx7manual/manuals/1984Training/7B%20Automatic%20trans.pdf

Although the scan quality is quite bad, I really think this is the same generation box we're using.

I say the same generation because, although the ratios are different, it has the external oil line and it has the thicker torque converter.

My point is,of course, it also features, new for 1984, non electronically controlled TC lockup.

What do you guys think?

[Socrates]

the 4 in its name means it has 4 gears, whether or not it has a lockup TC makes no difference to that.

[Peter I]

the 4 in its name means it has 4 gears, whether or not it has a lockup TC makes no difference to that.

Yes, it has 4 gears, that's the whole point of doing this conversion. I wouldn't have gone to this expense and effort otherwise.

That this gearbox has TC locking is an added bonus that I wasn't expecting.

For anyone contemplating this conversion (3 speed to 4 speed), here's a quick run down:

You need to get the flex plate, gearbox and tailshaft from the donor vehicle. The old flex plate will not fit the new TC and the gearbox output shaft is larger on the 4 speed.

I had to fabricate new gearbox mounts for the 280zx, I expect the R30 would also need modification.

I had to get the front yolk from the R30 tailshaft grafted to the 280zx & have it shortened. This may not be needed for an R30 to R30 conversion?

I had to get the exhaust modified to clear the gearbox mount being further back.

There's a bit of wiring to be sorted, and I had to fit an extra relay for the reverse lights.

I recommend this conversion to anyone running the 3N71B behind an L series engine.

My motorway revs have dropped from 3400 at 110kph, down to 2250rpm. After I swap to a 3.9 diff, it'll still only turn about 2500rpm.

[JMT240KGTR]

I commend your work Peter I, it's always been in the back of mind to attempt this conversion in a 240K. What seems like a natural progression to improving the drive of an auto L6, the conversion isn't that popular, everyone goes the manual conversion.

When I had an auto 240K this was the path I was going to go down, but eventually I had to sell.

Great work nonetheless, keep the car original spec, plus the bonus of a more pleasant, economical drive!