4 speed auto conversion?

My 280zx has an original 3N71B auto fitted and I'm fairly happy with it but I'd like to drop the revs a bit on the Motorway.

My Nissan Nomad has a 4N71B box fitted and I read on an American site that gearboxes from any L series or Z series motor use the same bolt pattern. Does anyone know if this is correct? Has anyone put any other 4 speed auto into a 280zx?

Pete.

Hi pete,

Sorry i cant answer your question, but just out of curiosity what kind of RPM are you doing on the motorways say at 110km/h?

Same bolt pattern but and this is the kicker - the L leans to driver side of the car (RHD that is) but the Z blocks lean to the left = if you put a Z series gearbox/auto behind the L engine it will bolt up fine but the angle will be way way wrong sorry to be the bearer of bad news.

Hi pete,

 

Sorry i cant answer your question, but just out of curiosity what kind of RPM are you doing on the motorways say at 110km/h?

Motorway revs are 3500+. Not a lot, but as this is my daily ride and fuel economy counts, it seems worthwhile asking. With a different final ratio I could split the difference and get a bit more takeoff maybe.

You never know 'til you ask.

Pete.

Hi. Any update on this?

I've been doing some highway driving as of late.  I'd get better fuel economy from a tank.

It has gotten so bad I'm now considering an engine swap to counter fuel and heating problems.  I never thought I would.

Is the front half or the rear half of the gearbox housing the difference? If its the front half with the bell housing, could you perhaps swap the front housing to suit the engine?

Use the 4sp Auto auto of a late R30 Skyline - it's a bolt in.

Use the 4sp Auto auto of a late R30 Skyline - it's a bolt in.

if they are any thing like the 4 speed auto in the z31 300zx they have horrible ratio's, My 300zx cali couldn't make full use of the turbo because the ratios are to wide

if they are any thing like the 4 speed auto in the z31 300zx they have horrible ratio's, My 300zx cali couldn't make full use of the turbo because the ratios are to wide

And Lurch is correct just find an auto from a later than Oct 83 L24E power R30 and it should have the 4 speeder in there - same ratios as the Z31 stated below but bolt in

Lurch is close, the 84/85 R30 skyline 4N71B should bolt in (according to the writeup on Zcar.com), but it means custom rear mount, custom exhaust, custom tailshaft, plus using the flywheel from the R30.

I'm still thinking about it for my 280ZX and have discussed it with a local auto trans guy. He said the original 3N71B bell housing should bolt onto any 4N71B, which would solve the problem of finding the right skyline box.

I'm taking the 4 speed auto out of my '90 Nissan Nomad (no electronics), if anyone near Sydney has a spare 3N71B bell housing I'd like to see if he's right.

Pete.

Well, I'm one step closer to giving this a go.

I picked up an '85 model R30 4N71B drive train, from flywheel to diff (inclusive) on the weekend.

Unfortunately, I've got a couple of donor cars (Mitsubishi) blocking access to the garage, so won't be starting this mod until I can strip and dispose of these shells.

Pete.

Pete! I guess you got in contact with 'daewoo' on the skyline forum! good pickup

Not sure about the Cali ratios but here is the AU spec ratios for the S30 aka 240z/260z vs the Z31 aka 300zx

 

And Lurch is correct just find an auto from a later than Oct 83 L24E power R30 and it should have the 4 speeder in there - same ratios as the Z31 stated below but bolt in

I've done the conversion in my P330 Cedric aka 280C. The 4 speed R30 'box has different ratios to the ones you mentioned.

They are 1st 2.842, 2nd 1.542 3rd 1.00 and 4th is 0.686 I don't know what's wrong with those  gears, they're fine as they are!!

I don't know why Nissan didn't put this box into the S130 chassis. Would've sold more cars for sure if they did. They used it in an ordinary R30 with the L24E.....go figure!

PS the post reply box in this forum is fuckin retarded...what gives! 

Pete! I guess you got in contact with 'daewoo' on the skyline forum! good pickup

As luck would have it, I bought one from an ebay contact 2 days before I saw Daewoo's post.  :'(

I'll see if I can snag this second one anyway and if the first box is OK, I can pass it on to another enthusiast.

Pete.

Well, I finally got around to doing this and I'm very pleased with the result.

I'm still running the original 3.54:1 diff at present and the engine only turns 2250rpm at 110kph.

This gearing is a bit too tall driving through the mountains, so I'll swap in a 3.9 diff as time permits. This should still only turn about 2500rpm at 110kph.

Fuel consumption with the 3.54 diff has dropped from about 10.5 l/100km to 9.5 l/100km. The 3.9 diff will probably improve this figure despite the higher revs on the motorway.

Glad to hear it.

What were the actual modifications you made to make it all work?

Well, I finally got around to doing this and I'm very pleased with the result.

 

I'm still running the original 3.54:1 diff at present and the engine only turns 2250rpm at 110kph.

This gearing is a bit too tall driving through the mountains, so I'll swap in a 3.9 diff as time permits. This should still only turn about 2500rpm at 110kph.

 

Fuel consumption with the 3.54 diff has dropped from about 10.5 l/100km to 9.5 l/100km. The 3.9 diff will probably improve this figure despite the higher revs on the motorway.

OK, this is how I did it:

Note: You need to cut the original gearbox mounts off the tunnel to fit this, so don't change your mind halfway through. 

Source and fit the flex plate, oil lines and gearbox from a series 2, R30 Skyline. After the old mounts are gone, these are a straight swap.

You need to fabricate new gearbox mounts. The original cross member is still used, but the mounting foot on the gearbox is smaller, so there is some fiddling.

The gear shifter linkage from the R30 is a straight fit, but I'm sure you could shorten the original one if you had to.

The gearbox output shaft is bigger, so a new/modified tail shaft is required.

I used the front yolk from the R30 shaft, welded to the shortened (24mm?) 280zx shaft.

The guy that did the tail shaft, recommended looking for a VL Commodore or early Navara tail shaft if I need to get another one done, because these have replaceable uni joints. They would still need to be modified though.

The standard front exhaust section no longer fits, because the rear cross member is now about 160mm further back. That got extended and the middle section shortened the same amount. It's not perfect, but it works OK.

Most of the wiring is a straight swap, except for the bits that aren't.

I had to add a relay to get the reversing lights working and of course had to add an overdrive disable switch in the cabin.

Note: There are other gearbox options out there (RX-7), but you would still need the R30 bell housing to make it fit easily.

Pete

This gearing is a bit too tall driving through the mountains, so I'll swap in a 3.9 diff as time permits. This should still only turn about 2500rpm at 110kph.

What about a higher speed stall convertor. There should be a lot of sceond hand ones arund the forums.

In regards to the final ratio, I didn't mean that the L28 hasn't got the nuts to pull top gear through the mountains.

The issue is that TC lock-up happens about 90kph at present and the speed limit is only 80.

A 3.9 will give me the same gearing that the R30 had and should bring lock-up down to a usable speed.

Because lock-up isn't externally controlled like the VL electronic boxes, I don't know how else to change when it locks, except maybe opening it up and altering spring tensions?