R200 to 240z Bottom Line

[getoffmyinternet]

Okay, so I've read the differential sticky a couple times and it's all a bit over my head. I'd like to convert to an lsd r200 soon (need a higher gear to boot) and I want to make sure I buy the right stuff, build it to last, etc. What is the bottom line for a solid rear end that is very functional and hopefully doesn't break the bank? To start, at least mine is a 72, so I don't have to worry about the forward mount issue.

 

From what limited understanding I have, it seems that there are a lot of if's in the swap department. For instance, if I get a short nose I'll need to get a longer drive shaft and remanufacture the mount. If I get a finned cover, I need to move the sway bar. If I get a late model, I need to either use older half shafts or buy the necessary adapters. The list goes on.

 

It seems like a long nose, 3.9, four pinion, strong clsd, cv shaft diff doesn't exist, and the next closest things are very rare, so here's what I assume to need in order to retrofit my own. Please chime in if I'm missing something such as mismatches, more necessary parts, or things to watch out for in purchasing the items.The problem to me lies in the fact that the older differentials are the proper shape but lack the quality of the newer, while the newer differentials have the quality in strength, but lack the physical interchangability of the older ones. The solution then is to get an old pumpkin and a new center, or at least a different one that will bolt up.

 

1. A 280 r200 long nose housing to mount in the original 240z location

2. An aftermarket clsd center (unless another r200 variant will match up?)*

3. A 280 mustache bar to mate the new cover

4. Z31T cv's to clear the sway bar and add strength

5. modern motorsports stub axles and companion flanges

 

*Obviously the amount of money one can spend is limitless in this area. What I'm looking for is something about or just under 4:1, and 4-pinion so that it will deliver and not fail. Also, the old clutch packs are known to be skimpy, but the viscous are to my knowledge not as aggressive and can have slip problems if not treated right, so an aftermarket clsd with a thicker pack seems to be the solution as long as I can find one to mount up. I would think that for all intents and purposes, I'm just looking for a 280z upgrade. The third option is a helical clutch, but I'm unfamiliar with those, so anyone want to give a synopsis of the pros and cons?

 

On a side note, would it prove more difficult to find good long nose internals than shortnose, or are they interchangeable? of course if anyone knows of a long r200 clsd that is already good to go, then stop me now.

 

In terms of odds and ends, it would be nice to incorporate Ron Tyler's front mount remedy or something to that effect.

 

So, what's the total?

[SATAN]

Well, what are your goals? I don't know a whole lot about your build. But from the sound of it, you are looking at drag racing and getting it into the 9's?

 

If that is not what you are planning on doing then please enlighten us. The modern motorsport axle stubs I would not think would be needed unless you simply HAVE to have them to run the z31 cv shafts. That part I don't know about on the s30's. I guess it would make sense though.

 

You can take the carrier out of an 4/87-89 turbo and bolt it right into your 280z r200 case. If you get a good one, then the lsd action is not too bad at all. As far as finding your lower gearing goes, I'm sure there are some long nose ring and pinion setups out there you could find to get you around the 4:1 mark.

 

From what it sounds like, you know exactly what you need to do, now you just need to do it. You will answer a lot of your own questions once you start taking things apart and seeing for yourself.

[getoffmyinternet]

Well I don't know if I can do 9s or not anytime soon, but I'd like to have some real power yet reliability on a daily. The plan so far is to turn it up to a bar and go power fc after I redo the interior. It's just that right now my diffy sounds like it's in pain and I'd like to do something about it before it takes a dump.

 

I think the modern motorsports stubs and flanges are necessary if you use the 280 or 300 half shafts. Otherwise I could use the 240 half shafts but they become the weakest link and I've heard they are left with a little more play because the fit loose.

 

Yeah, the z31 center is probably solid enough despite the skimpier clutch pack. One thing I was unsure of though is how to make sure I get a 4 pinion. In the diff thread Jon seems to go back and forth on whether 280s and z31s all had 4 or only if some did, unless I read wrong. Perhaps he meant that all the lsd are 4 pinion, but not all models had the lsd.

 

I know it's pretty much impossible, but ideally I'd like to have access to almost all the parts before I get started since it's my only method of transportation, which is why I ask. That and I don't want to buy stuff on false pretenses.

[getoffmyinternet]

Okay, so according to the z parts wiki The only clsd r200 came in the 5/87-89 z31t and it is a 3.700. Not a huge step up though. I'm pretty sure the one I have is a standard 3.364 r180. I haven't heard anything suggesting that the short nose and long nose diffies dont interchangeable centers except for that 90-96 q45 with 30 splines (but I've heard the helicals might not match up) so this still doesn't rule out getting any aftermarket r200 clsd that's closer to 4.000. That or getting the 3.700 and just buying a new ring...

[blue72]

The earlier 280Z and 280ZX ('75-'83) R200 diffs use 10mm bolts to secure the ring gear to the carrier. The later 300ZX longnose R200 diffs use 12mm bolts to secure the ring gear to the carrier. The two aren't interchangeable.

 

IIRC The shortnose R200 diffs in the 240SX and a few other cars use the 12mm style and are interchangeable with the '84-'89 longnose R200's. If you combine the two you could potentially purchase a used rear diff from an early 300zx and buy a new LSD from, say, Courtesy Nissan. You'd have a nice new NISMO LSD cheaper than many other routes aside from buying a whole limited slip diff used.

 

Choices of gear ratios include: (via z31.com)

84-87 NA = 3.7:1 open

88-89 NA = 3.9:1 open

84-86 Turbo = 3.54:1 open

 

I've got an '88 Z31 3.9:1 longnose R200 in my '72. Just waiting to get some money together before giving in to the LSD myself.

[jeffer949]

Why do you want a 4.11 rear end any way? Your car is turbo right? Its my understanding that you want a taller gearing on a turbo to put load on the motor longer so your not off boost all the time while shifting. My car was originally the 3.36 r180 i bought a z31 lsd diff with 3.7 and threw that in there and i hated driving with it. 1st gear was useless unless i was putting around. As soon as i hit boost the tires would spin. and i was constantly changing gears and it was just annoying. So i swapped out my 3.7 for a 3.54 R200 and kept the center section from the LSD. Im still searching for a 3.36 R200 though.

 

Also on the "wimpy" clutch pack you can get more disks and take out the spacers. Thus making it stronger.

[getoffmyinternet]

I'm not sure I'm picking up what you're putting down. Did you mean put load on the motor longer so I'm not on boost all the time? Why where you always having to change gears--the peak powerband was at an inconvenient speed for any gear? I would think having a wide rev range would help make it easy to find a comfortable gear for any speed, but of course I'm not the one who has actually tried it.

 

The problem as I see it is that I'm delivering too much torque to the wheels as is, meaning the throttle seems to snap on more like a light switch than it should. I can barely roll it on in any gear without spinning the tires because the gear seems too low and they just break loose. Plus on the highway I barely get out of third and don't even really use fifth because it's too low. I'd rather have a 3.90 than a 4.11 because a taller gear isn't great for highway use and taxes mileage. The 4.11 on the gtr's seemed to work and they probably had bigger tires than I.

 

High gears are admittedly not as user friendly, and something like 4.11 sounds like more for a drag queen, but I'm hoping to find a happy medium. I mean, if I can't keep the wheels down at all, then there's no point in ever getting any more power than I already have, I'm already wasting some by not being able to throttle even 75%, unless I'm just missing something.

 

A penny for your thoughts?

[getoffmyinternet]

Blue, thanks for the input.

 

I gather that now in looking for a longnose I shall stay away from anything before 84?

 

My one speculation is that if the center I bought were 10mm I'd just have to make sure it came with the ring or I got a 10mm ring seperately, so long as the splines will accept the 300 cv's. Albeit, those are probably harder to find since there's going to be less shelf support for the 280 than the newer 300.

 

Unless, that is, if you mean to say the centers for the later models with 12mm bolts simply don't fit in the 280 long nose and the only way is to get a long nose from a 300. If so, this opens the can of worms that involves fitting a 300 diff into the 240. I'd need a custom mustache no less, right? Or just a matching cover from a 280 diff?

 

I think I just made myself more confused than I was previously.

[getoffmyinternet]

OH, jeff I think I got it. I didn't see the taller in there. You're saying the main reason people get taller gears (which is to stay on boost longer) is the very thing that makes the car harder to drive.

[jeffer949]

I think your backwards. Play with this calculator and you can see what im talking about. http://www.geocities.com/z_design_studio/ If your tires are already spinning, going to a 3.9 or so is going to make them spin more.

[woldson]

Smaller gear ratios equal more tourqe at the rear wheels.

[getoffmyinternet]

I guess torque was the wrong word. I meant speed, whipping force, a term I just made up. A smaller gear means the wheels will go faster, sooner. If the ratio was 1000:1 I don't recon they would ever break loose no matter how much power you had because there is barely any wheel acceleration--you're crawling even at full throttle. Whereas 1:1 would break loose very easily even with little power, because they are coerced to spin more rapidly and something has to give. When the wheels don't break loose at all it's because there is too little power to overcome the friction to the street, hence getting wheels with better traction for higher power applications. I was thinking that increasing the ratio also helps keep the wheels down because the power is applied more smoothly. Am I wrong on this assumption?