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Yet Another Axle Thread - Chosing the right setup in 2022


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Hi All, I'm fairly new here but I've had a 1978 280Z for a few years now.  I'm looking for some guidance on a build in which I'm targeting 350-400 whp with similar ft-lb torque (leaning towards a turbo K24).  This will mostly be a street car, maybe occasional track time but no drag racing.  I've read and searched a ton of threads on here about the known weak points in the drivetrain: the stub shafts and U joints, but it seems peoples experiences vary wildly:

  • Some people seem to have failing U joints with even stock cars.
  • Many appear to upgrade to weld-on adapters with 300zxt CVs with just stock power but have some of issues with fitment and binding
  • Others seem to be running decent hp swaps on OEM 280Z half shafts and stub axles without issue somehow

 

The options as I understand them are:

  1. Trying the "plug-n-play" CV axle like that offered by T3 and others: https://technotoytuning.com/nissan/280z/long-nose-r180r200-cv-axles-240260280z
  2. Weld on CV conversion w/300zxt axles
  3. Leaving it stock until something breaks
  4. Upgrading to a full rear end kit by Apex Engineering or T3, swapping the diff out (https://www.apexengineered.com/store/p63/Rear_Suspension_Kit.html)

 

The Apex Engineering or T3 kit may be overkill (and it's expensive) but has the benefit of getting me easily to a 5 lug conversion, new bushings/bearings, and I'd expect some increase in rear end rigidity.  I spoke with T3 about their plug-n-play CV axles and they stuck to the "don't use it over 250-300hp".  Which makes me wonder if all of the options that keep the OEM stub shafts (i.e. options 1-3) will fail prematurely.

 

Does anyone have experience with any of these options on vehicles in the range of 400whp/ft-lb and have any recommendations?  Is it the smallest headache to fork over the money for a full rear end conversion kit or complete overkill?

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You seem to have a pretty good grasp of the issues and most available options; and yes, the outer stub axles are "generally" the weakest link in the system.  However, there are a couple other considerations which will factor in to your overall result:  which transmission you end up with; which tire/wheel setup you end up with, and driving usage.

1)  Auto trans are generally kinder to the drivetrain.

2)  Big, sticky tires are generally less kind to the drivetrain.

3)  Heavier cars are generally less kind to the drivetrain.

4)  A smoother/gentler driving style is ALWAYS more kind to the drivetrain.  (By far, the biggest factor within your control.)

 

The stock half-shafts are surprisingly stout, when maintained in good working order.  Mine have lasted several years of hard autocross and track use with 275-width R-compound tires (I've broken the R180; but no problems with the half-shafts, side axles or stub axles) .  If yours are working now, I would suggest continue using them until they fail.  By then, you'll have a better idea on your objective setup and goals for the car.  Making big changes to the rear end now is really just a lot of time and expense for something that you may never actually need. 

 

FYI -- if you decide you really need CV axles, keep in mind that many (most?) of those solutions limit your rear sway bar options. 

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Thanks for the input.  It'd be a manual transmission and mostly mild driving.  But I'm sure one pull in spirited driving could break things.

 

My largest concern with leaving the rear end stock for the engine swap is having to spend the time/money to fix the current old items (mustache bar bushings, differential bushings, probably new wheel bearings, eventually coilovers) then to snap a U joint as soon as it gets on the dyno. Which would mean rebuilding the rear-end and basically undoing the work I put in already.

 

Obviously we can't predict the future and the life of my current parts but if nobody is saying "oh your stock setup should be fine" I'm leaning towards just doing the full upgrade - super 8.8/ApexEngineering/T3 to prevent redundant labor

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Z Car Garage makes a great bolt in solution that appears to be able to handle plenty of power, much more than what you're planning. Expensive, but totally bolt in. The super 8.8 setup basically requires that you change your entire rear end, and if you're putting big brakes, 5 lug, etc. in the rear, then you kind of have to do the front now too. Lots of scope creep, vs simply dropping in the ZCG axles and being done. 

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If you’ve already decided to swap in cv axles; DriveShaftShop makes a very stout pair for less than the Z Car Garage units.  Both are way overkill for your intended setup IMHO.  Also, neither of these address the stock stub axle; which is what your original post seemed to focus on.  Good luck with it.

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Something to consider is that a k24 swap is going to want a 4.09 or even 4.56 final drive... and as others already mentioned, the 280z outer stubs are now approaching 50 years old... micro fractures and other issues will eventually rear their ugly head.

 

Consider the cost of an lsd unit, the intended ratio that fits your drivetrain needs, and the cost of disc brake conversions, future diff rebuilds and so on.

 

There's a LOT of factors there.

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29 minutes ago, Invincibleextremes said:

Something to consider is that a k24 swap is going to want a 4.09 or even 4.56 final drive... and as others already mentioned, the 280z outer stubs are now approaching 50 years old... micro fractures and other issues will eventually rear their ugly head.

 

Consider the cost of an lsd unit, the intended ratio that fits your drivetrain needs, and the cost of disc brake conversions, future diff rebuilds and so on.

 

There's a LOT of factors there.

Yes, lots of factors for sure.  And I have a ton of questions but figured I'd start here at the rear end.  Expect to see more threads from me 🙃

 

As for the final drive, I was actually hoping to have taller differential gearing, like a 3.36 with the goal of highway drive-ability assuming I matched up with a CD009 or s2000 6spd.  I'm just learning about planning out the gearing - is this a bad plan? Do you recommend the shorter gearing mostly for the acceleration benefit and maybe paired with a 5 speed to keep on boost for longer?

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If you're planning on making enough power to fully use a 3.36 gear then don't bother keeping the r200 or trying to find one and then put an lsd in it...

 

3.31 mustang diff is already 34 spline lsd and they're 100 bucks plus shipping on ebay.

 

The 31 spline explorer diff can be 3.27 as well, but they're nowhere near as reliable or strong and the kits from every company that sells explorer swap kits has SERIOUS issues and an unacceptable failure rate.  Several of the guys who swapped to the mustang super 8.8 had catastrophic failure at moderate to low hp levels when they had other setups... and some of them were expensive and name brand...

 

Mustang brakes are 150 bucks for the rear,

 

Mustang hubs are 150 for the pair

 

And a diff is anywhere from 100 to 1200 bucks depending on ratio.

 

Ironically the taller 3.31 and 3.15 gearing is dirt cheap.  The 3.55 can be had for a decent price, but 3.73 and 4.09 start going up.

 

Granted, this pales in comparison to r200 lsd prices, and the cost of replacing the axles and stubs with something advertised as stronger than stock... nevermind trying to find the elusive 3.36 r200.

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I wouldn't plan on ever going past 500hp.  Likely staying 400hp or lower on initial build. I'm unsure if the the taller gears would be optimized for that power on the drag/track, but road drive-ability is #1 concern.  I know you've seen some crazy builds @Invincibleextremes - is low/moderate hp levels considered 400hp in your book?

 

For your kit, is notching/cutting the beam required to fit the mustang diff?  I'm having trouble finding pics/info on how this notching is done well for the larger differentials.

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