280Z stub axle vs. 240Z stub axle

[CruxGNZ]

After seeing this here (post #3) and seeing that the two stub axles are identical except for that the 280Z has 2 more splines, as seen here , (CAD drawing, 1/4 the way down). I know it is said that 280Z stubs are stronger, because more splines equals stronger connection, but how much does .080" diameter give you strength wise? Also, each stub axle I have seen has broke at the base of the splines, weather it's a 240Z stub axle or 280Z stub axle. I know John Coffee has said the stub axles also have been know to break at the fusion weld.

 

Just thought I would throw a little discusion out here.

 

!M!

[wheelman]

Matt,

I looked at that site before doing the CV conversion on my 240. The difference being only in the splined section is what caused me to decide to skip the 280Z stub axle swap. My thinking being that the weak points are not the splined sections but the transition from splined to non-splined which is the same on both the 240 and 280 stubs.

Now I'm no expert so don't use my logic in making decisions for yourself.

The guys who've been racing Z's for years say the 280 stubs are stronger and they have much more experience than I do so I believe what they say but I question if they are that much stronger to make it worth the extra money an hassle to swap them.

 

Wheelman

[ezzzzzzz]

That .080 difference amounts to over 5/64th inch overall diameter. If you were to overlay two circles to see the difference if is actually dramatic. There is a lot more material and hence more overall strength. The higher spline count spreads the loads applied and the depth of these splines is likely to be less the the 240Z version. That amounts to more metal, more thickness and more strength. In the old days, all slip joints were of heavy low number splines. There has been a consistant movement over thirty years towards more splines and shallower depths. The Nissan engineers performed a reasonable compromise to add strength without the need to completely fabricate a new stub axle, housing and related bearings/seals. It was also done within the constraints of the power plant installed from the factory. They weren't thinking outside the box to those wanting V8 power or other major modifications.

[Pop N Wood]

At 35 years old and counting, my 240 stubs are coming out to get inspected anyway. Since I will be replacing the bearings in the process, I might as well upgrade AND do the 240sx disc brake conversion all at the same time. That way the disks will at least keep the wheel and broken stub axel in the same lane as my car. Some things just aren't worth risking.

 

My only real question is to use JY 280 stubs and flanges or go with Ross's 4340 axels. Anyone know if the 280 inner flange is compatible with the 240 half shafts? Tempted to do the CV conversion at the same time, but that would put me well over $1000 in parts alone.

 

Also JohnC has often said that big tires and hard corners can break the stubs, so don't know that this is an issue for the V8 guys only. I have seen pics of broken stub axels posted from cars with stock engines.

[JMortensen]

The 280 stubs will bolt up to 240 halfshafts no problem. If you do the CV conversion with 280 JY stubs and 300ZXT JY CV's it shouldn't be that bad. I spent ~250 on 280 stubs and the CV's, need to put another $210 to Ross for the adapters, and that's it. So under $500. Add in your $420 for Ross's 240SX setup, and you're still under a grand.

 

In reading all the stories, it appears to me that stub axles break when they get a shock loading, like when drag racing or in road racing if you lift a tire, and it speeds up, then when it comes back down and gets traction suddenly. I have never broken one, but I think kind of like you it's something I just don't want to have to worry about.

 

At least after the rear disc conversion the wheel won't fall off if it does break...

[Pop N Wood]

Actually I already own the 240sx brake kit. What I was talking about was Ross's $695 4340 axels

 

http://www.modern-motorsports.com/catalog/product_info.php?manufacturers_id=&products_id=62)

 

mated to his $395 4340 companion flanges

 

http://www.modern-motorsports.com/catalog/product_info.php?manufacturers_id=&products_id=63

 

Then I just need the 280 ZXT shafts, bearings and seals to get it all to work with my R200.

 

JY 280 stubs and the stock 240 U joints don't sound so bad for now. Think I would rather get an LSD before worrying about axels and halfshafts.

[srgunz]

I have seen a few broken stub axels over the years.

They all had one thing in common.

They were all using welded differentials for autoX or road race.

My 2cents.

[blueovalz]

Good question, and it's the primary reason I've decided to stay with the 240 stubs. Even with slicks (road, not drag) I never broke anything (except the U-jointed shafts). Some pictures show the break before the splines, and one past the splined area. In the most technical sense, the 280 stub will be stronger only in one particular area (base of the splines), which if you'll looking for all you can get, then it's reason enough. My little ol' 289 ain't never gonna torque the 240 stubs in half, so they are fine for me.

[Drax240z]

I broke a 240z stub axle without being terribly abusive... open rear end. I'm not making stupid amounts of power either, I'd guesstimate ~240rwhp and 280ft-lbs.

[fastzcars]

You know those 240z stubs held up fine on the street with street tires. But with the shock load of drag radials and a sticky track, I twisted those stubs for all there worth. So I agree with most that the 240z stubs are good for the street. But be carefull on the track.

[johnc]

A well designed part going from perfectly fine condition to complete failure from one load is actually pretty rare. What happens more often is a crack developing at a stress riser as a result of a load applied. The crack begins propgating through the part following the path of least resistance. This propogation starts at a very slow rate (it probably took a long time for the crack to start in the first place). Each load applied to the crack will increase the rate of propogation and the size of the crack. Then, maybe months later, yet another load is applied and the rate of propogation pushed the crack beyond the tensile strength of the remaining uncracked material. The part then fails.

 

The failure appears to us as something that happened suddenly, but the part separating into two pieces actually took a long time to occur. We were just ignorant of everything until we heard the bang.

 

200hp ITS 240Z races cars can break stub axles and they are often replaced ona regular schedule. Stub axles used in road racing tend to separate at the fusion weld where the flange meets the stub axle. This is due to the cyclical lateral loads (over 1.1G) experienced on a race track. Also, large rear toe-in number can contribute to failure.

[johnc]

This gets to a fundamental problem I see with a lot of modified cars: preparation.

 

Once a person decides to start modifying their vehicle, they assume the responsibility of designer, engineer, chief mechanic, and driver. You may not be able to perform all of those roles, but you are responsible for them regardless of who actually performs the work.

 

This vehicle is now your creation and you must get very intimate with it. Think of it as a prototype that is being tested for the first time. Inspect everything regularly and replace parts that are suspect.

 

Is there a bolt head with one corner slightly nicked from a wrench? Replace it.

Is that washer no longer flat? Replace it.

Is this crossmember so dirty that I wouldn't be able to see a hairline crack radiating out from a hole? Clean it and inspect it.

Is that lug nut a little hard to thread on at first? Replace the nut and the stud.

I don't know what this cracked vacum line does? Figure it out and replace it.

 

I see a lot of people who really only assume the role of driver of their highly modified cars. I usually won't even go for a ride with them.

[Guest JAMIE T]

Great points John. Did you get my email? I'm not letting THAT cat out of the bag until I've actually used it myself under severe(what else?) loading.

[johnc]

Nope. Didn't see a message but I'll check again in a bit.

[G-rib-73-240z]

from what i read on this thread, so far and think i understand. i should be good if i just replace all of my u joints and CAREFULLY inspect the halfshafts often, and not do smokeshows? and that failure takes longer then (really hard launch, "laud boom from rear end")" so inspect it often and make sure there well greased, and that the shock from running drag radials at a strip can cause them to "sudenly" break?

 

did i understand all that so far?

 

hope i understood it all.

 

Thomas

[john turner]

Have Experienced 240z Stub Axle Breakage At Spline Base. In The Shop Where I Worked, We Always Used An Impact Wrench On Stub Axle Nut Removal. Wonder Whether Such Use Could Have Contributed To The Failure. Thoughts?? Jrt

[jsmith5]

While replacing (2nd time, a separate story) rear wheel bearings on my 240z, I twisted off the stub axle near the base of the threads (not the base of the splines) with about 110 ft-lb applied torque.  The car has been used for vintage road racing with essentially two long race weekends since prior replacement.  Possible contributing factors: .005-.006" end play, .005" difference between inner bearing i.d. and axle o.d. allowing wheel "wobble", possible prior overtorquing of axle, axle was chilled in freezer in attempt to make assembly easier, used impact wrench to start makeup until progress too slow, and this was potentially the original axle.  

 

I expect to switch to new 280z axles and companion flanges (assuming that they are still available) as precaution against future failures.  This info is just to keep adding to the cumulative knowledge in this posting. 

Edited January 30, 2016 by jsmith5

[johnc]

Over torquing was the likely cause of the failure of the threaded end. 280Z stub axles are NLA from Nissan. I suggest you source used axles and companion flanges or aftermarket. If you get used have then crack tested. In a road racing application the most common failure mode is the flange separating from the axle.

 

Check your bearing housing for roundness. If it's off by the .005" you mention it should be replaced. You might be able to use it if you use Loctite bearing lock.

[Miles]

If you find some used  stub axles, also check the runout on the wheel mounting flange of the stub axle.  The flanges are soft and can be bent just hitting a curb. Not much of a problem with drum brakes, but with disk brakes the warped flanges can cause the the brake pads to rub on the rotors.  The flanges can be machined if they are not bent  or warped too much. Caused me a major headache with rear disk brakes overheating. After checking the runout of the flanges I replaced the stub axles with these:

 

http://www.chequeredflagracing.net/Datsun.html

 

See pictures for typical stub axle failure points.

[jsmith5]

Thanks for the insights.  I had different problems and different tentative solutions on the left and right sides.  Just got everything back together today.  So far everything is tight, but I need to put the car on the road and see if it still tight afterwards.  If so, I'll try to explain problems and solutions for reference for future.