Datsun Roadster Forum-311s.org

I pulled the rear end apart this afternoon and from what I can see the only thing broken was the driverside axel. The LSD looks good, and there were no large pieces stuck to the drainplug. The end of the axel failed and was still stuck in the carrier. There were no large pieces floating around the carrier either, everything stayed where it was. Perhaps by Solvang I will have everything back together and reliable like it was last year. Now to find a good set of axels and get them magnafluxed, that will be cheaper than messing with the LSD any day of the week.

Will

Will,

That is good news. I think I have a spare set of axles from a 66 that I think are compatible, but I am not really sure. Won't be cheap to ship...

I have to say that I am amazed that you broke an axle, are you sure everything is setup right in that carrier? Seems odd to break one of the beefiest parts of the car (Even if you were trying to burn all of the rubber off of the wheels!)

TR

It failed in the splined area, effectively the weakest portion of the axel. You can see the sheer stress in the broken part, the splines are all offset in one direction. No I'm not positive that everything is correct, I was having wierd tire wear on the insides of the rear tires for some reason before it failed. I just got it all apart, I havent really explored much. I will take it to a friend who races a 510 and is a very good mechanic (for a living) and see what he has to say about it. I'm thinking of leaving the 3.9 in for a while once I get it fixed, having the freeway cruser might be fun.

Will

Rear axle failures are not that uncommon for stock rears with LSD units, more than stock power and less than gentle driving. Col. Joe Hauser experienced that problem and came up with a solution - a full floating axle. His information is detailed on Fairlady.org. Here is a link to the axle info:

http://www.datsun.org/fairlady/JoeDiff.htm

Enjoy the read!!

Yup. I know of a small collection of broken LSD's. right at the splines is where they break and they often take out the side gear with them when they go. I've even heard of one where the diff case itself split where the side gear fits into it. Don't be doing those drag race starts!

I didn't see any damage on the side gear, but I will have a pro take a look at it. By the way, I don't do drag race starts, I like my tires thanks. Anyone can go fast in a straight line, its all about being fast through a corner.

Where does the damage in the side gear happen? Is it in the spline area or else where?

Will

I had no idea, I figured that these parts would hold up to all kinds of abuse. If yours broke and you were not trying to make a 'burnout of the month' photo, I might sell mine and save up money for some kind of conversion...TR

When my axel let go I was on my way to lunch, the engine was still cold and there were 3 cars in front of me, I did endup doing a 1 wheel burnout through 3 gears however . The gears are massive, I bet they will hold huge amounts of power, its the axels that are suspect. A materials enginer looked at the broken part of my axel and thinks it was a weak forging/casting. I don't know. I do know that they fail from time to time under all sorts of driving. Infact a friend of mine broke one on a one owner bone stock 66 1600 driving to school in LA one day. I have a 3 strikes rule, if the same part fails 3 times it gets the boot, and I find another alternitive. The custom ford 8 inch setup is a possibility if I can't keep this together. (I have to autoX OSP due to the engine, I will never win that one. On the same note, I won't be out there to win, just to have fun and improve my driving skills.)

We shall see,
Will

When you think about the metalurgy back in the day and notice how thin the metal is on the body and chassis of the car it is no wonder how a beefy looking axle can fail on a light car. I am still a fan of the axle conversion whether it is a ford 8.8 or a chevy 10/12 bolt rear. Parts are cheap and plentiful. Will, maybe if someone could remake the axles with today's tech it would help with the problems but probably be cheaper doing the axle swap?

Alexi

SLOroadster wrote: Where does the damage in the side gear happen? Is it in the spline area or else where?

The splined end of the axle can sort of explode (there's a whole lot of force in that thing at the point at which it'll break) inside the side gear causing the side gear to deform. To the point that on occasion the diff case will crack. It's not a common problem but it has been known to happen if the car is used under extreme conditions such as a lot of drag race type starts.

Col. Joe's full floating axle conversion was implemented to solve a different type of problem experienced when road racing. Due to the huge cornering loads, the wheel hub can break right off the end of the axle shaft. As a result, the car usually winds up upside down! The stock roadster axles have to carry the drive torque and the bending loads generated from cornering forces. With sticky race slicks, I normally see over 1.5g's of cornering force.

The full-floating conversion separates the load carrying functions. Axles carry the drive torque but the hub loads go directly into the axle housing.

I went with a slightly different solution with my race car. A full floating conversion from Dwarf Car Products. The ends of my axle housing were cut off, and hubs from a toyota were welded on. Custom axle shafts connect the spline inside the diff with the spline inside the new hubs. I also got rear disk brakes and some negative camber built into the axle as well. Total cost for this conversion was about $2k, but the safety aspects make it worth the cost. No one should ever, ever roadrace a roadster without converting to a full-floating setup. I know of three instances of the axle failure with race cars, and I believe one of those ended in a fatality.

Happy Roadstering,
Chris C.

This full floating setup sounds cool, the next time I have $2000+ burning a hole in my pocket (its happend in the past....) I'll have to look into that. In the mean time, I will take the whole diff assembly to a friend and see what he thinks. I don't want this thing to granade on me for a number of reasons, being dead is a big one, but the fact that I can't get another is up there as well. I try not to do any dragrace launches (draws way too much attention, and is hard on tires), but sometimes it just has to be done (no clutch dumps from 6k with the new engine, that will blow something up for sure). If some yahoo rolls up next to me in a riced out honda, odds are I will bite. Its only happened about 4 times, 3 of wich I have won, the 4th, I backed off right after the start.

I have put way to may hours into making my car straight, I do not wish to find out if my roll bar works.

Will

Will, just a thought, might be way off base...Was the tire worn on the inside edge all the way around, or just on half the tire? All the way round sounds like the axle tube may be bent, but half way could be a bent axle flange. Either would explain the axle snapping from fatigue at the weak point of the splines. Used to see this with trucks all the time when someone thought they were on the Dukes of Hazzard.
Hope it helps

Dave,
both rear tires wore evenly on the inside. It looks like I have way to much toe-in, but its only on the rear end. The front tires have 2.5 degrees negitive camber and wear evenly. Go figure. I'm thinking of reassembling the whole rear end in my other housing that wasn't eating tires to see what happens.

Will

I could be wrong, check with some of the hardcore race guys....I think some people intentionally bend the housings for better cornering in auto cross either way good luck