broken hub again

[coyled]

Well, a year ago, I broke the right rear hub. I ran PIR a week ago. In inspecting my cobra tonight, the left rear hub is broken. Its a hi-tech with the jag style spline and pin drive hub. The hub broke in half at the outside of the outside bearing, same as the right rear a year ago. Thank you for the nut and cotter pin or by by wheel. I have always thought that the bearing placement on these hubs are not correct. The outside bearing is still inside of the wheel face. Both sides were set up with new bearings and adjusted properly, similar to a front hub adjustment wise. It does not have the jag crush washers/bearing just regular taperd bearings on both sides. I don't know if I should redesign this or get a harder compound for new hubs. Anybody else heard of this happening? Bob Putnam? Any suggestions? And this is with a small block and bias ply slicks. help. Scott

[Aussie Mike]

Not specific to your application but I often worry about the strength of hubs on hot rod and component car applications. Most of the time rear ends are narrowed and have different offset wheels to what they were originally equiped with.

The center of the tyre tread is roughly where most of the force generated by your engine and brakes ends up being transmitted to the road. As your suspension moves and cornering loads are added this can move anywhere across the width of the tyre. Most factory rear suspensions are designed so the center of the tyre is roughly inline with the axle bearing. The bending stress these forces have on the bearing and hub is kept to a minimum by keeping them close to the pivot point. By putting this rear end in a component car and adding some big sticky tires on rims with a big offset length of the lever is increased dramatically. Then add an engine that makes much more HP than the original car did, bigger brakes etc.

I'm surprised we don't hear more stories of people breaking hubs and carriers. I guess the over engineering car manufacturers have to add in to make their cars last in harsh conditions (pot holes, rough roads, women drivers etc) is saving our bacon.

Cheers

[A Snake]

I'd have to see the break to be sure, but what you describe, sounds like the hubs may be too hard already. You might want to have someone do a hardness test at various points on both halves of the broken hub and at the point of breakage. I'm referencing other steel here, but I would estimate you should not exceed 48-50 Rockwell C scale if your hubs are 4140. Better they bend than shatter.

Questions for you: Does the break have very smooth edges and a fine textured look or is it a little rough textured with a rougher look to the inside of the break? How thick is the cross section where the break occurred?

Also, is the bearing surface part of the hub or does it come as a race and bearing set with race press fit into the hub?

Al

[coyled]

Al. I think they are billit hubs, whatever that means, I will check tomorrow. The texture looks rough, but that could be due to it going around the track a few times after the break. It does not look like a clean break. I found it because I was prepping for willow springs and found what I thought was a loose bearing that needed adjustment. The cross section is roughly 5/16's at the break. The shaft is inside the hub. The hub has 2 bearings on the outside of the hub, both press fit on the hub. The outside of the bearings then ride inside their races. The races are located in the uprights. Scott

[Specialk]

Kirkham has some nice uprights made of 7075 aluminum forgings. They take a Porsche 930 style bearing. Since your car sees a bit of track time, this may be you solution.

[David Brown]

I've experienced Hi-Tech rear axle problems, but not to the degree you have.

My right rear inner bearing begn spinning on on the hub, which allowed further bearing degradation to occur, resulting in a minor degree of hub wobble (the left rear also exhibited minor bearing spin on the hub but it never developed a failure).

The wobble allowed the brake rotor to oscillate within the caliper causing the pistons to be forced back into their recess each time I negotiated left and right turns. This resulted in a persistent spongy brake pedal. I pumped quarts of brake fluid through the system for nearly 2 years trying to rid the air I thought was present in the plumbing. It was after many frustrating hours, months and years into the spongy brake pedal problem before I discovered the wobble, tore the assembly down and found the spun and worn bearing assembly to be the root cause of several problems.

I then had both hubs resized slightly to allow for a tighter bearing/hub relationship, and then put on new inner and outer bearings, left and right rear. Fifteen hundred miles later the right rear inner bearing overheated, toasted the lubricant and about 25% of the bearings fractured. The failure occurred at 45 mph and sounded like someone had jammed multiple wooden broomsticks through one of the rear wheels, and each being suddenly snapped into pieces. It's amazing how much noise fracturing dry bearings make!!

Subsequent disassembly and inspection by a driveline specialist revealed bearing pre-load problems to exist because of an internal shim that was slightly improper in thickness.

Eight hundred miles after the most recent fix I'm enjoying my car, but now wonder what surprise may lie ahead now that I've read about your woes. By the way, my vehicle was constructed in 1994, is a big block car and I now have just 9,000 miles on it.

[A Snake]

Coyled,

Billet just means that they are machined out of a solid piece and not cast. Normally, such things are machined first, then heat treated. Final machining (grinding) brings the piece into tolerance after the distortion of heat treating.

It may be hard to spot after having the broken parts rubbing eachother, but look for (or have a machinist do it) crystallization. This could indicate either excess hardness when made or, enough heat was generated from stress to make the metal brittle.

Do you see any colors on the metal near the break that are different from the rest of the hub? You're looking for colors ranging from a light straw color to a dark blue. These are heat indicators and may tell us more of the story.

Al

[coyled]

David, are your inside bearings crush or taperd style? Mine are taperd but the original jag rears had crushed and I did not know what the original Hi-techs had? I was told by Hi-tech, that when you adjust the rear bearings, you do it just like the front hubs. I asked this question when the first hub broke. I baught new bearings and races on both sides and made the adjustments after the first broken hub. I have done this 500 times in the last 20 years, no problems. Well, I spoke to the maker of the hubs today and hears the problem. These hubs do not break unless they are not adjusted properly. The proper adjustment includes cranking the nut down to 120 pounds plus. At that point you check the end play on the hub and it needs to be between 3 thousanths and 6 thousanths. There is a spacer/shim that slides on the shaft before it goes thru the hub. If the clearance is to loose, you add shims. If its to tight, you take away shims. Kind of a cut and paste deal until you get it right. I never had the nut cranked to 120 pounds plus and I know there was too much clearance. The hub not being dead solid, add slicks and 660hp and they eventually break. My rear pad wear was always uneven and left the rotors grooved. I never worried much about it as the fronts did most of the breaking and the cobra stoped on the dime. I did it the way I was told. Now I am going to try the new hub with the proper adjustment. Thaks for the help guys. Scott

[David Brown]

Tapered.