Half shafts broken

[lotus401]

My Westfield Megabusa is raced in autocross events and has a serious appetite for half shafts. It has a Landrover Freelander diff with LSD conversion and independent suspension. Last year I broke the left side half shaft at the start line. A couple of weeks ago I broke both half shafts at the start line.

 

Does anyone out there have any sugestions about why the shafts are failing? The Westfield factory run race teams in the U.K and they tell me they have never had a failure.

 

Anyone know a source in the Chicago/Midwest USA area that could build custom stronger shafts?

[JohnCh]

So much for the theory that BEC don’t have much torque… Have all three halfshafts broken in the same spot? Any pictures?

 

-John

[manik]

Hi Jeff,

 

Welcome aboard. I'd love to find out what all has been done to your Hayabusa. As John noted, the halfshafts really shouldn't be breaking. There are some uprated replacements though, and I'll drop you an email directly.

 

 

tm

[Ian7]

I'd be cautious about throwing money at better (and presumably more expensive) replacements until the failure of the old ones is better understood.

So many questions possible:

has it always done this?

if not, whats new in hardware and/or usage?

are all shafts from same supplier? same batch?

where are they breaking? at a stress riser? same place on each shaft or random?

any flaw in material obvious on exposed internal surfaces?

is failure a torsional overload, or a fatigue over a period of time (fracture surface tells you this)

etc

etc

[RDROCKT]

Is it the actual shaft that is breaking or is it the CV/universal joint?

 

What tires are you using?

 

How do you launch the car?

 

Is the halfshaft parallel to the ground or does it have a mislignment?

 

 

[lotus401]

The car had done four or five seasons of autocross before the first shaft failure. It was the left side shaft that had failed. The parts are Westfield factory parts, as are the replacement parts. Nothing different, no changes over the life span of the car. the car was professionally built by Alamo Sportscars in Texas. I will post pictures later of the failed parts from the first failure. Do not know if the second failure is the same since I have not dismantled yet.

 

The failed shaft broke in two places. The splined hub at the wheel end shattered into several pieces and the shaft itself sheared inside the differential leaving a piece of shaft and several pieces of metal in the oil seal area. I had to remove the diff and make sure that it was OK, which it was.

 

The universal joints did not fail and the shafts are parallel to the ground. The tires at time of both failures were Falken Azenis but I have used Hoosier autocross tires and soft compound race slicks during earlier seasons. Wheel/tire sizes are rear 225/50/R16 on 7.50in rim and front 205/50/R15 on 7.00in rim. Westfield spec is 13" or 14" wheels so the car rides about 1 1/2" higher than factory specs.

 

On the question of torque the Hayabusa engine develops about 115lbs/ft which seems OK for a 1300 engine and an 1132lb car. The biggest problem driving it is the limited clutch travel, lack of flywheel effect, short stroke and small reciprocating mass - it stalls very easily! It has a great spread of power all the way from 5500 to 10500rpm and with this rev range it hits 60 in first and 80 in second. most autocross courses are run entirely in first gear.

 

Autocross starts are pretty rough, the tendency to stall so easilly means that starts require getting the wheels spinning then modulate the throttle/back off to get grip before the start time lights.

[Ian7]

"The splined hub at the wheel end shattered into several pieces and the shaft itself sheared inside the differential"

 

OK, it strikes me there is way more than a simple failure here. If you overload a part in torsion, or fatigue it through repeated overstress, you're typically going to get a failure at a single weakest spot in the part. "Shattered in to several pieces" as you say seems somewhat alarming to me...

[lotus401]

Attached are some photos of the first half shaft failurehttp://www.usa7s.org/aspnetforum/upload/145946844_Half shaft 5.JPGhttp://www.usa7s.org/aspnetforum/upload/2114900613_Half shaft 4.JPGhttp://www.usa7s.org/aspnetforum/upload/1043833504_Half shaft 3.JPG

[RDROCKT]

Hi Jeff,

 

We met at Rt 66 a couple of years ago. Sorry to hear you are having problems but you have a very nice car otherwise.

 

I agree with Ian7. Have you checked the wheel/hub bearing to see that it is turning freely? Shattering may just be another word for broke but the use of it tells me (us) that you had a sudden catastrophic event. Check all other parts from the drive shaft back for binding.

 

I was also thinking about your use of a 3-4" larger diameter tire. You are imposing a greater resistance to turning and the force needed to do so may well be beyond the design spec of the halfshafts. Hard to believe but you may want to ask the Westfield people. Manik will be able to do that, I am sure.

 

HTH

 

[Ian7]

Top picture with the three-piece female spline hub is a "burst"; all I can think is that huge misalignment of the male/female parts caused this, but not sure how to generate that much misalignment without something else going wrong first.

Bottom right picture of shaft failure is classic torsional overload, giving the "45 degree twist" appearance. Check the fracture surface for internal flaws in the material.

[Arya Ebrahimi]

In my hobby(rockcrawling) broken axle shafts are common. I wonder if that burst failure isn't from the shaft breaking torsionally and then getting bound up somewhere. OR it could have been a recoil type situation where the release from torsional failure shocked the rest of the system causing the breakage.

[BirkinBernie]

You might give a call to Craig Taylor at Taylor Racing in Dallas.

 

http://www.taylor-race.com/contact.cfm

 

Solving problems like this are Craig's business. He is also a very Se7en's friendly guy - he has given fantastic tech presentations at two Southwest Se7ens Festivals in past years.

 

Good luck!

Bernie