A new 1st???

[Zambo]

Dear All,

With speed comes the demise of some parts.

At the Sprints this year, I am told that I achieved a new first for the group. I broke the my new 300M input shaft while exiting T-14. Any new solutions? My newly separated 300M input shaft had about 28 race days on it.

I also had a chance to speak with Kevin from Comprent who indicated that Elite has a input shaft that is significantly less expensive than others.

Steve

[Tifosi]

Any new solutions?
Steve

Stay off the curbs Zambo!

[Keith Carter]

This seems to be a pretty common issue we're finding out. Seems to be an easy answer too... Make less HP or make the shaft stronger or beefier. I'm sure we could detune these things to 100hp and not break any drivetrain parts. I don't like that option though...

[mousecatcher]

i broke a 300M input shaft 2 (3?) weeks ago at the Reno Fernley National. Put in an elite replacement.

[Paul LeCain]

There's got to be something odd going on here. That shaft looks at least as beefy as the input shaft in a Ralt RT-41 (Staffs input shaft).

I don't recall ever seeing one of the Staffs shafts break. I've even done standing starts with them.

Is something in the chassis flexing?

[Rennie Clayton]

There's got to be something odd going on here. That shaft looks at least as beefy as the input shaft in a Ralt RT-41 (Staffs input shaft).

I don't recall ever seeing one of the Staffs shafts break. I've even done standing starts with them.

Is something in the chassis flexing?

Paul,

I've broken a Staffs input shaft in our RT-41, long time ago at Buttonwillow during testing for the LBGP. Dang thing flopped around in the aluminum carrier sleeve and dumped the oil contents of the bellhousing all into the diaper.

The combination of frequent 1st gear use, frequent use of entry - apex - exit curbing / rumble strips, and bumpy track did it in. Something about all of that in combination with a decent amount of torque harmonic, and they can get all snappy on you. Given the relatively larger motor and torque signature of FE engines, I'm not surprised to see the same thing happening here...


Cheers,
Rennie

[Paul LeCain]

People seem to be saying this is a relatively common problem for FE.

We do a lot of testing at NHMS, which has a really bumpy 1st gear corner (45 MPH). Pocono has two pretty bumpy 1st gear corners.

[smcqueen]

This just looks like an overload fracture vs. most of mine were fatigue. My original Elite input shaft lasted about 19 race weekends plus a number of track days. The material analysis was an odd chrome-moly steel, 42 Rc hardness, probably around 200ksi ultimate tensile. My second input shaft (Williams) lasted four weekends. Material was verified to be 4340, 36 Rc hardness puts it at about 175 ksi ultimate tensile. My current input shaft is Taylor, and I verified as 300M material 46 Rc which is going to be about 240ksi ultimate tensile. Neither the Taylor or Williams had any kind of surface finishing. Polish and shot peening would greatly improve the fatigue life of the parts, but probably not going to solve overload failures.

I don't think the problem is so much the torque of the engine but rather the size of the shaft and available traction. Even a 1600cc engine can create enough inertial loading to fail the shaft if the available traction is there at the other end. Also keep in mind that the clutch on the car is capable of 500 ft-lbs torque, so your clutch is not going to give at all. The input shaft on these cars is only about .64 inch diameter. Even though it looks like an Atlantic input shaft, just a tenth of an inch on diameter makes a huge difference on strength since the torque capacity is proportional to the cube of the diameter.

I probably sit around and think about this too much, but I kind of fix things for a living.

Just increasing the diameter of the shaft is not a simple solution. You are limited by the spline diameter that goes into the layshaft (or is it mainshaft). The current shaft is properly designed for the spline diameter on the end of the shaft. If you just increase shaft diameter, you will fail at the spline. In order to increase the spline diameter, you would need to redesign the layshaft (or is it mainshaft) with larger female spline, which would probably require larger OD on that end of the shaft, requiring larger bearin in the front of the transmissio case, which you would need to modify the case.

I am sure all of this could be done, but you probably would be looking at $2-3k for parts and mods judging by current pricing of parts.

What can we do as a driver to prevent failure? Both of mine failed on first lap of a race after I had done aggressive first gear tire warming on the warmup laps. Also, stay off the big curbs (do as I say, not as I do). I personally believe you are better off not using the clutch, since its use typically leads to rpm mismatch on the downshifts, but that's just my opinion.

If you are going to install a new shaft, if would be a good idea to poish the radius of the fillets, and possibly send to an expeirienced shop for shot peening. I polished mine, but did not have time for shot peening.

scott

[jcorsico]

There's got to be something odd going on here. That shaft looks at least as beefy as the input shaft in a Ralt RT-41 (Staffs input shaft).

I don't recall ever seeing one of the Staffs shafts break. I've even done standing starts with them.

Is something in the chassis flexing?

Could it be a misalignment of the engine and the transmission? When I first assembled my car last year, I didn't take the time to check the alignment carefully and just bolted it together since all of the bolt holes lined up pretty easily. This winter I had a chance to check the alignment, and had to add about 0.063" (on the left) and 0.113" (on the right) of shims in between the frame (by the fuel cell) and the engine bay triangular support legs to tilt the transmission downwards, since there was a misalignment between the engine and the trans (the car was essentially sagging in the middle, where the trans connected to the engine). I imagine such a misalignment could have caused a slight bend in the input shaft, which certainly wouldn't be good for fatigue life.

Jon

[jcorsico]

The combination of frequent 1st gear use, frequent use of entry - apex - exit curbing / rumble strips, and bumpy track did it in. Something about all of that in combination with a decent amount of torque harmonic, and they can get all snappy on you.

What can we do as a driver to prevent failure? Both of mine failed on first lap of a race after I had done aggressive first gear tire warming on the warmup laps.

Just so I understand, what does the use of 1st gear have to do with the breakage? If we're talking about the input shaft, the engine puts out the same amount of torque no matter what gear is used. The torque multiplication happens in the gearbox, and you'd see increased loading only in the axle shafts going to each wheel in first gear as opposed to any other gear. Right? Or am I missing something?

Jon

[smcqueen]

Very well could be aggrevated by trans misalignment. I have thought about this, but very difficult to measure.

Problem with first gear is shock loads due to spinning rear tires then gripping, also reversal loading when on and off the gas. You will transmit more reversal loading through the transmission.

scott