LXi and WideBody PTO/Pump Splines

[davidbrady]

(04-30-2013 00:44)Arcticdude Wrote:  So add the 1" pump and you're good to go?

That's right John, add the 1"-15T Quality Control Corp Pump (CPC 1049 CPC 030-R-2-AF-BC) and you're ready to go.

It was quite a process coming to a conclusion on the PTO/Pump spline early failure. I eventually showed my worn splines to a metallurgist and a gear specialist. The gear specialist gave me a spread sheet which I've attached two copies of, one for the 7/8" and one for the 1". The spread sheets show that the 7/8" isn't strong enough. The 1" is, but with a slight safety margin. The cause of the failure is most likely fretting due to shaft misalignment along with undersize splines. There's no sign of shock loading or load reversals as I had initially thought, so prolonged engine idle isn't an issue. I spoke with a long time Chelsea tech person who said that the tolerances of the PTO are poor and have gotten worse after outsourcing manufacturing. Muncy also offers a full time PTO but word is that their alignment isn't any better then Chelsea's. So the best root cause we have to-date is misalignment which initiates fretting and overloading of the spline due to undersized splines.

If you look at the attachments you'll see the "shear stress in teeth" and "compressive stress in teeth" for the 'Fixed Spline': 1) 'compressive stress in teeth' margin-of-safety of -0.129 for the 7/8" shaft and 0.349 for the 1" shaft, and 2) 'shear stress in teeth' margin-of-safety of -0.032 for the 7/8" shaft and 0.487 for the 1" shaft. My gear guy would like to see safety margins no less than 1.5x to 2.0x. The 7/8" shaft just isn't adequate. The 1" shaft is markedly better, but it's still too wimpy to make an overall wet-spline recommendation.

Given the slight safety margin of the 1", folks will have to make their own call as to whether to go wet-spline (AF) or grease (GF).