PTO/Hydraulic Pump

[jwm470]

I have read all the information regarding the subject, and only saw one entry addressing rebuilding the PTO, and the pump with new shafts, bearings, and seals. Does anyone know the long term results of a rebuild vs replacement?

[Itchintogo]

I believe most people switch over to a wet system if repairs are in order so that may be why you don't see much. There is a thread on converting to a "wet kit" on WaGu. The idea is that it is less maintenance and better longevity.

[davidbrady]

Hi Jeff,

You can definitely rebuild the PTO. My local hydraulics tech very much supports this. I'm not so sure about the pump. You may want to get together with your local hydraulic shop to find out. I know when QCC builds their pumps they bed in on the first run. The gears actually slice into the body to get the fit QCC is looking for. If you put in a new pump shaft, which also has a gear milled into it, you may not achieve the needed tolerances. PTO yes, pump not so sure.

Here's a study I did a long time ago on the SAE B to SAE BB upgrade:

I've attached two outputs from a spreadsheet given to me by a gear professional. One is for the 7/8" shaft, (SAE B), the other for the 1" shaft, (SAE BB).

If you look at the "shear stress in teeth" and "compressive stress in teeth" for the 'Fixed Spline' you'll see:

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. I'd like to see even better but we can only accommodate an SAE BB upgrade.

[jwm470]

David,

There is a 1"-15T upgrade shaft available for my PTO that uses the existing flat end plate without the grease fitting (it is an early unit with a 265 model number). Lubricating would require separating the PTO from the pump to grease, which I prefer as the condition of the splines could be monitored more closely.
Based on your research, do you see a reason why this would not be a viable alternative?
For the pump a 1"-15T shaft is available as well for a third of the cost of a new pump which should limit the cost of the upgrade to approximately 600 dollars plus filters and fluid.

[davidbrady]

Jeff,

I think it's a great solution. Have you looked at trying to wet spline it?

Here's what QCC says in their manual about their pumps. I'm not quite sure which pump your WB uses:

QCC CP Series gear pumps utilize an external spur gear, positive displacement, and pressure balanced design, providing superior efficiency. These "heavy duty cycle" pumps are three-piece construction utilizing an aluminum flange and cover with Compacted Graphite Iron gear housings. This design offers superior resistance to contamination and excellent strength to survive in the harsh "construction type" environments but are light in weight. Oversized journal bearings (DU) are utilized to provide maximum life. By design, the gears of this pump on initial running track into the gear housing and create their own radial tip seal for high volumetric efficiency.

[jwm470]

Several previous posts expressed concern over the possibility of transmission damage if a failure occurs in the seals. I am in the manual grease camp because of those concerns. Is that concern real or imagined?

[davidbrady]

It's real; I'm in the manual grease camp too, but my greasing was easy. Greasing should be done every 3500 miles. I don't know how you're going to manage that on long trips? I'm in the manual grease camp because the 1" 15T splines solution is better but it still misses the factor of safety objective of 1.5 to 2.0x.

Here's a pic of the QCC one piece output shaft and gear:

[jwm470]

Thanks David. You confirmed my decision. Greasing on mine is easy as well, loosen two fasteners on metal u-pipe and remove 2 bolts that separate pump from PTO, clean old grease add new in less than 10 minutes. Too bad changing coolant, oil etc. is not that easy!

[GregOConnor]

What takes out the oem pump shafts, maybe that is where the work needs to be done. Maybe it it the abrupt start up of the fan. That action is just plain scary for me. This is why I cycle my fan on with low rpm before I head up a grade. I don't want the temp sender to start up the fan when the bus is in high rpm.
While under factory warranty, a charge pump on one of my Skidsteers was replaced 6 times /(2,000 hours). Once out of warranty I called the factory and asked a tech for advise and a reason why. She advised me to replace a valve in the block that is designed to place a phantom load on the pump to keep it from chattering. it was not the spline that had failure.
Startup is where hoses are broken and fittings are turned loose.

[davidbrady]

In our BB's chatter isn't the issue. If you look at the spline wear closely you won't find any evidence of a reversing load. My hydraulics shop said the PTO's coming from Asia are poorly built with bad tolerances and bad shaft alignment; couple this the a 7/8" 13T spine which doesn't offer sufficient tooth cross section for our application. Misalignment shows up initially as fretting wear of the spline material as shown by the red-brown discoloration which is fretting debris. From there we have sliding wear which results in material transfer, or galling, from one component to the other. Some owners get over a 100K miles out of the units, while other owners only achieve tens of thousands of miles before replacement. This is due to the sloppiness of the components. Some owners are lucky and have better built units. That's why if you have a good PTO you're probably better off rebuilding it.

BTW, the LXi uses a PWM (pulse width modulated) signal to start the fan. You're taking steps you don't need to by starting the fan early. The LXi automatically starts the fan slowly and ramps up speed gently to minimize shock loads. This is also true for the '97WB, but I don't think its true for any of the earlier Wanderlodges with hydraulic fans.