Repeating PS pump failure

We have several W9 gliders with 3406Es in them, all using the same TRW style power steering pump resold by various brands, e.g. PS2524-15L103, and Sheppard gearboxes. It's also worth noting that we don't have PS coolers. These pumps have been a fairly constant recurring problem for us, often partially failing within a few months of installation, but usually lasting a year or two. To clarify on the "partial failure", I've had it where I lost the ability to turn the wheel while stopped but it worked okay otherwise, then after several months or more they fail completely. I've got some ideas which I'll spell out momentarily, but I'm hoping someone here has figured this out already. No one I've spoken with has had this problem.

We've accumulated a pile of them and opened two for failure analysis, the only issue we found was bad internal o-rings, everything else looked perfect. This makes me suspect fluid and/or temps. We've been running Dexron III ATF per the TRW and Sheppard specs, we did also test Dexron VI by accident. I'm not finding much to support the ATF degrading the o-rings but the information I'm seeing is mixed. I also don't know what material they're using for the o-rings, but I'd assume nitrile as they are black. Although one of the smaller ones that isn't failing is brown which I believe is Viton. They could all be Viton which is rated up to 450F, but if the large black ones are Nitrile...The 250F rating probably isn't enough. I've considered adding a cooler but I have my doubts about Nitrile holding up even then, assuming they are Nitrile.

Any of y'all have experience with this problem or have any ideas?

 

1- Hadn't thought to do an analysis on PS fluid, we do it on our engine oil through Cat, I'll look for someone who can do that.
2- For sure, that's why we run the Dexron III, it meets the spec for both the TRW pump and the Sheppard gearbox. I'd rather run 15w40 as the gearbox allows it, the manual from TRW looks to have previously included 15w40, but it's been edited to now only list Dexron II, III, Mercon, and ATF +4.
3- We've had a mix, mostly OTR but various other reman suppliers and I believe at least one new ZF. They've actually been kinda hard to get so we've been having to order and get what we can in a reasonable amount of time. I was hoping to get new ZF units, but I don't believe they're made anymore due to restructuring of the company.
4- I flush and change the filter every time, the KW reservoir has a filter in it.
5- I've wondered about the pump spec for the application but couldn't find a different style pump for the 3406E. Being a glider, nobody has any info on parts, Cat says the truck manufacturer handles that and Kenworth says it's a glider so they don't have any info. I've done a lot of looking around online and it all leads to the same pump we have which is made by ZF/TRW.

Thanks for the input!

 

That certainly sounds promising, I feel like I tried looking at their pumps online but hit a dead end. Thanks for that, I'll definitely give them a call!

 

I've got a positive update on this. Firstly though, Sheppard was unfortunately of no help, they just told me they don't deal with pumps at all and can't speak to what will work with their boxes.

Anywho, on to the positive, turns out these gliders were sold to us with the wrong pump. I did some digging and found the the M100 box takes 4gpm while the PS2524-15L103 flows 6gpm. I asked/looked around and called Power Steering Specialist in Columbus, OH, they never got back to me. Eventually I got a recommendation of Power Steer Inc in Dallas, they were extremely knowledgeable and happy to help. When I told them the setup they immediately knew that I needed a PS2516-15L103 instead. I figured the higher flow pump was the problem but wanted confirmation from an expert. Turns out having too big of a pump produces a bunch of additional heat, that in turn causes the o-rings to fail, which is exactly how ours were failing.

In case any of you need it, this manual linked below has a break down of how the model numbers work, you can tell the flow and other key specs from it. Just get the specs that your steering box needs then use this to figure out what model of pump you need.

https://www.trwaftermarket.com/glob...ature/pumps-lit/pumps-sm/ps-pump---pspump.pdf