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Thread: Rod to build up trunnion shaft on skidsteer hydrostat pump

  1. #1
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    Rod to build up trunnion shaft on skidsteer hydrostat pump

    I have a Gehl 4625 with a leaking trunnion seal. It's a Eaton 70344 double piston pump. I replaced the trunnion seal while the pump was still in the skidsteer...and it didn't fix the leak. The shaft has very slight visual wear, but I'm a hobby machinist and using a micrometer could detect no measurable difference in diameter within a couple 10 thousand's. However you can feel a very slight wear on the shaft.

    Question: I'm considering turning the shaft down on a lathe in the local area (to give the braze something to fill/stick to), braze the shaft back up and then turn it down to exact dimension? I've heard of that being done for shaft repair before. What type of rod should I use??

    For those not familiar, the trunnion shaft sticks out the top of a gear driven, piston hydrostatic pump. It connects to the levers in the cab to change hydraulic flow to the wheel motors. It's a 1" diameter shaft. It's also be described the part of the camplate that the shift lever connects to. The camplate is what actually pivots inside the pump housing, changing the pistons to redirect fluid flow.

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    If you are gonna tig it, just build up with steel or some other strong material that will not wear like bronze. Tigging with bronze will leave islands of steel anyway that will not clean up the same as bronze, and may catch your cutter and chip it.

    If you are dead set on braze, I would Oxy/Acet silver braze a layer of Easy-Flow 50 or some other high strength silver braze if the shaft is not sensitive to annealing.
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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    From the sounds of it you might want to look elsewhere for the cause of the leak. The slight wear you're describing shouldn't cause a leak.

    Two possibilities come to mind right off the bat. One is the drain hose for the case is stopped up (unlikely), kinked, or otherwise not functioning correctly. It will be the really small hose connected to the case somewhere and routed back to the tank.

    The other thing is bearing wear in the shaft/case causing the shaft to shift sideways to much.
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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Irish fixit, Im sure it's coming from the trunnion shaft. But you make a very good point on the bearings. I need to check the bearings - actually just replace given it's all apart - and mic the shaft where the bearings ride.

    Shovelon, I don't have a TIG (yet). So for me it's MIG, Oxy/Acty, or Stick. Since it's a gear shaft - vs a drive shaft - im not worried about safety of making the shaft brittle, etc. Just want something to build up and then work down with the lathe.

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    The reason I state to check the case drain is because that seal should never see much pressure. But if the case drain is stopped up in some way it can see to much pressure and not be able to hold it.
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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Hello jbar, have you considered a "redi-sleeve", many moons ago when I was doing a fair bit of industrial/agricultural mechanics we would use them on seal surfaces that were worn and they generally worked quite nicely. Now if the area is "chewed up" to any great degree, NO, but if it's simply worn by the seal itself these work very well. Something for you to consider. Good luck and best regards, Allan
    aevald

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Quote Originally Posted by aevald View Post
    Hello jbar, have you considered a "redi-sleeve", many moons ago when I was doing a fair bit of industrial/agricultural mechanics we would use them on seal surfaces that were worn and they generally worked quite nicely. Now if the area is "chewed up" to any great degree, NO, but if it's simply worn by the seal itself these work very well. Something for you to consider. Good luck and best regards, Allan
    . This. To add to this if the shaft is somewhat chewed up an epoxy like JB weld can often be used to fill any grooves or torn up spots before installing the repair sleeve.

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Hello MJD, that's great additional information. Best regards, Allan
    aevald

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Sometimes you can just not drive the new seal in flush with the case, so that it is riding a few thou proud of the old seal, and on fresh material. Agree with the others that it is likely a bearing issue.

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    a rubber seal will wear a thin line on the shaft and cause a leak ... eventually.

    pull the shaft ... TIG it or MIG it, and turn it back down. make sure your weld starts sway from where the seal will ride and ends away from wear the seal will ride. Pitting on a shaft or undercut on a shaft is no big deal ... unless its where the seal is riding.

    its been done millions of times ...
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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Below are a couple pictures of what I've been talking about.

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Good point walker, when I installed the seal I kept thinking it would press down a little further. I was comparing it to the existing seal on the aft (back) pump. I finally did get it but it wasn't as easy as it should be. Below are a couple more pictures showing it leaking after I put the new seal in and another showing what the seal looks like. Like I said in a earlier post, the seal is a spec seal and it has a spring that helps the seal grip the shaft. Note in the picture showing the shaft, I had already removed the cover plate.

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    I would think that would polish up and seal.

    Another option a local motor shop has is the ability to spray weld a shaft. The process will build up the area then they finish the shaft with a tool post grinder. It works good for seals or where a bearing will be installed over the repair area. They will not do it in an application where the repair area is subject to compressive rolling forces. The repair will start to spall off.

    Also, you should avoid pushing a seal over a key way. The edges of the key slot will cut the seal lip and will leak for sure. Electrical tape covering the key slot while installing will prevent this.

    Dan D.
    Last edited by DanD78; 08-03-2015 at 11:44 PM.
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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Thanks for the idea. However, I'm bound and determined to fix myself or go buy a new one.

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Looking at the picture of the trunnion shaft, it appears that there is a lot of wear in the bearing area. I say this based on the discoloration in the picture. I would seriously consider replacing the swashplate and the bearings at a minimum.

    Mike

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Quote Originally Posted by DanD78 View Post
    I would think that would polish up and seal.

    Another option a local motor shop has is the ability to spray weld a shaft. The process will build up the area then they finish the shaft with a tool post grinder. It works good for seals or where a bearing will be installed over the repair area. They will not do it in an application where the repair area is subject to compressive rolling forces. The repair will start to spall off.

    Also, you should avoid pushing a seal over a key way. The edges of the key slot will cut the seal lip and will leak for sure. Electrical tape covering the key slot while installing will prevent this.

    Dan D.
    Good advice on not pushing over the key way, I did that last time. I piriced the swash plate today, paperwork is in the pickup, but it was around $500 just for the swash plate. Throw in another $100 for seal kit and bearings and might as well buy a new one. I think if I build up shaft, turn down on the lathe, put in new bearings and seals and I'll be fine.

    Does anyone know what case pressure is on a pump such as this? Also, can I get a local shop to pressure test it once I have it rebuilt?

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    The part may be either a steel forging or an iron casting. You don't show enough of the parting line to get a good idea. Have you hardness tested it with a file?

    I wouldn't touch that shaft with a welder. I'd do like walker suggested and move the position of the seal. If they can't be left proud, I've trimmed the seal so they will push in further.

    My wag is a new hydrostat pump will be $2,000+ depending on the size of your skidder.

    Case drain pressure should be slight. Your operators or service manual should give directions for checking pressure on the machine. Or you should be able to get them from your dealer.

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Quote Originally Posted by bent View Post
    The part may be either a steel forging or an iron casting. You don't show enough of the parting line to get a good idea. Have you hardness tested it with a file?

    I wouldn't touch that shaft with a welder. I'd do like walker suggested and move the position of the seal. If they can't be left proud, I've trimmed the seal so they will push in further.

    My wag is a new hydrostat pump will be $2,000+ depending on the size of your skidder.

    Case drain pressure should be slight. Your operators or service manual should give directions for checking pressure on the machine. Or you should be able to get them from your dealer.

    The link below says I can get a pump for $819. Assume there's freight.
    http://www.loaderpartssource.com/geh...ber-4625.html#

    Regarding seal location, there's a thick washer that goes just underneath the seal, maybe I can eliminate that washer???

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    I fix crap just like this on a regular basis..
    Measure it..should be a standard size...
    TIG it up with 70-S and remachine in a lathe and call it a day.

    Be careful around the key but it should be just fine.


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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Quote Originally Posted by jbar View Post
    The link below says I can get a pump for $819. Assume there's freight.
    http://www.loaderpartssource.com/geh...ber-4625.html#

    Regarding seal location, there's a thick washer that goes just underneath the seal, maybe I can eliminate that washer???
    The picture you link to shows a hydraulic pump for lift and dump, not a propel pump.

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    One thing that concerns me is that I'm betting that piece is hardened. With the pistons sliding on the plate all the time it's a good possibility. If so then it could make for some problems building up and turning down. It might also be cast iron but I consider that a low probability considering the wear the plate has to resist.
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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Quote Originally Posted by jbar View Post
    Does anyone know what case pressure is on a pump such as this?
    I don't have info on your Eaton unit but the series 90 Sauer-Danfoss pumps I'm familiar with have a continuous case drain pressure rating of 40psi and max. (cold start) of 75psi.

    Case drain line size is typically sized large enough to avoid back pressure thereby keeping case drain pressure very low.
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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    I don't think you realize the precise fit of parts in hydrostatic pumps and motors, the swash plate in the picture is beyond worn out. I can only imagine what the slippers and pistons/bores look like. That could easily be causing so much internal leakage that it will never seal up. While I've done my share of build up and machining jobs I don't think it's a good idea in this case. I'm not trying to be negative here, it's just my opinion after many years as a mechanic in a JD industrial dealership.
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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Quote Originally Posted by bent View Post
    The picture you link to shows a hydraulic pump for lift and dump, not a propel pump.
    You are correct, I thought that pump sounded too cheap. Hopefully I won't need to buy one anyway.

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    Re: Rod to build up trunnion shaft on skidsteer hydrostat pump

    Probably looking more like $4-6000

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