No need for apologies. I only wanted to let you know that I have seen some really weird things through the years. Usually exploding pumps are a relief problem.

Ok, so I removed the relief valve. Found the bottom O-Ring blown and some metal shavings. Not exactly clear on where the metal came from. I am assuming one of the pump failures sent some metal to the control valve. Then caused relief valve failure. Rebuilt the control valve and inspected closely. Ordered new relief valve. Going to put a kit and end cap on one of the hydraulic pumps and change the return filter. I appreciate all the help.

yep Brewski has a good point, a sticking relief valve could very well be the cause. I wasn't going to qualify myself with my years in this field of work because i don't feel that is necessary, but I've been in lifttruck business since 1977 so like him i've seen alot and learned alot also ;o)

but all of the mentioned possibilities are most certainly things to check

sticking relief valve, clogged return filter, customer abuse situations, and just plain old sub-par aftermarket parts.
If they have other units and they run fine the parts scenario is just a slim possibility though, based on that there has to me some other scenario causing it to blow out the end housing.


As for your question about the sprocket and chain and bearing alignment where it mounts?
i think you would hear abnormal noise or see damage to the shaft end of the pump, or see broken chains or gears before it would blow the outer end housing like that.

Like brewski says, over pressure being created from somewhere is the problem, and the weak spot is that end housing on that pump.
The fun part is just figuring out what is causing it.
what mrfixit said is a big possibility, is why i mentioned the accumulator part, checking that, but even if it is working good an abusive situation like he describes would still create havok on the systems tolerances. Somethings gotta give ;o)

I've had this happen twice on Toyotas. I think it was from abuse. The customer was extremely rough on their machines. They would use them to settle pellets in huge boxes by lifting them up and shaking them violently by holding throttle wide open and jerking the tilt lever back and forth as fast as possible. I was able to just buy that aluminum end plate from Toyota and all was good. I think the pump is probably not quite strong enough and maybe the releif vavle doesn't react quick enough but once they were fixed they didn't keep doing it like the problem you have.

Brewski, my apologies if my response seemed disrespectful. You have my respect if you have been in this field for 43 years. I appreciate your response. It all makes perfect sense. I will give it a try. Also going to rebuild the control valve. See if there is any trash in it etc... Thanks again for the kick in a direction.

I have been doing lift truck repair for 43 years. I have seen quit a few blown pumps from sticking relief valves. Most of the time the relief valves stick open. But when they stick closed it is an automatic blown pump. A clogged return filter would blow the hose before it would destroy a pump. A bad input bearing should cause a shaft failure not a blown pump.

I have purchased one pump from Toyota and 2 from SMH. The Pumps are identical. Manufactured by KYB. I have sent an email to them asking for help. Here is a thought... Clogged return filter?? or maybe the gear in the front cover, is chain driven but has a bearing on the front and back side. Could worn bearings cause the shaft in the pump to wobble enough to cause a failure? The forklift is in route to my shop now. Will start digging into it soon. Not saying the relief valve isn't the cause, but it seems highly unlikely. Have any of you actually seen a relief valve failure?

I would replace the relief valve. If you are sure the engine is being governed properly, the only cause for multiple failures in such a short period of time is over pressure.

using an aftermarket part?
might need to go with OEM to stop that , we all know about sub-par aftermarket parts and the gamble we take when using them.

When i worked for Yale years ago we had a similar issue happening and they wound up having to change the pump mfg , they had switched to all aluminum pumps which is great for heat dissipation but bad for durability.
The new pumps they came up with had aluminum housings with cast iron end housings.
I was going to suggest the pressure relief being the issue but since you changed the adjustment to under spec that sort of rules that out and made me think of the part source and design of it.

and then there is the offshoot thought of if the units hydraulic system is being put under some sort of extreme shock by the operator. Oh another thought, hydraulic system accumulator? does it have one?