Hydro Modification to speed up reverse

[mike melillo]

Originally Posted by J-Mech

By no means will I argue that logic. I was stating what I was told when trained in hydrostatic transmissions. We did actually hold a piston in our hand and it wouldn't go back in the bore. I will admit it was not a small pump like these. I have never seen anyone pull the pistons out, put them back in randomly and have a failure.... But they taught us to mark them and not to randomly install them. I did not mean to make a failure sound like a guarantee..... Just what I always do and what I've been taught. Sam, I think that your advice is the most sound, and your right on about why the pumps/ motors fail. We were taught that with proper service a hydrostat should never fail. Best of luck Mike!!

Thanks for the good wishes, always a welcome sentiment!

I found the attached note in a hydro repair manual, likely an early addition. It clearly states that these were serviceable individually, which means that they were not originally exclusive to the bore.

Based on that I'm feeling fairly confident I wont have any trouble.

I also realize that these today are only serviceable as a complete unit, pistons, block and supporting parts.

My take on the whole thing is that these pistons are better left in the bore they have been broken into over the course of operation. Much like a valve lifter in a bore, or a tappet to a cam lobe, they become mated, and serve better matched than unmatched. However I believe the greater condition here is the slippers being out of acceptable tolerance.

But the note also indicates a potential for mix up based on the wall thickness of the pistons if replacing with what seems to be a later version (thin wall) piston. Either way though they make no reference to concern of swapping bore location.

Either way I really don't know, but time will tell.

Thanks for the info
Mike