Hydro Modification to speed up reverse

[mike melillo]

For those who have a lot of knowledge with Hydro unit, I would like to know if you have ever ground down the cast tab of the basket that holds the swash plate? (see image)


One side is significantly thicker than the other. It seems that the thickness sets a limit for the amount of stroke for the pistons, and that a greater stroke will increase the output speed. So if thats true I should be able to get a little more forward speed too.

But, I am a little apprehensive because I don't want to experience any unexpected and adverse affects. \

I would appreciate your thoughts.

Mike

[Sam Mac]

Not sure I try for more forward but you are correct about the limit in reverse. The swash plate tab limits the stroke in reverse. You may also need to rework the linkage. After that is said and done do you need to go faster in reverse?

[J-Mech]

I would not do that. Sunstrand build these units to precision. If you grind it off you will bind the swashplate and pistons. The piston holder can only move so far. If you grind it off, they will mis-align and you will tear up the slipper pads. Is it really worth it?.... BTW I hope you didn't pull the pistons out of their bore. They are matched to the bore they are in....

[mike melillo]

Originally Posted by J-Mech

I would not do that. Sunstrand build these units to precision. If you grind it off you will bind the swashplate and pistons. The piston holder can only move so far. If you grind it off, they will mis-align and you will tear up the slipper pads. Is it really worth it?.... BTW I hope you didn't pull the pistons out of their bore. They are matched to the bore they are in....

Your probably right, and I don't need the headache of trying to reengineer it. I had no intent on disassembling the unit, but the further I went the more problems I found, and I figured I would replace the seals and the input shaft with the square hole. The cork gasket was almost completely disintegrated too.

I did not intentionally disassemble the pistons from the bore, but on one of the cylinders, the pistons stuck to the thrust plate and they did come out. Are they matched like a lifter to its bore from wear, or were they matched at the factory based on tolerance?

[J-Mech]

Originally Posted by mike melillo

Your probably right, and I don't need the headache of trying to reengineer it. I had no intent on disassembling the unit, but the further I went the more problems I found, and I figured I would replace the seals and the input shaft with the square hole. The cork gasket was almost completely disintegrated too.

I did not intentionally disassemble the pistons from the bore, but on one of the cylinders, the pistons stuck to the thrust plate and they did come out. Are they matched like a lifter to its bore from wear, or were they matched at the factory based on tolerance?

Nothing like a lifter to bore. Or a piston to a sleeve.... No, MUCH tighter than that. They are sized to the bore at the factory. If you take one out of it's hole, hold it in your hand to warm up.... It won't go back in the hole you just took it out of. The only thing close to the tolerance of this is inside a diesel injection pump. You can put them back in... but the hydro may not last long. If your lucky, they will have enough wear on them they will be ok. But, don't be surprised if it fails.

[mike melillo]

Originally Posted by J-Mech

Nothing like a lifter to bore. Or a piston to a sleeve.... No, MUCH tighter than that. They are sized to the bore at the factory. If you take one out of it's hole, hold it in your hand to warm up.... It won't go back in the hole you just took it out of. The only thing close to the tolerance of this is inside a diesel injection pump. You can put them back in... but the hydro may not last long. If your lucky, they will have enough wear on them they will be ok. But, don't be surprised if it fails.

Well, thats not good news. I wish they marked them. I don't see how I have much choice but to go with it. Even if the parts are available I'd bet they cost a mint, and even if it sizes up I still have to buy it. Do you have any first hand experience with these units failing due to this?

I'm going to check into this a little, and I'll let you know what I learn.

Thanks for the input.
M

[J-Mech]

Yes and no. I have worked on LOTS of hydrostats. But never took all the pistons out. So, never had one fail. But do know that they are factory sized. Been trained in them. Yes, they are expensive. My experience is that a rebuilt is about the same price as parts to fix it. Hydrostats aren't something that you should take apart....

[Sam Mac]

Jonathan

I agree with you about not pulling the pistons on larger piston pumps but that does not seem to be the case on the pumps in the Cubs. Reading the service manual it makes no mention of them being matched to the bore, in fact it tells you to inspect them for wear. I had my pump on my 2182 totally apart when I replaced all the seals and did not worry about what piston went in what bore when I put it back together. It runs great.

[mike melillo]

Hi Sam, I actually read the service manual after that post, and it was very specific about certain aspects of the procedure, but it did not make any mention about exclusivity. In fact it said to clean with solvent and dry with compressed air. (if all else fails, read the directions)

One thing it did say that I question is about the wear on the pads that ride on the thrust plate. They were really specific about the wear not exceeding .002 from each other, but they didn't offer a reference on where to measure.

Thanks for all the response.

Mike

[darkminion_17]

I am not sure how this happened but it did not have hytran in it.Iv'e had 8 of these apart and the brass plungers are always scratched up on the bottom.
Did yours have any Sam?