Hydro Modification to speed up reverse
 

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

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?

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.... :bigthink:

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.

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

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....

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.
:bigthink:

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

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?

If it's not broken then why fix it?

If anybody is willing to try this theory out I have a rear out of a 1250 ill donate to the cause. I'm just tripping over it at the moment

Wow! I have never seen one puke like that. Don't think it's because of not running Hy-Tran, more likely the PO never changed the filter and it went into bypass allowing unfiltered oil into the system. Piston closed loop systems recirculate the oil so one they start to fail the junk in the oil just keeps going around in the system making things worse. The only oil that gets filtered is what the charge pump supplies for makeup oil that is needed to keep the piston pump full. I love hearing people complain about how expensive it is to change the oil and filter. OK don’t do it then you can change the hydro and the oil and filter all at once. Once a year, new oil and filter. Did the same with the 20 ready mix concrete trucks I owned that had a much larger version of the Sundstrand pump and motor to turn the drum. If one of those fails not only do you need a new pump and motor but the concrete gets hard in the drum. Never had one fail and I had some that went 20,000 hours before they showed signs of needing overhaul. We used Mobil 1310 engine oil in them, 1310 was a 10W diesel engine oil. Also used it in the hydraulics on my Cat loaders and in our Allison transmissions.

Lew the brass parts are called slippers and they ride against the swash plates. If you are seeing scratches it's from contamination. They should be nice and smooth. I'm guessing these are old units with a lot of time and very little or no maintenance. Sorry I don't have more pics of this. This is the inside of my 2182 pump, you can see the swash plate and the slippers. Also something I do is cut filters open and see it I see signs of a failure starting. You can buy a filter cutter from places like Summit racing or Jegs.

I had another dirty thought... On my 149 the pump shaft goes completely through the housing and comes out the back with a hole in the shaft for a pin to drop through...

Turning the rear end around in the chassy would be a neat trick to go fast in R! :)

Still unsure why you would want to, but why not?

Without a doubt i'm a glutton for punishment. My whole life I have to tamper with things. This has resulted in both good and bad experience, but has also taught me many things you cannot learn without the experience.

mike

I'm with you, Mike! Grind that thing down to a nub if it makes you happy!

I have a spare (and very whipped, based on the gear lash in the diff) 149 rear you can have if your experiment goes sour. Just come and get it!

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!!

Sam...
Thanks for the correction.A good filter and fluid change at the correct intervals and these pumps should last a long time.What happens to the guy who lets the concrete set up in the drum,clean it out then fire him?

We did a pour on time and the guy did a quick wash out on the job,figured he wash out the rest in a stream nearby...
just in time for the cop to drive buy...

Lew

You are giving me flash backs and the reasons I am no longer in the concrete biz.

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