Yup! Worn out.

A new one is $263.54 from Sears (parts item #26), and $277.76 from Jacks.

With the valve plates that bad, I'd take a real close second look at the cylinder blocks.

Someone used way too much RTV.

 

Thanks, Tudor, that's a big help. I'll take another look at those blocks, but they looked really good when I pulled them out. I'm thinking that somebody replaced the two cylinder blocks but skipped the center section (maybe cause it's so pricey).

Guess I'll have to decide about whether I want to order a new center section, or just buy a good, used tranny for similar money.

 

Given the amount of RTV sealant used, I wonder if the previous 'repair' was done a bit sloppily. Don't mean to cast aspersions, but those grooves are from grit being fed through the system. It may have been that the center section had good surfaces, but during the repair, dirt was left in the sump, and worked throughout. Pretty soon, no more pump, no more motor.
I have not take one apart, but wonder if it would be possible to machine the surface with the scoring. Unless there are length limitations whereby the assembled length determined the 'fit', a slight cut would make the parts seal again. For the cost of the replacement part, it might be worth checking for a local machine shop that could 'fly cut'(I think) the surface.
tom

 

I'm fine with you casting aspersions, Tom! The PO never bothered to tell me that this mower wouldn't climb a hill (and, of course, his lot was dead flat when I did my testing), so I figure he's got it coming.

I wondered the same thing about the machining process and agree that it's worth checking into with a shop. Thanks for your comments.

 

It's not just a case of machining the valve plates, and you're right, there is a fit dimension that must be accommodated, but there is also the method of machining. In this case, a centerless grinder. Not every shop is so equipped. The surface is polished.

Cleanliness is critical. The interior of the case must be thoroughly cleaned before reassembly.

 

It's not just a case of machining the valve plates, and you're right, there is a fit dimension that must be accommodated, but there is also the method of machining. In this case, a centerless grinder...

Tudor, would you think that it's worth talking to a good machine shop about resurfacing? Like already mentioned, it seems possible that some critical dimensions would change, by however much material was removed...

 

If you take parts to a good machine shop I believe you can save those parts, but get price first no by the hour, I don't know about centerless grinder but good man with a lathe and tool post grinder might help you, or a surface grinder, my two cents.

 

That surface is called a valve plate in other hydros. The other half of the valve is the end of the cylinder block which is machined to ensure an acceptable seal against the fluid pressure. Machining the surface increases the gap allowing fluid to escape too quickly to develop the rated maximum operating pressures when doing work.

It is, in effect, the relief valve for the hydro when machined to spec. A couple of thou extra clearance over that broad an area can dump a lot of fluid at 1000 psi with very noticeably negative performance characteristics.

 

After everything is machined, bolted back together the clearance should be back to original, should be no extra clearance, right ? I would still try it, my two cents.

 

Think of it this way, grind 0.002" off of a crankshaft journal, install original size bearings, and torque down the original caps.

Q. What do you have?

A. Someone else's engine. :hide:

 

Essentially, the 'end clearance' will be changed by any machining of the damaged surfaces. The end clearance or side clearance allows rotating motion of the moving parts, but keeps the majority of the fluid under pressure from just leaking out past the end of the piston cylinders. Fluid comes in one of the 'arc' openings, into the cylinder, and then is forced out the other 'arc' as the piston moves in the opposite direction.

If you can adjust the end clearance on assembly, and I do not know how this thing is assembled, you can machine for a good surface, and re-use the part. If the assembly is fixed, such that the pump body & motor body cannot be attached to the machined center section and have proper clearance, the case where the machined parts are just bolted in place, and the clearance is fixed, then there will be excess leakage and as the hydraulics master Tudor stated, it won't work as designed. If there is the possibility of using a shim or doing some machining to essentially increase the length of the pump/motor body to make up for the length decreased by the amount machined off, while keeping all other functions, it might be made to work. If the piston carrier can be made to be held against these surfaces by shimming, for example, a seal can be achieved and the pump put back to work.
I'd have to see the other two parts. I haven't looked at hydraulic pumps & motors of the 'swash plate' style in some years, essentially when I was in the USN back when.
The part of a revolver that carries the bullets and rotates after each firing is similar to the part in the pump which has the pistons & cylinders. It must rotate and present each piston/cylinder to the arc openings, inlet and outler. If the piston / cylinder carrier can be tightened further against the surface that is currently damaged, the seal could be restored. I don't know how it is attached.

 

I believe it can be machined and work fine, you do what you think is best, I worked in a REPAIR shop that repaired parts not just changed parts. The one thing we didn't do in our shop was grind crankshafts, but if for some reason 0.002 was taken off and we needed a bearing you could not buy the shop would have made one, my two cents.

 

Great discussion, thanks everyone for weighing in.

As I've been thinking through this myself, I had this idea: From what I can see, the force that holds each cylinder block firmly against the center-section faces (i.e. the damaged areas) seems to be the springs within each piston; these pistons push out of the opposite end of each block and ride against the swash plate. Seems like those springs will continue to hold the block against the center section with the same amount of force, regardless of the machining... although possibly the piston travel could alter slightly (?).

In other news, I found another parts list that has a different Hydro-Gear PN for my tranny center section, #70250... and it's quite a bit cheaper than expected.

 

ctgriffi:the force that holds each cylinder block firmly against the center-section faces (i.e. the damaged areas) seems to be the springs within each piston; these pistons push out of the opposite end of each block and ride against the swash plate.

But but but .. what do you do about sealing the cylinder block against the center section? In the original design, the pistons rode in the cyinder block and were held against pump pressure by the connecting rods against the swash plate. Using springs limits the pressure that can be placed on the swash plate. They, the springs, will push equally in both directions against the fluid pressure and the swash plate. The pistons vary their stroke and actual pumping direction based on the swash plate position. The cylinders that make up the cylinder block must be sealed against the center plate or fluid will go out past the end and flow back into the sump. The pistons move internal to the cylinder block, pushed by fluid pressure against the swash plate, and as they ride 'down' the swash plate, will cause the center section to rotate, and viola, we have a 'motor'. The fluid pressure will want to go wherever it can go easiest, and leaking past end plate sealing is a lot easier than moving a piston against a swash plate. The 'revolver' looking cylinder block must be sealed, surely at the end closest to the center section, and by the pistons internally within the cylinders so there is a controlled (varies by swash position) volume for the fluid to expand into. The question at hand is what holds the cylinder block against the center section. The pistons 'float' in the cylinder block, and thus will not hold the cylinder block tight to the center section. If there is a 'center bolt' that holds the cylinder block to the center section, it would have to be spring loaded to apply pressure to effect a seal, and adding a shim to re-store the spring pressure seems possible. If there is no spring, and sealing is determined by dimensional machining of the exact length of the cylinder block, then no shim would help.

If the center section surface can be machined, a smooth cylinder block surface maintained, AND the cylinder block pressure against the center section adjusted to counter the effective reduction in overall length, it should be doable.

tom

add: After googling, I found some drawings of a "Waterbury Speed Gear", which is the pump/motor old name. The drawing showed a coil spring at the end of the cylinder block that appeared to be the force that pushed the cylinder block to seal against the center section. If a spring is used in this transmission to seal the cylinder block to the center section, it might work without further adjustment.

See the peekshure:

The Fleet Type Submarine - Chapter 13

Not exactly the same application, but Waterbury designs date back at least to 1912... so many varieties exist.

 

I have never taken one apart, and don't want to.But I like reading, what little info.there is, just in case.Great post.Ive also read,that this rotating center section gets damaged from heat,viscosity break down,lack of a oil cushion between parts I think.

 

I'm about to order a new center section, filter, and seal kit but thought I'd go ahead and post photos of the two cylinder blocks. The piston end on each of these look perfect, and here are the opposite ends that face the center section:

In person, to my eyes, they look very good, like they've been replaced recently. What do you guys think?

 

To my untrained eye, they look a lot better than the center section. I think you will get some scoring, which is more evident in the upper picture, no matter what you do. Is there enough to allow too much leakage? I can't say for sure. I think they will work well enough.
Given the accessibility to a 'flat' surface, you could polish them on a sheet of fine abrasive held tightly to a sheet of glass. At least that is what is done to flatten the surface of cylinder heads. Personally, I'd get some product in the 500 range, oil it up, and move the cylinder blocks in a random mode, wipe clean, and inspect. I think you could polish them if you take your time. Be sure that you know how the blocks are held against the center section, as you are going to remove a thousandth or hundred-thousandth of material.(just enough to clean up the scoring a bit)
If there is a spring-load, you'd likely be fine. As noted previously, if it is a 'bolt in place', and the clearance is set totally by machining, with no external pressure holding the cylinder block against the center section, you run the risk of opening the clearance too much. Is there a spring hidden in the drawing somewhere, or is there a 'shoulder bolt' to hold the cylinder block to the center section? Picture perhaps?
tom

added: Really, what do you have to lose? Some time, and a portion of a tube of RTV. When you do go to put it back together, make sure to lube everything, literally pour lube over every part before you put it back in place. The lube protects from friction and provides the seal to the pistons and end pieces. But, be sure the mating surfaces are absolutely clean and dry, or the RTV will allow seepage.

I have disassembled and re-assembled power steering pumps, and there was some scoring in them, but they still were functional. They were of the 'slipper' type rather than pistons & cylinders, so there is some difference. The 'end seals' had some scoring, but they still worked. Still working now, though the vehicle isn't driven nearly as much. From what I remember,the assembly was spring loaded, and needed me to 'stand on it' while putting it back together. It has been some years...
tom

 

From what I see in those pictures, I think I would clean those surfaces up before putting them against a new center section, my two cents.

 

New parts are coming in today... hope to get this thing cleaned up and reassembled soon enough. I do plan on doing a very light polish of the cylinder block faces, like a few of you have mentioned (thanks!).

I've got another question: There's a small vent on top of the hydro, and I don't think I have the original fitting and cap for it. It appears to be a basic 1/2" threaded hole, and I'm wondering 1) what's the point of this and 2) can I simply cap it off tightly or does it need some kind of 1-way check valve? (The parts diagram seems to show a small fitting with a rubber cap, but what purpose would that serve?)

 

I would not suggest capping it off tight. as the oil heats up & the air inside the hydro heats up it expands, I may blow a seal if not vented properly

 

I guess that makes sense, but I don't understand how the OEM fitting with a rubber cap helps the situation...

 

Got my new parts in the mail today from Jack's Small Engines. I'm a little concerned about the new center section; it wasn't sealed in a bag, and it looks far from pristine to me—kind of dirty, actually. From what I understand, this thing needs to be pretty near perfect, right? Also, it rattles when you shake it back and forth (the check ball valves?), which isn't the case in my existing part.

What do you guys think?

 

If you 'wash' the casting with a shop rag drenched in solvent, you will leave 'red threads' to hang on any and all irregularities. If you use a paper towel, you'll get fibers left behind, especially at the edges where the raw casting meets the machined surface. If you have a 'parts brush' or paint brush that won't shed, I'd use some ATF and give a bit of a cleaning to remove any 'stuff' picked up in shipping and handling.
I wonder if the designers added an anti-drainback check valve (captured ball bearing) to help keep prime after shutdown. That would explain the noise.
The machined surfaces look pretty good, and should develop more pressure than the scored center section.
Did the old one make whining noises when in operation? Many times a leaky hydraulic will make singing or whining noises as the fluid escapes past 'new' spots. Ford power steering pumps were known to be 'whiney', and Powerglide front pumps were also noisy, especially in neutral, at idle.(Al case trans)
tom

additional:
The fluid will expand when heated from pumping and operation. Automatic transmission fluid level is checked fully warmed up due to the expansion. The cap should not be tightly sealed, or the sump will pressurize and the fluid get forced out the easiest exit to equalize the pressure. I have used the cap from a WD40 spray to replace the one stolen by squirrels on my vapor canister in my truck. I used a sheet metal screw through the cap into the neck of the canister. It has ribs inside that will prevent full sealing and allow pressure to escape as needed. Factory part, no, but I don't think they make them any more, and this keeps water and debris out, which is what you need for this hydro.
tom

 

I discovered that the noisy rattle in the new center section is the two check balls, located within the two hex-head fittings seen in the top photo above. I need to check the original part, but I thought those check balls were supposed to be spring-loaded, so I don't know why they're bouncing around like that...

Regarding your question, Tom, about the whining noises: Yes, my hydro definitely whined loudly, probably almost all of the time.

In terms of a new breather cap, I think I might go with something like this item on eBay.

 

Finally got my rebuild completed and the hydro reinstalled in the mower. So far, I'm happy with the results: I'm able to get up and down the hills, over and over, without crapping out like it used to do. Also, I've got no more fluid leakage all over my garage floor, so that's a big plus, too.

It probably would've been beneficial to replace just about every internal part on my hydro, but I wasn't going to spend more than about $250 in parts/materials (new center section, all new seals, new filter, tons of shop towels and four cans of brake cleaner). I spent a lot of time removing and cleaning every part inside the case, spraying them down profusely with brake cleaner and then dabbing carefully with clean microfiber rags. Every time I finished cleaning a part, I wrapped it tightly in plastic wrap, until I was ready to do the final assembly.

Appreciate all the help from you forum guys. Many, many thanks...

 

Oh yeah, so for the breather cap, I went to a local hydraulic shop and they set me up with an adapter fitting and one of these: breather cap. Seems to do the job just fine.

 

Glad that it worked out.This thread will be good for future reference

 

I do not know 'for fact' that the many models showing 'parts lists' actually have any of the shown parts currently available. Many on searspartsdirect are NLA, with no substitute.
To have parts available indicates to me that the unit is likely more than a 'consumer grade' throw-away-when-it-breaks type.
You should get 'as new' performance and service life after doing all this work.
tom

 

It looks like the machining marks are not the same on both sides to me. maybe it has been remachined, if they are hard to get, I do not believe it should rattle, my two cents.

 

Update after a year of heavy use:

The hydro is still working well, getting me around and up/down, without the whining that it used to have, prior to the rebuild. However, it is leaking pretty badly at the left axle now, which is the same place that it used to leak in the very beginning. IIRC, each each axle has two identical seals, and I know that I replaced them all when I did the repair work. Since it's leaking from the same axle (right where the shaft exits the case, of course), I'm thinking that either the axle or the case had some prior damage that I must've overlooked.

Guess my only options are: 1) keep refilling the leaky hydro 2) pull the trans again, split the case and try to fix the leak OR 3) junk this old mower. (If the Kohler motor didn't start up and run so well every time, I'd have gone with option #3 a long time ago...)

 

Update after a year of heavy use: The hydro is still working well, getting me around and up/down, without the whining that it used to have, prior to the rebuild. However, it is leaking pretty badly at the left axle now, which is the same place that it used to leak in the very beginning. IIRC, each each axle has two identical seals, and I know that I replaced them all when I did the repair work. Since it's leaking from the same axle (right where the shaft exits the case, of course), I'm thinking that either the axle or the case had some prior damage that I must've overlooked. Guess my only options are: 1) keep refilling the leaky hydro 2) pull the trans again, split the case and try to fix the leak OR 3) junk this old mower. (If the Kohler motor didn't start up and run so well every time, I'd have gone with option #3 a long time ago...)

Leaky seals are quite often caused by the a bad bearing or worn shaft causing excessive movement which the seal isn't able to cover. I understand this is an old thread, I just wanted to add this as I deal with industrial equipment for my job. I'm still reading trying to figure out if machining the center section surfaces worked? And for the people who think it won't due to fit issues after taking off 0.020" to get past the groves....there are tolerances in every part. And I'm pretty sure that taking 20 thou off that surface would still keep the assembly within tolerance. That's just an educated guess though, obviously.

 

If the seal is a standard, pressed-in metal-rubber seal, why not pull the old one, and press in a new one? If it is captured in a groove, that won't work.
If it can't be replaced externally, you are running at such a slow rpm that using leather as an external seal might be very effective. Remember that when it is working, it is may be(likely) dripping or drooling oil onto the ground as you move. The spot in the garage is resting leakage... Do not let the fluid level get low, or you'll cook the gizzards, unless you really want to buy a new machine.
Leather thongs, or even small sheet, can be stretched over the axle sealing area, near the case, and bound in place using zipties or ???. I'd lube the leather before using it, though it will likely be lubed by the seepage.
A co-worker related stories of his youth when he'd be low on funds, and would repair the connecting rod bearings temporarily in, I think, a Chevy stove-bolt, or maybe a Studebaker. When it started to knock too loud, he'd pull over by the side of the road, drain & catch his oil, remove the pan and the offending cap, wrap the journal in leather, re-install the cap & pan, and dump the oil back in. He'd then be good for a couple hundred or so miles. Surprising what leather can do. Not perfect, but serviceable.
I think a blob of thongs, held in place by a 'sheet' with an axle hole, fed over the axle and retaining the thongs or strings, and the sheet retained onto the housing 'stub' with zip ties, or more thongs, would do a lot to slow down a leaky seal. There is no pressure developed in the case, so it is only gravity wanting to force the lube out, which is definitely containable with leather. Your Mileage Will Vary
tom