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The mysterious pump between our legs that provides our forward and reverse momentum as well as the extra oomph for lift cylinders isn't really that intimidating when it comes time to rebuild one.

It actually took about 10 times as long to write the following than to do the actual tear down and re-assembly.

Pop open a cold one, lean back in the recliner, and with new bi-focals, you too will have all the confidence needed to tear it down, identify the flaws and why the power has dissipated and what to do in short order to have it back running at its peak performance.

Sundstrand Series 15 Inline Pump/Motor Rebuild

The purpose of this guide is to try and take some of the mystery out of the rebuilding process.

WARNING: The following is being written in a very simple step­-by­-step manner. If you find it condescending or to simplified then stop here. The goal was to take the fear, trepidation, and mystery out of a Sundstrand Hydrostat.
Many of us can tear down and rebuild any engine but the idea of tearing
into a hydro can bring
fear in the heart of the uniformed.

I will not take credit for the information; it is the culmination of information gleaned from many posts and the advice shared by a Mr. Terry Maxell owner of Pump Recon in Independence, Missouri. Terry has been patient and pointed me in the direction to successfully rebuild
my series 15.

Tools needed:
Good 6-­‐point sockets (there are only 8 bolts holding the unit together) Snap ring pliers (this is your opportunity to get a good quality: choose
the best quality you can afford)
Clean putty knife
Compressed air
Oil DrainPan
Cleaning parts brush
and bucket Magnet

The two rules of the re-­‐assembly process are:
1: The work area must be clean.
2: All parts must be thoroughly clean

To facilitate clean components I have tried 3 different approaches.
First using lacquer thinner to clean all the parts. It's good solvent but it evaporates quickly leaving a short dwell time to remove any gasket adhesive.
Second I tried using Carb cleaner. It too helped in removing gasket adhesive (permatex) but it's dwel ltime was less than lacquer thinner and it also dries the flesh in your hands.
Third approach and the most successful were using mineral spirits. It has a long dwell time, isn't as hard on the skin as the former, and it will soften and allow easier removal of gasket material. You can also use a siphon spray parts cleaner in the jug to pressure clean components. Buy it at the local hardware store. Its $15.00 a gallon or you can get a 2 gallon container for about $26.00 Buy the 2 gallon jug if you will use it. Afte the assembly is removed from the tractor remove the oil filter and drain as much oil as possible from the unit prior to pulling the 4 bolts from the rear section (motorend) .Before the next step take a scratch awl and scribe a mark the full length of the top of the entire unit. It may be helpful in remembering which pieces were up in the re-assembly process. Do Not scribe the bottom side,as you do not want a scratch mark where the oil filter sits. Using newspapers or old rags,remove the 4 bolts from the rear section. Depending on the previous mechanic, you may have the rear, and center section separate easily or find them stuck from the previous ovehauler using gasket sealer. In either event
as the sections are separated you are going to have oil escape and the rags or newspapers will absorb the spillage. If the rear and center sections are stuck together get a wide blade
putty knife and start the process and sliding it between the sections. You will have 3 major sections that will come apart and for the most part it will look like the exploded diagram attached with this report.

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There will be the rear pump motor housing with its shaft, barrel assembly (including its pistons). Set this section aside with the pinion gear down so that the barrel and pistons do not fall out. If the pistons do fall out DO NOT panic, they are not installed in any certain order and can go back into any barrel hole. Next will be the center section and it most likely will have round valve plates(one on each side of the center
section) that may appear to have a bronze finish. They are different and if you can, try to keep them matched to the pump or motor section they
came from. If you get them mixed up, again don't despair. The following
photo will show you their difference.

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The third section will be the front end or the pump. This is the end that has the spline shaft that is most troublesome to Massey 1655, and 1855 owners. This end has what can be the most complexing components: Barrel assy, pistons, swash plate, and charge pump. Now it's time to go into the kitchen and grab 4 zip lock sandwich bags and ba mark a lot. Do it in a quiet and stealthymanner and she will never know.
Label the bags Pump pistons, pump barrel, motor pistons, and motor
barrel. It doesn't matter whether you start at the pump or end but pull
the barrel assembly (they slide off) and place it and its respective valve plate in the respective bag. Then gather the pistons and bag them in their respective bag. (Some have said the pistons are all the same and
it doesn't make a difference, but truth be known, there can be some
wear differences and I have been told its better to put them back in the
barrels they came from, sometimes better to be safe than sorry).
Once you have done one barrel and set of pistons,go to the other end
and repeat. Now grab a magnet and use it to pull 2 washers labeled in
the diagram as #49. One will be in the moveable swash plate of the pump and the second in what looks like a fixed swash plate (actually a
part of the casting) in the motor section.

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Next you will want to pull the swash plate in the pump. To do this you will need a 3/16" punch that is between 1&3/8- 1&1/2 inches long.
I bought one at the hardware store stuck it in the lathe and polished
the shaft with emery paper to make it slightly smaller than 3/16 of an
inch. Take the punch and a small hammer and tap the 2 roll pins out
of each end of the swash plate. They will fall down behind the swash
plate in a recess within the casting.

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Now is the time to take notice of the first potential wearing point. As you pull each control shaft from the swash plate note is it easy to remove or tight. If it's very easy you need to inspect the shaft that was pinned to the swash plate for wear and check the bearing clearance in the housing (#55) in the diagram. Excessive bearing wear will cause transmission creep. Once the control shafts are pulled the swash plate will fall out.

You will also want to check the input shaft and motor shaft for wear indicators where they ride on the caged needle bearings in the center section.

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Now remove the 4 bolts holding the charge pump housing. Make a note is the LH or RH side that is up. If it's a Massey 1655 or 1855 it will be the LH.

The charge pump has 2 gears inside and the inner gear is held in place by a hardened steel pin through the shaft. It slides out. Do not lose it, as it is small and easily lost if not paying attention. Inspect both gears for wear and if in good condition set aside for cleaning. NOTE ** There isn't a right side up on the charge pump gears.

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Turn pump housing over and remove the snap ring on the inside right next to the large ball bearing assembly. Once removed the shaft and bearing should slide out. Do not beat on the shaft with a hammer. If additional pressure is needed use a small press.

At this time you have the unit torn down far enough to start soaking and cleaning parts. Routine cleaning of the pieces should be the order of the day. Again as a lesson learned, soak them in mineral spirits and use compressed air.

On the pistons you may be tempted to use a small wire to clean the openings in the top of the pistons DON'T! Those openings are very small and of a size specifically designed for metering fluid. Soak the piston and use compressed air to clear any dirt. To make sure they are open and clear use a flashlight pointed from the bottom of the piston so you can see if light comes through the top opening. If there isn't light visible in the top of the piston opening re-clean with solvent and compressed air. Any grooves or ridges on the top of the pistons indicate wear and the piston will need to be replaced.

Before re-assembly check all of your shafts and bearings closely for wear. Now is the time to replace any bearings that are worn and have excessive slop or play. Seals will be in the seal kit and you can replace them as well.

Center section Notes: if you suspect leakage past the check balls in the center section. Lay the housing flat and fill the openings (where you see the ball) with WD-40 and leave it sit. If it immediately leaks past they need to be removed, cleaned and inspected for wear and or replacement. If the WD-40 doesn't leak past them don't remove them they are ok.

Center section needle bearings. These are subject to high wear and inspect them closely. Also look at the end of each shaft that rides in the bearings. Any marks on the shafts will indicate the bearings are worn. My unit had Torrington NJ 47 bearings. Torrington sold its needle bearing division and its been resold again. You may need to contact someone like IBT to locate the bearings for you. When you replace the needle bearings note they are not flush with the center section. So when re-installing them make sure they are sticking out approx. .070 - .100 of an inch. This allows the valve plate to be centered.

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Swash plate washers; time to inspect them. If this is the first tear down of the unit one side will be smooth as silk and the other side will show signs of wear. If it's the first tear down turn them over and have the smooth side against the pistons. If both sides show wear do the following. Get a sheet of emery paper approx. 1200 grit (auto paint supplier will sell single sheets) lay it on a piece of glass and polish the sides using a circular motion. Clean and re-clean the washers after each attempt to polish them. Using your fingernail slide it across the washers if you feel anything in the fingernail, it isn't smooth enough. If the gouges are deep you will have to buy new washers.

Swash plate washers; time to inspect them. If this is the first tear down of the unit one side will be smooth as silk and the other side will show signs of wear. If it's the first tear down turn them over and have the smooth side against the pistons. If both sides show wear do the following. Get a sheet of emery paper approx. 1200 grit (auto paint supplier will sell single sheets) lay it on a piece of glass and polish the sides using a circular motion. Clean and re-clean the washers after each attempt to polish them. Using your fingernail slide it across the washers if you feel anything in the fingernail, it isn't smooth enough. If the gouges are deep you will have to buy new washers.

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Barrels and Valves; Here is my painful lesson learned. Anytime a unit is torn down both barrels and valve plates should be lapped. Seek out a machine shop that has the time and equipment to do it for you. My pump shop charged $35.00 per barrel and valve assembly. When properly lapped the barrels, pistons and valve plate will be within millionths of an inch and given the viscosity of the hydraulic fluid less clearance is better for greater hydraulic efficiency and pressure.

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The final piece to be inspected for wear is the caged ball bearings in the pump motor. Pull the snap ring holding the pinion gear, followed by the much larger snap ring adjacent to the ball bearing. The shaft and bearing can be removed. NOTE*** the large snap ring is NOT flat on both sides. The topside that you see is beveled and the snap rings flat side goes against the ball bearing. Pay attention to this small factor when re-installing the snap ring back in place.

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Once all the components are clean its re-assembly time,

There are 2 schools of thought on gasket sealers. One is to use a sealer like permatex, and the other is no sealant at all. The person coaching me on my most recent rebuild says do not use a gasket sealer, as the gasket will seal itself. If your housings and center section don't have gouges it will be your call. Just remember if you do use a gasket sealant use it sparingly and also keep in mind you will have to clean it off with the next rebuild.

Here is a caveat to gasket sealant issue. I was about to start making a new gasket for the flange between the pump motor and differential. Mr. Maxwell told me that because this isn't a high-pressure area, and because of the shape of the differential flange I could use Loctite 515. So on this rebuild I will be laying a very small bead of Loctite 515 on the differential and then bolting the transmission assembly in. If you too chose to use Loctite 515 expect to pay between $15.00- $17.00 a tube for 1.69 oz., or 50ml.

The O-Ring in the charge pump must be replaced in the rebuild. If you chose not to, you can expect a leak to occur. The seal kits I am buying only come with 1 #60 gasket. The seal kit is approximately $ 30.00 it comes with O-Rings (3), 1 #60 gasket, and multiple seals. You may need to trace #60 and make a second one or order a second gasket, they will sell individual ones but they get pricey on an individual basis.

Here is a link to the seal kit supplier
The part # on the packaging for a 15 series is P419510354001

Re-assembly is very straight forward, with some thoughts.

First thought is to pack the ball bearing in the pump motor with Mystik #2 grease. The reason is to insure plenty of lubrication during the initial start up. This grease is available at TSC.

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Second thought is to coat the charge pump gears with SAE 30 weight oil. This insures they have lubrication as well during the first few seconds of the starting process while all parts are being primed.

Third thought use grease to hold the 2 O-rings in the center section where they mate to the pump housing. Vaseline is not acceptable in this location. A small mount of Mystik grease is all that is needed. (Remember the BrylCream ad? A lil dab will do ya?)

Input shaft has been packed with grease and is ready to install.

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Next step in to insert the input shaft and install the snap ring. Unlike the rear snap ring this one is flat so there is not a concern with it being installed upside down.

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With the input shaft in place insert the charge pump pin

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Once the charge pump pin is in place you will follow with installing both charge pump gears. Once they are in place lubricate them with SAE 30 oil. The purpose of the oil is only for initial start up lubrication.

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Then insert the o-ring into the charge pump housing cover and slide it over the shaft. Keeping in mind to orientate it with the correct RH / LH upward.. The housing will not immediately slide over the pump gears.. Rotatae the hosuing and it will slip easily over the 2 gears, and then you will be able to inset the 4 ½" hex headed bolts into place.

Next will be the swash plate in the pump end. There are 4 3/16" roll pins that hold the swash plate to the control shafts. Each one is supposed to 5/8" long. The casting of the swash plate is 1.5 thick, and this will require the 2 pins to be pushed below the surface approx. 3/16"-1/4" to insure the bottom roll pin has used as much of the lower portion of the swash plate casting as possible.
The following photos will help better explain.

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Please do not attempt to use a single longer pin in the swash plate. Its removal will become what nightmares are made of.

At this point you can install the swash plate washer. Place the best side of the washer outward (visible to you) for the pistons to ride on. You can lightly lubricate the backside of the washer with either a very light coat of grease or SAE 30 oil.
Set the entire assembly aside and proceed to the motor section.

I personally have learned that building the components in this order makes the final assembly easier and the pistons fall out less frequently.

Take the pistons and insert them into their retainer plate. Keeping in mind the flange goes up as it rides on the barrel. Before you insert them into the barrel make sure they are clean and give them a light coat of SAE 30 oil.

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Place the pump motor housing so that it is leaned backwards and resting on the pinion gear. Lubricate the worst side of your washer and insert it into the casting. Now lean the casting forward so that it is almost vertical and slide the barrel assembly with pistons onto the output shaft. Once it has been pushed all the way on you can lean the housing back again allowing it to rest on the pinion gear.

Now is the time to pour a small amount of SAE 30 oil into the barrel openings to lubricate the pistons, and some oil around the barrel to give additional lubrication to the tops of he pistons.

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Place 2-3 bolts into the motor housing and then slide on a gasket.

Followed by coating the valve plate that has 4 wales with SAE 30 oil. Coat both sides. The tension in the oil will hold the valve plate to the center section. Make sure the vertical notch on the backside of the valve plate aligns with the pin in the center section.

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With the center section stood vertical, and the motor section vertical (note look for your previously scribed mark to insure the motor is right side up) slide the 2 pieces together. The 2-3 bolts previously inserted will help hold the gasket in place and align the motor and center section.

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Note *** theses 2 sections will be apart by approximately ¼-3/8 of an inch because of the springs in the barrel assembly. This is normal and not a reason for alarm. You will be able to take your hands and squeeze the 2 sections together but once you relax your hands they will separate slightly. Again there is no reason for alarm.

Coat the valve plate for the pump with SAE 30 oil and set it into place on the center section. Again the tension in the oil should hold the valve plate over the bearing and against the guide pin.

Then you will place the 2 O-rings in their respective places around the check balls.

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Push the bolts through a little farther than they have been and slide the second gasket over the center section. Make sure the 2 O-rings have not fallen out or slid out of their recesses.

Bring the center section and motor section vertical, and align with the pump section, and push the pump assembly to the center section. You may need to rotate the input shaft a little but all 3 sections should come together.
Again the pump section may have a gap of ¼ inch but this should not be cause for concern.

Start 2 bolts in opposite corners, insert the final bolt and tighten the other 2 bolts. As is customary tighten the bolts finger tight only and use a criss cross pattern to keep the gasket from being pinched or deformed.

Snug up the 4 bolts and then tighten them down. Check the charge pump housing bolts and make sure they are tight. You are now ready to reinstall you Sundstrand Series 15

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