OldandWorn
Senior Member
Thanks for documenting this Cmark. Lots of WOW's and OMG's here. The precision, cleanliness, and the cost to make parts like this is amazing to me.
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Cat hydrostatic transmission overhaul.
- Thread starter Cmark
- Start date
We put grease on the back of the port plates to stick them to the head while it's hanging upside down.
And then tie them on for safety. You can just see the little loops of string through the holes. The one on the right has fallen off already. Good thing we had the string! As per the barrels, dings or scratches on the port plates are unacceptable.
And the head's bolted down.
A pin anchors the servo cylinder barrel.
And a cap goes in the hole.
And then tie them on for safety. You can just see the little loops of string through the holes. The one on the right has fallen off already. Good thing we had the string! As per the barrels, dings or scratches on the port plates are unacceptable.
And the head's bolted down.
A pin anchors the servo cylinder barrel.
And a cap goes in the hole.
The input gear is a little corroded so we spin it in the lathe and hit it with the scotchbrite.
And make sure all the abrasive is washed off.
The little pie oven we use for heating up bearings (and pies).
And put the cones on the input gear.
And make sure all the abrasive is washed off.
The little pie oven we use for heating up bearings (and pies).
And put the cones on the input gear.
Forgot to mention the sump is one area where there is a difference between the models. Some have a large one like this, some have a small one simillar to the top cover.
I've not done any extensive research on this or anything, but I know that I've seen a lot with a small sump and the working oil level almost to the top of the HPCU. I'm guessing that this caused problems with the rotating components being submerged in oil (power loss, overheating maybe?) so they went to the bigger sump and lower oil level.
I've not done any extensive research on this or anything, but I know that I've seen a lot with a small sump and the working oil level almost to the top of the HPCU. I'm guessing that this caused problems with the rotating components being submerged in oil (power loss, overheating maybe?) so they went to the bigger sump and lower oil level.
HATCHEQUIP
Senior Member
looks like a GREAT JOB thanks
Shrink the input gear bearing cups and install them, but not the seals at this stage.
Install the housing without sealant.
And check the endfloat of the input gear. Adjustment is with a shim under the cup in the housing.
And when we're happy with the endfloat, take it apart again, install the seals and fit the housing. No gasket here, just the Loctite sealer.
Install the housing without sealant.
And check the endfloat of the input gear. Adjustment is with a shim under the cup in the housing.
And when we're happy with the endfloat, take it apart again, install the seals and fit the housing. No gasket here, just the Loctite sealer.
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Now we move on to the other components which go to make the thing work.
These are what Cat call the replenishing valves. There's one for the right side and one for the left. They handle all the high pressure side of things after the main drive pumps. They're both identical apart from the component on the bottom left. This component is on the RH valve only. Its job it to allow some oil to bleed between the two circuits when the drive pressure is low which helps to keep the machine going in a straight line when needed. The LH valve (pic 4) has a needle valve in this position which is used to disable the function during certain tests.
The main function of the valve is to "replenish" the oil in the drive loop. That's handled by the spool (right) which also allows the main relief valve (top) to sense drive pressure in both fwd and rev.
Note the long thing on the left with a plug on the end. This is found on later machines. Earlier ones had a spool valve with some extra exlernal lines instead. This allowed to the machine to be towed once the parking brakes were released. It can lead to specific problems with the drive which aren't covered in any of the Cat troubleshooting.
In later machines such as this, this plug has to be removed instead. In practise, it's 100000% easier to just pull the drive shafts if you need to tow it.
This is the LH replenishing valve. Note the tube sticking out on the right of the picture. It connects both valves together.
This tube is a later example with two O rings and backup rings at each end. The early ones only had one. This is a favourite source of leaks on the early machines. If you ever find yourself in the position of removing the replenishing valves to fix a leak here, I suggest you upgrade to the two-O-ring tube.
I hope you're all keeping up. There'll be a quiz later
These are what Cat call the replenishing valves. There's one for the right side and one for the left. They handle all the high pressure side of things after the main drive pumps. They're both identical apart from the component on the bottom left. This component is on the RH valve only. Its job it to allow some oil to bleed between the two circuits when the drive pressure is low which helps to keep the machine going in a straight line when needed. The LH valve (pic 4) has a needle valve in this position which is used to disable the function during certain tests.
The main function of the valve is to "replenish" the oil in the drive loop. That's handled by the spool (right) which also allows the main relief valve (top) to sense drive pressure in both fwd and rev.
Note the long thing on the left with a plug on the end. This is found on later machines. Earlier ones had a spool valve with some extra exlernal lines instead. This allowed to the machine to be towed once the parking brakes were released. It can lead to specific problems with the drive which aren't covered in any of the Cat troubleshooting.
In later machines such as this, this plug has to be removed instead. In practise, it's 100000% easier to just pull the drive shafts if you need to tow it.
This is the LH replenishing valve. Note the tube sticking out on the right of the picture. It connects both valves together.
This tube is a later example with two O rings and backup rings at each end. The early ones only had one. This is a favourite source of leaks on the early machines. If you ever find yourself in the position of removing the replenishing valves to fix a leak here, I suggest you upgrade to the two-O-ring tube.
I hope you're all keeping up. There'll be a quiz later
This is the charge pump. Nothing very sexy going on here, just a simple gear pump, but....
It's direct driven at engine speed which means its output flow is directly proportional to engine speed. The system senses this flow (note flow, NOT pressure) to tell how fast the engine is running and prevent the drive system from stalling the engine. More on this to follow......
It's direct driven at engine speed which means its output flow is directly proportional to engine speed. The system senses this flow (note flow, NOT pressure) to tell how fast the engine is running and prevent the drive system from stalling the engine. More on this to follow......
One word of CAUTION here if you pull the sun gear shafts for towing. Take out the end cover thrust plugs and put in your tool box. They have a habit of falling out and ruining the planetary gear set. Upon pulling a shaft the planet bearings should be checked as well. The planets will stay in mesh with the sun gear installed with failed bearings but get out of mesh by themselves and break the ring gear.
Later Bob
Later Bob
wyomingjet
Member
- Joined
- Feb 5, 2014
- Messages
- 18
- Location
- Gaylord, Michigan. Old USA.
- Occupation
- Staying Alive, Semi-Retired, Jack of most trades n
Yeap, count me in as well, sounds interesting for sure. Never too ole a dog to learn a thing or two. Ty
Scrub Puller
Senior Member
Yair . . . Cmark. Fascinating stuff. About what expectation of hours do you expect from such a transmission assuming proper maintenance?
Cheers.
Cheers.
cb75
Well-Known Member
Cmark, Good stuff, very interesting and well done thread. Did you go thru the track motors as well?
Hey Scrub.
IMO these transmissions should last tens of thousands of hours, given proper maintenance. But as your question implied, proper maintenance is sometimes a subjective thing.
This particular machine is getting on a bit. To be kind, I would call the hourmeter reading "unreliable", but looking at the overall condition, I would say it's around the 15 - 20k mark. This is not the first time somone has been inside the HPCU as it has someone else's paint marks are in there.
This customer runs several hystat track loaders and with routine oil and filter changes I think he gets excellent reliability out of them. We've been looking after his gear for around 8 years and this is only the second major tranny problem we have seen.
Yes we always strip and inspect the motors in a situation like this.
In this case, luckily, the motors were OK. Just wear commensurate with age to the port plates. The main bearings in these motors are, IMO, very large for the size of the motor and the wear was negligible. We simply rebuilt the motors with lapped port plates.