L48 split for HST repair

[MHarryE]

Any idea as to how the bearing came loose? How did you diagnose it prior to removal? Not surprising the parts made it into the filter doing no damage as the cradle is in the case and not in the high pressure loop so the parts would stay in the case if too large or would get flushed out and would need to go through the filter before once again entering the system. Cradle bearings need to be very low friction so the swash plate can pivot easily. All the units I work with have needle bearings but I’ve never been inside a low cost CUT transmission.

 

[radios1]

Here's a WSM page showing where the cradle bracket goes in the unit. After bolting it in I solvent cleaned the surfaces and put the port block back on with Permatex Ultra Grey (no gasket). HST is ready to reinstall.

after blowing up the picture 400% it still looks like brown paper over the bearings, you can even see it crinkled..

 

[MHarryE]

Any idea as to how the bearing came loose? How did you diagnose it prior to removal? Not surprising the parts made it into the filter doing no damage as the cradle is in the case and not in the high pressure loop so the parts would stay in the case if too large or would get flushed out and would need to go through the filter before once again entering the system. Cradle bearings need to be very low friction so the swash plate can pivot easily. All the units I work with have needle bearings but I’ve never been inside a low cost CUT transmission.

Ремонт гидронасоса хода Rexroth A4VG56 катка Komatsu - YouTube

I’m afraid that after posting I searched YouTube for one of my favorite hydros and came up with this. The video shows fretting on the cradle from the needle bearings. Interesting look at the hydro guts.

 

[radios1]

Ремонт гидронасоса хода Rexroth A4VG56 катка Komatsu - YouTube

I’m afraid that after posting I searched YouTube for one of my favorite hydros and came up with this. The video shows fretting on the cradle from the needle bearings. Interesting look at the hydro guts.

look here. NSK - Fretting

 

[rbargeron]

after blowing up the picture 400% it still looks like brown paper over the bearings, you can even see it crinkled..

The pic was an online image. The new part looks the same - its coated with light brown grease (for that crinkled look) and sealed in plastic wrap. I cleaned it, coated it with UDT and bolted it into the case. The bearing faces are bronze - high copper, low zinc, maybe a couple percent silicon for hardness.

 

[rbargeron]

Any idea as to how the bearing came loose? How did you diagnose it prior to removal? .............Cradle bearings need to be very low friction so the swash plate can pivot easily. All the units I work with have needle bearings...........

Rolling bearings trade low friction for high contact stresses - fretting (same as potholes - shear failure below the surface). Shell-type bearings spread out the load better than rollers. But they're not perfect either.

With everything immersed in oil, the unit will run a long time even with worn cradle bearings - as long as they stay in place. In this case the head of the shell's retaining screw was gone (worn away).

My guess is root cause was debris in the fluid sometime in the past. I don't know the machine's history - prior owner said the dealer serviced it. When I opened it up, one bearing was out of position in the corner blocking swash plate travel.

With a new bracket and bearings it all glides freely now - ready for a couple thousand more hours.

 

[arto98607]

......................................... ready for a couple thousand more hours.

Interesting rebuild story, thank you!

How many hours in the unit now?

 

[rScotty]

I can never resist talking about sealers and gaskets. So anyone who finds that boring this is where to tune out. When I assemble without a gasket I get really picky about the RTV. I also like the Permatex Ultra Grey and use it a lot. I also like Permatex fuel resistant and hi heat silicon RTVs. Great value for the cost. For me, the trick to using them is to apply a thin layer to both sides and then not assemble until it is very tacky and nearly cured. You don't want to force strings of RTV out of the joint - especially not in a HST.

For the ultimate silicon goo, there is always Dow Corning 3145 Grey. It's an industrial product not often sold retail - but it is the "go-to" grey silicon for high$$ hi-tech and for aerospace applications. I get it from Pilot Gear Online.com....$33 for a 3 oz. tube and worth every penny. Handled carefully & resealed with care it will last five years or more. Very sticky, capable of high temp and pressure. it cures to a tacky surface quickly & then takes overnight for final strength. It is also non-toxic, and doesn't affect sensitive surfaces since it cures by a different catalytic process so that it doesn't outgas any acid fumes (that distinctive organic acid smell). 3145 has no odor and can be safely applied and shaped with a wet finger.
Great stuff, but crazy expensive.

Looking at the pumpshaft PDF you posted, that's just the kind of place I'd use 3145 if available, but I haven't had or seen any problems with Permatex Ultra Grey either. Very thin layer, though....and wait for tacky before assembly.
I'm currently doing a set of vintage Norton motorcycle engine/transmission cases that way.
rScotty

 

[rScotty]

The pic was an online image. The new part looks the same - its coated with light brown grease (the krinkled look) and sealed in plastic wrap. I just bolted it into the case. The bearing faces are bronze - high copper, low zinc, maybe a couple percent silicon for hardness.

Thanks for posting that explanation, I was beginning to join radios1 in worrying if it really could be paper.
BTW, I think that is an area where I would prefer shell bearings to roller bearings... as long as there was a dedicated clean oil feed to the sliding surface. Given good oiling, I really can't understand why rollers would have any advantage in a high load oscillating movement like that.
rScotty

 

[mopardude318]

I can never resist talking about sealers and gaskets. So anyone who finds that boring this is where to tune out. When I assemble without a gasket I get really picky about the RTV. I also like the Permatex Ultra Grey and use it a lot. I also like Permatex fuel resistant and hi heat silicon RTVs. Great value for the cost. For me, the trick to using them is to apply a thin layer to both sides and then not assemble until it is very tacky and nearly cured. You don't want to force strings of RTV out of the joint - especially not in a HST.

For the ultimate silicon goo, there is always Dow Corning 3145 Grey. It's an industrial product not often sold retail - but it is the "go-to" grey silicon for high$$ hi-tech and for aerospace applications. I get it from Pilot Gear Online.com....$33 for a 3 oz. tube and worth every penny. Handled carefully & resealed with care it will last five years or more. Very sticky, capable of high temp and pressure. it cures to a tacky surface quickly & then takes overnight for final strength. It is also non-toxic, and doesn't affect sensitive surfaces since it cures by a different catalytic process so that it doesn't outgas any acid fumes (that distinctive organic acid smell). 3145 has no odor and can be safely applied and shaped with a wet finger.
Great stuff, but crazy expensive.

Looking at the pumpshaft PDF you posted, that's just the kind of place I'd use 3145 if available, but I haven't had or seen any problems with Permatex Ultra Grey either. Very thin layer, though....and wait for tacky before assembly.
I'm currently doing a set of vintage Norton motorcycle engine/transmission cases that way.
rScotty

I am assembling a hydraulic pump and the gaskets determine the gear to case clearance. The first set of gaskets I made were .004” thick and they compressed.002” when I tightened the pump body studs, the clearances were too tight and the internals bound up. Would not turn. I may double up on my gasket material to get the correct clearance.

Would you happen to know the compressed thickness of that 3145?