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cat 236 - i just rebuilt lift cylinders, but lift arms keeps leaking down

makesumwake

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Dec 12, 2015
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miami, fl
ok thanks ill get it.

also is there a general consensus on the best aftermarket hydraulic oil recommendation for these cat machines?
the dealer wants $18/quart

some people are using 10w30 motor oil instead ($3/quart or less)
and ive found a general hydraulic oil on walmart.com, 4.75 gallons for $30 ($1.60 /quart). called "Sinopec L-HM 32"
 

Nige

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G..G..G..Granville.........!! Fetch your cloth.
ok thanks ill get it.

also is there a general consensus on the best aftermarket hydraulic oil recommendation for these cat machines?
the dealer wants $18/quart

some people are using 10w30 motor oil instead ($3/quart or less)
and ive found a general hydraulic oil on walmart.com, 4.75 gallons for $30 ($1.60 /quart). called "Sinopec L-HM 32"
If you want to get the CD version containing the same info here’s the link - https://www.servicemanualpro.com/?page=Products&searchbox=4YZ04598

That Sinopec hydraulic oil seems to get good reviews from others on here.
 

lantraxco

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Elsewhen
Thanks Nige!
18/15 has been burnt into my brain. 10/8? Wow.

Everyone thinks I’m crazy when I mention new hydraulic oil needs filtered before going in the machine. And not with a rag or coffee filter. Lol

Ain’t nobody gots time fo dat. It’s new oil. It must be clean. It’s new oil. It’s in a shiny blue drum.
The CAT dealer I worked at had an issue with high numbers coming back consistently on machines they were contracted to service for the customers. Somebody finally suggested sampling the oil coming out of the service trucks, then the bulk tanks at the dealer, then the supplier's trucks, then his tanks, etc. All dirty, with shiny fresh from the tank farm oils. Better pumps and 25/10/3/3 medium pressure filters daisy chained at the dealership and something similar on the lube trucks solved that problem, but WTF? eh?

Oh, BTW, from one oil company I bought from, if you went by their yard you could watch them fill drums and 5 gallon buckets with various products, from their tank trucks which they filled from the bulk tanks with overhead drops. Wind blowing dust everywhere. Cleanliness is next to... impossible?
 

lantraxco

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"the overall leakdown rate of the lift arms is about the same as before the bebuild, but there is an initial quick drop after i stop raising the lift arms.
so with a bucket full of dirt, when i return the joystick from lift to neutral, the lift piston immediately sinks back into the cylinder about 3/4 of an inch over 4 seconds, and bucket drops accordingly.
and this DIDNT happen as much before i tried to do the rebuild. it happened a little but its way worse now."

This sounds to me, and bear with me, like you're piston(s) is/are bypassing enough to put your cylinders into displacement mode, in other words the piston packing is still leaking a little, so the rod packing takes all the pressure, and it will be higher than normal due to the small size of the rod, which is acting as the cylinder piston. Still going with that assumption and the fact you said one old piston seal was broken, it probably settled less at first because the broken seal had the cylinders acting in displacement mode basically all the time.
 

makesumwake

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Joined
Dec 12, 2015
Messages
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Location
miami, fl
[QUOTE="This sounds to me, and bear with me, like you're piston(s) is/are bypassing enough to put your cylinders into displacement mode, in other words the piston packing is still leaking a little, so the rod packing takes all the pressure, and it will be higher than normal due to the small size of the rod, which is acting as the cylinder piston. Still going with that assumption and the fact you said one old piston seal was broken, it probably settled less at first because the broken seal had the cylinders acting in displacement mode basically all the time.[/QUOTE]

interesting theory.
so correlated side note: when i installed the tilt pistons, they were really hard to get out and get back in. BUT when i installed the lift pistons, the ones in question, they came out super easy (by hand, no tools required) and went went back in super easy. i was really surprised.
a loose fit would create the effect you are referring to i believe.

so i bought this machine used, in Miami (my first mistake), where the cubans here are well known for jerry rigging everything to save a few dollars. the drive joystick is installed backwards on it. someone working on it didnt know what they were doing.
the oil seals on the lift arms had been replaced already, so someone before me already had had the lift cylinders apart before i bought it. all the main oil seal that keeps oil from leaking past the piston was not spec, it was a different color than what CAT supplied. and one was broken in half.
im wondering if someone didnt swap out damaged lift pistons in this machine for some other wrong size lift piston and call it a day?
is that even possible?
on the other hand, both of the lift pistons were loose like this. and this is just me guessing why the lift pistons would be not tight. i bought the new lift seal kit directly from Cat. and the other rings and seals appeared all to be the same as the ones i was replacing.

maybe there are size specs i can look up, and then measure the diameters on the lift piston parts i have and double check to make sure i have the right piston installed.

why else would a piston be loose like that right after a rebuild?
 
Last edited:

Coaldust

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Why would a Piston be loose?

Here is a possibility. Slim, but worth noting.
Caterpillar sells oversized remanufactured cylinders and offers oversized seal kits. Which allow you to hone a scratched cylinder oversized to salvage it. Maybe your lift cylinders are oversized and you used a standard size seal kit?

My Pro Tip for the day ( no charge, totally free!) Measure cylinder bore dia. before ordering parts. :)
 

Welder Dave

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It's also possible something simple like an internal O-ring on the piston to rod was missed or damaged on installation.
 

makesumwake

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Dec 12, 2015
Messages
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Location
miami, fl
Why would a Piston be loose?

Here is a possibility. Slim, but worth noting.
Caterpillar sells oversized remanufactured cylinders and offers oversized seal kits. Which allow you to hone a scratched cylinder oversized to salvage it. Maybe your lift cylinders are oversized and you used a standard size seal kit?

My Pro Tip for the day ( no charge, totally free!) Measure cylinder bore dia. before ordering parts. :)

wow, that is a pro tip! never would have thought of that.
 

Coaldust

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Welder Dave,

The Cat publication PEKP1020-08 or newer, Hydraulic Cylinder And Seal Reference Guide is a handy book to keep around. Not sure what the newest edition is. I'm a little out of the loop. It's been a dealer only publication.

The general idea is you can go up to about .014" over-size and still use the original size seal kit, then you can go to .030" and lastly to .060". Bolt on heads with oval head seals sometimes have to be machined for a flange face o-ring seal.

Here is a link to a bootleg copy: not sure what version.

http://dozerparts.ru/f/tsilindry_i_uplotneniya.pdf
 

Welder Dave

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In a quick look I see where the gland has oversize seals available but they have them for the piston seals as well where presumably the cylinder could be honed up to .060" oversize? I've never heard of oversize seal kits for cylinders. O-rings and such sure but not all the cylinder seals. Anytime I've needed cylinder seals there's only been one part number for the seal kit. .060" could take out some pretty deep grooves.
 

Coaldust

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Honing a scratched cylinder is a great way to save a few bucks and salvage a expensive component. You can also purchase Cat Reman oversized bare cylinders vs purchasing new.

I spent a long 18 long month rotation in a Cat dealership hyd spec shop rebuilding cylinders. Holy cow, that got old after about two months.
 

Jonas302

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Some really good information in this thread
Thanks for the link to the hyd book
 

Welder Dave

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I would guess oversize cylinders/seals would only be available for larger machines and not skid steers or TLB's.?
 

muddog1975

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knoxville tn
If you still think its in the cylinders, (bypassing internally) raise your boom up safely hold the boom up in the air. Release your hydraulic pressure from the machine( key on no start...rotate and move joysticks) to release pressure. Remove your lift cylinders hyd hoses ( both) and cap both of them off with metal caps. Take a permanent marker and mark your rod. Then releases the boom from whatever you where holding it up with. Watch to see if the boom drops down. If it does its in your cylinders...if not you know its bypassing some where else. Possible control valve spool...etc. good luck... let us know what you find.
 

92U 3406

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Has this machine got an emergency loader arm lowering valve? I've seen them malfunction and cause a creep-down condition.
 

lantraxco

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Not to be argumentative, but capping both lines will create a displacement cylinder, still won't tell you if the pistons are leaking by?

you can also just raise the bucket up a little bit prop it up with a short wood block, disconnect one rod end hose at a safe place and put the hose end in a catch can. With an appropriate tool knock the block out from under the bucket. If one piston or both are bypassing you will get oil coming out of the rod end port(s) Safety first though.
 
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