Two plane clamp rising after being lowered.

[LeeB]

My two plane clamp has started rising about an inch after lowering it. Frustrating to say the least. It will lift the cant if I don't wait for it to stop and I can't use it to pull down any slight bow in a cant. Anyone ever have this issue before?

[Old Greenhorn]

Sounds like you have air in there somewhere Lee.

[Magicman]

Yes Lee I have and it's not air in the system.  Get the kit and rebuild the hydraulic cylinder.  (I looked for the pictures where I rebuilt mine but so far have not found the link.  I'll keep looking.)

Bleed the cylinder both ways before you start the rebuild or you will get drenched with fluid.

Anyway, put the cylinder in a vice and turn the top ccw.  There is a square ring inside that will exit through the slotted hole toward the top.  You may have to take a screwdriver and sorta help the end of the ring to exit.  After the ring comes out the end plug/gland, will come out of the cylinder, and then the piston.

The rebuild kit will have everything that you need including a new ring.  There is a topic here where someone else rebuilt theirs last year with some good pictures.

LINK

I have rebuilt mine twice.

[customsawyer]

Put a seal kit in it and you'll be good to go.

[Magicman]

Lee, your mill and mine are the same age.  At various times, I have rebuilt every cylinder on my mill.  The claw started raising up on the "sand box" job.  I took the cylinder off and carried it to a shop who rebuilt it and I only lost about 3 hours. LINK. The side supports started raising up and with some help here on the FF, I rebuilt that cylinder myself.  LINK.
My log clamp started gradually releasing and I had it rebuilt.  On a Cypress road trip, my loader arms started gradually raising.  This was not a problem while I was sawing but when I folded up and headed home the loader feet started letting down. LINK.  And finally while Luke and I were sawing in 2020, a toe board started raising.  I could have removed the mounting bolts and let it swing but I needed the toe boards so we removed both of them and carried them to the shop that afternoon.  LINK  We were back sawing the next morning.

Yup, every cylinder has been rebuilt and the log clamp twice.  That cylinder is stressed when a cant falls on it while it is partially raised so it does take a beating.

[DanielW]

I agree with the cyl. rebuild others have suggested - I saw it on a friend's father's WM. Maybe try bleeding first just in case air is in there causing havoc, but most likely the piston seals: It doesn't show itself when dropping the clamps most of the way, because it doesn't take any substantial pressure to lower. Once it bottoms out, however, that half-second or so of pressure still applied to the rod (retract) port bleeds past the leaking piston seals, ultimately resulting in both sides being pressurized (depending on valve spool shift times, orifice sizes etc.). Because there's more surface area on the bottom end due to the rod being on the top, you're effectively creating a 'regen' cylinder cycle: Applying the same pressure to both sides of the piston will result in the cylinder extending due to more surface area on the lower (extend) side.

I can't remember exactly what style of clamp is on the LT40 - never really paid too much attention so I could be misremembering. If I remember right - some models WM have misalignment couplings to prevent side-loading of the cylinders, and others have the cylinder rod capture the clamp with a groove cut in the rod end, with lots of clearance so they don't get side-loaded. Whatever the case, there will definitely be some mechanism to make sure those cylinders aren't side-loaded. You'll want to make sure it's functioning correctly or you'll burn through seals fast (and possibly bend a rod).

[Magicman]

Just as information, the hydraulic system does not need to be bled after a cylinder is rebuilt or for any other reason.  It will very quickly bleed itself.

I don't know how, I just know that it does.  I was told by Wood-Mizer tech support not to be concerned about bleeding when I rebuilt the clamp cylinder the first time which was many years and cylinders ago.  I have also replaced hoses without bleeding.

[LeeB]

Looks like the seal kit is about $26 plus shipping. I'll get one ordered. 

[LeeB]

Seal kit came this evening but I don't don't see a new wire in it.

[Southside]

I have reused those retaining wires many times when rebuilding that style of cylinder.  It should be fine. 

[Magicman]

It is actually square with a 90° bend on one end.  The bend is captured in the gland and forces the "wire" to rotate inside of the cylinder as the gland is turned.

I never found it but someone on here had one that the bend was broken off and he had a struggle to get the wire to move.  He finally was able to snag the end and get it out. 

Mine always came with a new wire.  Hopefully your old one will be reusable.

[LeeB]

I guess if you order the right seal kit you probably get the wire. I ordered the seal kit for the cylinder.  >:(

[Magicman]

The in/out clamping cylinder I suppose.  Not the clamp up/down.  ??

[LeeB]

Correct. The in and out ( horizontal) when I needed the kit for the clamping ( vertical) one. 

[Magicman]

While you are down, rebuild them both since they are the same age anyway.  Heck, you already have the kit.  My in/out started gradually releasing it's grip while I was sawing a job so I had to have it rebuilt at a shop so that I could resume sawing the next day.

[LeeB]

Good idea. The in out does seem a little weak sometimes. 

[LeeB]

I have not ordered the kit. I'm having a serious problem with $42 shipping on a $26 seal kit hat would fit in an envelope. 

[Magicman]

I agree, that it too high even for an overnight shipment.  ??

I would talk with the desk tech.  They often can pull a rabbit out of the hat.

[LeeB]

Finally got around to rebuilding the piston today. It was easy after i finally figured out how to get the wire out. The old one was round and not square like the new one. It also had the bend on the end 90 deg out from the old one so I reused the old one. 

[barbender]

I don't know why hydraulic systems bleed themselves, but they do. Not like brakes. Maybe @fluidpowerpro could explain how it works?

[Magicman]

It's good to see you gitting-er-done Lee.  8)

[fluidpowerpro]

I think the main difference is that in a brake line you've got a single column of fluid that is being pressurized and depressurized. There is very little movement of the fluid. In most hydraulic circuits, there is more fluid movement and oil will at some point be routed to the reservoir. 

[SawyerTed]

To add, on a hydraulic system there's a high pressure side (doing the work) and a low pressure side (return to reservoir).  The low pressure side is vented via the reservoir vent.  Air in the system escapes the system by way of  the reservoir vent. As long as there's enough oil, the bubbles of air in the oil escape before the pump picks them up. 

On a brake system, no vent.