Bypass valve leaking

[Thatoneguy 197]

So I washed my rear end and sundstrand 90-1136 and now the by pass valves leaks when I screw it in past a certain point.  If I screw it all the way in I can sit there and watch the fluid start seeping past it.   I changed the o-ring with an R-04 i believe is what it was.   Do these require some sort of thread sealer? There was nothing on it when I took it out, and when I used the valve to push the tractor in my shop it worked fine and has never leaked. Any ideas would be wonderful! 

[oliver2-44 9,601]

Maybe it always had a tiny leak that formed a seal of thickens oil around it, so you washed the seal away. 
I suspect some of us wished ours leaked a little and turned versesbeing frozen up. 

[Thatoneguy 197]

13 minutes ago, oliver2-44 said:

Maybe it always had a tiny leak that formed a seal of thickens oil around it, so you washed the seal away. 
I suspect some of us wished ours leaked a little and turned versesbeing frozen up. 

@oliver2-44 who knows? I know I need to figure out what to do about it! 

[oliver2-44 9,601]

 

Just speculating, but that O-ring looks a little narrow in the slot that it fits in.  If you can find a size slightly wider, which probable would make it slightly taller as well.

@daveoman1966 can you comment on what the correct O-ring size is for the TOW valve?

[ranger 1,741]

I’ve personally had no dealings with these transmissions, but, looking at the corrosion/staining? on the area between the thread and the anti-extrusion ring/‘O’ ring section, I wonder what the condition of the bore in the valve block is? Any ‘Pitting’, etc could cause damage to the seal, and potential leakage, when valve is assembled, or operated. After you find the cause of the issue and fix it, I think this could be another area to apply, @peter lena,s tactics, identify a potential issue, and fix it, before it becomes major! In this case ‘High’ temperature grease on the valve section, thread and up to the ‘O’ ring, to protect against moisture ingress, and corrosion. It’ll also ensure that when you need to use the valve, it won’t be seized! It’s surprising how moisture can be drawn into, (over time)  a, (‘Sealed’ by threads) compartment after being exposed to heat, and then cooling down in a damp environment. (High humidity, washing down, etc). The air expands with the heat, is forced out via the threads, and the partial ‘vacuum’ created on cooling draws in the moist air. Witness some automobile lamps that seem to accumulate water! As for the ‘O’ ring, is it from a seal kit for this particular product?, or is it from a ‘Selection’ box of ‘O’ rings? The ‘O’ ring kits, I’ve always found have a larger section, and don’t usually work well in valve blocks. In this case though, a slightly larger section ring may deform into a ‘squarer/wider shape, and might then seal, (if you can assemble it without any damage?).

Edited July 9, 2023 by ranger

[squonk 40,950]

I would be hesitant to put any grease/ sealant or anything else in a hydro. Like Oliver says you need a thicker o-ring.

[ranger 1,741]

3 hours ago, squonk said:

I would be hesitant to put any grease/ sealant or anything else in a hydro. Like Oliver says you need a thicker o-ring.

The grease would not be in contact with any of the inner workings of the hydraulic circuits, only to protect the ‘Atmospheric’ side of things against corrosion, etc. Sealant on the threads, in this case, would be the same as putting a bucket under a hole in a leaking roof, rather than fixing the hole. In 40 odd years of working on specialised vehicles and hydraulic equipment, I’ve come across many, many leaks caused by the replacement of the correct size ‘O’ rings with larger ones, especially where they are attempting to seal a cartridge valve or fitting into a block. The thicker section ‘O’ actually prevents the cartridge from fully seating, and it is then always ‘Loose’. However, in this case the gap between the’O’ ring and the ‘Anti-extrusion’ ring may allow the O ring to deform, fill the gap and effect a seal??

Edited July 9, 2023 by ranger

[pfrederi 17,617]

with tow valve on the side under the fender the valve uses WH# 971012 based on WH numbering system I would guess it is Dash #012

[peter lena 8,560]

@ranger  having built / serviced  various hydraulic set ups , was always looking for a reason / cause of failure . another frequent failure point is the  O  ring itself , getting the exact spec ring , chemical make up , specific to it .would often use , a light film of  super lube to insure seating , and full fitment  , when dealing with a consistsnt failure , obviousely if it calls for a dry o ring fit ,there is a chance for o ring pull, thinning , creating a base line to leak . when all else fails , would go to a new swage lok fitting . we used , stainless swage / lok compression fittings , for a fail safe connection . 2 am call in , pete 

[squonk 40,950]

                 i.d           +/-        CS              INCHES

 

                    

-012

0.364

0.005

0.070

 
   

Edited July 9, 2023 by squonk

[Thatoneguy 197]

I think I will start with a new o-ring then. Is there a certain place to get a thicker o-ring or should I order the part number listed in my book? 

[pfrederi 17,617]

O rings are sized by Dash #.  If you have a good hardware store ask for a Dash 012

[pacer 3,160]

FWIW ... I'm in the 'O' ring change camp.

[pfrederi 17,617]

I  may have some in the workshop will check later today

 

or get a life time supply

 

[Thatoneguy 197]

18 minutes ago, pfrederi said:

I  may have some in the workshop will check later today

 

or get a life time supply

 

I think i will buy the lifetime supply! 

[pfrederi 17,617]

I have them..  PM me your address i will send you one

 

Is your plastic backer ring OK

Edited July 9, 2023 by pfrederi

[pacer 3,160]

I dearly love McMaster, they got just about anything a feller would need around the shop and FAST shipping ..... but.... geez would'nt it be nice if they had a way to get a wee bit less than 100pcs of so many items?? 

[Kenneth R Cluley 515]

Like pfrederi says check your nylon backer. Must be in good shape to limit extrusion of O-ring. if continues to be problem you can also consider using a "quad" ring of same dimensions to see if eliminates leakage. Basically a different shape profile that has seal properties better than standard O-ring. Have had success with this in some seal applications that O-ring would not work. Also, check the profile of the end of stem, if memory serves me that should seal off when screwed in and no fluid or pressure should go by that bevel to leak past O-ring. When open bleeds or by-passes fluid to allow movement of tractor.

Edited July 9, 2023 by Kenneth R Cluley

[ranger 1,741]

I think that with the bypass/tow valve bridging the main lines between the pump and the motor, when it is closed, the ‘O’ ring seal will always see ‘charge pump’ pressure in neutral, and forward, but full, (Drive) pressure in reverse. So the seal is always under pressure even if the main pump is not producing any flow, ie, neutral. Due to charge pump always running keeping circuits ‘full’ of oil.

Edited July 10, 2023 by ranger