Brake Block Drain Plug Leak

[ldegraw30]

Finally, after nearly 4 years, I've got my 1974 John Deere 510 Backhoe running and functioning. I only have 1 persistent issue left, and it's driving me nuts! After repairing numerous leaks, I'm left with one at the hydraulic brake block that appears to be coming from the drain plug. I've replaced the plug's metal screen and both o-rings .. but the original leak remains. Other than a possible hairline crack in the drain plug or in the brake block itself, I am out of ideas.

Is there a known issue with these machines leaking at that location? Any experience sealing / repairing such a leak?

Thanks in advance!

 

[Jim.ME]

Are the O-rings from JD or at least the correct size? The one on the plug is JD # R26375 (.644 ID, .087 cross section, 90 durometer). The one behind the screen is JD # R28776 (.500 ID, .07 cross section, 75 durometer). If the plug O-ring is correct and won't seal, is it tightening correctly? beyond that look for a defect in the O-ring sealing area of the valve body, defect in the O-ring area under the head of the plug, or a crack in the vale body.

Are you 100% sure it is not coming from higher on the valve and running down to and off that plug?

 

[ldegraw30]

The o-rings are all the proper ones from John Deere, identified by the appropriate parts manual. How do I tell if it is "tightening correctly"? It will tighten to the point that it's difficult to remove again. I resealed the entire brake valve body with the correct o-rings. An experienced local mechanic and I both agree that the leak is coming from the drain plug, although it looks as if a small amount of fluid could possibly be coming from the upper brake line?

My fear is that it's a defect in the valve body. The drain plug ... I can replace if necessary.

 

[Jim.ME]

Tightening properly would be the head of the plug coming down against the valve body and the O-ring not visible.

Dry the valve with brake cleaner. Spread powder on/around the plug and on the valve above the plug. Start the tractor, quickly get where you can see it and watch for where the powder gets damp first.

 

[ldegraw30]

By your definition ... the plug tightens properly. I appreciate the suggestion, re: use of powder to help locate the leak. I'll give it a shot, when I have the time again.