When disassembling a brake valve it's not uncommon to find an internal component that can't be easily pulled or pushed out using mechanical pressure. Heat from a propane torch coupled with compressed air sometimes works, but when can you do when compressed air doesn't get the job done, either? I've found that using hydraulic pressure will typically do the trick, and it's relatively easy to apply hydraulic pressure using a common grease gun. The challenge is connecting your grease gun to the ports on your brake valve. How can it be done?
Let's start with the typical grease gun that is machined to accept 1/8" NPT (National Pipe Thread) fittings. The gun has a female port that will accept a flexible hose or a steel line. At the end of that hose or line you have a 1/8 NPT male fitting. This won't fit the typical port on a brake valve, which is threaded using Unified Thread Standard (UTS) threads. UTS threads come in Unified National Coarse (UNC), Unified National Fine (UNF), Unified National Extra Fine (UNEF), and Unified National Special (UNS) varieties. Modern cars use brake valves with metric threads. Given the thread mismatch, we can't just connect the grease gun to a fluid port on the valve. We have two choices: adapt the grease gun to the fluid port, or adapt the fluid port to the grease gun. Let's look at both approaches with a focus on UTS threads. The approach for adapting to metric threads is similar, though I haven't researched the availability of specific metric adapters.
Please understand that the specific adapters described in this article may not work for your application. Everything depends on the size of the fluid ports on your brake valve and the availability of adapters to fit those ports. Success may depend on using adapters to fit other adapters.
Adapting the Grease Gun
This approach involves finding adapters to convert the grease gun's pipe thread fittings to an adapter with UTS threads that can be screwed into a fluid port. I've found two adapters; each will typically require use of another adapter for fit to a brake valve fluid port (click on the links for source and price information).
|1/8" NPT Female to 9/16"-18 Male Inverted Flare Adapter||1/8" NPT Female to 1/4"-28 Male Adapter|
|This adapter can be used to directly attach your grease gun to either a fluid port with 9/16"-18 threads or an additional adapter with a 9/16"-18 female fitting.||This adapter can be used to directly attach your grease gun to a fluid port with 1/4"-28 threads or an additional adapter with a 1/4"-28 female fitting.|
Adapting the Brake Valve Fluid Port
This approach involves finding grease fittings (also known as zerk fittings) to one of the brake valve fluid ports. Zerk fittings come in a limited number of sizes, though, so an adapter may be required to attach a zerk fitting to a fluid port. Here are some zerk fitting possibilities (note that each is sold in packages that contain more than one fitting):
|1/4"-28 UNF Male||5/16"-24 UNF Male||3/8"-24 UNF Male|
Note, though, that the port into which you need to inject grease to apply pressure may be larger than all of these zerk fittings. In that case you need an adapter that includes a male end to fit the fluid port and a female end to receive the zerk fitting. Here are some adapters made by Dorman from the RockAuto.com web site:
|7/16"-20 Male to 3/8"-24 Female Adapter||1/2"-20 Male to 3/8"-24 Female Adapter|
Each of these will receive a 3/8"-24 zerk fitting and adapt it to a fluid port. A complete list of Dorman fittings available from RockAuto can be found using this link. You may be able to find other sources for Dorman products, including your local auto parts store.
So that's the basics on the fittings and adapters. To put them to use, we now need to attach an appropriate combination of fittings and adapters to the brake valve so that your grease gun is attached to the valve at a fluid port that is behind the part that you're trying to push out. The basic idea is to block off all of the ports except for the one that will receive the grease. When you apply pressure, the grease will push against the stubborn part with enough pressure to pop it free. You may also need to apply heat to the valve with a propane torch. On the valve pictured below you can see how I've installed a combination of inverted flare plugs, an adapter, and a zerk fitting that allows me to push grease into the valve and push out an internal piston.
As mentioned above you're also going to need a combination of inverted flare plugs (what you need will depend on the sizes of the ports on your valve) that can be used to block off the other fluid ports. These plugs can usually be found at your local auto parts store. I've been able to find all that I need at my local NAPA.