Can I Rebuild My Power Cylinder

Seal kits are readily available for the Power Cylinder but the instructions (if any) are very poor. Even the Ford shop manual doesn't provide a "real world" description of how to re-seal the cylinder. Their instructions are more for warranty replacement of fairly new cars and not for a 25+ year old cylinder with hardened seals and corrosion buildup.
There are two areas of difficulty in re-sealing a Power Cylinder; getting the old pieces out and not damaging other areas in the process.

There are two identical seals used to seal the Rod as well as a Rubber Ring meant to "squeegee" the Rod clean before it slides through the seals. Removal of the Plastic Retainer can be difficult depending on whether it is still elastic or has become brittle. Many "How-To" articles suggest forcing compressed air into the Cylinder to blow the Seals out of the end of the Cylinder. This doesn't work. Not enough air can get to the back side of the Seals to blow them out, and what little does get behind the Seals just leaks past them because they are worn. You can dig them out with a pick but care must be taken not to punch the pick into the Metal Washer under the first Seal. This will often expand the Metal Washer enough to cause it to bind inside the Snout or bind on the Rod. If you dimple the metal around the hole that the Rod comes out of, you can distort the hole enough that the Rod will bind in it and not slide freely, scratching the Rod surface. If this occurs the Cylinder is ruined.

The Stud can become worn and loose in its socket, but it is most often damaged by improper removal. If the Stud has actual play in its socket, the Cylinder is ruined. If the threads are damaged or the end flared out, it may be repairable. This is often difficult since the Stud twists easily in its socket and is hard to clamp to keep it from rotating while trying to clean the threads with a die.

Ford used Bendix brand power cylinders throughout the 1950's. There were different mounting styles, and most used only a single true oil seal, but by the early 1960's Ford began to use a double-seal cylinder that they stayed with for nearly twenty years. There were several variations of these cylinders (see Power Cylinder Pictures), but their basic construction and seal structure was the same.

Rod shiny surface worn through, pitted, rusted or scratched in the area that slides in the seals
Rod end that is so badly rusted away that the end is thin and weak
The rod binds or jams up somewhere in its travel inside the cylinder
Swivel Stud is loose in its socket

Rebuilding a Ford/Bendix Power Cylinder unit is seldom an easy thing to do. Before you consider or attempt a rebuild, there are some problem areas you should be aware of. This first part is not designed to scare you off from attempting your own rebuild (well, maybe just a little), but to show you what you may encounter along the way. We have done many power cylinder rebuilds and see these problems on an almost daily basis. These are the things not mentioned in any instruction sheet or shop manual.

Can you rebuild your own power cylinder? It depends. It depends on the condition of your cylinder and rod, how you remove it from the car, how good of a rebuild kit you are using, and how good the instructions are. Any one of these items can cause you trouble and many cylinders have at least one of these problems during a rebuild. The biggest problem is - you don't know what condition your parts are really in until you remove the assembly from the car, tear it down and inspect it. By that time you are into it pretty deep and will have to decide whether to continue on your own or turn it over to a professional.

By definition, a rebuild means that there are some parts you will retain while reconditioning them to proper working order. There are several important parts inside the power cylinder that are not accessable and that are not a part of a rebuild kit and these are the parts you hope to reuse. Unfortunately, these parts are often damaged due to rust, wear or improper removal/installation. We will start with the areas that are universal to all power cylinders and are most often damaged.

Now, certain rebuilders have the resources to replace the rod in the power cylinder. This involves cutting the cylinder apart at the welds, installing a specific design rod and piston, and then carefully re-welding the cylinder back together. Needless to say, this is a fairly costly process in both parts and labor. Currently, there are several companies making new reproduction power cylinders for popular applications such as the 1965-1970 Mustangs. It is generally more cost effective to purchase a new cylinder for these cars than to have a new rod installed in an original cylinder. Unless you are trying to retain your original numbered and date coded power cylinder for show purposes, it is usually better to buy a new replacement cylinder or search for another rebuildable core.

Frankly, getting the old seals out without damaging the rod surface or the inside of the snout where they sit, can sometimes be very difficult. This is often due to corrosion of the area inside the snout and the "spreading out" of the pieces as you attempt to spear them and pry them out. If you attempt to replace the seals and components on your own, try to avoid if at all possible to scratch or score the smooth surface of the rod so as not to damage the surface the new seals will slide on.

If the major hard parts of your Power Cylinder are in good condition, you have a rebuild kit with all the seals, sets, boots and bushings that your Cyinder will need, you have a good set of instructions to show you how to disassemble and re-seal your Cylinder, and you have the tools and skill to do all the needed work yourself - then you can probably rebuild your own Power Cylinder.

If you are not confident that you can replace the seals without damaging the Rod or cylinder Snout, are not sure which external pieces your Cylinder rebuild will require, are not sure if you can remove and replace the Hose Seats, and have damaged threads on the Stud and Rod end - then you probably should consider having your Power Cylinder professionally rebuilt.

If your Power Cylinder is dented and the Rod binds inside it, the Rod is bent and binds when moving in and out of the Cylinder, the Stud has play and clearance in its socket, the Rod surface where it goes through the seals is pitted, scratched or worn through, or the Rod end is eaten away with rust - then you should consider scrapping your Cylinder and buying a new one.

If you are in the middle of a rebuild, or are thinking of doing one on your own, we will be glad to help you as best we can. Because we are busy rebuilding during the day, we cannot always help you by phone. But if you send us an email with a description of your problem, we will try and get back to you within 24 hours.

The Rod has a hard-chrome finish that must remain free of any damage from wear, corrosion or abrasion. It must be perfectly straight to prevent binding in the cylinder housing and excessive wear. If any part of the Rod is damaged in the area where the Seals slide, the Rod must be replaced. This involves cutting the Cylinder apart and welding back together. If the Rod is damaged on the frame mount end by corrosion or physical abuse, it must be replaced.

Rebuild kits for Power Cylinders do not usually come with replacement tube Hose Seats included. Some national name-brand rebuilders do not even bother to replace Hose Seats when doing a rebuild. It is not a competent rebuild without installing new Hose Seats. The old seats will almost always have grooves worn into them from the flare of the hoses. Most are badly grooved from over-tightening of the hose fittings or the twisting action of the hose flare against the seat while tightening down the fitting. Even if new hoses are installed, chances are great that they will leak if installed on old Hose Seats.
The Hose Seats must be installed without any damage to their sealing surface. Be aware, if you install them the way the Ford shop manual says to, you will damage them and shed metal into the Cylinder. They should be pressed into place while leaving the flared surface free of scratches, nicks or grooves..

There are two major ways the swivel stud is damaged. First is by hammering on the end of the threads trying to pop the stud out of the centerlink. The second is by using a "pickle fork" to perform the same task. Never do either of these actions as it will almost always cause greater damage. Using a pickle fork to pull the swivel stud out of the centerlink will tear the stud boot and may pull the stud out of its socket in the cylinder. Use the proper tools to remove the cylinder from the centerlink. If you are not sure how to do this, see the section on Special Tools for more information.

All the rust pitting and scratch marks are caused by driving the car with a torn or missing stretch boot. This allows dirt and moisture to get to the rod and allow corrosion to start. Dirt on the rod is "squeeged" off by the wiper seal, but eventually dirt becomes impreganated in the seals and will cause scratch marks in the rod surface. The wear-through of the shiny rod surface is due to the rod being bent and rubbing on the metal surface of the hole in the end of the cylinder as it goes in and out. All of these conditions will quickly destroy and new seals that are installed, so it is a waste of time to re-seal a cylinder with rod damage.

If the inner tube walls are rough and pitted from rust, the Cylinder is ruined. If the Piston has become too worn to seal sufficiently, it must be replaced. This involves cutting the Cylinder apart and welding back together. With the Cylinder empty of fluid, put your fingers over the two hose port holes and move the Rod in and out of the Cylinder. If you can feel a suction and pressure on your fingers, and there is resistance to the movement of the Rod, the Piston is probably good inside. If the Rod moves in and out easily with little resistance, the Piston is worn out and must be replaced.
If there are deep dents in the tube body of the Cylinder, and the Rod binds up at some point inside, the inner tube has been crushed and the Cylinder is ruined.

Though they don't always come with a rebuild kit, the Stud Boot and Stretch Boot should always be replaced if damaged or torn. Both of these boots go a long way in protecting and sealing the Cylinder from the elements. The bushings where the Rod end mounts to the Frame Bracket must be in good condition to prevent looseness which will cause severe wear and to seal out water which will rust and damage components.

Keep in mind - the outside of the cylinder that you can see, is not the cylinder that the piston slides in. There is an inner cylinder where the piston is. The outer part that you see acts as a transfer section for the fluid to get to one end of the inner liner. Just because there is a dent on the outer cylinder does not mean the inner cylinder is similarly dented and damaged. With all the fluid drained from the cylinder, see if the rod moves smoothly all the way in and out. If it moves smoothly without sticking or binding, then the inner cylinder is still round and the unit is usable. See How A Power Cylinder Works for a cut-away picture of how the cylinder is assembled and works.

The Swivel Stud Boot seals moisture from the stud socket. There is no grease fitting for this socket, so what ever grease is in it when the boot goes on is all it gets. Fortunaely, the stud requires very little lubrication as it moves in a very short arc and pivots only slightly in its socket. As long as it is not hammered on and the boot stays intact, it is good pretty much forever.

The Stretch Boot usually comes in a kit with the bushings and washers that mount the threaded end of the cylinder rod to the frame bracket. There are two rubber bushings - one goes on each side of the bracket. Through the center of these bushings, and slid over the end of the rod below the threads, is a metal sleeve. This sleeve is to protect the rod in case it comes in contact with the bracket. Not all stretch boot and bushing kits come with this sleeve. Always be sure to install this sleeve (and grease it) to protect the rod from wear and corrosion as shown in one of the pictures above.