Bendix Hydrovac



The Bendix Hydrovac Brake Booster Overhaul


With winter and shorter days fast approaching and my 1964 Chevy C60 dump truck stripped down to a rolling chassis, I decided to push her into the back yard until Spring and work on a few of the smaller parts that I had removed during the disassembly process. The two 10’x12’ sheds that I had built the previous year came in handy for my toys. One housed my two Honda 500cc utility 4x4 ATV’s and the other all the parts that I had removed from my truck. I bought 3 wire Metro racks and after assembly bolted them to the studs and then inventoried all the parts on the shelves. Having already restored the heater box assembly, radiator support panel top cover, cab cowl vents and several other smaller items, I turned my attention to the Bendix Hydrovac brake booster.


Initial Prognosis


As you can see from the thumbnail images below, the Hydrovac unit, although functional, was pretty tired looking and required more than a casual cleaning and repainting. All external surfaces were rusted and partially covered with tar and debris from years of road abuse and, as I later found out, most of the internal rubber components were in pretty sad shape.  In reality the unit was in surprisingly good shape given the fact that it hung beneath the cab and endured 40 years of the elements.






After removing the unit from the chassis of the truck I noticed a small identification tag on the locking ring bolt with an alpha-numeric identification code. The first line of the code was 2501847 and beneath that was 4E23 A3. I contacted “Spanky” Hardy, an expert on Cab-Over Engine (COE) rigs and frequent contributor to The Stovebolt Page and he graciously offered his expertise and research services. Spanky indicated that those were Bendix part numbers and that they cross referenced to GM part number 3874183.  

An exhaustive search of the web didn’t yield any information regarding parts or overhaul kits for this Bendix Hydrovac unit. Just when I was about to abandon the project for the winter and work on something else, I stumbled across a link that lead me to another link that lead me to Reman Incorporated. I checked out the site and it seemed encouraging, so I dropped them a very detailed e-mail with all the particulars about what I was trying to obtain. The very next morning I received a response from one of their customer service representatives indicating that they not only had an overhaul kit for my Hydrovac but also offered completely remanufactured units (core charges applied). I subsequently called the company to get verbal confirmation and also just to say hello. I had a great conversation with their representative and, as an added dividend, discovered that they can also provide master cylinder and brake cylinder overhaul kits (or remanufactured assemblies) for my 2-ton truck.




With the overhaul kit on order it was time to disassemble the Hydrovac. Prior to tearing it apart I studied my 1963 Chevy Truck Shop Manual. One chapter is devoted to various brake boosters and includes a very detailed overview of how to disassemble, inspect and reassemble the various power booster units that came in our trucks. Also included are detailed illustrations or “exploded views” of the various booster units. I took many digital images from all angles to properly photo-document what goes where. Although the unit is pretty simple I like to get into the habit of photo-illustrating all the restoration activities for future reference and inclusion into my web site. I then took it apart and kept all the parts in a small Rubbermaid tray for safe keeping.






Initial cleaning was done with a stiff bristle brush to remove the heavy dirt and debris. After subsequent cleaning in the parts tank to remove any grease and oil I washed the parts in soapy water and dried them. This may seem like over-kill, but it helps keep the reclaim unit on the sandblaster cleaner and eliminates the possibility of getting grease and oil products in the system. Prior to sandblasting the valve body I used rubber cap plugs and/or electrical tape to cover all the valve ports and cylinder bore. I knew that some media would find its way inside, but this precaution was simply to prevent pressurized media from hitting the honed areas. Sandblasting was pretty straight forward and in a mere couple hours I had all the pieces of the Hydrovac cleaned to bare metal. I used clean cotton cloths pre-moistened with isopropyl alcohol to wipe any media residue for the larger assemblies. For the valve body I used a variety of nylon bristle bore brushes and warm soapy water to clean the cylinder bore, ports and threaded openings. I didn’t want to take my nice clean bare metal assembly and put it in a sink full of warm water, but I couldn’t think of a better way to completely remove any and all media residue that undoubtedly found its way into the valve body. After a thorough washing and rinse in warm water, I dried it using a clean towel and then further with a heat gun to ensure there was no residual moisture. This approach may seem odd, but I couldn’t justify the cost and time necessary to find a company that has a chemical dipping tank.




I am restoring my truck as close to original as possible; however, I am not going overboard because I plan on using my truck and, other than an occasional weekend rally, have no intentions of showing it. As such, I decided to choose my own colors for the Hydrovac unit. Given the few pieces I had to paint I elected to use Rustoleum from the can; a product readily available at most hardware stores and home centers. The primer was a standard light grey and I chose Hunter Green for the valve body and a hammered finish Gold for the diaphragm dome halves and locking ring. I again inserted cap plugs into the plumbing connections of the valve body, and also masked a circular area on the half of the dome that mates with the valve body. Given the inherent porosity of spray can paint,  I applied 3-4 light coats of primer to each piece, allowing approximately 15 minutes between coats to allow the previous coat to partially dry and also to prevent running. Once the final coat was applied the pieces were allowed to dry for a minimum of 48 hours. Each piece was then lightly sanded using dry #400 wet-or-dry sandpaper and wiped down with a clean dry cloth. The color coats were applied in the same manner as mentioned above.





Parts Arrived


The overhaul kit from Reman Incorporated arrived via UPS which included the main and control valve diaphragms, cups, o-ring, seals and control valve spring. I also purchased 3 new bolts used for securing the valve body to the dome assembly.






Assembling the Hydrovac was simple and straightforward and step-by-step instructions were clearly illustrated in my 1963 Chevy Truck Shop Manual. Putting the Hydrovac back together was merely a reverse of the steps used to disassemble the unit. As received, several areas of the rubber diaphragms were covered with a white powder-like residue. I suspected this was a release agent used during the molding process, so I cleaned it off using “Bleach-White” (a readily available product used for cleaning white walls and raised white letters on tires) and warm soapy water. All rubber components were lubricated using a light coat of brake fluid prior to installation. The hydraulic cylinder components were assembled first and inserted into the cylinder, then the control valve was assembled and installed and finally the main diaphragm assembly. All moving parts were exercised to ensure free movement prior to completing the reassembly process. The following pictures illustrate the completely restored Bendix Hydrovac Power Booster.




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