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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Apr 2010 Posts: 42 New Guy | | New Guy Joined: Apr 2010 Posts: 42 | I posted to the welcome forum last week about my 1948 1.5 ton that I got in April. You can see pictures of her there if you are interested. She is in pretty good shape and rust is not a problem on her.
My truck has a hydrovac booster and I've search the site for answers about bleeding and filling but haven't found anything helpful. It is suggested to fill the power cylinder with air tool oil and fill the hydraulic part with brake fluid...looking at the drawings it is not clear to me where these places are located. I'm guessing the power cylinder is filled at the little square plug about 3/4" of and inch from the bottom of the unit...where do you add the brake fluid? Do you just fill it from the master cylinder under the cab floor and force it thru the hydrovac or is there a place on the hydrovac to add brake fluid? I know it sounds stupid but I don't want to add the wrong in the wrong...u know? Thanks for any help.
Motoswiz | | | | | Joined: Jul 2001 Posts: 3,887 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Jul 2001 Posts: 3,887 | there's a good hydrovac build tip here, should learn ya all about'em Bill | | | | | Joined: Apr 2010 Posts: 42 New Guy | | New Guy Joined: Apr 2010 Posts: 42 | Thanks Bill, yeah, I read all that and it still doesn't address adding brake fluid to the hydrovac unit itself...I guess I just pump it from the main under cab cylinder. there is a plug on the top of the unit but the drawing and part description don't address it becasue it is on the other side of the drawing.
| | | | | Joined: Apr 2010 Posts: 42 New Guy | | New Guy Joined: Apr 2010 Posts: 42 | Very similar to the one in that picture, crenwelge, but mine is longer in the main cylinder section. ...thanks for posting it. I'm charging my camera batteries so I can post a couple pix of the plugs.
Thanks, | | | | | Joined: Feb 2006 Posts: 1,867 Shop Shark | | Shop Shark Joined: Feb 2006 Posts: 1,867 | It is suggested to fill the power cylinder with air tool oil and fill the hydraulic part with brake fluid...looking at the drawings it is not clear to me where these places are located. I'm guessing the power cylinder is filled at the little square plug about 3/4" of and inch from the bottom of the unit...where do you add the brake fluid? Do you just fill it from the master cylinder under the cab floor and force it thru the hydrovac or is there a place on the hydrovac to add brake fluid? Simply put, yes. You won't need more than an ounce or two of fluid in actually lubricating the power cylinder. The internal parts are lubricated as the brake fluid passes through the hydraulic cylinder. There aren't any other places to add fluid. Jeff | | | | | Joined: Aug 2010 Posts: 32 Apprentice | | Apprentice Joined: Aug 2010 Posts: 32 | http://chevy.oldcarmanualproject.com/There is a section dedicated to just the hydrovac booster. I'm sure that it will tell you how to service the unit. | | |
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