View Full Version : power brakes conversion

10-25-2006, 12:54 PM
has anyone out there had experience upgrading from the old hydovac p/b to a newer vacum assisted sytem. What all would be invalved. Is it even addvisable.
My hydrovac seems to work but seems like your pushing thru a straw and the pressure required to stop seems excessive. I'm most likley comparing it to my 95 chev truck which stops very easily with not very little pressure on the peddle.

10-25-2006, 04:54 PM
No experience yet, but I'm thinking about the same modification on my Hawk. I've never had a Hydrovac that impressed me. If you have to move the battery and starter relay to the trunk. House the battery in a marine case and bolt it to the ledge under the rear window shelf. Use #00 welder cable for the heavy stuff. Drill a hole in the floor and route the negative cable down thru, using a steel electrical box connecter. Clean off a spot on the frame and attach the negative cable. Drill a second hole for the starter cable, fasten it the same way and run it along the frame to the starter, using plastic stays on the frame rail. The relay can be mounted anywhere close to the battery and you can then extend the old wiring to the relay.
As far as the brake system, the 63 Lark has a suspended pedal, but the underdash mount is too large for a Hawk. You'll have to cut and reweld it, then reinforce the firewall with some 14 gauge and mount the lark booster and dual master. Over the years, I have pictures of probably 5 different setups, mostly GM applications, so it can't be rocket science. I'm trying to stick with Stude parts, but the disk brakes may need a larger MC bore.

John Kirchhoff
10-25-2006, 05:09 PM
My Hydrovac was rebuilt not long before I bought it and the brakes work as easily as any other vehicle on the place. On an old Hydrovac I worked on, it wouldn't work either until I found the small piston (can't remember the official name) located behind the "breather" was stuck. It's pretty small and it doesn't take much rust to bind it up.

One chore everyone ignores (myself included) is the failure to change the brake fluid. The old stuff absorbs moisture and when it can't hold any more, any additional moisture is free to go eating on the metal parts. However, I have changed fluid regularily on my 27 year old motorcycle and the brakes have worked flawlessly the entire time and have never been worked on. By the way, the DOT 4 brake fluid isn't an answer to moisture absorption. Sure, it won't do so, but any moisture that gets into the system then immediately settles to the bottom where it can go on its merry way rusting up things. At least the old stuff will keep a certain amount of moisture in suspension and out of trouble unless you wait too long. That's why I've never considered switching fluid types.

Dan White
10-26-2006, 09:07 PM
The other issue on the Hydrovac is that you need to add 1 oz of Needsfoot oil (annually) through the little hole with the rubber stopper on the back side of the Hydrovac body where the main piston is located. See the service manual. If that has not been done in a long time the Hydrovac will slowly become unusable. This may be your problem. My '64 Hawk's unit will put you through the windshield if you punch on it, does not take much effort at all. One other thing if you replace the fluid make sure you bleed not only the brake cylinders but also the Hydrovac unit itself there should be two bleeders on the front of the unit.

Dan White
64 R1 GT
64 R2 GT

10-26-2006, 09:15 PM
If you think a Hydrovac requires too much pressure on the pedal to stop the car, there's something wrong with the Hydrovac. I have never driven one that didn't require an adjustment period because the brakes were too sensitive.


55 Commander Starlight