Thanks to a lot of helpful advice 8 months ago I finished rebuilding my '49 Hydrovac, and finally installed it last week along with new master cylinder. However I didn’t put the oil in its tank yet, where would you pour it in? And how much? I know it’s not much, maybe a cup or less. I read of one guy using mineral oil, does that sound right? Thanks much
1949 Chevy 6400 two ton, 2 speed rear end, 235 engine, 13 foot hydraulic dump bed.
Can you take and post pictures of the rear of the Hydrovac canister body? From what I've read in the shop manuals, there seems there should be an oil filler plug on the back side of the main canister that is where the oil should be placed. The 1948-51 Chevy Truck Shop Manual (see below) in the rebuild reassembly instructions for the Hydrovac says to fill to the level of the filler plug. It does not indicate a capacity there.
In the Lubrication information portion of the shop manual (see second pic below), the portion covering the Hydrovac says "One ounce of Bendix Vacuum Cylinder Oil should be added every 10,000 mile intervals or each six month period...".
My guess since you just reassembled it after rebuild would be to fill to the level of bottom of the filler plug, then maintain based on mileage/time as noted in routine service.
On the type of oil to use, many recommendations I read about to replace "Bendix Vacuum Cylinder Oil" which is no longer available, is to use "Neatsfoot Oil". It's formulated to be used on leather products, so should work for your new components.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
A day without laughter is a day wasted- Charlie Chaplin When wrestling a grizzly bear, you have to keep at it until the bear gets tired, not when you get tired. 1948 Chevy 2-Ton
The Bendix HydroVac has a small pipe plug (1/8" npt) at the bottom front of the vacuum canister, fill to the level of the plug with the unit in a level horizontal position. The oil is only to keep the leather vacuum piston seal pliable, as the piston moves within the cylinder, the oil wicks its way around the leather. I used motorcycle shock oil.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
Good to know, thanks for all the good info. I'll be back out there in a couple days and get it done. I was thinking it might wick up to the top. When I took it apart there was only about a teaspoon of oil in it, but the brakes were still working pretty good. I only took it out to make sure it was in top condition, as long as the master was off.
1949 Chevy 6400 two ton, 2 speed rear end, 235 engine, 13 foot hydraulic dump bed.
I have been curious about this as well. I looked and sure enough there is a plug on the front end of my Hydrovac unit. Here is a picture, the plug has a square head. The diagram in my 1955 shop manual does not show this plug, but it gives a clear description of the operation. Focusing on this plug, a simple description:The power cylinder has vacuum in it on both sides of the power cylinder piston when the engine is running and the brake pedal is not being pressed. When the brake pedal is pressed, atmospheric pressure is applied to the front end of the power cylinder. So from this the plug needs to be air tight. I've never added oil, I will now.
Yeah - The cutaway drawing in the manual through me for a loop until I looked at an actual hydrovac too.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
