I grew up with 60/70's cars with real power brakes including 3 Caddys, a couple big Mopars, a 1971 98 sedan and 1975 LaSabre. As I recall (and maybe this is nostalgia) in all those cars the brake pedal-throw was a half-inch or so and I had to use my little toe or would lock up the brakes. The brake pedals always felt "hard" and required very little movement to apply the brakes. Fast forward 30 years and I got my 70 98 with everything on the car stock. I initially replaced the M/C, drums and rear hardware, calipers and rotors (finding them was a miracle), flushed the system and ran DOT 5. The brakes work fine to stop the car, but the pedal feel is like modern cars, it travels an inch or so before the brakes start to engage, and then maybe another 3/4 before they are fully applied.

I tested the brake booster and it was losing vacuum a little, so I had it rebuilt. The car at warm idle has 19 inches vacuum at the booster hose end. I replaced the hose between the booster and the metal pipe going into the manifold. The check valve is new. I rebled the brakes a couple times now. I don't know why, but not having face=windshield stopping power is driving me crazy and I am becoming fixated on it and may need to start therapy.

Am I remembering the brake sensitivity of my old cars wrong, or is there something else I could do to make mine more sensitive? Or are some cars just more sensitive than others?

 

Yes, there is.

You could go back to the stock system.

The stock system uses conventional brake fluid.

You installed DOT 5 silicone brake fluid.

Conventional brake fluid tends to absorb water, which promotes rust and lowers the boiling point, but which otherwise does not affect the compressibility of the fluid.
Silicone brake fluid absorbs air, which makes it slightly compressible, leading to spongy brakes.

Your system will probably be fine if you install DOT 3, BUT I'm not sure whether you can, because there are compatibility issues between silicone and conventional, and I do not recall which way the problems go, whether it's conventional-to-silicone or silicone-to-conventional.

Someone else here can answer the question of whether all the rubber dissolves when you add conventional to silicone or the other way around.

- Eric

 

I think either way requires a complete flush, except I heard to DOT 5 from DOT 3 is nastier since the silicone will glob when it comes into contact with glycol making a real mess in all the lines, etc. When I chose to use DOT 5, I knew people said it was "spongier", but I didn't think it would mean an inch or more of pedal travel spongy. I run DOT 5 in my Harley and my front break locks up with hardly any lever travel.

Do you think DOT 5 makes real power brakes feel like modern power assist brakes? Is the sponginess that bad?

It is possible I still have air in the lines due to using a Mighty Vak for the bleeding. Maybe I should try again with the two-man method.

 

My experience has been that most brake feel complaints are due to air still in the lines. Also, pedal travel is a function of how well the drum brakes are adjusted. Excess travel until the shoes touch the drums translates to excess travel at the pedal.

 

Let me give the brakes another monster bleed and I will check those star wheels and see how it turns out.

 

It's purely subjective, but every car with silicone fluid that I have driven has felt distinctly odd and spongy, and borderline unsafe (though I'm sure they were safe).
It's just an odd, "unnatural" feeling.

Certainly, it could be an incomplete bleed, but my money's on the brake fluid.

In my personal opinion, silicone is great for collectors who have a lot of cars but drive them very seldom, and need to have operable brakes for moving around the garage and in and out of trailers, because it will not promote decay, but for cars that are driven, regular brake fluid is the only option.

- Eric

 

They're supposed to feel GREAT!

 

I run dot 5 and my brakes are great with only 1/2" travel or so. And I only run around 14 inches of vacuum.

 

As I have never run dot 5, I don't know if it will make a difference. I agree with Joe that freeplay in the pedal is set by the brake adjustments. Spongy brakes are usually caused by air in the system.