Brake experiment

If a new booster doesn't solve the problem like it has for some folks -
You could consider putting a manual-brake pedal on with the vacuum booster (and evaluate as prudent).

I did this to my 65 Fury years ago by mistake, before I knew that the pedals differed between MB and PB. (by years ago, I mean about 30 of them)
I converted the car to disc brakes, installed the disk-brake booster (all parts from a 71 C-body), had to modify the '65 pedal bracketry a little for the nose of the booster, but otherwise everything fell together like it belonged. Modifying the brake pedal seemed par-for-the-course as the parts were 6 years apart, Fusey vs Slab.

When finished, the brake pedal always felt soft. (I'll spare all the diagnostic checks and all the 'experts' who couldn't solve the problem)
But the car stopped really well, better than our then-new 91 Buick, and on par with our 91 Camaro.
The pedal has the longer travel of the manual brakes and reduced effort of power brakes.

Might it give the desired result here? You would need to decide for yourself, though.
It definitely would need review for whether it over-strokes the booster, but that might be a simple geometry calculation between the 2 pedal setups. (i.e. do they have near-equal pushrod travel?)
My hunch is that it might not matter, as the MC piston travel (and therefore pedal travel) depends on when the hydraulic pressure causes the brake parts to bottom out at the wheels.

As I think about it, I suppose one might be able to over-pressurize the hydraulics due to extra mechanical leverage with the vacuum boost, but I suspect that SAE engineering principles dictated for safety factors in the seals, hose construction, etc, to be far more robust than the hydraulic pressure in the system. Or does the booster simply add a constant amount of additional force, independent of the force from the brake pedal?

And regardless - in normal driving, you won't be pushing the pedal anywhere near as hard as in a factory MB or PB setup, and obviously you'll adjust your leg to the required braking.

So it would boil down to - if you pushed the brake pedal as hard as physically possible, harder than you'd ever need to, like you were trying to break something - what happens?
Does somethign break? Hose burst? Wheel cylinder cups blow out? Does the MC piston merely bottom out in the bore? Or nothing unusual happens?

One advantage in this setup over mine - it is using the drum-brake booster, which gives less boost than the diskbrake booster in mine, so less force available to break something.
I also considered switching to manual brakes but at this time I am going to try the vacuum limiter first. It should reduce the power of the booster so that I don’t get that touchy feeling. It will require some testing to get it right but that’s easy. Once done I will let everyone know how it works out.
 
But keep in mind that the hard MB pedal might not get wife approval, which is your main goal, correct?

For the vacuum limiter:
Rather than that expensive red one, you could try a simple ball valve and some barbed fittings and see how it works?
Then buy the expensive one as a permanent cure?

I would be curious how the limiter affects maximum braking, so please report back when you've completed.
 
But keep in mind that the hard MB pedal might not get wife approval, which is your main goal, correct?

For the vacuum limiter:
Rather than that expensive red one, you could try a simple ball valve and some barbed fittings and see how it works?
Then buy the expensive one as a permanent cure?

I would be curious how the limiter affects maximum braking, so please report back when you've completed.
A ball valve would act like an orifice simply restricting vacuum during brake application. When you’re not using the brakes the vacuum would still build in the booster and your first brake application would still be at full vacuum. The regulator would only allow the set vacuum at all times. Also my experience tells me to buy something that is good and reliable not a cheaper model because I want a good test and if it works it will stay on for the long run. It’s a price of doing this.
For sure I will advise everyone of the results. I have formulated a test procedure to confirm if this is good.
As for the wife we had a 69 Monaco with standard brakes and she loves driving it so a harder pedal is no problem.
 
A ball valve would act like an orifice simply restricting vacuum during brake application. When you’re not using the brakes the vacuum would still build in the booster and your first brake application would still be at full vacuum. The regulator would only allow the set vacuum at all times. Also my experience tells me to buy something that is good and reliable not a cheaper model because I want a good test and if it works it will stay on for the long run. It’s a price of doing this.
For sure I will advise everyone of the results. I have formulated a test procedure to confirm if this is good.
As for the wife we had a 69 Monaco with standard brakes and she loves driving it so a harder pedal is no problem.

Any news on the touchy brakes?

What you are describing is poor pedal modulation. In other words, it's not how hard you push the pedal but how far it travels. Bad news in rain or frozen. That's a bad thing. We don't want that.
What we want is how hard we push, not how far we push.

As I'm sure you know by now your 66 single pot power m/c piston is 1 inch. The 69/70 Fury twin pot power disc/drum m/c is 1.125 inch. That would make a noticeable improvement. The larger front brake reservoir will not come into play. No proportioning valve needed.
But the little pressure retaining spring valves at the m/c line connection that keep the shoes from backing off to far would be a consideration?

Reasonable thing to do, as you said, is to go with a twin m/c. I'm to chicken to drive without them.
 
Any news on the touchy brakes?

What you are describing is poor pedal modulation. In other words, it's not how hard you push the pedal but how far it travels. Bad news in rain or frozen. That's a bad thing. We don't want that.
What we want is how hard we push, not how far we push.

As I'm sure you know by now your 66 single pot power m/c piston is 1 inch. The 69/70 Fury twin pot power disc/drum m/c is 1.125 inch. That would make a noticeable improvement. The larger front brake reservoir will not come into play. No proportioning valve needed.
But the little pressure retaining spring valves at the m/c line connection that keep the shoes from backing off to far would be a consideration?

Reasonable thing to do, as you said, is to go with a twin m/c. I'm to chicken to drive without them.
To be honest I haven’t gotten around to it. This summer is quickly slipping by and I have been too busy with other things. I am still hoping to get to it this year before I park her for the winter. I thought retirement would give me more time but apparently it doesn’t.
 
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