Upgrades to improve braking
73 duster drum in rear disk up front manual brakes. any thoughts on common upgrades to improve braking. Car does stop ok with heavy foot pedal. Not sure how safe in a panic stop though.
Looks like I am only pulling 12 vacuum so I think a power booster is out
Ok so the only time he booster does not, or may not, work 100% is when the vacuum drops below it's minimum threshold required vacuum to achieve maximum assist. So when does this occur during braking? It doesn't,unless you have a monster cam and a loose convertor.
The faster you drive, the higher the rpm, and up to a point the higher the vacuum. The point is,if the car is moving, it is almost always higher than the minimum required.
Imagine this;
you are going 108mph and doing 5000rpm at WOT with 3.55s when you lift throttle and hit the brakes. If your check-valve is working right, that booster is fully evacuated and ready to provide maximum assistance.It has been since right after the car started moving. So now you are rapidly decelerating, and engine braking is keeping the vacuum up. So everything is working as it should.
So imagine you are crossing 60mph, now at 2650rpm, still hard on the brakes in third gear, and the throttle valves are closed.And engine vacuum is at or near maximum. So the assist is still 100% functional.
Now imagine crossing 40mph now at about 1760 rpm, with the throttle valves still closed. And engine braking is now fast fading, but the vacuum is still above the minimum threshold. Now we are getting to the nitty-gritty.The engine vacuum is approaching the minimum threshold, so the check-valve better be working. As long as you do not lift off the brake pedal, the vacuum chamber is more or less sealed, so braking continues as usual.
Now imagine, still hard on the brakes at 20mph, rpm now close to idle, but you haven't lifted so it's still business as usual.
Now from 20 to zero, you will be lifting off the brake pedal to prevent loc-up. So this is the critical zone. But guess what? you are reducing pedal pressure anyway. So even if the vacuum drops below the threshold, it doesn't much matter; cuz you just lift a little less.
The way I see it,for a streeter, there are just 3 times when the minimum threshold might be an issue;
1) At first start-up and backing out of the driveway,with an automatic,and with a warm engine off choke. In reverse, braking requires a bit more pedal pressure, due to the way the rear brakes work. And with an automatic two things happen; Firstly, the idle usually drops about 50 to 100 rpm when you drop it into gear, which reduces vacuum, and secondly, you don't blip the throttle before easing out the clutch. So the easy cure for this is to blip the throttle to evacuate he booster, before putting her into reverse, problem solved.
2) Multiple modulations with the trans engaged,and the throttle closed. Try to imagine the situations when this would occur. I get parallel parking, and slow traffic. Here the solution is the 15/16 M/C; I like it a lot.
3) Sitting at a stoplight, in gear,with a leaky check-valve. Simple solutions.
So my point is; yeah the fellows gave you a few good options, but if all you want is a little assist, don't think a booster can't work at low idle vacuum. I have a manual trans, and have had the 292/292/108 cam and the booster worked just fine. In fact I didn't even know it was supposed to be a problem until I came to FABO. With the current 230 cam, I never give the booster a thought, I just drive.