Switch to manual brakes makes car run better?

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1973dust

1973dust

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I wasn't sure which sub-forum this belongs in but here goes. I finished converting from power disc/drum to manual a few weeks ago and love the manual brake feel. I also installed a new 15/16 master from Dr Diff. Car is a 73 Duster with a 74 318 smogger with Summit K6900 cam, Performer intake, 600 Edelbrock carb, decent advance curve, and duals off the stock manifolds. Drivetrain is a 904 with stock converter and a 2.76 rear. It's obviously no race car. It seems like I have more power and better throttle response after the brake conversion and I'm trying to figure out why. I've got a few ideas but would like opinions from people much better at this stuff than me. 1. Ported vacuum advance adding to the timing curve due to no vacuum lost to booster. (Booster was possibly leaking vacuum?). 2. Better stronger vacuum signal to the carb. 3. Fuel curve issue on some cylinders due to the location of the booster vacuum tap on the dual plane intake although the plugs have always looked the same between cylinders. The most obvious to me was more brake drag before due to some booster/master/brake pushrod issue but the car seems to roll the same in neutral as before and coasting while driving seems no different. I also had never noticed any lining smell or abnormal brake heating. All I can think is that the change in vacuum fixed a tuning issue I didn't know existed. If you took the time to read this short novel, thanks for any and all thoughts. I feel like I made a "demon tweek".
 
Apologies for the format of the above. It looked good on my phone before I posted.
 
I’m gonna be going from power drums to manual disc in my 68 Dart.. the booster just takes up so much room around the engine are.. I figure manual disc is still a great upgrade and have more room for activities
 
Your booster was causing a vacuum leak. Could have been all the time or just sometimes.

Did you do ANYTHING else to the car? Or just remove the vacuum booster?
 
Nothing but remove the booster, install the new master, and bleed the brakes. From day one with that rebuilt booster, the brakes were super touchy. I'm wondering if it was ever right.
 
FlamesAreWicked said:
I’m gonna be going from power drums to manual disc in my 68 Dart.. the booster just takes up so much room around the engine are.. I figure manual disc is still a great upgrade and have more room for activities
Click to expand...
Yeah, I can actually see the bulkhead connectors now.
 
I assume you're being serious. That is an odd one.
 
I know you're just joking but I notice every little tick, rattle, vibration, etc way more if my wife is with me.
 
My wife got banned from riding with me some two decades ago.
I got sick and tired of hearing her chirping as regards her neck getting a workout, no matter how gentle I drove; and she being almost 4 years my junior, sheesh.
Not to mention her right foot constantly looking for a brake-pedal, sheesh.
Or
the more than once she instinctively reached for the steering wheel, double-sheesh!
Or
there's no radio, the car is too loud, or too rough, or too something; fine
then stay home ....... darling........................... don't wait up, honey.
 
AJ/FormS said:
My wife got banned from riding with me some two decades ago.
I got sick and tired of hearing her chirping as regards her neck getting a workout, no matter how gentle I drove; and she being almost 4 years my junior, sheesh.
Not to mention her right foot constantly looking for a brake-pedal, sheesh.
Or
the more than once she instinctively reached for the steering wheel, double-sheesh!
Or
there's no radio, the car is too loud, or too rough, or too something; fine
then stay home ....... darling........................... don't wait up, honey.
Click to expand...
Lol
 
It could absolutely run better removing the power brakes since they are operated by engine vacuum. Any vacuum leak from something malfunctioning could have made it run a little rough, idle a bit high and have an erratic, hard to control idle.
 
RustyRatRod said:
It could absolutely run better removing the power brakes since they are operated by engine vacuum. Any vacuum leak from something malfunctioning could have made it run a little rough, idle a bit high and have an erratic, hard to control idle.
Click to expand...
That's one of the funny things. I don't notice much difference at all in idle quality. It always seemed to be running well before but maybe a little weak. I had just decided I was expecting too much but it never felt as strong as other 318's I've had. it honestly feels like I put the missing plug wire back on when driving it.
 
AJ/FormS said:
My wife got banned from riding with me some two decades ago.
I got sick and tired of hearing her chirping as regards her neck getting a workout, no matter how gentle I drove; and she being almost 4 years my junior, sheesh.
Not to mention her right foot constantly looking for a brake-pedal, sheesh.
Or
the more than once she instinctively reached for the steering wheel, double-sheesh!
Or
there's no radio, the car is too loud, or too rough, or too something; fine
then stay home ....... darling........................... don't wait up, honey.
Click to expand...

Man, can I relate to that.
 
1973dust said:
That's one of the funny things. I don't notice much difference at all in idle quality. It always seemed to be running well before but maybe a little weak. I had just decided I was expecting too much but it never felt as strong as other 318's I've had. it honestly feels like I put the missing plug wire back on when driving it.
Click to expand...
Then it wasn't too bad of a leak, but a leak nonetheless. But you fixed it! lol
 
1973dust said:
Car is a 73 Duster with a 74 318 smogger with Summit K6900 cam, Performer intake, 600 Edelbrock carb, decent advance curve, and duals off the stock manifolds. Drivetrain is a 904 with stock converter and a 2.76 rear. It's obviously no race car.
Click to expand...
278/288/112, and 204/214@050
on a ~ 7.8 Scr smogger, with a stock convertor and 2.76 gears.
How is your power below 3000rpm?
How you liking passing gear at 60 mph?
 
FlamesAreWicked said:
I’m gonna be going from power drums to manual disc in my 68 Dart.. the booster just takes up so much room around the engine are.. I figure manual disc is still a great upgrade and have more room for activities
Click to expand...
I have a 70 Swinger and have been thinking the same thing, have you come across a thread outlining the conversion/parts involved? I have power drums/front disc. I guess with all the talk about master cylinders, bore size, lack of master cylinders, etc, Im just wondering what MC we should use.
 
AJ/FormS said:
278/288/112, and 204/214@050
on a ~ 7.8 Scr smogger, with a stock convertor and 2.76 gears.
How is your power below 3000rpm?
How you liking passing gear at 60 mph?
Click to expand...
It actually is no worse than stock on the low end, at least at part throttle, and midrange power is much improved. Idles at 650-700 with 18" of vacuum. I seldom really lay into it and it would probably run about as well with the stock cam but I'm pretty happy with how it runs. I've got a 3.55 rear to install when I get to it but I enjoy driving it pretty well as it sits. I will say I may have got a lucky tolerance stack up in the engine as it still pumps 150ish with that cam. Shortblock and heads are 100% factory original with about 42000 miles.
 
70SwingerGuy said:
I have a 70 Swinger and have been thinking the same thing, have you come across a thread outlining the conversion/parts involved? I have power drums/front disc. I guess with all the talk about master cylinders, bore size, lack of master cylinders, etc, Im just wondering what MC we should use.
Click to expand...
FWIW, the consensus I found was to use a 15/16 bore rather than factory 1 1/32 when going to manual brakes, at least for my 73. I assume that would also apply to a 70. I purchased a 2 bolt master and adapter plate from Dr Diff and I already had a manual pushrod from the original non-power 4 wheel drums. I was able to easily reposition my NiCop lines to the master as they bend pretty easily. If still running factory lines I think you might have to replace from the master to the combination valve as I don't know that it would be very easy to tweak those steel lines. I will say, if you value original appearance, the 2 bolt is not for you. I have had both rebuilt and new original style and neither worked properly for very long so I decided to try my luck with a newer style master.
 
No problem, if you have any other questions, feel free to ask. I'm just regurgitating the info I've stolen from others on here. It would be hard to convince me that there's a more knowledgeable group of people anywhere. FABO has become my go-to for even non-Mopar info. It seems that, no matter what info you need, someone on here can help and it's nice to be able to be the someone once in a while.
 
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