need brake suggestion

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joshua dewitt

joshua dewitt

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1973 dart swinger, sb...a/t... planning on removing the power bakes, and going with a manual brake master cylinder, has factory discs up front, and 10" drum in rear, axle form a for with the same sized 7/8" wheel cylinders as the mopar.. I did add a line lock in system. whit master size would be best for daily street use?
1.125....+/-.... or 15/16" bore... don't want a rock hard pedal, but want it to stop comfortably..... and lock up when wanted.... suggestions?
 
IMO and I have researched and installed 1 1/8 , inch, 15/16, and 7/8 . One inch is the way to go.
 
ok so 15/16 or 1.0" does either one make a difference on the brake pedal feel, I know close to the same. I have a factory p/b unit, but not enough vacuum to keep working, added a canister and electric vacuum pump, feels like crap, almost a manual, rather it be that way and stop in my opinion. its a 318 raised compression, high rise air gap, with carb spacer, and 268/270ish mp 340 cam.... a/t with 3.50 gears. 28" tires. I also have to change converters. likes to drop out of gear rev up and goes, possible valve body issue. its a 1978/79 a999or a998 lock up model, planning on taking out and putting original a904 back in with a stall converter....@2000rpm.... thoughts?
 
I run a 15/16" lightweight m/c from dr diff on my Duster and now my Challenger as well. The challenger was converted to manual brakes from power. The 15/16" bore will create a little stiffer pedal than a larger bore, but it also produces a higher line pressure. IMO the 15/16" is the way to go. The pedal effort isn't bad at all, and the braking feel and responsiveness is great. My cars are my daily drivers too, so they get driven in all conditions, traffic, etc. The manual brakes aren't a problem at all. After converting the Challenger to manual I don't think I'd run power brakes on any of my Mopars again. And it's not a small car.
 
I'm running a 15/16 mc from a dodge Dakota (in a Demon front ssbc disc kit) and it works well. As 72bluNblu says the pedal effort is good and line pressure in a panic stop seems real good. I had a 1 1/16 mc but that small difference made a large difference in pedal effort. You do get a bit more pedal travel with the smaller bore mc but pedal feel and travel is real good. What I found is the more I drove the car the more I liked the 15/16 mc especially in a panic stop.
 
joshua dewitt said:
15/16 from doctor diff that much better than the factory 15/16 model?
Click to expand...

Well it weighs half as much, and you get rid of the old clamp style lid. As far as how it actually functions it shouldn't be much different as long as the stock one you're using is in good repair. I like the newer style better than the original. Not a fan of how the plastic reservoir looks, but oh well.

The only issue I've had with the new ones are the caps and gaskets they come with. They seem to seal for a little bit and then stop. But new caps and gaskets are easy to come by and even the Dorman versions work well. Just not the OE ones for some reason. Couple bucks to fix, the replacement ones have never caused me any issues.
 
I have tried 7/8, 1-1/32 and 1-1/8 in the same car with the same brakes? 68 cuda with 73-75 front disc's and 10 X 2-1/2 rear drums.

1-1/8 was too hard a pedal.

Currently 1-1/32 old Direct Connection alumunum. And it is pretty firm bordering on too firm. But a 110 lb female friends drove my car and she had no problem. (But she likes to go not stop)

IMO, I liked the 7/8 bore best. Order a 73-75 power disc brake MC but run it manually to get it. (Cheap at any parts store)
 
I have a 7/8"D MC bore in my 64 Valiant w/ manual brakes. I still have a hard pedal (even using DOT 5 silicone).
 
thanks for the info, going to call dr. diff for the updated 15/16 style with adaptor plate, already wining a stock manual brake push rod on e-bay right know. then will be al good.
by the way.....anyone, used ford rear axle and upgraded to large wheel cylinders for the7/8" to 1" before? any difference.
 
well got master cylinder from dr. diff. today... with the 4 to 2 hole adaptor... now once I get the manual brake factory push rod in and take out the power one, all should blot right in correct? it looks to be a modified Dakota master cylinder...
 
Your only possible issue will be with the pedal rod length and that particular MC and adapter plate. There seems to be some variation there. My son and I went with the standard MC for that reason.... no issues with the standard rod length. You'll just have to try it.

Make sure you get the new MC bench bled 100% so that any low pedal will not be due to that.

As for the larger rear wheel cylinders, that will increase braking torque on the rear brakes. That can be good or bad... it all depends on where the front-to-rear brake balance ends up. Going from 7/8" to 1" ID wheel cylinders will increase rear brake torque by over 25%; that is a significant change. I would put in the new MC first, make sure things are all working right, and then go out on some gravel and try various braking pressures at lower speeds to see which end wants to lock up first before making any further changes.

If this is too strong in the rear (evidenced by the rears locking up in the tests on gravel), then you can correct with a prop valve in the rear line or by changing the front pads to a higher coefficient-of-friction material.
 
I've had great success with the 15/16 M/C in the stock style M/C.

I've changed several 7/8 to 15/16 rear wheel cyls on vehicles with bigger boots, and a stock proportionng valve with good results. Never found a need to go 1 in.

Most important, - no complaints.
 
OK now I'm confused..... The larger bore should make the pedal stiffer and the smaller bore will have a greater mechanical advantage so it should take less effort but travel farther... What am I missing?
 
The extra travel is very little in exchange for the mechnical advantage achieved, the "feel" and ability to modulate the pedal is greatly improved, for any kind of performance applications.
 
72bluNblu said:
I run a 15/16" lightweight m/c from dr diff on my Duster and now my Challenger as well. The challenger was converted to manual brakes from power. The 15/16" bore will create a little stiffer pedal than a larger bore, but it also produces a higher line pressure. IMO the 15/16" is the way to go. The pedal effort isn't bad at all, and the braking feel and responsiveness is great. My cars are my daily drivers too, so they get driven in all conditions, traffic, etc. The manual brakes aren't a problem at all. After converting the Challenger to manual I don't think I'd run power brakes on any of my Mopars again. And it's not a small car.
Click to expand...

This is what I was wondering about.... pretty sure he meant to say otherwise but don't need to have some guy buy a large bore master and have to use two legs to stop!
 
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