booster addition to manual brakes

Hi Guys,
Hoping you can point me in the right direction. I had my first drive in my 68 Plymouth Valiant on the weekend. It is a base model 2 door with a slant 6 = manual drum brakes all round. The brakes did the job but compared to driving my other cars I think it can be improved. As you know safety first. So the question I have is what would be the best way of adding a booster to my current set up without spending big bucks IE is there a booster that I can buy and simply bolt onto the master cylinder? Or will I need to make other modifications to the brakes? Any ideas or recommendations you have will be much appreciated. Thank you, Ron.

You could change to a smaller bore M/C, that will give you a better "mechanical advantage/ leverage",, this will reult in less pedal effort with slightly longer stroke..

Check you M/C bore,, and if over 1 inch,, replace with a 15/16 bore M/C,, or with adaptor plate,, one of the newer plastic 7/8' bore M/C..

You might just want to put some miles on,, exercise you leg,, and you may feel it's quite acceptable..especially if they're new brakes.. jmo

hope it helps..

inertia said:

You might just want to put some miles on,, exercise you leg,, and you may feel it's quite acceptable..especially if they're new brakes.. jmo

hope it helps..

Click to expand...

Unless you are travelling on a highway behind a BMW! Don't hope. Do it right. O

I'd ditch the front drums for some disks before adding a booster, disk brakes stop a lot better, front drums just plain suck. Power brakes are no safer than manual brakes, the booster just makes the pedal easier to push.
Seeing that you're from Australia means this is probably right hand drive slant 6 car, right? You won't have enough space on the firewall for a typical vacuum booster. Every Aussie slant six car I've seen with power brakes has a funky hydro-vac set up on the passenger which I would shy away from just because of the added lines and the additional slave cyl just means more potential failure points in the system. If you have power steering you can run a hydro booster if you have enough room.

No reason for a booster w/ drum brakes. The design makes the shoes "self-jam" against the drum, which greatly reduces pedal effort. As mentioned, a smaller bore MC would make the pedal easier, for slightly more travel. I would first refresh the brakes. Drums are much more sensitive to gunk on the liners.

Don't believe all the claims that drums can't stop the car. If they can skid the tires, you can't do any more braking than that. Drums will overheat easier, like if one (stupidly) rides the brakes downhill (reason for U.S. mandate for front disks ~1973). They should not overheat and fade from an occasional stop from 70 mph. Might be marginal if braking from 100 mph.

Treblig said:

If you switch to 73/74 charger brakes (rotor and calipers) you can disconnect the rear brakes. My '69 Barracuda stops so good I only need rear brakes to pass inspection (emergency brake). The difference is day and night with no brake fade!! The most expensive part was the 73 and up B body spindles and those were only $75-$125/pr and the used LBJ upper control arms.....all the other parts came from O'reillys (rock auto is even cheaper).

Treblig

Click to expand...

Sorry, but running without rear brakes cuts your stopping power by something like one-third. Yes, the front brakes do most of the work, because of weight transfer. But you can only stop as fast as you can generate friction between the tires and the road, and the rear tires DO generate friction. You are giving away 25 to 35% of the potential stopping power. Not to mention you are also giving up directional control over the rear half of the car under braking and in many other circumstances. You seem to think that because these disks are better than your old brakes that you only need fronts. But if you hooked up the rear drums you'd stop even better (given correct proportioning) -- why wouldn't you do it?

BillGrissom said:

No reason for a booster w/ drum brakes. The design makes the shoes "self-jam" against the drum, which greatly reduces pedal effort. As mentioned, a smaller bore MC would make the pedal easier, for slightly more travel. I would first refresh the brakes. Drums are much more sensitive to gunk on the liners.

Don't believe all the claims that drums can't stop the car. If they can skid the tires, you can't do any more braking than that. Drums will overheat easier, like if one (stupidly) rides the brakes downhill (reason for U.S. mandate for front disks ~1973). They should not overheat and fade from an occasional stop from 70 mph. Might be marginal if braking from 100 mph.

Click to expand...

Bill is correct. Disks provide improved cooling for repeated stops -- that's why they are superior. Of course, it's possible that 11" disks might have more effective braking surface or more clamping power or more easily controlled modulation than 9" drums, and out-perform them all around. But if your drums can lock up all 4 wheels, you can't be more effective than that, insofar as a single stop.

mvh said:

Sorry, but running without rear brakes cuts your stopping power by something like one-third. Yes, the front brakes do most of the work, because of weight transfer. But you can only stop as fast as you can generate friction between the tires and the road, and the rear tires DO generate friction. You are giving away 25 to 35% of the potential stopping power. Not to mention you are also giving up directional control over the rear half of the car under braking and in many other circumstances. You seem to think that because these disks are better than your old brakes that you only need fronts. But if you hooked up the rear drums you'd stop even better (given correct proportioning) -- why wouldn't you do it?

Click to expand...

I was being sarcastic...my rear brakes are hooked up. But my point was that my braking ability greatly increased especially when you have to stop quickly over a long distance. The pedal is very light and the car stops super nice. For directional control (especially in a turn) rear brakes are very necessary.

treblig

As to those 9 inchers; they were designed for 13 inch tires, which are very easy to overpower. If you upsize your wheels and tires, there is a whole world of difference in stopping power available to you, with bigger brakes.
The spindles that go with those 9 inchers may not be the strongest either. Back in the day, they were known to break under heavy loading.It even happened to me. I will never run those on anything I drive. I have no idea how common it was.
I installed 295 tires on the rear of my A. Then I was able to increase my rear braking power through wheel cylinder sizing, elimination of the P-valve and drum size/ shoe material.With the KHs up front it stops pretty nice.And finally the back stays there.

AJ/FormS said:

As to those 9 inchers; they were designed for 13 inch tires, which are very easy to overpower. If you upsize your wheels and tires, there is a whole world of difference in stopping power available to you, with bigger brakes.
The spindles that go with those 9 inchers may not be the strongest either. Back in the day, they were known to break under heavy loading.It even happened to me. I will never run those on anything I drive. I have no idea how common it was. ...

Click to expand...

Perhaps with sticky drag tires w/ a large OD (jacked up rear), 9" drums wouldn't be able to skid the tires. Depends on how hard you can press the pedal. Not sure what "stopping power" means. If power refers to "energy", the same heat energy will go into the brake drum regardless of the tires. The energy is simply the kinetic energy of the vehicle: E = 0.5*mass * (velocity)^2.

I have read reports of 9" spindles failing. It is forged metal, so hard to imagine what could cause that. Perhaps if you hit a high curb hard, it could break the goose-neck, but that might not be a bad thing (prevents other damage). The weak point I know of is the smaller wheel bearings. The outer bearing spun on both sides in my 69 Dart. I think most slant six engine cars came w/ 9" drums (thru 1973), but never say "all" w/ Mopar.

Well. What I meant was I have greatly reduced my stopping distance, and need way less leg effort to do it. And in fact I am now wearing out rear brake shoes about 2 to 3 times faster than front pads. That indicates to me that the rear brakes are doing much more of the braking than what the factory designed them to do. But since there is so much more rubber back there, skidding is not an issue and the rear end coming around is no longer an issue either.And nose dive is also greatly reduced. Now when I hammer on the brakes, the entire car seems to drop a bit and then its over, Im stopped.
I call that stopping power; the ability to stop in a short distance with no drama and minimal personal effort.

I remember in 71,while still in high school,I had a 70 Swinger 340-4spd. Those were the hot cars to have back then. It went 98 in the qt and like all the other factory stock muscle cars of the era we thought that was killer fast.I thought those KH brakes on that car were pretty good. They saved my hide quite a few times.
Well, one day, a fellow offered me a ride in his brand new Corvette. He was planning to scare me in his Vette, the way I had been scaring him in my Dart. Well that BB brute wasnt that fast, but it cornered pretty good.And the brakes were absolutely killer-awesome.That impressed the dickens out of me.It stopped so hard it was a good thing it had shoulder belts cause my face was dashboard bound.I will never forget the brakes of that car.That was brake power. I think my FormulaS is at least on par with that, now.
Polyglass tires were state of the art tires in 1970. The Dart had E70-14s from the factory. Today I wouldnt put them on my trailer.
Ah the memories.

As to answer the the OP original question, if the brakes you have now function 100% as the factory intended, and you feel unsafe, then I would convert to disk front brakes, keep in mind it my be expensive since you are over seas, also consider that your front rims will not work if stock. Dr Diff used to have a reasonable conversion kit.

As AJ stated factory 4 wheel disks on vette from the 70's are awesome, I have a C3 vette and I swear it handles better and stops as good as my new challenger.

Hi guys, not to jump in the middle to much but when you put disc brakes on the front from a 73/74 dart don`t you need to use the power brake front lines? Jus thinking out loud.

Swingerman
Stop thinkin out loud. lol
The brake lines only have to connect point A to point B. And since they end at the frame rails, only the soft lines need to be changed. That is; the flex hoses, commonly called rubber lines.
But you do kinda bring out a point;to keep your eye on the big picture.
Going from drums to discs requires a mod to the M/C(namely the removal of the Residual-valve to the front brakes), and possibly different P-valving. And going from non-boosted to boosted can (personal preference)use a different M/C again.
And I know nothing of right-hand drive cars.