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Petal firmness- manual drums vs manual disk
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Author:  Bren67Cuda904 [ Sat Nov 11, 2006 9:45 am ]
Post subject:  Petal firmness- manual drums vs manual disk
As some may know I got the MP's disk brake conversion for my 4 wheel 9" drum Barracuda. I also got the power brake booster with the kit. As some have said the power brake option is indeed a large bulky esembly. The orignal drum system had a petal hardness that is a bit tiresome for city driving. I have been thinking about not installing the booster because of its size and just installing the disk master cylinder that came with the kit.
My question:
Will petal effort be lot less with just a manual drum to manual disk conversion or will it be about the same? If using the booster will provide night and day difference I'd likely use the booster, but if the disk conversion with the disk master provides a petal that won't tire your leg out, maybe thats the way to go.
Author:  Joshie225 [ Sat Nov 11, 2006 10:13 am ]
Post subject: 
What's this about flowers? Petal firmness?

You bought the kit from someone. Go ask them.
Author:  SlantSixDan [ Sat Nov 11, 2006 10:24 am ]
Post subject: 
Pedal (not "petal") firmness will depend on a lot of factors. Master cylinder bore size, wheel cylinder bore sizes front and rear, pedal leverage ratio, how carefully you bleed the air out of the system, what brake shoe friction material you use, what brake fluid you use, and how you define "firmness".

What exactly is it that you are hoping to achieve?
Author:  Bren67Cuda904 [ Sat Nov 11, 2006 1:39 pm ]
Post subject: 
It's Saterday and their closed so I can't ask them. I am sure that someone has did a disk brake conversion and didn't go with a power booster, and has an feeling on the ease of pushing the brake pedal afterwards. Same, harder, easier. I know stopping power is increased but thats not what I am asking. I'd just put on the master both ways assisted and unassisted, but there is some line work that would have to be done both ways. Just trying to avoid doing it both ways if some one here says there isn't much difference between the two. If thats the case I 'll just go with the booster.

I have found your advice very helpful in the past and it is apreicated. I know my spelling is bad and my writing style is seemingly cold. I don't mean it that way. I am by no means a writer, but I am starting to catch a negitive tone from returned responces and I am hoping I am just misreading this and its the same inability to write affectivly.
Brennan
Author:  AnotherSix [ Sat Nov 11, 2006 1:53 pm ]
Post subject: 
Yes it is rather subjective. Something to consider is how much vacuum you will have. If you are running a hot cam a power booster will not work well. It's bad enough with a v-8, a six won't be better. The idea that you will have plenty of vacuum when you let off the gas pedal is not a valid one, but something I have heard several times. Your foot will be down on the brake pedal before any vacuum can build in the booster. Aside from the power assist not working well with a hot cam having a booster can cause stalling when the engine trys to raise vacuum in the booster right after a hard stop. I don't know about the KH style calipers, but with the larger bore 76 calipers (2.7" if I remember correctly), 15/16" rear cylinders with 10" drums and a 1 1/32" master cylinder the pedal pressure in our 71 is not bad at all with bendix semi metallic pads. Much less effort to stop that with the 9" drums. The manual setup gives very good feel and control to the driver. To me it's one less thing and less weight to boot. Depends on what you want out of your car.
Author:  AnotherSix [ Sat Nov 11, 2006 2:00 pm ]
Post subject: 
I assume that setup has the 4 piston calipers. Check the bore size and see if it matches the factory bore size for the early disk brake cars. Then see what master cylinder bore they used. Then you will know if you are right in there with your new master cylinder. I am pretty sure the older cars used a 1 1/32" master, which is likely what your kit has, but check everything to be sure.
Author:  SlantSixDan [ Sat Nov 11, 2006 3:45 pm ]
Post subject: 
A power booster does not increase stopping power. All it does is make the pedal easier to press. The only way that increases stopping power is if you are a tiny little 5-foot grandmother who hasn't the leg strength to press an unboosted pedal.

My preferred setup for Kelsey-Hayes 4-piston disc brakes is original-type organic brake pads, a 1" master cylinder bore, and no power booster.
Author:  emsvitil [ Sat Nov 11, 2006 4:59 pm ]
Post subject: 
Drum brakes have a multiplying effect that discs don't.


With the Duo-servo type (which the drum brakes we have are, this effect is about 5 (aka brake factor))

Disk brakes have a brake factor of .75

So if you swapped disk brakes for a drum brake, the area of the caliper pistons (or area * 2 if sliding caliper) needs to be 6-7 times larger than the drum brake it's replacing (5 / .75 = 6.66).

So with a 1" drum cylinder you'd get .785 sqin of piston area (only do 1 piston not the 2 in the cylinder) the equivalent piston area for a caliper is around 5 sqin for similiar feel.......... (or a piston about 1.8" diameter for a 2 opposed piston or 1 sliding piston caliper)
Author:  sandy in BC [ Sat Nov 11, 2006 6:45 pm ]
Post subject: 
What Mr Svitil is saying (I think ) is that you need a manual M/C with manual discs and a power M/C with boosted brakes. You purchased a power setup and will need to buy an appropriate M/C manual to go with your nude erection (new direction).

I wonder if the rear brakes will still grab........?

I use a stock 73 manual M/C with my stock 73 discs/drums. The car stops better than anything else in the fleet except GFs Talon TSI awd. Pedal effort is low. Feel is superb.

This story has been told in previous posts BUT.....

I had a cop (RCMP) going in the opposite direction nab me on radar at cruising speed in 5th gear (83 MPH according to His Occifer)....he swung around ala Kojac and preceded to tailgate me at 83 MPH with lights and siren. Im a big fan of "Fear and Loathing in Las Vegas". Once he was close enough (4ft) I jumped on the binders and signalled left. ....and turned right onto the shoulder.
I noticed a great deal of swerving in the rear view.........

His Occifer had not seen F+L and was not amused. He surmised he could have rearended me. I inquired meekly if he was following too close or had inadequate brakes? Imagine a Crown Vic not being able to outstop an old Valaint I sez.....

He was pissed off and gave me a ticket and I gave him a warning "not to follow so close....and get that car with bad brakes checked out"

Apparently Crown Vics have traction control ...cuz his burnout was way less effective than mine.....
Author:  64'4$peed [ Sun Nov 12, 2006 9:01 am ]
Post subject: 
crown vics have traction control that really sucks on early to mid 90's models. the second RW speed increases over actual speed the engine RPM's shut down. IT SUCKS!!!! and the newer ones have two gear ratios one for highway use and one for quicker city driving. they both suck for doing burnouts. but no active traction control like the older ones. Any inquries as to the handling capabilities of CV's can be directed towards me. I get paid to beat on em daily.
Author:  kesteb [ Sun Nov 12, 2006 7:28 pm ]
Post subject: 
My disk brake system is from a '75 Dart. The rear drums are also from the same '75 Dart. The master cylinder is an aluminum manual disk brake one from an '80 Aspen. The distribution block is from a '73 Duster. All the brake tubing is new. My car stops straight and sure with no rear lockup. The pedal is noticably firmmer then with drum brakes. But to me, it is not unreasonable, but then I am 6' 1" and weight 215lbs.

Talking about distribution blocks, I once had a very interesting conversation with a fellow that I bought my first disk drake setup from. He had a 340 Duster and he experimented a lot with the factory disk brake setup. He tried many differant distribution blocks and found that the '73 a-body one was the best. All the others caused his car to lock the rear brakes and he tried some really odd ball combinations, like 1/2 ton pickup truck, etc.

I have always been of the believe that power brakes and power steering is a waste on our light A-bodies. Both systems were designed to allow granny to parallel park with ease.

When I had my '98 Plymouth mini-van the steering was firmmer and the braking wasn't any better then my 40 year old Dart and that was with ABS. My new Nissian Frontier has about the same steering feel and better brakes the my Dart. But then my Frontier has 4 wheel disk brakes and ABS, it also weighs 4000 lbs while my Dart is at least 1000lbs lighter.
Author:  Patrick Devlin [ Sun Nov 12, 2006 7:37 pm ]
Post subject: 
I think that when it comes to using manual brakes, the seat you are driving from is really important-- it really affects how well you can move your leg to apply the brakes. Try applying manual brakes while sitting on a seat with sagged springs versus applying the brakes from a seat that is firm and at the right height. Also, even the seat adjustment can make a big difference.
Author:  SlantSixDan [ Sun Nov 12, 2006 8:50 pm ]
Post subject: 
Quote:
He tried many differant distribution blocks and found that the '73 a-body one was the best. All the others caused his car to lock the rear brakes
Good info, but your guy must've got a bunch of typically badly-working distribution blocks, 'cause the very same one (3549 947) was used on disc brake A-bodies in '71, '72, '73 and '74, and quite possibly '75 and part of '76 as well (parts books I have here at the house only go up through '74). The factory distribution block wasn't very well designed, and they don't age well. Sometimes you get one that works OK, most of the time you don't.
Author:  440_Magnum [ Thu Nov 16, 2006 2:08 pm ]
Post subject: 
Quote:
Apparently Crown Vics have traction control ...cuz his burnout was way less effective than mine.....
Yeah, the Crown Vic has HIGHLY effective traction control. Its called a Ford 4.6L engine. :-p
Author:  440_Magnum [ Thu Nov 16, 2006 2:15 pm ]
Post subject: 
Quote:
It's Saterday and their closed so I can't ask them. I am sure that someone has did a disk brake conversion and didn't go with a power booster, and has an feeling on the ease of pushing the brake pedal afterwards. Same, harder, easier.
When you change from manual to power brakes or vice-versa, you should also change the pedal linkage appropriately. Power brake pedal assemblies move the pushrod further for each inch of pedal travel than manual brake pedal assemblies, and count on the power assist to keep the pedal feel manageable (and thats why power brake cars have ROCK hard pedals if the power assist goes out).

I've converted two cars to manual front disk brakes ('69 Coronet R/T, '66 Polara). The Coronet had was just a power-to-manual conversion, it already had disks. The Polara was a drum-to-disk conversion. In both cases, the pedal is firmer than with power, but I like it. It feels much more precise and is easier to modulate the brake pressure. What I don't like, but have learned to live with, is that manual brakes require so much pedal *travel* which is accomplished by having the brake pedal resting height off the floor be quite a bit higher with manual brakes than with power. I learned to drive on a car like that, so I quickly reverted back to picking my foot UP off the accelerator and moving it over to the brake, but if you've never driven a manual brake car it will feel wierd. My wife grouses about it when she drives the Polara (she's scared to death of the R/T, so its not an issue :-) She's used to just sliding her foot straight left from the accelerator to the brake, and that will scrape your toes along the underside of the brake pedal on the Polara.
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