1966 Fury Brake Pedal Assembly

[Another Generation]

The quick question...... Does this look like a factory brake pedal assembly for a 1966 Fury?

The long story .....

I used to run A bodies but not that I have teenage children I wanted something big enough for all four of us. So I bought this 1966 ragtop fury. When I bought it the previous owner told me that a 'custom shop' had done a disc brake conversion and that 'the brakes had never really been right' since that time. I figured I've done brakes before.... how hard can it be?? Worst case scenario I buy a Wildwood conversion and replace whatever they had done.

Well I've spent quite a while trying to get them working properly. The pedal goes about 2/3 of the way to floor and is hard as a rock. However, the car just gradually slows to a stop. The kit was a 'Right Stuff' kit and I've replaced the master cylinder, the combination valve, and the power brake booster. No change. I checked today and when the pedal is depressed the front cylinder moves about 10ml of fluid which seems OK to me. I was reading the documentation on the Wildwood website and discovered that they recommend between a 4:1 and a 5:1 pedal ratio. That got me thinking and I pulled the pedal assembly to take a look. The 'custom shop' apparently drilled a new hole in the brake pedal lever to connect to the power brake booster. The measurement from the pivot point to the master cylinder connection is about 6.5" while the overall pedal length is around 17". That only gives me a 2.6 ratio. Therefore, my current thinking is that I just don't have enough brake pressure.

So...... my initial question is if that is the factory brake pedal assembly then how did it ever work? The original connection point might be 1/2" closer to the picot point which would get me to something like 2.7 but that still seems very low. I'm not sure whether the car had power brakes originally or not, but manual brakes require an even larger ratio. Am I missing something here? Does someone make a brake pedal assembly with a better ratio? I can probably fab something up, but it seems odd to me that it would have worked with the original drums and be so far off with the disc brake conversion.

 

[68 4spd Fury]

Was/is the car power brakes? I know there is a difference between power and manual pedal assemblies from the factory, the pivot points differ for greater leverage in the manual version. How this effects an aftermarket conversion I'm not sure. Your in the right place though, allot of members on this site have done disc conversions.

 

[Another Generation]

I'm not sure whether the car was a power brake car to begin with. I'm pretty sure it was a 4 wheel drum car.

Here is a pic I came across in my online search. This is reportedly for a C body (with a manual transmission obviously) with power brakes. If you zoom in it appears as though the distance between the pivot point and the MC connection point is very similar to mine. That seems to confirm that I have a stock assembly for a power brake setup.

However, the question remains.... do I need more leverage to make the disc brakes work. Almost everything I see seems to indicate a pedal ratio between 4:1 and 5:1 is required.

 

[rkrochen]

I'm not sure whether the car was a power brake car to begin with. I'm pretty sure it was a 4 wheel drum car.

Here is a pic I came across in my online search. This is reportedly for a C body (with a manual transmission obviously) with power brakes. If you zoom in it appears as though the distance between the pivot point and the MC connection point is very similar to mine. That seems to confirm that I have a stock assembly for a power brake setup.

However, the question remains.... do I need more leverage to make the disc brakes work. Almost everything I see seems to indicate a pedal ratio between 4:1 and 5:1 is required.

View attachment 593923

Drum style brakes are self energizing simply put the front shoe grabs the drum and rotates forcing the rear shoe into the drum. On disc brakes this doesn’t occur which likely means it needs more energy to apply. That’s why they use such a big piston in the caliper. My guess is that the master cylinder isn’t the correct bore.

 

[Another Generation]

I considered that..... I've tried both a 1" and a 1.125" with the same result. In truth, the pressure is slightly lower with a larger bore. The larger bore moves more fluid, but at a lower pressure. I just can't get over the fact that Wildwood, Speedway Motors, Summit Racing, etc all suggest at least a 4:1 ratio for power brakes. Either this is a real limit, or they're all reading the same internet posts!!

I know some of you have done disc brake conversions before.... did you have to think about the brake pedal ratio or did the factory brake assembly work?

The other issue is that I don't really want to start cutting on my only brake pedal assembly. If I could find another one then I'd have one to test with and still hold one as a backup but if I hack up the one I've got and destroy it then I'm SOL.....

 

[Ross Wooldridge]

I used factory parts to do the swap on both my C bodies, and couldn't have been happier. I don't trust those aftermarket kits - I hear a lot of problems, and I don't like the brackets either.

Try to find a 70 - 73 C body with disc brakes, and use the parts from that car. You'll be pleased. The most challenging thing to find will be the correct disc power booster. However, if your car is a console shift, then you can use the later 71 - 73 booster and it will bolt up fine with no issues. The issues occur when the later booster is used with column shift cars - it interferes with the column shift linkage, preventing the manual engagement of Low 2 and Low 1. Not a big issue actually...

Don't cut your brake pedal - keep looking, the right part is out there. Power brakes (with booster) uses a pedal assembly with a lower pivot point (farther away from the push rod), for lower leverage, allowing the booster to do its job, and resulting in easier brake pedal pressure for the driver. A manual brake pedal assembly uses a pivot point MUCH closer to the pushrod to up the leverage considerably.

Search here on this forum for Disc Brake conversion articles and parts lists.

 

[Another Generation]

For any of you interested...... I have found at least one resource that suggests that drum brakes do indeed run on considerably less pressure than disc brakes. The quoted figures were

Drum --- 300 - 400 PSI
Disc --- 900 PSI and higher

With my factory 2.6 to 1 ratio that means I'd have to exert between 115 and 153 pounds of force on the pedal with the drum brakes to get the full affect. This is a little high according to many estimates, but doable.

With the disc conversion I'd have to exert better than 300 pounds on the brake pedal to get the full affect!! This is clearly not doable (at least by me!!!) and explains the condition I'm experiencing.

My situation is further compounded by the fact that a previous owner did the conversion. He decided on the 'high performance' brake conversion which includes fixed-mount, four piston brake calipers on all 4 corners. Therefore, I need to move a fairly significant amount of fluid in order to move all 4 pistons on all 4 calipers but I need to generate quite a lot of pressure while doing it! Most disc brake MC are 15/16" or less in diameter so that they can generate enough pressure. However, that MC diameter may not be sufficient to move enough fluid to activate all the pistons.

If I can get this working properly then I will have a fury with brakes sufficient for a world class racing machine! I've decided not to modify my factory pedal (at least not yet) but instead to fabricate a new assembly for testing purposes. Once I find the 'sweet spot' for pedal ratio I'll decide whether I'm modifying the factory pedal or not.

 

[Big_John]

For any of you interested...... I have found at least one resource that suggests that drum brakes do indeed run on considerably less pressure than disc brakes. The quoted figures were

Drum --- 300 - 400 PSI
Disc --- 900 PSI and higher

You have to take the surface area of the disc brake piston into account. I'll let you do the math, but I think it's around 7 times the piston area.

I actually think 900 PSI sounds low for a single piston caliper but I could be wrong.

 

[Another Generation]

You're absolutely right!!!

If the operator applies 100 pounds with a pedal ratio of 5:1 then 500 pounds are applied to the MC piston. If the MC piston has a diameter of 15/16 (common disc brake piston) then that 500 is distributed across an area of about 0.7 square inches. This would result in fluid pressure of about 724 PSI. This math ignores the effect of the power brake booster. Theoretically, the power brake booster ought to bump me up to around 1050 PSI.

The biggest issue I have is that I have to balance the need to move fluid with the need for pressure. If you run a single piston sliding caliper on each wheel with a diameter of 2 inches then you need to move about 12 ml of fluid to move the brake pads 1/8". If on the other hand you run 4 piston fixed calipers with 1.25" piston diameter then you have to move about 20 ml of fluid to move the brake pads the same 1/8".

The high performance fixed calipers are really great if you need them, but if I were doing this conversion myself I would not have paid for them. I'm going to shoot for a 6:1 pedal ratio with a 1.125" MC bore and see how it works out. I have a 1" on hand as well, but I'm worried that I might not be able to move enough fluid with that one.

I'll throw my lot in with the other people on this board endorsing the use of factory parts if possible!!!

 

[Dads300]

I think your volume estimates are high. Disc brake calipers do not retract anywhere near 1/8”, you’d need feeler gauges to measure the actual travel. 6:1 is manual brake leverage territory, you shouldn’t need that much. I would say you certainly need a dual diaphragm booster. I would look at 70s corvette brakes and compare your booster, master, and pedal ratio. They were 4 wheel disc and I’m pretty sure they ran 4 piston calipers, or at least fairly large 2 piston calipers, you may gain some insight as those cars stop pretty well.
Travis..

 

[Another Generation]

You're absolutely right!!! I suspect the actual pad movement (especially given a rigid fixed caliper) is more like 0.0125 instead of 0.125!!! I just picked that number for ease in my analysis.

As far as the double diaphragm booster goes, that's an interesting idea. From what I've read I'll pick up somewhere around 400 PSI with my existing (single diaphragm) booster so the 300 PSI I'm exerting on the pedal is probably something like 700 PSI to the brake calipers. With the current system, this boost is likely the only reason I have brakes at all!!

Dual or single, I need more pressure than I have now so I'm going to have to modify my pedal ratio. Since I don't want to start chopping up my factory pedal assembly I'm going to have to fab something up. Since I'm building it, I think I'll just fab it with separate holes for 6:1, 5:1, and 4:1. Hopefully, one of these ratios will move enough fluid, apply enough pressure, and feel good to the operator. If not, then I may have to start thinking about the double diaphragm booster.

 

[Ross Wooldridge]

That's the reason the factory engineered disc system uses a dual diaphragm booster.

 

[Dads300]

I think I’d try a 15/16 master and see what that does. It will give you slightly more pedal travel, but will offer more pressure. I really don’t think you need to re-engineer anything, you just need the right combination of parts. That’s my take
Travis..

 

[fury fan]

That's the reason the factory engineered disc system uses a dual diaphragm booster.

71-newer uses a larger-dia single-diapragm, which can be used on earlier cars if they don't have a column shifter. (it can be used on them but cannot get the shifter down into the 1 position).

 

[C-440-300]

71-newer uses a larger-dia single-diapragm, which can be used on earlier cars if they don't have a column shifter. (it can be used on them but cannot get the shifter down into the 1 position).

Thanks for your comments. Would you suggest I keep my 9" dual-diaphragm Midland (that needs some internal check valve I'm told) and send it in, and/or, buy a 10" single-diaphragm that is much easier to get? I could do both, I guess, to keep it on the road. Note: Was a power brake 4-drum. Converted to 4-disc. The original single-diaphragm replaced with dual-diaphragm. I can't figure the model of the dual, but not easy to find pictures. It looks like the 9″ Can (62-217) on Harmon's website: Boosters and Parts - Harmon Classic Brakes. (4 stud).
It was stopping the monster really well(!) and nice easy pressure. 66-300. I'd be happy to just buy something that works without cutting/drilling too much. It's not a matching car and made for fun with the family. Thank you!

 

[C-440-300]

On another note: Aren't there other boosters from B-bodies that would mechanically hookup where a C-Body power booster used to? Assuming some rod exchange maybe?

 

[Another Generation]

OK..... finally got some time to work on this!!

I tried several combinations. I fabbed up a pedal assembly with a 6 to 1 ratio. I still have the factory 2.7:1 and I got a 7" dual diaphragm booster. Here was my testing:

1) 6:1 pedal assembly, 7" single diaphragm booster, 15/16" bore master cylinder
This worked 'OK'. Not much 'feel' to the pedal and it went pretty well all the way to the floor. Never could lock up the brakes, but it did stop much better.

2) 6:1 pedal assembly, 7" single diaphragm booster, 1" bore master cylinder
Same result as option #1 pedal still went pretty well to the floor, but the brakes would lock up

3) 2.7:1 pedal assembly, 7" dual diaphragm booster, 1" bore master cylinder
This was the sweet spot. The pedal goes about 1/3 of the way down and you start to 'feel' the brakes engage. By the time the pedal is 1/2 way down the brakes are grabbing pretty hard. Just past 1/2 way and the brakes lock up. I am really glad this worked because I'm able to use the factory brake pedal assembly.

C-440-300...... I used a 7" dual diaphragm booster I got from Speedway Motors.

It's got the standard 4 hole pattern on I believe 4 3/8 center to center. It mounted right up to my master cylinder that looked like this:

You can get the brake booster on Amazon.

 

[Another Generation]

Correction...... I'm using a 9" dual diaphragm booster, not a 7"

 

[Dads300]

Cool, sounds like you worked your way around to basically a stock set-up. FYI for anyone else, I believe all jeep TJ wranglers (97-up) have a smallish dual diaphragm booster that should be easy to get and likely bolt up easily being from ma-Mopar.
Travis..

 

[Ross Wooldridge]

While it's probably workable, the later masters have 2 bolts.