Do disc brake kits need power assist?

[studegary]

My 1962 GT had manually adjusted drum brakes, no self adjusters. One reason for my swap to disks, they worked reasonably well but needed constant adjusting to do so, was something missing?

Perhaps the part that keeps the self adjuster from moving on its own.

[bensherb]

In days of yore, one would have to manually adjust drum brakes, usually via a star wheel, but I think the last of those were phased out in the 1950s.

My 1962 GT had manually adjusted drum brakes, no self adjusters. One reason for my swap to disks, they worked reasonably well but needed constant adjusting to do so, was something missing?

[Waydon]

A few years back, I installed The Turner disc brake kit on our 63 Lark, 2 dor and the brakes worked great without power assist. It did require a little more effort, but I ever had to stand on the brakes to stop. I have since installed a power booster but mainly because I had a new old stock unit I bought years earlier. Just be sure your master cylinder is in good shape and be sure the master cylinder is bled thoroughly and you should be good to go.

[jnormanh]

But doesn't that mean the brake pedal has to move 27% farther?

Yes, of course. On this particular car the maximum pedal travel is bout 4", The brakes are full on at about 1.5" That's one of the benefits of discs, they self compensate for wear, retracting only as far as the rotors push them. Of course modern drum brakes incorporate a ratchet and star wheel or other mechanism to self adjust. It's activated when stopping in reverse.

In days of yore, one would have to manually adjust drum brakes, usually via a star wheel, but I think the last of those were phased out in the 1950s.

Change the oil, grease the chassis, flush the radiator, replace the anti-freeze, clean the plugs, file the points, tune the carburetor, adjust the valves, and adjust the brakes. Back when "Service Stations" did more than sell gasoline.

[sals54]

I only buy Callahan brake pads. The warranty on the box makes me feel good.

THAT WAS HILARIOUS ! ! ! ! One of our favorite movies. And one of our favorite movie quotes.
But... I used a conversion to disc brakes decades ago which used Ford Galaxie rotors and Chrysler calipers. So the brakes were huge. 12" ventilated rotors with calipers from a 5000 lb Chrysler. I used the stock master cylinder under the floor and never had an issue with pedal pressure being too great. It tracked straight and I swapped out the rear wheel cylinders to get an even activation on the lock up of the tires when braking hard. Like others, I never thought to catalog everything back when I did the conversion, but I drove the car for 30 years with that setup on it. I never had an issue in any regard.

[Jerry Forrester]

[QUOTE=jnormanh;The change from 7/8" to 3/4" reduces pedal effort by (calculated) 27%
[/QUOTE]
But doesn't that mean the brake pedal has to move 27% farther?
One needs to be sure that the master cylinder push rod has the required clearance and the master cylinder bottoms out (or almost) at the same time the pedal hits the floor.

[BobWaitz]

I added a Turner kit to a '53 Commander, using the dual master and the proportioning valves. The rear end was upgraded to a 8-inch F*rd. While it requires more pedal effort than a modern power disk setup, there is never any question that you are going to stop.

I added a power-disk setup to my M5 (259 V8, Nova rear end) and it is just like driving a modern car.

I'm completely OK with either.

[jnormanh]

I'm going to itemize my response here:

1) When you changed to disc/drum did you add a proportioning valve? Also the brake contact area is important. It's not exactly apples to apples, but the short answer is still no, you don't absolutely need a power booster.

2) Why would you disconnect a power booster? A poor comparison as the entire system was designed with the booster functioning. As I had mentioned, I have a car with discs and no power and it stops just fine with great pedal feel.

3) Again, the factory would have set things up as a system. I don't see what you mean by "correctly". Anyone can add an adjustable proportioning valve, or one from a disc/drum car. They're not expensive and will greatly influence how the car responds.

4) I was stating that I'm locking up on gravel with (large) power disc brakes on all four corners with very little pedal input, implying that my I don't need as much braking as I have.

Regardless, as stated below, there are far more variables at play and I'm stating my own experiences having both built custom brake systems and upgrading stock systems with aftermarket components.

Responses to your points/questions

1. & 3. I did not use a proportioning valve as the factory used none on the later cars which had discs on the front. I DID use the 3/4" master cyl as did the factory on front disc cars. The change from 7/8" to 3/4" reduces pedal effort by (calculated) 27%

2. I have not disconnected a factory booster. The factory used none on the disc brake cars. What I was saying is: if a factory booster were removed, the pedal effort would be much higher.

4. I don't see how being able to lock the wheels on gravel is relevant. If you can lock up on clean dry pavement with reasonable pedal effort, then, no, you don't need a booster. However if you are 6', and weight 200#, then you may be okay with un-boosted brakes whereas someone older, smaller or of a different gender might not be.

[53k]

It would be interesting to hear from members who have personal experience with any of the disc brake conversion kits that are available for Studebakers like Turner and Hotrodandbrakes. Most modern cars with disc brakes have power assists. The few times I've heard talk about cars with factory disc brakes and no power assist it has sounded like the pedal pressure required was very high. What is the feeling from people who have used the kits? I know the stopping power is much improved, but is the pedal pressure something that might be a deterrent perhaps to your wife or teenage daughter? And what have users done to convert the disc systems to power assist? Thanks.

Not exactly an engineering report, but some years ago I bought a '64 GT that had been sitting for at least nine years, part outside and part garaged, without running, It was a four-speed with power disc brakes. I winched it onto my trailer and took it home. When I got it home and started checking it I found that the hydrovac was in the trunk, but the lines were hooked up in the engine compartment, no booster of any sort. With some fresh gas and a new battery the GT started up very readily and ran beautifully. I decided to try it on the road even though the brakes were not boosted at all and I found that it was no trouble at all to stop. It just felt like conventional brakes to me. I got bolder and took it on the highway- still no problem. I have no idea if the master cylinder was different from original.
I sold the car at the next York.

[hitbyastick]

I have to disagree. Not a Studebaker, but I converted my '59 Sprite from drum brakes to front discs, no power boost. The pedal effort went way up, perhaps double. I was able to reduce the pedal effort by going to a smaller (3/4" bore) master cylinder from the original 7/8" bore. A larger bore master cylinder increases the pedal effort.

Disconnect the vacuum boost on any modern disc brake car, and you'll need both feet on the brake pedal.

Factory original is a different animal. Those cars will have the correctly proportioned cylinders.

Locking up on gravel is meaningless. If you can't lock up on clean, dry pavement, your brakes are not good enough.

I'm going to itemize my response here:

1) When you changed to disc/drum did you add a proportioning valve? Also the brake contact area is important. It's not exactly apples to apples, but the short answer is still no, you don't absolutely need a power booster.

2) Why would you disconnect a power booster? A poor comparison as the entire system was designed with the booster functioning. As I had mentioned, I have a car with discs and no power and it stops just fine with great pedal feel.

3) Again, the factory would have set things up as a system. I don't see what you mean by "correctly". Anyone can add an adjustable proportioning valve, or one from a disc/drum car. They're not expensive and will greatly influence how the car responds.

4) I was stating that I'm locking up on gravel with (large) power disc brakes on all four corners with very little pedal input, implying that my I don't need as much braking as I have.

Regardless, as stated below, there are far more variables at play and I'm stating my own experiences having both built custom brake systems and upgrading stock systems with aftermarket components.

[Mike Van Veghten]

NO...no system "needs" a booster.
One just needs to do their, do diligence and do a little bit of study on what needs to be used where.

As long as the proper master cylinder piston size is used vs. caliper piston size, no booster required.
I have two Stude wagons that can easily prove that.
Very easy pedal.

Mike

[Colgate Studebaker]

To K. Corbin, the pads you are asking about are EBC "Green Stuff" per prior threads on these pads. Supposed to be very good, and I intend to find them for my Hawk when the time gets here. Hope this helps you, Bill.

[Michidan]

To add some serious content, I do run non-power disc front and drum rear on my Studebaker. But there is nothing Studebaker in the entire system so not sure how relevant my experience would be. I read up on pressure and pedal ratio a lot first, so tried to engineer it properly. I don't mind the brakes, but it does require a pretty heavy foot. I used a pedal from a power brake truck, then relocated the hole to get a better ratio. It's still not ideal but better.
I never once considered brake pad material, but after reading this thread I might now.

[Michidan]

I only buy Callahan brake pads. The warranty on the box makes me feel good.

[DEEPNHOCK]

OK Hijack time.... Does anybody know what that pad material is called that some folks are using? it's supposed to be much better at stopping non-power discs.

A legitimate question.
The answer is as clear as marketing mud.
But... In basic terms...
The more aggressive the brake pad/shoe material, the more aggressive the braking will be.
The tradeoff is disc/drum life and brake noise. The softer the pad/shoe, the smoother the braking effort is, and the longer the disc/drum life will be.
Usually the softest pad/shoe lining is the OE initial install. The OE's major concern is customer satisfaction and getting through the warranty period.