The Stovebolt Site Forums The Shop Area General Truck Talk Decreasing stopping distance

I have been talking about this on someone elses sort of related post but thought I'd start a new topic do discuss stopping distance specifically.
We always hear about needing better brakes, especially if your going to increase your horsepower and torque.
In the past 2 years, I've had 2 close accidents. One was when a car ran a stop light and I had to hit the brakes hard and fast at about 30mph. The next time was on the freeway when I came over a hill at 75mph to suddenly approach a hard slow down due to an accident ahead. Both times, my stock manual drum brakes were able to stop the wheels. In other words, I went into a skid. Both times. The second time I got completely sideways and yes, I was trying to pump the brakes.
So here is the question. How is a booster w/ front dics and enhanced rear drums going to help decrease my stopping distance? It seems to me that a setup like that might just make it even easier to stop the wheels and go into a skid. Am I completely wrong? Maybe they do a better job of slowing the vehicle without locking them up? If so, I would like to be enlightened as how that would happen. The bottom line is, do I really have to upgrade my brakes to reduce stopping distance in an emergency situation? P.S. I don't think ABS is an option.

Could it be that boosted disc brakes are easier to operate, as in they take less pedal effort, this translates into ease of use, especially when in a panic situation? So, you stomp on them hard, they lock up, you back off and try again, because this is easier to do (less pedal effort) you can do it faster and more controlled, and that's where the better stopping distance comes from. Not the fact that the wheels lock up easier, but that they are more easily controlled between lockups?

I don't think you are asking the right questions, you seem to think that if the wheels can be locked up on two completely different brake systems then they are effectively equal?

I think not. I drove my 52 1 ton with stock brakes, they seemed fine, and I had no problems with them, never worried about it.
Then I switched to hydroboosted disc brakes on the same truck, and I can't begin to describe the difference. Almost look at the peddle and the truck would stop, and quickly.

What ever the difference I soon found myself driving harder up to a stop and braking harder in the last moments, not good things, but the brakes were different, and I unconsciously took advantage of that.

Grigg

Personally I think the differences arent as noticeable with different brakes. Maybe its a little easier, I havent had many problems. Its all about the tires. When I eventually started dinking around with my toyota pickup I went from stock wheels and 50$ tires to Y-rated low profile street traction tires. I could take corners going way faster then I ever would have dreamed of and the lowered suspension and tire combo made it possible. They only came with about 30K mile rating but those things could come to a dead stop in the pouring down ran in no time flat, even if they locked up.

When I got tires for the 53 I spent more then I had planned and went with a nice set of Toyo street tires, even though that truck wont go fast enough to be an issue. Better tires have softer rubber and grip awesome! The downside is they dont last very long.

When I got those tires on my toyota I had a biker friend tell me about how he hated riding behind someone in the rain. He said it was like having a hose sprayed directly on you due to how well they moved water through the tread and out the back.

Look at your car, brakes can help but ultimately your relying on that rubber in contact with the ground to stop you. By no means am I putting down brake systems in lieu of tires, you still need a functioning brake system and thats not the place to save a buck.

My .02 cents, Jeff

Jeff, I've already spent the money on high quality radials and that definately helps. And you're right about the Toyos. I have them on my van and that thing will stop on a dime. Even here on the wet Seattle roads. But the tread does wear quickly. It also has ABS and AWD.
Grigg, I think I am asking the right question and you've partially answered it. Maybe it is the feel and sensitivity in the pedal. When I did lock them up, it didn't seem hard to do, but then again, the adrenaline was flowin! I am looking for testimonials from those who have done the upgrade and what their take is on how there truck might be easier to bring to a shorter stop. I've suspected that it may just be reaction time of the pedal. I really want to know if it makes that big a difference before I spend the money.

Big, my '50, 3604 has the stock Huck brakes that have been completely rebuilt. With firm pressure they will lock up the brakes. I’ve never had to make a stop from 75mph since she tops out at about 50. The hard stops that I have had to make are straight with no pulling and I think locking up the brakes is simply a matter of feel. Once the tires have broke traction the heat immediately begins to build from fiction and you are literally rolling around on little balls of hot rubber that are scrubbing off. Very few people even professional drivers have the ability to keep from locking up the tires in a panic stop. We all bow to the tendency to press harder to stop faster in an emergency. That’s the whole purpose of the ABS. How many times have you stepped down to hard on you ABS and felt the throbbing in the pedal, that would have been a slide had you been in a vehicle with standard brakes.
The guys are right on when they are talking tires. This is where the vast majority of you stopping ability comes from. The modern construction of tires, i.e., radial plies, aspect ratio, tread design, compounds, the pressure that your running and the weight of the vehicle all inter into the grip that you have on the road. The best examples of these improvements come from the racing world. Dragsters in excess of 300mph, and g’ loadings on circuit cars in the corners that can darn near rip you head off.
Bottom line in my opinion is, if your not sticking to the road I would look to the factors that apply “where the rubber meets the road” and not to the mechanics of the brakes.
Denny Graham
Sandwich, IL

OK, so tires are important, I agree.

My 1 ton I had some old Goodyear "high miler" 7.50X17.
After the brake upgrade I ran some new but 25 year old 8X19.5 Goodyear's, same tread pattern, but a few inches taller.

I still felt the boosted disc brakes at both ends made a huge difference.

Grigg

I put boosted discs on the front of my '64 burb & in the process of putting them on the other '64 pickup('71 GMC donor), & its a night & day difference in stopping distance. The discs just stop way better w/o locking-I'm sure it has to do w/dynamics/physics/leverage. I can put you into the windshield before the discs ever lock up.
Old black truck had stock drums all around, I added a booster & it worked well under normal conditions, but in a panic stop(like on the freeway where everyone goes from 70 to stop in about 100ft)you'd hit folks, as the drums would lock & away you go.

Let's not forget that when installing Disc's on the front that we are removing one of the human elements, brake adjustment. I have been twisting wrenches for a number of years and getting manually adjusted brakes even on all 4 corners is a ongoing deal. Power disk's in the front and automatic adjusters in the rear, makes us a little lazy and a lot safer.

Where bigger, more powerful brakes make the difference is in two places: Long downgrades and heavy loads. Discs run cooler for longer than drums, generally speaking, and cool brakes work better. That being said, once you lock up your tires in a panic stop, you have relinquished control and your stopping distance increases. Under certain conditions, a skidding vehicle will actually pick up speed. It will NEVER slow as quickly as it would if traction was maintained.

that's because of the difference in static and dynamic friction.

Think of sliding a heavy box on the floor, it takes more force to get it moving, that's he high coefficient of static friction.
Once moving it is easier to slide, that's the slightly lower coefficient of dynamic friction.

Regular braking, without lockup is static friction, and that coefficient is always higher than dynamic friction (sliding wheels).

Grigg

Things in motion tend to stay in motion!

Under certain conditions, a skidding vehicle will actually pick up speed.

Like (only), when you are going down a hill where the force of gravity is less than the friction.

''Under certain conditions, a skidding vehicle will actually pick up speed.
Like (only), when you are going down a hill where the force of gravity is less than the friction.''
'' Things in motion tend to stay in motion! ''
both true statements.
having the upgrades is better than not
it's one of those things that you;ll get used to using on a daily basis

look at it this way
if you improve HP /torque
or drive on crowded roads
carry loads
or wife & kids
do the upgrade to better brakes
some of the mid 70's rear ends have 2.75'' wide drums rather than the 1.5'' stock and those slave cylinders are bigger. installing a pulsing system i guess wouldn't be much more work than the above, but you'll have to locate the bits and do that conversion. on the other hand the newer rear ends allow you to go faster on freeways because of gearing.
disc conversions on the front all work better than old drums. either way both front and rear double your stopping power.

my.02

Big,

If you are going sideways, its because your rear brakes have locked up. Most vehicles and drivers are not balanced well enough to similtaneously lock all 4. Lock the front and you can't steer. I belive drum brakes are more prone to locking since they are self-energizing. As the drum rotates, it tends to pull the shoe into the drum. Most stopping is done by the front brakes (due to weight transfer & load) and the biggest bang for the buck is by switching to front discs.

Repeated use, high loads and long descents will all cause a drum brake to fade. The drum expands as it gets hot and moves away from the shoes. Too hot and it would distort. The lining material for drum brakes just becomes less effective the hotter it gets, this limits how hot a drum can get and protects the brake at the expense of stopping ditance. When a rotor gets hot, it expands into the brake shoes and becomes more effective. Fade is much less an issue with a disc brake.
I can't see it on TV, but watching the Nascar/Busch guys at IRP, their brakes are glowing red goiong into the corners. A disc brake can easily be designed to work at 600-800F. Drums may be topping out around 400-500. Drums brakes pull due to differences in adjustment, brake shoe condition, drum condition. Discs don't pull because of their self adjusting characteristics. An oily or contaimined pad/rotor will still cause a problem. If you aren't mentally having to correct for pull you can focus on stopping. I also agree with Grigg that power discs are easier to modulate.

As others have said, tires are a huge part. Short & skinny are easy to lock up. Tall take more brake to stop. Wide should put more rubber to the road, but hydroplane easier. It's all a balance. Tread is important too. If you have average size tires
in good shape, changing them out won't solve your problems, I'd go front discs and work with the proportioning to get good solids stops and limited rear lock-up.