OT- Why do front brakes wear out faster than rears?

There's a couple of flaws with this. First, I don't think I've ever seen the same calipers on the fronts and rears. Second, my comment above doesn't imply they should have the same area, it implies the rears (which already have less area than the fronts) should be smaller yet.

======== My 74 SAAB EMS had the diagional split brake set-up. Worked fine for the 11 years I had the car.

Unka' George [George McDuffee]

------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).

Nah, The front ones need to be even larger so they don't wear out as fast! ;-)

Seriously, you do NOT want all to wear out at the same time. In these tough economic times some will have difficulty getting ONE set of brakes repaired at the time. If both the front and rear wore out at the same time they'd be tempted to, or would actually, drive around with no brakes at all, except the resistance created by metal scraping metal which would result in even more expense later -- along with many accidents, some fatal.

...Then YOUR uninsured motorists premium would go up! :-8

Al

Well, in the context of this thread it's fair to state the following.

First, the front brakes primarily stop a vehicle because that's where most of the weight is in a vehicle with the engine in the front.

Second, manufacturers like to standardize this sort of stuff to the extent possible. I've got 13.5 inch diameter front rotors and 12 inch rears but when delivered, the car had twelve incher's all the way around. The principal difference between calipers was what got machined as far as porting and mounts between the front and rear calipers, any wheel could go in any position in a pinch. The tires are directional in this case and so are the wheels (ventilation) but the offset is the same.

Anyway, if you want rotors that last essentially forever, have them Cryogenically treated. In ordinary use, you won't be able to wear them out and it isn't all that expensive. Cross drilling or grooving in advance will add tremendously to pas life and if you by carbon fiber/metalic pads and put them on cross drilled and cold cryo'd rotors you will have done you last break job. The only thing to watch out for is heat dissapation. Use DOT 7 fluid IIRC. There is a place in Indianapolis that does a set of rotors for $75.00, or they did. Price might be more today. Carbon fiber/metalic pads take and make a lot more heat than other systems and you can end up cooking things unintentionally, like brake fluid and hoses. In extreme cases, you can cook the bearing grease. I'll find the cold cryo info if anyone wants it. Dumb name that, cold cryo. Of course it's cold - it's cryogenic FCS.

Anyway, this is something I do to stabilize the materials we build LOX manifolds, as well as chamber flanges of rocket motors made from stainless steel. Works on vehicle brake rotors as well - maybe better.

JC

I've had Volvos since the 1970s. They all had dual brake systems. Each system did both front wheels plus one back wheel. The front calipers had two sets of pistons, one set per system. The manual claimed that one could achieve 60% of the normal stopping power even if one system had leaked dry. I never had the opportunity to test this, but it seems plausible to me, and I never read or heard anything to the contrary.

Joe Gwinn

On Fri, 17 Oct 2008 23:05:17 -0500, the infamous F. George McDuffee scrawled the following:

Yabbut, luckily, you never had half a master cylinder fail.

Hmm, interesting. I guess I missed seeing them because I worked primarily on domestic and Japanese vehicles.

I see that it was pretty much a 4-wheel disc/Swedish (and 1 Italican) thing in the 60s through 80s. I'm guessing that the 4-wheel disc feature is what made it possible, but I sure wouldn't want to test it.

-- "Politics is the art of looking for trouble, finding it whether it exists or not, diagnosing it incorrectly, and applying the wrong remedy." -- Ernest Benn

I think my dad's plymouth duster had such a set up.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

No. He's right. At least the SAAB s were the first ones with the diagonal braking system in the Late 50s or early 60s, I believe. At that time I was driving a SAAB 850 GT and so was following the foreign car "developments" quite closely. ...lew...

The front wheels need bigger brakes for two, maybe three reasons: 1. The front is often heavier. 2. The rear end tends to get a bit light as the car rotates around the center of mass as the braking forces are applied. 3. You DON'T want the rear end breaking loose. In the days before ABS, rear brakes that were as strong as the front could cause the rear wheels to lock up, and if you've ever done the park-brake-skid thing, you'll know that once the rear wheels are locked you might as well have a skid plate back there. There's no particular direction the wheels will want to go, and so the car will try to swap ends. Dangerous. Much better to make the rear brakes weaker than to risk breakaway.

Dan

In article , Larry Jaques wrote: :On Fri, 17 Oct 2008 17:47:37 -0700, the infamous Jim Stewart : scrawled the following: : :>

:>Most cars have two independent systems, :>right front/left rear and left front/right rear. : :Are you nuts, Jim? That would put a car in a spin in seconds flat if :one reservoir were dry. I believe that all the cars I ever worked on :up through the 90s had separate circuits for front and rear. I see no :reason they'd change that. It's a real safety issue. : :If you know of crossed systems, please post a link. I gotta see this.

Without ABS, if you lost the front brakes you'd almost certainly lock up the rear wheels in a desperate effort to stop with 70% of your braking power lost, and that would be very likely to put you in a spin too. That was the reasoning behind dual-diagonal split. My Saab had it back in the 60's, and I believe the Fiat I owned back around that same time did too.

Of course the Saab was so spin-prone anyway that a little extra didn't matter much. A friend of mine once told me, "Everybody I've known who owned a Saab has done a 180 in it." Yes, I'm in that category too, even without a brake failure.

I drove my GT850 for quite a few years in central PA with lots of snow and ice and never did any. Now I did do one on ice in my Citroen ID 19. :-) ...lew...

Seconded! Cites, please.

It's theoretically possible to make a cross-split, but also technically difficult - you need either two residual valves for rear drums, or four wheel discs that parking brakes are a nightmare on. Or a parking brake system totally separate from the service brakes.

And theoretically very unstable on system half-failure - I'd rather stomp on the pedal and get nothing than a guaranteed spin.

You SAAB owners must be cursed, or just not paying attention - I put

Most cars will give you a bit of advance warning that the stiction is going away if you know to listen and feel for it.

-->--

========== Most of the problem seemed to be on slick surfaces with the front wheel drive.

With a rear wheel drive when things get a little goosey on slick surfaces, you generally let up on the gas, and the engine drag on the rear wheels helps things straighten out. With a front wheel drive, the engine drag is on the front wheels and nothing on the rear so the car wants to swap ends even more. When you get used to this and learn to feather the throttle so there is just a

Another problem with many new SAAB owners is that they expected some sort of super snow car. While better than most, SAABs would still spin on glare or black ice. Even with studded snow tires you can still spin, but you will be going faster than anything else on the road when you do it. [File under the category "so soon old, too late smart."]

Wish I still had my 74 EMS, but the front U-joints cost more to replace [after c.200k miles] than the entire car was worth [and it was about a 5 hour drive to the nearest dealer].

Unka' George [George McDuffee]

------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).

As I understand it, the lines and a proportioning valve are plumbed into the system. As a safety measure, there is also a "check valve" plumbed into the system so that if a brake line blows open, the check ball goes to that particular side, blocking the flow of fluid to those lines - - - and incorporated into the design is "crossed" plumbing so that even with a blown line, you will have braking on right front/left rear or left front/right rear until you get repairs made. Sometimes when bleeding a system, the check ball will move to the "side" and turn on a brake light on the dash, and fixing it involved bleeding a bit of fluid from the other side to "center" the ball. Ken.

After reading a bit on triangular brake systems (two hydraulic systems; both systems go to both front wheels and one system goes to each rear) I find myself wondering if there have been auto manufacturers that have used duplicate hydraulic systems, both running to all four wheels.