Why the rear drum brakes on the '09?
#22
06-03-2008, 04:09 PM
Re: Why the rear drum brakes on the '09?
Well smartass, One thing I can say is that I have performed dozens, maybe hundreds, of brake jobs in my 50 years. When the wheel is off the floor, and I spin it, it drags on a disk brake system. Just how many disk brake jobs have you done? I don't need "HowStuffWorks" to look this up, I knew it, but I figured I would at least include one reference.
#23
06-03-2008, 05:01 PM
Join Date: Apr 2008
Location: Los Angeles
Posts: 895
Re: Why the rear drum brakes on the '09?
Well smartass, One thing I can say is that I have performed dozens, maybe hundreds, of brake jobs in my 50 years. When the wheel is off the floor, and I spin it, it drags on a disk brake system. Just how many disk brake jobs have you done? I don't need "HowStuffWorks" to look this up, I knew it, but I figured I would at least include one reference.
One question - if there is drag, why is the disc brake preferred - is it cooler, more efficient, less complex?
#24
06-03-2008, 05:30 PM
Re: Why the rear drum brakes on the '09?
Gee Steve, I thought we were having a discussion.
In my 60 years I've done lots of drum brake jobs but never a disc brake job because I've only had to replace them a couple of times on warranty when I had warped rotors .
I'll defer to your experience but, if the drag is significant, why isn't there enough return spring force added to eliminate it? It seems like a 10 cent part.
In my 60 years I've done lots of drum brake jobs but never a disc brake job because I've only had to replace them a couple of times on warranty when I had warped rotors .
I'll defer to your experience but, if the drag is significant, why isn't there enough return spring force added to eliminate it? It seems like a 10 cent part.
#25
06-03-2008, 08:16 PM
Re: Why the rear drum brakes on the '09?
We are, but I made the reference to HowThingsWork, and you mad a smartass remark about it, thus me calling you a smartass. 
The drag is not significant. And I assume auto manufacturers are willing to give up that lost energy. After all, there is so much lost energy in heat due to the braking process itself, why quibble about a little drag. Just give that truck some more HP. And the pad wear would be insignificant. I suspect that this area will be revisited now that we want to squeeze out all losses in newer, more efficient vehicles. Perhaps it already is done, I have just never seen one (with a return spring).
The drag is not significant. And I assume auto manufacturers are willing to give up that lost energy. After all, there is so much lost energy in heat due to the braking process itself, why quibble about a little drag. Just give that truck some more HP. And the pad wear would be insignificant. I suspect that this area will be revisited now that we want to squeeze out all losses in newer, more efficient vehicles. Perhaps it already is done, I have just never seen one (with a return spring).
#26
06-04-2008, 07:41 AM
Re: Why the rear drum brakes on the '09?
I still stand by my original statement that the inherent "wobble" of the rotor during cruising speeds keeps the pads off the rotors for a large portion of the time. How else do you explain water's short term effect on braking performance in a disc system? If there were substantial friction wouldn't the water evaporate or be pushed off without pedal effort?
Also, as highly engineered as the FEH is to increase FE, I can't see why Ford wouldn't put a return spring in the caliper if this really were a measurable drag event. At the least they would have mentioned it since they took the time to measure the FE effect of running the radio.
Mark: Isn't the weight and rotational mass of a hub system greater than that of a disc system? Especially in a drag racing scenario where super light, thin, rotors can be used.
Also, as highly engineered as the FEH is to increase FE, I can't see why Ford wouldn't put a return spring in the caliper if this really were a measurable drag event. At the least they would have mentioned it since they took the time to measure the FE effect of running the radio.
Mark: Isn't the weight and rotational mass of a hub system greater than that of a disc system? Especially in a drag racing scenario where super light, thin, rotors can be used.
#27
06-04-2008, 09:30 AM
Re: Why the rear drum brakes on the '09?
Mark: Isn't the weight and rotational mass of a hub system greater than that of a disc system? Especially in a drag racing scenario where super light, thin, rotors can be used.
I can't see why Ford wouldn't put a return spring in the caliper if this really were a measurable drag event.
#28
06-04-2008, 10:45 AM
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Re: Why the rear drum brakes on the '09?
As risky as it is to disagree with "How Stuff Works", I'm going to.
Brake fluid is incompressible.
Wrong, patently incorrect.
Two examples.
As a kid we used to put a matchstick head in a coke bottle full of water and then cause it to sink into the water by using our thumb to "compress" the water.
Many VC's, Viscous Clutches/Couplings use a specially formulated (high rate of volume expansion when heated) fluid enclosed in a hermatically sealed container. As the clutch plates "stir" the fluid it heats and absent the ability to expand the viscosity increases thereby increasing the coupling coefficient between the clutch plates.
While driving the brake pressure is essentially atmospheric. When the pedal is depressed the master cylinder increases the pressure, When the pedal is released, the system goes back to the original state. If it doesn't, a vacuum is created and either the pad is pulled back or more fluid is sucked in from the master cylinder reservior.
No, the brake fluid actually compresses slightly along with the brake lines expanding (very slightly) due to pressure and then collapsing when the pressure is released.
Looking around on the Internet, I found this paper on finite element modeling of a disk brake system (which was submitted to the Society of Automotive Engineers):
http://www.simulia.com/download/solu...c03_delphi.pdf
In the abstract it says:
"The rubber seal performs the dual function of sealing the piston bore
and retracting the caliper piston after a brake apply."
In the standard disk brake system the seal does act as a return spring. If the piston bores become corroded/dirty, this may not be enough and the brakes drag. If you do an internet search you will find many patents for supplementary return spring systems to minimize this drag. My recollection is that some cars have implemented some of these systems and it was advertised as an improvement a few years back, but I can't seem to find that. One of the features of the 2008 Dodge trucks is "reduced drag brake caliphers" but I don't know the details.
Brake fluid is incompressible.
Wrong, patently incorrect.
Two examples.
As a kid we used to put a matchstick head in a coke bottle full of water and then cause it to sink into the water by using our thumb to "compress" the water.
Many VC's, Viscous Clutches/Couplings use a specially formulated (high rate of volume expansion when heated) fluid enclosed in a hermatically sealed container. As the clutch plates "stir" the fluid it heats and absent the ability to expand the viscosity increases thereby increasing the coupling coefficient between the clutch plates.
While driving the brake pressure is essentially atmospheric. When the pedal is depressed the master cylinder increases the pressure, When the pedal is released, the system goes back to the original state. If it doesn't, a vacuum is created and either the pad is pulled back or more fluid is sucked in from the master cylinder reservior.
No, the brake fluid actually compresses slightly along with the brake lines expanding (very slightly) due to pressure and then collapsing when the pressure is released.
Looking around on the Internet, I found this paper on finite element modeling of a disk brake system (which was submitted to the Society of Automotive Engineers):
http://www.simulia.com/download/solu...c03_delphi.pdf
In the abstract it says:
"The rubber seal performs the dual function of sealing the piston bore
and retracting the caliper piston after a brake apply."
In the standard disk brake system the seal does act as a return spring. If the piston bores become corroded/dirty, this may not be enough and the brakes drag. If you do an internet search you will find many patents for supplementary return spring systems to minimize this drag. My recollection is that some cars have implemented some of these systems and it was advertised as an improvement a few years back, but I can't seem to find that. One of the features of the 2008 Dodge trucks is "reduced drag brake caliphers" but I don't know the details.
#29
06-04-2008, 10:50 AM
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Join Date: Sep 2006
Location: Beautiful Pacific NW
Posts: 1,678
Re: Why the rear drum brakes on the '09?
Well smartass, One thing I can say is that I have performed dozens, maybe hundreds, of brake jobs in my 50 years. When the wheel is off the floor, and I spin it, it drags on a disk brake system. Just how many disk brake jobs have you done? I don't need "HowStuffWorks" to look this up, I knew it, but I figured I would at least include one reference.
Oh, and almost all disc brake piston seals/boots have an integral return/retraction spring, oftentimes embedded inside the rubber seal/boot itself.
Last edited by wwest; 06-04-2008 at 11:13 AM.
#30
06-04-2008, 02:55 PM
Re: Why the rear drum brakes on the '09?
Willard,
Can you specifically name one domestic vehicle caliper that you have found to have a return/retraction spring anywhere within?
If you are referring to the "ribs" in the outer dust seal, that is simply so the piston can expand out and the boot can compensate and continue keeping out the dust.
There is no caliper made that I know of to have any type of retraction spring "in the caliper"....
There is no "wobble" in the rotor either. If a rotor had enough of a wobble or high spot in it to push a brake pad away, it would also cause an undesireable pulsation.
The brake pads in a disc brake system always have a slight contact with the rotor when the brake pedal is not applied....
08feh
Can you specifically name one domestic vehicle caliper that you have found to have a return/retraction spring anywhere within?
If you are referring to the "ribs" in the outer dust seal, that is simply so the piston can expand out and the boot can compensate and continue keeping out the dust.
There is no caliper made that I know of to have any type of retraction spring "in the caliper"....
There is no "wobble" in the rotor either. If a rotor had enough of a wobble or high spot in it to push a brake pad away, it would also cause an undesireable pulsation.
The brake pads in a disc brake system always have a slight contact with the rotor when the brake pedal is not applied....
08feh
