Simultaneous Application of Gas and Brake Pedals
On Fri, 28 Jan 2005, Steve wrote:
> Bill Putney wrote: > > > The downside of power brakes, which is a necessity with disk brakes > > because they do not have the designed-in mechanical amplification, > > Why do people keep saying this? The parrot effect, I'm guessing. > Disk brakes DO NOT "require" power assist at all. You are correct. They don't. > I much prefer the feel of manual disk brakes to any other > braking system out there. Well, to be perfectly semantic about it, the only "manual brakes" out there are the ones on vehicles specially modified for the handicapped. But yes, I agree with you, a properly set up and dialled-in unboosted disc system cannot be beaten in terms of pedal feel. > My '69 Dodge currently has stock Kelsey-Hayes > front disks and stock rear-drums, activated by a MANUAL disk brake > master cylinder and a MANUAL pedal linkage. The feel is just wonderful, > and really only slightly higher pedal effort than when it had a power > booster, MC, and pedal setup. There is much more pedal *travel* which > allows finer control over braking with the manual setup. The car stops > on a dime. Unboosted discs are terrific in slick winter conditions, too. We're looking at deleting the brake booster from my '92 Spirit R/T clone. It'll doubtless take a different master cylinder, but there's an enormous variety of MCs that'll fit. I think the mistake most people make is in thinking that power brakes without boost are the same as unboosted brakes. They're very definitely not. The mechanical advantage of the brake pedal over the cylinder is much greater in an unboosted setup than it is in a power setup. DS |
Daniel J. Stern wrote: > On Fri, 28 Jan 2005, Steve wrote: > > > Bill Putney wrote: > > > > > The downside of power brakes, which is a necessity with disk brakes > > > because they do not have the designed-in mechanical amplification, > > > > Why do people keep saying this? > > The parrot effect, I'm guessing. Probably because the vast majority of disc brake cars do have power assist - dating back to the first installation of modern discs on American passenger cars in the '63 Studebaker models, where the disc brake package came with a mandatory power booster. > > > Disk brakes DO NOT "require" power assist at all. > > You are correct. They don't. > > > I much prefer the feel of manual disk brakes to any other > > braking system out there. > > Well, to be perfectly semantic about it, the only "manual brakes" out > there are the ones on vehicles specially modified for the handicapped. But > yes, I agree with you, a properly set up and dialled-in unboosted disc > system cannot be beaten in terms of pedal feel. > > > My '69 Dodge currently has stock Kelsey-Hayes > > front disks and stock rear-drums, activated by a MANUAL disk brake > > master cylinder and a MANUAL pedal linkage. The feel is just wonderful, > > and really only slightly higher pedal effort than when it had a power > > booster, MC, and pedal setup. There is much more pedal *travel* which > > allows finer control over braking with the manual setup. The car stops > > on a dime. > > Unboosted discs are terrific in slick winter conditions, too. We're > looking at deleting the brake booster from my '92 Spirit R/T clone. It'll > doubtless take a different master cylinder, but there's an enormous > variety of MCs that'll fit. > > I think the mistake most people make is in thinking that power brakes > without boost are the same as unboosted brakes. They're very definitely > not. The mechanical advantage of the brake pedal over the cylinder is much > greater in an unboosted setup than it is in a power setup. > > DS True, although with a reasonably heavy car it does become almost a necessity to have the power booster because you are trading off pedal travel against line pressure, and both need to be kept at a reasonable level. Personally the only car I've driven with unboosted discs was my '71 914/4, and the feel is spectacular... nate |
Daniel J. Stern wrote:
> > I think the mistake most people make is in thinking that power brakes > without boost are the same as unboosted brakes. They're very definitely > not. The mechanical advantage of the brake pedal over the cylinder is much > greater in an unboosted setup than it is in a power setup. > > DS Absolutely, the pedal LINKAGE is often different in addition to a different bore size in the master cylinder when comparing power brake and non-power systems for the same model car. In the case of Mopar B-bodies like my '69, the power brake cars had a bellcrank mechanism that moves the master cylinder piston FASTER than the pedal moves. The loss of leverage is more than offset by the power booster... UNTIL the booster quits working and mashing the brake pedal is like stepping on a block of lead. The manual brake pedal linkage is a direct connection from the pedal to the MC piston and has much more mechanical advantage, at the cost of more pedal travel. All other power brake cars have a similar mechanism for reducing pedal travel, or simply attach the pushrod closer to the pedal rather than closer to the pedal hinge (another way of changing leverage)I LIKE the added pedal travel- for one thing it makes "sudden acceleration" a lot less likely (just to tie two threads in a knot... ) ;-p |
Daniel J. Stern wrote:
> On Fri, 28 Jan 2005, Steve wrote: > > >>Bill Putney wrote: >> >> >>>The downside of power brakes, which is a necessity with disk brakes >>>because they do not have the designed-in mechanical amplification, >> >>Why do people keep saying this? > > > The parrot effect, I'm guessing. No. The reality of modern consumer vehicles that will be driven by quite a range of ages, mental quickness, and physical strength. I used to drive an International Travelall (similar in size to a Chevy Suburban). Unfortunately the mfgr. figured it didn't need power steering - but, man, you should have tried to parallel park that thing - quit4e a feat even for a teenager. I think there would be similar problems selling a modern vehicle with unpowered disk brakes as selling ones without power steering just due to human factors. Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x') |
On Fri, 28 Jan 2005, Bill Putney wrote:
> >>>The downside of power brakes, which is a necessity with disk brakes > >>>because they do not have the designed-in mechanical amplification, > >>Why do people keep saying this? > > The parrot effect, I'm guessing. > No. Rawk! Yes. > The reality of modern consumer vehicles that will be driven by > quite a range of ages, mental quickness, and physical strength. Right, 'cause women and little old men *never* drove before what you arbitrarily consider the "modern" age. Pfft. > I used to drive an International Travelall (similar in size to a Chevy > Suburban). Unfortunately the mfgr. figured it didn't need power > steering No, the original owner decided it didn't need power steering. In any event, that's irrelevant to the topic at hand, which deals with *brakes*. > I think Not hard enough, as it seems. |
> I think there would be similar
>problems selling a modern vehicle with unpowered disk brakes as selling >ones without power steering just due to human factors. My 1946 Cessna had completely reliable, effective, simple, light, cheap, unboosted hydraulic disc brakes. My understanding is that a major problem with disc brakes is that they don't work well as automotive parking brakes. Discs tend to loosen as they cool (exactly what nobody wants) while drum brakes tend to tighten as they cool. More better. Quent |
On Sat, 29 Jan 2005, QDurham wrote:
> My understanding is that a major problem with disc brakes is that they > don't work well as automotive parking brakes. This has been solved for decades: A small drum brake exclusively for parking brake usage in the "hat" section of one or both sets of discs. |
>> My understanding is that a major problem with disc brakes is that they
>> don't work well as automotive parking brakes. > >This has been solved for decades: A small drum brake exclusively for >parking brake usage in the "hat" section of one or both sets of discs. > Exactly. Problem solved -- at some minor complication. I was told that Jag solved this problem by "twisting/warping" the disc brakes. Thoughts? Quent > > > > > |
> I used to drive an International Travelall (similar in size to a Chevy
> Suburban). Unfortunately the mfgr. figured it didn't need power > steering - but, man, you should have tried to parallel park that thing - > quit4e a feat even for a teenager. I think there would be similar > problems selling a modern vehicle with unpowered disk brakes as selling > ones without power steering just due to human factors. I'd have paid extra to get my car without power steering, but that wasn't even an available option. Power steering is great until your engine stalls in the middle of an intersection; then even a wrestler will have trouble avoiding a wreck. |
Daniel J. Stern wrote:
> On Fri, 28 Jan 2005, Bill Putney wrote: > > >>The reality of modern consumer vehicles that will be driven by >>quite a range of ages, mental quickness, and physical strength. > > > Right, 'cause women and little old men *never* drove before what you > arbitrarily consider the "modern" age. Pfft. Oh - I'm sorry - I thought we were living in the present. How silly of me to exclude cars from 20 and 30 years ago from the here and now. >>I used to drive an International Travelall (similar in size to a Chevy >>Suburban). Unfortunately the mfgr. figured it didn't need power >>steering > > > No, the original owner decided it didn't need power steering. In any > event, that's irrelevant to the topic at hand, which deals with *brakes*. No - it was a poorly designed standard package that also included an AMC automatic transmission with no external cooling - fluid needed changing every 20,000 miles - you knew it needed it when the tranny started slipping. They quit making them for a reason. Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x') |
All times are GMT +1. The time now is 09:29 AM. |
Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
AutoBanter.com