Re: Simultaneous Application of Gas and Brake Pedals

Apparently it used to happen all the time in the 1950s. Just listen to the endless parade of bloody, tearful teenage-love-cut-tragically-short-when- car-stalls songs...

;-)

And the pedal effort in a 4400-lb 1969 vehicle with manual disk brakes is NOT significantly higher than the pedal effort in a Honda Accord of today. And disk vs. drum makes no difference at all. I just don't see whay the staement that power boost "is a necessity with disk brakes" keeps popping into discussions.

'Scuse me while I pick my jaw up off the floor!

I've *NEVER* run anto anyone who thought AMC ever built their own transmissions before.

I don't know about the middle of an intersection, but one time I had the belt pop off while in stop-n-go traffic on the freeway. I did alright, but my wife would've wrecked for sure. It was a nasty surprise.

--Geoff

I'm not typing my explanation of it again. It is far more likely to be necessary with discs than with drums. search this thread for it.

nate

Not that uncommon for engines to stall when you let off the throttle. I've had the problem in both of my current cars, when there were various minor problems with the engines.

Fortunately you can still steer when the engine is stalled, you just have to use a bit of muscle. It's loss of power braking that worries me more (in a previous car, you simply could not slow down the car with the brake pedal, once you'd used up the bit of boost that was saved up. Either that or I have weak legs).

I liked my 900kg car with no PS (it was easy to do power-u-turns in), but when I'm steering my 1300kg PS car with the engine stalled, I feel like I'm about to rip the steering wheel off.

Only if they had no clue how parts are sourced and put together, or what the difference between a part made by a company & just installed.

Anyone who thinks International Harvester products were

I say this as the owner of a forty year old four cyl. scout that came factory with sodium filled valves, just because it seemed like the way to do it.

Bernard

Why, thank you!

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

There is that, but I didn't pick on Putney for it 'cause his claim that "AMC automatic transmissions" was crying out louder for attention.

They did have their downsides, chief amongst which was parts interchangeability. Ever look at the Hollander Interchange Manual for just about any "light duty" IH product? Six different and non-interchangeable front brake drums for one model, for instance, depending on production date!

But yeah, IH was never *ever* known for putting out marginally-engineered products before the company failed and was reborn as "Navistar".

Yup. Very typical of IH.

DS

Nate, there's absolutely NO engineering basis for that statement! That was my whole objection in the first place. The fact that there have been several (incorrect) assertions made in this thread about "why" disk brakes "need" power assist does not make it true. Disk brakes do not "need" power assist any more than drum brakes, whether or not the drum brakes are of the self-energizing variety.

Accord of

brakes"

So you're saying that all those years of engineering school and experience actually working as an engineer with automotive braking systems were for naught. The fact that you don't like my explanation doesn't mean it's not true. Discs *do* require more line pressure for a given brake torque than self-energizing drums, assuming similar diameters and normal piston sizes. Simple, indisputable fact.

nate

(damn, I really hate it when I have to play the "credentials" card, but willfully ignorant people just piss me the f**k off!)

marginally,

Very true!

Kelsey-Hayes

I don't like hydroboosts, just for the simple reason that a lot of times the PS pump is not adequately sized. Thus, if you do a few quick slalom maneuvers and then slam on the brakes, the pump may "gulp" for a second to catch up. Not something that happens in everyday driving, to be sure, but IMHO that makes it even more dangerous, as it can be alarming when it happens.

I don't remember ever having this issue in my old BMW 535i but I've experienced it in several light trucks and SUVs (only vehicles I've driven with hydraulic assist.) Of course, the Bimmer had another issue which was the hydraulic accumulator "bomb" was dead, which made initial application of the brake pedal, um, interesting, but that was more due to the fact that it was ancient and had 200K miles on it rather than a design flaw. Likely with the dead "bomb" it would have experienced the same problems, but I never had it on a test track to find out.

nate

Definitely simple and indisputable, but why are you being so obtuse as to pretend this is even close to half of the story? "Needs more line pressure" does NOT necessarily equate to "Needs a power booster".

There are *many* ways of varying the mechanical advantage of the driver's foot over the disc caliper pistons.

DS

I don't like hydroboosts, for the simple reason that it's a doglick, failure-prone, needlessly-complex system that gives rotten pedal feel.

A simple machine design textbook proves you're right nate. The self energizing feature is the advantage of drums.

True, but requiring more line pressure isn't the same thing as requiring power assist. This is only true if the additional line pressure required increases the pedal effort so much that a typical human hasn't enough leg power to make them perform adequately. I don't think this is the case across the board with disk brakes. I think that is the other person's point.

Matt

True, but a lot of them involve tradeoffs, usually in the "stroke" of the master cylinder. A smaller bore in the MC will provide good pedal feel and acceptable pedal effort, BUT is not often workable in modern braking systems as the pedal will eventually "bottom out" on a full-effort, high-speed, ABS-active stop - definitely something you don't want to happen. Likewise, there may not be enough room to leave enough pedal left in a one-circuit-failed condition. Yes, it *can* work, but there's plenty of reasons why it doesn't.

That said, in a light car (

That's an honest question. So you are telling me that, in the otherwise same vehicle, a non-vacuum assisted disc brake will take no more pedal pressure and at the same time no more pedal travel than a non-vacuum assisted self-energizing drum brake? If you answer "yes", then I will defer to your experience and knowledge, though I was sure that the disc brake in that example would require either a lot more pedal pressure or a lot more pedal travel or a combination (again, depending on the games played with the master cylinder design).

What say you?

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')