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Underbody braces, turbos and more!

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PostPosted: Fri Aug 19, 2005 4:13 pm 
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fordem wrote:
It's in there because costing downhill in neutral is dangerous and can get you killed. Most people coasting downhill will attempt to control the speed using the brakes - it causes them to overheat and you end up with no brakes, either because of brake fade from the overheated pads/linings or because you managed to boil the fluid.


For this to happen, I think you'd need a SERIOUSLY under-engineered braking system. Think about it this way, my Silverado 1500 has an automatic transmission with overdrive. Going downhill at say, 90 km/h, with my foot off the gas, generates practically NO engine braking, since the tranny is in O/D and the engine is barely turning above idle. That's for a 5500 lb. truck. I'd be shocked to discover that doing practically the same thing in an 1800 lb. car would toast a set of brakes. I could maybe see it if you were doing 130 km/h and towing a trailer that weighed as much as the car......

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PostPosted: Fri Aug 19, 2005 7:14 pm 
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graymeeguts wrote:
For this to happen, I think you'd need a SERIOUSLY under-engineered braking system. Think about it this way, my Silverado 1500 has an automatic transmission with overdrive. Going downhill at say, 90 km/h, with my foot off the gas, generates practically NO engine braking, since the tranny is in O/D and the engine is barely turning above idle. That's for a 5500 lb. truck. I'd be shocked to discover that doing practically the same thing in an 1800 lb. car would toast a set of brakes. I could maybe see it if you were doing 130 km/h and towing a trailer that weighed as much as the car......


Slightly different scenario - look back at my post - did you notice I said in L or 2? I'm talking about something a little steeper than you are.

Now let's say you're on a long downgrade in your Silverado, you're in D, with your foot off the gas and you find the speed creeping up above 90, what are you going to do? Step on the brake or downshift?

@CMA - Care to tell us why you feel engine braking is not good for the engine?

Gentlemen I invite you both to find the owner's manuals for your vehicles and read them - on page 5-5 of my Suzuki Swift manual I find the following warning.

Reduce your speed and change down to a lower gear before going down a long or steep hill. A lower gear will allow the engine to provide braking. Avoid riding the brakes or they may overheat resulting in brake failure.


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PostPosted: Fri Aug 19, 2005 7:37 pm 
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Location: Vancouver, BC, Canada
sorry i don't have a manual with me

anyway i think its not good for enigne and transmission because my engine is like go-kart and very small engine. if i put strong gear such as 1 or 3 gear and you can feel like you stop the car plus rev the engine....so it probably can burn something the engine ..


if big powerful engine like truck or semi then thats okay.

if i have a brake fade ( highly doubt) then i will put the gear to very low gear ( not r) slowly if fail then turn my car to the curb or whatever and slow the my car.

i live in a few hills ( langley to be exact) and opening city... so i won't be worrying about it anyway.

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PostPosted: Sat Aug 20, 2005 11:09 am 
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The smaller engine in your Suzuki is able to withstand being revved higher and longer than larger engines because it has smaller lighter parts that won't suffer from stress as much as larger heavier ones will. Diesel engines can't engine brake like gasoline engines do, as they don't have intake throttle plates to fight against. Semi trucks use an exhaust brake, which when modulated on and off makes a loud, repetitive noise.

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PostPosted: Sat Aug 20, 2005 5:55 pm 
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fordem wrote:
Slightly different scenario - look back at my post - did you notice I said in L or 2? I'm talking about something a little steeper than you are.

Now let's say you're on a long downgrade in your Silverado, you're in D, with your foot off the gas and you find the speed creeping up above 90, what are you going to do? Step on the brake or downshift?


Fordem, I think you're missing my point. I wholeheartedly agree downshifting and using engine braking is better, in fact, I do it all the time in the aformentioned truck. The point I was trying to make is that making it ILLEGAL to coast seems a bit extreme. The chances of a brake failure resulting from a downhill coast are almost zero, unless you are towing something significant. In fact, I'll wager that 90% of drivers that have automatic transmissions NEVER downshift to brake, regardless of the steepness of the incline, and therefore rely almost entirely on the braking system to stop their car.

Regardless of what the owner's manual said, the only braking failures I have ever heard of happened while towing heavy loads. Therefore, I think the risk of brake failure, IN ITSELF, is not a valid argument for proper use of engine braking; although I recognize that identifying appropriate times to use engine braking is part of good driving.

The whole idea of coasting down hills to promote fuel economy seems a bit whacked anyway.....

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PostPosted: Sat Aug 20, 2005 6:03 pm 
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EDIT: the OTHER point I'm making is that auto manufacturers engineer things like braking systems with the idea that they should hold up regardless of how well or poorly a car is driven, as long as it is not overloaded or otherwise abused. Coasting won't cause a failure unles you are trying to drive down the face of a cliff :D

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PostPosted: Sat Aug 20, 2005 8:12 pm 
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Vehicle braking systems convert kinetic (moving) energy into heat energy, the heat energy is then dissipated into the surrounding air - they are not designed to do this on a continuous basis - if abused in this fashion they will overheat and fail.

The chances of a brake failure caused by a downhill coast are directly proportional to the slope and length of the hill. Increased load whether in or behind the vehicle simply increases the probability.


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