What heats brakes more?

[deepsleep]

I'm trying to avoid over heating my brakes going down some steep hills for long periods at a time. Would driving really slow prevent overheating?

[Lincolnmania]

drive in a lower gear.....dont keep on the brake all the time going down the hill......pump the brakes

[deepsleep]

What speed should I try to maintain?

[mrltd]

it's not really a speed thing, it's how often you are applying them. They need time to cool between applications or they will overheat.

[Don7887]

I just got back from south carolina and driving there and back we were on the highways doing 70. I just locked the car out of overdrive and only had to use the brakes a few times for a couple seconds on the bigger hills, being in 3rd really held the car back, on the lesser grades you might even need to apply some throttle in order to maintain your speed.

[1987cp]

Guessing you're going to spend a lot of time with the gear selector in "1" if your local roads are at all like the ones my mother-in-law describes.

[Archangel]

drive in a lower gear.....dont keep on the brake all the time going down the hill......pump the brakes

Yeps, downshift - general rule (well, a trucking rule, but still) is that you down a hill in the same gear that you'd use if climbing it. Works freakin great.

it's not really a speed thing, it's how often you are applying them. They need time to cool between applications or they will overheat.

That's correct, which is why half the folks at the SF cruise had very weak brakes towards the end - most were riding their brakes to control their speed all through the trip to Centralia. I personally never had any brake fade or anything, brakes didn't even smell, and I could have stopped on a dime if needed, but I was using an old trucker's trick for that - you drop down to the proper gear and then just let her run as fast as she wants to run, just before the corner you brake hard to bring your speed down, then you fly in the turn and let her run again till the next turn comes. I nearly ran David over like that a few times, I had to leave plenty of space between us cause I was catching up with him on the turns. If you're about to do that tho, you better make sure your brakes are up to it, old worn out wheel cylinders and
calipers and rusty brake lines may not last long.

Guessing you're going to spend a lot of time with the gear selector in "1" if your local roads are at all like the ones my mother-in-law describes.

I've done that, we went on a field trip once to see Frank Lloyd Wright's "Falling Water" house, and the hills there are scary on the descent, I was running in 1st and 2nd most of the time (I had the Lincoln at the time). There was a nice Camaro in our group, and he was using mostly the wheel brakes to maintain speed, after we pulled over at the bottom of one of the mountains all four discs were glowing orange.

[mrltd]

That's correct, which is why half the folks at the SF cruise had very weak brakes towards the end - most were riding their brakes to control their speed all through the trip to Centralia. I personally never had any brake fade or anything, brakes didn't even smell, and I could have stopped on a dime if needed, but I was using an old trucker's trick for that - you drop down to the proper gear and then just let her run as fast as she wants to run, just before the corner you brake hard to bring your speed down, then you fly in the turn and let her run again till the next turn comes. I nearly ran David over like that a few times, I had to leave plenty of space between us cause I was catching up with him on the turns. If you're about to do that tho, you better make sure your brakes are up to it, old worn out wheel cylinders and
calipers and rusty brake lines may not last long.

.

I was glad to be towards the front for all that stuff, and it made the drifting easier....

[1987cp]

Glowing brakes on the street!

All that would be only part of why I prefer to have little to nothing to do with roads built on the sides of hills ....

[deepsleep]

just before the corner you brake hard to bring your speed down, then you fly in the turn and let her run again till the next turn comes.

This is what I thought might be the best way but the hills I'm on are steep enough in some places where I need to brake throughout the decent. Going up was no problems. The long 1 gear is awesome. what rpms is it in first @25 mph w/2.72's?

[Archangel]

Fuck if I know, depends on tire size too. But I can tell you this - if you need 1st gear to go up those hills, then you should stay in 1st gear on your way down. No brakes will be needed for that, except for cornering. Yeah the engine will revv up, but trust me that noise ain't got nothing on my diesel turning past 3000 rpms while slowing down a 30ft car hauler down a few miles of 10% grade - if I can stand that, you'll be just fine

[1987cp]

You can probably use one of those online gear calculators for that ... just figure in about a 27" tire and 2.40:1 First gear ratio.


If you punch in a gear ratio of 6.55 (2.73 rear times 2.41 First gear), you get right about 25 mph at 2000 rpm with the calculator at the bottom of this page:

http://www.revlimiter.net/scca/calc.html

... so if that is correct, you should only be spinning 2000rpm at 25mph in First. Not a big deal in the least.

Actually, if that output is at all representative, you should be shifting 1-2 at WOT (4000rpm shifts with the stock Vic governor) at about 50 mph. Kind of makes sense, since my 2.26:1 car would be doing 70 when I tried winding it out to 5 grand in First.

[johnunit]

Those numbers do sound correct, as it'd have me shifting at 3700-800 out of first.

[P72Ford]

Michael, you didn't account for converter slip.

On that trip to Centralia at SF, I held 3rd gear for a majority of the time... but that wasn't enough down some of the hills... I didn't overheat the brakes on the trip to Centralia, though. But on the ride down 25 on the way back to Scott's, I got them hot, but not hot enough to hamper braking at all.

I suppose trying to haul down a near 5000 pound curb weight in short order was to blame for that.

[1987cp]

Michael, you didn't account for converter slip.

True, though that can be hard to predict in a simple calculation, and a stock converter is pretty tight anyway ....

If I plug in a 27.5" tire and 5.466 gear ratio (2.26 times 2.41 First), I get about 75 mph at 5000rpm, or 4675rpm at 70. That's 325rpm off at 5000rpm .... assuming the same margin of error, that would be an error of +130rpm at around 2000, or about 2100-2300rpm actual observed RPM for the 2.73 car at 25.

On the other hand ... during engine braking with an automatic and a stock converter, what would the relationship be between actual observed RPM and theoretical RPM assuming no slippage? Woudln't observed RPM actually be slightly *lower* than one would calculate?