Coming down the mountain at the weekend, I managed to overheat the brakes to such an extent that I lost virtually all braking.
I stopped the truck in snow, which cooled everything down again and managed to continue the rest of the way, admittedly gingerly, without issue.
Its in the shop being fixed, but I am curious. The guy who is looking at it tells me the pads and discs are fine, although he'll replace the pads anyway, but that he has to drain and replace all the fluid - loads of air bubbles apparantly.
Could I have got the brakes so hot the fluid boiled, did something else happen, or are the two things unrelated ?
Its not really an issue, since it is hardly an expensive job, even on the Dodge, but its never happened before and so I wonder what lead to it this time.
Mark.
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You boiled the fluid. How often do you have the fluid changed??
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One can buy very expensive silicone based brake fluid which does not absorb moisture. My servicing garage have a device which measures the boiling point of a smaple of the brake fluid and, if it is below a certain figure, it means there is too much moisture in it and it needs changing. Presumably this is regardless of the required interval (2 to 3 years). If it passes the test it doesn't need changing = money saved!
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Mark
It's possible that the brake fluid was contaminated with water, which can happen via natural ingress into the master cylinder when operating the brakes - i.e. the system "breathes". Brake fluid is hygroscopic and when it contains water it can, effectively, boil - and result in loss of brake efficiency.
This may be what has happened. Perhaps you can check the service records and see when the fluid was last changed. I think the recommendation is 2 years, these days - DW or one of the professional mechanics will probably have more accurate info.
Ian Cook
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Mark
You don't describe the symptoms exactly, but two different types of brake fade that could have occurred:
1) The pads overheated to the point where their coefficient of friction dropped dramatically, and therefore they could apply less torque to the discs/drums. Symptoms - the pedal stays high, but no matter how hard you push the car does not slow down properly
2) The brake fluid is heated to the point where the water in it boils creating vapour bubbles in the fluid. Symptoms - the pedal drops to the floor due to the extra compressibility, and you have no braking effect transmittted to the pads.
There's also 2A, where the fluid itself boils, causing similar symptoms.
They all correct themselves when the components cool, but often the discs and pads are not the same after a severe cooking. The 'vapour type' failures correct themselves when the car cools down and the vapour condenses, and are often responsible for those accidents where the driver says 'the brakes failed', but the police say they were fine after the accident.
Obviously regular fluid changes can prevent 2 & 2A failures, as normal brake fluids are hygroscopic - they attract and absorb moisture from the air. Also consider changing the pads before they get too thin, as they act as an insulator between the braking heat and the fluid. More frequent brake fluid changes are recommended in mountainous areas.
It could be the fluid (or at least the water content) vapourised, and there could have been some air ingress via the seals as it cooled. Sounds like the repair shop is doing just the right thing in replacing the pads and fluid.
Regards
John S
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There is also category 3, when the servo is exhausted by continuous braking.
This could be inherent in the design, ie not enough vacuum reserve for continuous use, or by a leaking valve or hose.
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John - really it was 1.5)
The pedal stayed high, but there was little braking effect although later on I began to notice that the pedal was lower. However, the dramatic effect was stamping on the brakes and getting virtually no effect.
AS for when the brake fluid was last changed, well, um, not recently, shall we say.
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Mark
Yes 1.5 sounds about right.
Looks like the pads overheated and faded initially, and the heat got through and subsequently caused problems in the fluid. Probably showed up when your chap removed the pads, so changing them isn't a bad idea, as the pad surface will be damaged. Certainly a fluid change is indicated
Funnily enough, my pal in the US was commenting that he borrowed a large 4WD truck from work a while back and had exactly the same problem descending a mountain. I wonder if the brakes on these things are a bit marginal. Plus, I believe the Americans like sharp brakes, and possibly use soft pads to get good initial bite. What's the wheel size? That limits the brake diameter, and when you think that even standard European saloons often have 15 inch wheels these days, whilst weighing about half as much..... In fact, most large 4WD's are probably limited in much the same way, although it's probably more significant for the heavier American SUVs.
On your favourite topic, I saw an advert for an uprated brake kit for Fr**landers. Offered 33% better brakes. Brake disc diameter was 5mm greater than my 1.8 Astra. Makes you think.
Regards
John S
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I have done hundreds, if not thousands, of miles in the mountains without any of this difficulty before. The brakes are normally excellent and can be scary for the person behind if I am on tarmac.
The only issue I ever get is that the back is lighter than the front (its a large engined pickup) and sometimes the back skips and hops on heavy braking on tarmac.
Also, I remember one occasion on the road coming back from the mountains having to emergency stop from about 120kph to 0kph. It stopped as efficiently as you could expect of something of that size & weight.
As for wheel size - I think they're 17". Certainly they are not smaller, but I would have to actually look to be sure. But I can tell you that the discs are absolutely huge.
>(freelander) ....offered 33% better brakes.
Probably means that all four brakes work, rather than the normal two or three.
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Mark(B)
I've just seen the 2003 Dodge Ram Heavy Duty on the Dodge web site. Now there's something to bring back to the UK with you!
Terry
PS Did you have to use the Andes brake to stop? :o)
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I wonder how they made it more heavy duty than mine ? It must be a frightening machine.
Have you got the URL handy ?
M.
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Mark
The heavy duty is shown in its glory on
www.dodge.com/autoshow/index.html?tsrc=home&tgrp=p...e
The full range can be got at from www.dodge.com
Have fun!
Terry
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Mark
Sounds like sharp brakes = softish pads, plus a serious front end bias. Combined with old brake fluid, could be the problem. Whatever, you had a case of classic brake fade.
17 inch wheels - not uncommon even on saloons these days; even our Astra runs on 16's. A BMW or Volvo probably scales 1.5t or thereabouts, and has vented discs. What does this thing weigh? Sounds serious!
Regards
John S
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>>What does this thing weigh? Sounds serious!
It is..............
Wheelbase, in............. 160.5
Overall Length, in........ 249.7
Overall Width, in...........79.9
Overall Height, in..........74.5
Curb Weight, lbs..........5082
Standard Payload, lbs.....1570
Fuel Capacity, gals. .......35.0
Seating Capacity ............6
Front Head Room, in.........40.8
Max. Front Leg Room, in.....41.0
Rear Head Room, in..........40.0
Min. Rear Leg Room, in......36.4
Size, liters/cu..............5.9/360
Horsepower @ rpm.............245 @ 4000
Torque (lb-ft) @ rpm.........335 @ 3200
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35 GALLONS?
And you want to bring it back and pay UK petrol prices?
:>)
Following on from a previous thread, what does a set of tyres cost for that beast?
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$ 300 US each. Maybe a little less. But those are full blown off-road tyres. Combination tyres are cheaper, and in the UK it will certainly only need combination tyres.
M.
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Hells bells! 21 ft long and over 6.6 ft wide. Where will you park it?
It weighs over 2.25 tons at the kerb, and can go up to 3tons. No wonder the brakes have to work.
Only 41 bhp/litre (about half the specific output of a decent European car engine) at 4000 revs. It'll probably last forever.
No mention of fuel consumption I see.
You can't be serious about importing it!
Regards
John S
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>>No mention of fuel consumption I see.
No, and best not. It isn't good.
Now you can imagine the problem on a steep mountain, and I mean steep, with 37 hairpins in the space of 8km.
Just as well they have run offs !
>>You can't be serious about importing it!
Oh, I am completely serious about considering it. I am working out cost/effort now. Whether or not I will actually do it will become clear over the next week or two. Adriana would be quite happy if I left the Dodge in Chile and took the 4Runner over. We shall see.
Its no worse than driving a large van/small truck, and a lot more manouverable.
Its a lot easier to drive than you might imagine. Multi-story car parks are an issue, its too tall, but other than its generally ok.
Roads in Santiago are no bigger than UK roads and the traffic is frequently worse.
And it is LOADS of fun, even buses are careful.
Mark.
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p.s. I don't know what its fuel consupmtion is, I never even try and measure it, but here is a quote from the website....
"Test Quad Cab 4WD with the 5.9 averaged just 11.9 mpg. With 4.7 V8, test 4WD automatic-transmission Quad Cab averaged 12.6 mpg and with 2WD and manual, regular cab averaged 14.1 Expect the overworked V6 to return no more than 15-16 in daily driving. All engines use regular-grade fuel"
Therefore I apparantly get 12mpg. Oh. It felt better when I didn't know.
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Is that US or Imp. gallons? I think there would be a market here, judging from the popularity of big 4WD's here. I think that as traffic density increases, people look for something that is less easily intimidated and allows a view over the rest.
A friend of mine imports larger non-UK variants of Japanese pick-ups and does well.
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