Weak brakes in cold weather - Hyundai Forums : Hyundai Forum
 
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post #1 of 8 (permalink) Old 12-18-2016, 02:32 PM Thread Starter
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Weak brakes in cold weather

I am almost sure, I have seen somewhere in this forum similar problem, I cannot find it right now.

Here is what's going on.
In cold weather (below 60 degree) looks like power brakes do not work. I presumed, it might be famous brake switch issue. So, I went yesterday and get it done in dealership.
My wife informed me, this morning, she had a same issue.
Solution to this point was to warm up vehicle in the morning and brakes start working. I examined it myself and found - if I drive slowly (on the driveway and while applying the brake, I would move shift to neutral and get the brakes working. It looks like brake switch (or something other) does not disengage transmission.
This is serious issue. But, I am not going to deal with dealership. I do have decent scanning tool and I might be able to find out something (or, probably and most likely NOT).
It might be an issue, also, with some ABS thing, who knows... ?
There is no warning lights on dashboard.
Is there anyone to enlighten me on possibilities? Thank you.
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post #2 of 8 (permalink) Old 12-18-2016, 03:35 PM
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Post is unclear to concern at hand..

Stop light switch does nothing for brake hydraulic action,, it is just there to detect pedal movement allowing plunger to close stop light switch and turn on stop lights,, does nothing for trans function either..

I assume car stops when you step on pedal ?

With engine off,, pump brake pedal to make pedal hard... now with light foot pressure on firm pedal, start engine,, the pedal should fall down when engine starts, this tell me the booster is working

Please clarify what we looking at.

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post #3 of 8 (permalink) Old 12-18-2016, 03:51 PM Thread Starter
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As I understood, brake switch should disengage transmission in the same time when turning brake lights on.
We never had a problem with brake lights. They work fine.
Brake pedal is fine with engine on or off. What is going on in cold mornings, while pressing pedal, it feels there is no power brakes on, at all. Vehicle keeps moving with almost no brakes. If I move gear shift to neutral (in that moment) brakes work fine and they stop vehicle as expected.
Warming up the car (with temperature inside above 72 degree) seems to be the trick. Pressing pedal couple of times, shifting gear shift couple of times from P to D (with pressed brake) seems to be the trick that restores brakes as expected.
I was hoping that brake switch was bad (as was described in many posts). But, it does not seem to have effect in this case. (I still need to confirm and see they ACTUALLY replaced the switch).
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post #4 of 8 (permalink) Old 12-18-2016, 04:07 PM
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Cannot move shifter,, interlock inop,,, stop light switch do that,, been to dealer in last couple yr and have 110 Stop Light Switch recall done if applicable to VIN (I assume you is USA,, no ;ocstion called out in profile to display in box at left under username) --- Got VIN for me to check claims history to VIN (if USA)?

Brake pads in good condition,, rotor faces not all rusted up to where friction co-efficient of pad to friction surfaces (rotor faces) poor grip..

All caliper slides free moving (clean and lubed)

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post #5 of 8 (permalink) Old 12-18-2016, 04:17 PM Thread Starter
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Yes, I am in US. I just went with scanning tool to check ABS error codes, It did show 3 active codes, one of which was 702 and the other two were 600something (I actually saved the codes in the reader and will exam it later on)
So, I just erased all "active" codes and see what it does tomorrow morning...
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post #6 of 8 (permalink) Old 12-18-2016, 04:22 PM
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Leave codes, write them down, and post them up in their proper Bxxxx / Cxxxx / Pxxxx format depending on which module they come from..

DTC point to defined circuit that the module has seen to be at fault (sensor fault, logic, open/short circuit)

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post #7 of 8 (permalink) Old 12-19-2016, 08:24 AM
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As sbr711 says, the brake light switch has absolutely nothing to do with operation of the brake hydraulic system. The switch is there to turn on the brake lights when you apply the brakes. As for transmission function, the brake light switch does have a set of contacts that are used to break the transmission's torque converter clutch circuit when you apply the brakes. This does not apply to low speed driving, though. The TCC is only activated/engaged in higher gears (probably 3, 4, and 5) with vehicle speed above about 40 mph and light throttle conditions. Bottom line: forget about the brake light switch -- it's not causing your van's poor braking action.

When you put the transmission in neutral, the RPMs and manifold vacuum level increase. It's manifold vacuum that powers the brake booster. So I'd be looking for a collapsed or damaged vacuum hose between the intake manifold and the brake booster. It's also possible that you have a defective brake booster. Sbr711's engine off/engine start pedal drop test is looking for that.

Low manifold vacuum also occurs when the engine has worn internal parts or the camshaft timing gets badly out of whack. Probably not the case here.
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post #8 of 8 (permalink) Old 12-20-2016, 10:16 PM Thread Starter
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Thank you, Pete, for such good explanation. I was considering that option. This vehicle has about 110k, what would not be considered worn out, especially when you know the vehicle had one previous owner, 70 year old couple. These days, we were doing experiments. Interestingly enough, when internal (cabin) temperature is below 74 degree F, brakes acting as was explained. When internal temperature reaches above 75 degree F, brakes working fine. It might not be directly related. But, that was observation.
When the weather gets warmer, I will try to measure couple of things, probably, try to replace brake's fluid in the entire system and will go from there.
Once again, thank you very much.
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