Date: Wed, 4 Sep 2019 19:16:14 -0700
Reply-To: Alistair Bell <albell@SHAW.CA>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Alistair Bell <albell@SHAW.CA>
Subject: Re: Brake fade on trip
In-Reply-To: <1eea01d56356$1135e660$33a1b320$@gmail.com>
Content-Type: text/plain; charset=utf-8
Hey Stuart,
Well I can’t say for sure if I boiled the fluid. Maybe localized with old brake fluid? Can’t say. And maybe it was the old flex line, that I subsequently replaced, was bulging.
It’s hard to describe the roads and our trip adequately. That wasn’t the only steep part but it was the stretch that was steep for the longest. No issues with brakes elsewhere.
And I did put on new rotors and pads back in the spring and I was super impressed by how well they worked. As good if not better than any rotor pad combo I’ve had on a van.
Life busy this year, may not get out to the steep and rough again this season. So I can’t compare after the flush and flex line replacement.
Alistair
> On Sep 4, 2019, at 12:22 PM, <stuartmacm@gmail.com> <stuartmacm@gmail.com> wrote:
>
> I experienced severe brake fade years ago in my '68 Westy descending the Grapevine on I-5. Lucky for me traffic was light and the road straight so I was able to ride it to the bottom. Scary stuff. That rig had four wheel drum brakes so I think it was the lining off gassing that caused the fade (my pedal was not spongy). My understanding is usually only disk brakes on race cars can boil the fluid and silicon DOT 5 fluid was invented to prevent this. If you did boil the fluid your braking may not have come back at all, and your pedal would feel spongy. Off gassing of pad materials is much more common, but water absorbed by the fluid lowers the BP, so who knows? See https://en.wikipedia.org/wiki/Brake_fluid. You might want to experiment with different pads now that you have flushed the fluid.
>
> Stuart
>
>
> -----Original Message-----
> From: Vanagon Mailing List <vanagon@gerry.vanagon.com> On Behalf Of Alistair Bell
> Sent: Tuesday, September 3, 2019 6:46 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Brake fade on trip
>
> Hi,
>
> I’ll stick with my terminology as brake fade can also include brake fluid boiling. I understand the function of the proportioning valve, and maybe you’re right in thinking that might be culprit or involved in the experience.
>
> But I’ve driven down that same stretch of road many times. And I’ve been down shorter stretches that are slightly steeper. Generally the max grade on those spurs is around 20 percent. I have measure 25 percent, and on loose rocks that grade makes stopping harder. I have never felt the brake pedal go soft as it did recently. But that doesnt explain your point of smelling hot brakes when it happened. I know that smell, I should have smelled it even if it was very windy.
>
> Perhaps the fluid didn’t boil, but perhaps the worn out near side front flex line expanded and that was the cause.
>
> I don’t want to belabour the point but the road was steep. I’m probably guilty of understatement there. But steep enough to be hard to stop and hold.
>
> I did apply the handbrake when I noticed the pedal softness. That helped.
>
> Summary: not my first rodeo, been on same road and steeper, never had the brakes go like that before.
>
> Oh one more point. The temp sensors on the front wheel valve stem caps showed increase in temp over a very short distance, maybe 1 km. Rears showed 20C, the fronts 30-34C.
>
> I’d like to have an answer, but even if my hypothesis is wrong changing the brake fluid and the faulty flex line was a good move. My understatement again.
>
> Thanks for you info Dennis, I’m not dismissing it, I’m trying to make it work with what I experienced.
>
> Alistair
>
>
>> On Sep 3, 2019, at 6:22 PM, Dennis Haynes <d23haynes57@hotmail.com> wrote:
>>
>> Going back to the beginning. Having a pedal go soft due to the brake fluid vaporizing is not the same as "brake fade". Brake fade is when the lining get so hot they no longer provide friction even though the hydraulics or in the case of trucks the air system is working. Vaporizing the fluid usually takes some effort and you will usually smell the brakes burning before that happens.
>>
>> More likely what you experienced going down the steep hill was the rear brake inertia valve taking over and reducing the brake pressure to the rears, pedal drops. It is mounted on the frame the way it is as it is sensitive to angle.
>>
>> Dennis
>>
>>
>> -----Original Message-----
>> From: Vanagon Mailing List <vanagon@gerry.vanagon.com> On Behalf Of Alistair Bell
>> Sent: Monday, September 2, 2019 8:49 PM
>> To: vanagon@GERRY.VANAGON.COM
>> Subject: Brake fade on trip
>>
>> Last week took a short trip, to a couple of places we often go to here n southern Vancouver island. Was the first trip with the new cheapo tire pressure monitoring kit I posted about a while back.
>>
>> So of course I’m glued to the screen on the Hwy part of the trip. The temp sensor being in the valve stem cap ain’t a really good way of observing tire temps. It’s great if you want to see what side of the an has been in the sun though.
>>
>> :-)
>>
>> The air flow over the valve stem cap, at speed, keeps the sensor close to ambient. I couldn’t see any temp changes at Hwy speeds even on steepish declines and hard braking .
>>
>> So we got to one of our fav spots. The road was as bad as I’ve seen it. It’s single track logging spur, parts of the road becomes a creek during rain. Last 5 km of it is steep, as steep as you get on logging roads ( think of the loaded trucks coming down. Honestly, some parts are so steep and narrow, and tight turns, I can’t believe anything longer than an f250 can make it ).
>>
>> It’s g gear for us, and the front wheels are grabbing. Second day, late afternoon the weather was changing and the wind coming up strongish. We decided to head to another spot, lower and less windy.
>>
>> Coming back down the road I was in first, but the roughness of the road had me riding the brakes a lot.
>>
>> Then the pedal got soft and I had less than sufficient brake. Got it into g gear and got the hand brake on once in a while. The temp sensors showed 34 front right , 30 front left, and 16 on both rear ( Celsius ) . I’m thinking the values are a good reflection of the wheel temps as we were going slow, no movement on speedo slow.
>>
>> On the level, the brakes came back. The front temps dropped.
>>
>> Brakes fine on Hwy travel back home.
>>
>> This event is what made me flush the brakes yesterday. And change that old front near side flex line.
>>
>> I’m hypothesizing that the front right brake was doing more work than the front left, thinking the front left flex line was bulging.
>>
>> Anyway, that’s my story and I’m sticking to it :-)
>>
>> Alistair
>
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