Date: Mon, 25 Sep 2017 19:25:17 -0700
Reply-To: Stuart MacMillan <stuartmacm@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Stuart MacMillan <stuartmacm@GMAIL.COM>
Subject: Re: Stumble and Loss of Brake Pressure Heading Up a Pass
In-Reply-To: <CAKLYf13Q-cjh138GDaMA4eb53poe38ARnHhE95j-dzaVYtVeUA@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
A hot caliper can cause loss of braking because there is compressible vapor inside it. This unbalances the whole system, particularly the front, which does most of the braking. Even without vaporizing the fluid you can get brake fade because the pad materials vaporize, creating a layer of gas between the pads and rotor. You should be able to smell this though if this is your problem, and the brakes would be smoking. The wheel(s) would likely be too hot to touch as well.
Brake fluid should be flushed every two years because it will absorb moisture. That moisture can cause caliper pistons to rust and not fully retract (the rubber seals provide the retraction force, which isn’t much), which leads to overheating of the fluid in the caliper and vaporization of fluid and/or water vapor.
A brake inspection is the next step.
Stuart
From: Ryan Perry [mailto:rjdperry@gmail.com]
Sent: Monday, September 25, 2017 6:45 PM
To: Stuart MacMillan; vanagon@gerry.vanagon.com
Subject: Re: Stumble and Loss of Brake Pressure Heading Up a Pass
Ok, makes sense. So question then, would the 30min regular highway drive prior not have created the boiling to make me lose pressure or are we thinking it's a combination of high vacuum with boiled brake fluids?
On Mon, Sep 25, 2017, 9:40 PM Stuart MacMillan <stuartmacm@gmail.com> wrote:
The standard test for the booster is to depress the brake pedal and start the engine. Pedal should drop a bit on startup. Like Dennis said, you might have a stuck brake caliper piston. The friction could cause the fluid to boil (or absorbed water to vaporize) which results in loss of braking. Time to have the brakes checked.
Stuart
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Ryan Perry
Sent: Monday, September 25, 2017 5:55 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Stumble and Loss of Brake Pressure Heading Up a Pass
Thanks Dennis, checked the level and was at max. I can't say how old the brake fluid is so maybe it's time to change it?
Is there a definitive test anyone knows for master cylinder and brake booster?
Thanks
Ryan
On Mon, Sep 25, 2017, 3:27 PM Dennis Haynes <d23haynes57@hotmail.com> wrote:
> Check master cylinder fluid level. Combination bad cylinder and brake
> booster can let engine vacuum suck the fluid out of the master.
> Next would be brakes dragging or otherwise overheated and you vapor
> locked the brakes. Problem could be compounded by the fluid being old
> and saturated with water.
>
> Dennis
>
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On
> Behalf Of Ryan Perry
> Sent: Monday, September 25, 2017 3:14 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Stumble and Loss of Brake Pressure Heading Up a Pass
>
> This one is new for me, taking it to the collective brain trust!
>
> '84 Manual with a newly installed 2.2l GoWesty. Runs fine in all
> normal driving conditions. When heading up a pass for camping this
> weekend, think Western NC, couple thousand feet elevation over 4 miles
> or so. The van was under moderately heavy load in 3rd gear, RPMs on
> the high side but nothing outrageous, was holding steady in power.
>
> About 4 mins in the power hiccups slightly then continues on. I had a
> bit of a corner so tapped the brakes lightly and find no pressure.
> Really weird. Made it to the top for a short flat and found I had to
> pump brakes to get pressure. This was short lived for a single
> application. As soon as I let off back to no pressure, had to pump
> again. Then back up the next section of the cut under similar load and
> had the same stumble at about 3-4min in then carries on fine. Top of
> that cut and the end of our trip out the van is running fine, though a
> bit hot as expected, but no brakes without pumping.
>
> Parked, camped, had a great time celebrating or 4th wedding anniversary.
> (Someday I'll show you all or vanagon wedding pics, you'll like them)
> Anyway, leave Sunday and brakes are fine, engine is fine.
>
> What do you think? Related? Coincidence? Vacuum line or booster? Fuel
> pressure or pump?
>
> Thanks for any ideas, i try to keep stopping at the top of my list of
> fixes!
>
> Ryan
> Asheville, NC
>
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