RE: {Chrysler 300} Rear brake proportioning valve

["Henry Schleimer" <henry.schleimer@xxxxxxxxxxxxxxx>]

Back when I was paid to reduce road fatalities through vehicle safety (I did a lot of work on truck rollover prevention) I recall seeing a graph plotting length of car wheelbase against incidence of rollover crashes.  It was a direct correlation with limos the least likely to roll over.  It's just a physics thing of wheelbase versus sideways resisting force of the rear tyres stopping the car pivoting about the front axle.  Of note though, when your rears lock up you lose virtually all that sideways tyre resistance.  I recall a panic stop in traffic with my (empty) station wagon and the rears locked (disc/drum factory setup).  The camber of the road made the rear slide sideways into the curb.  Luckily I missing hitting the car in front by a foot.  Chrysler claim my wagon has a proportioning valve built into the master cylinder but I doubt that even if it was working it would be calibrated for just one person in the car.

Obviously because of physics, likelihood of rollover is also directly proportional to centre of gravity height.  The worse offender back in the day was the short wheelbase Ford Bronco with a very high fatality rate.  I think the roofs used to collapse as well.  I remember because a friend had one, which was rare here in Australia.

Anyway, my new car has ABS and ESC which prevents all that instability.  It also has brake assist which basically slams the brakes full on if you stab at them.  Found that out the other day when I stopped way quicker than I wanted or needed to, to avoid a car stopping suddenly in front of me.  Because I stopped so quickly, I was more concerned about any car behind then hitting me!  Not so sure about that "safety" feature...

Henry

-----Original Message-----
From: 'James Douglas' via Chrysler 300 Club International [mailto:chrysler-300-club-international@xxxxxxxxxxxxxxxx] 
Sent: Monday, 13 May 2024 6:51 AM
To: John Grady
Cc: Zach Hietsch; Chrysler300
Subject: RE: {Chrysler 300} Rear brake proportioning valve

John,

You are welcome. A little story behind that...

About 20 years ago I was driving my daily driver, a 1947 Desoto Suburban with a 139.5-inch wheelbase, down a San Francisco Bay Area Freeway at 65 MPH. Coming close to a place called the Caldecott Tunnel a guy in a car cut me off and then stopped dead. 

With drum brakes I know I could not stop and I also knew that if I tried I was likely to fight the steering to keep it straight. I had to crank over on the steering to the right hoping my peripheral vision was correct that nobody was next to me.

When I made that maneuver to miss the idiot, I was now heading to the tunnel entrance wall. I had to swing the steering back straight and all the while I was sure the thing was going to snap and roll.  I figured I was dead.

The front of the Desoto tried to lurch over, but it did not. It felt like the very long wheelbase held it back as the car twisted in the middle. I got the car to settle down and through the long tunnel.

When I popped out the other side a guy cam up next to me in an SUV and rolled his window down and yelled at me that that was great driving. He saw the entire episode. I yelled back that I needed to change my underwear.

The next week I started on a front disc brake set up for that car so that a high-speed panic stop would at least have some decent directional control. Particularly for such a tall center of gravity car.

Doing that conversion, I learned all about "modern" brake systems and their components.  

James



-----Original Message-----
From: John Grady <jkg@xxxxxxxxxxxxxxxxx> 
Sent: Sunday, May 12, 2024 11:16
To: James Douglas <jdd@xxxxxxxxxx>
Cc: Zach Hietsch <zhietsch@xxxxxxxxx>; Chrysler300 <chrysler-300-club-international@xxxxxxxxxxxxxxxx>
Subject: Re: {Chrysler 300} Rear brake proportioning valve

that is really excellent ; more to it than i ever understood . needs a drawing ( i told them that) but a lot of  mysterious stuff and misinformation removed from my understanding of it . 
Thank you James 
Sent from my iPhone

> On May 12, 2024, at 1:20 PM, 'James Douglas' via Chrysler 300 Club International <chrysler-300-club-international@xxxxxxxxxxxxxxxx> wrote:
> 
> Zach,
> 
> Suggest you rear the following:
> 
> https://shop.wilwood.com/blogs/news/how-does-a-proportioning-valve-work
> 
> James
> 
> -----Original Message-----
> From: chrysler-300-club-international@xxxxxxxxxxxxxxxx <chrysler-300-club-international@xxxxxxxxxxxxxxxx> On Behalf Of Zach Hietsch
> Sent: Sunday, May 12, 2024 10:05
> To: Chrysler300 <chrysler-300-club-international@xxxxxxxxxxxxxxxx>
> Subject: {Chrysler 300} Rear brake proportioning valve
> 
> Hello All,
> 
> I am finishing up the brake lines for my conversion to front disks. My kit from AAJ brakes came with a prop valve for the rears.
> 
> Should I install it and if I do what is the correct procedure for setting it.
> 
> I have found a lot of different ways to do it and I am unsure on which one I should follow.
> 
> Thanks
> Zach Hietsch
> 
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