RE: brakes and lonnnng downhills

[DeWitt Harrison <de@aztek-eng.com>]

Not exactly. I was suggesting that everything is fine, but, due to
the adjustable bias design,  if you work the brakes hard in a long
downhill situation with a couple of lard butts - I mean adults -
in the back seat, the rear brakes are going to get hot. On the
other hand, if the rear brakes still became warmer than the
fronts without rear seat passengers, then the bias valve's control
arm may have come loose from its moorings or otherwise
become stuck in maximum pressure to the rear position.

You're on to something, though. I think locking up the brakes
(ABS off) would give Phil some information about the braking bias.

DeWitt

At 01:57 PM 10/9/98 -0400, you wrote:
>So, your response suggests that Phil should do several high speed stops on
>level ground before assuming that his bias is non-optimal.
>
>kirby
>
>> ----------
>> From: 	DeWitt Harrison[SMTP:de@aztek-eng.com]
>> Sent: 	Friday, October 09, 1998 1:13 PM
>> To: 	kirby.a.smith@lmco.com
>> Cc: 	quattro@coimbra.ans.net
>> Subject: 	Re: brakes and lonnnng downhills
>> 
>> On Thu, 08 Oct 1998 21:43:00 -0400,  Kirby Smith wrote:
>> >[ ... ]
>> >I am becoming ever more amazed at the responses to Phil's message.  I
>> >thought Phil's question was clear, but perhaps I am influenced by being
>> part
>> >of the original conversation.  Let me clarify.  Upon reaching the parking
>> >lot at the bottom of Mt. Wash., we felt the wheels to see how hot they
>> got.
>> >The fronts were warm and the rears were _warmer_.  (I've had much hotter
>> >wheels from marginal caliper retraction.)  This suggested to Phil that
>> >perhaps the brake pressure proportioning valve should have been set up
>> >differently after his car's UFOs were replaced.  Thus his question.  I
>> >expect Phil will be happy to receive any specific information on brake
>> bias
>> >setup that can be effected on his 200q if any listers have this
>> knowledge.
>> 
>> Right. The point of the question was largely missed. There is an
>> adjustable
>> front/rear proportioning valve on many of these cars which responds to
>> rear cargo weight - not to disparage Phil's rear seat passengers. The
>> valve
>> simply has an arm which moves as the rear suspension height changes with
>> loading. The point is to better utilize the rear brakes when the car is
>> more
>> heavily laden since the rear wheels will be less prone to lock up during a
>> stop when the front/rear weight bias is moved rearward.
>> 
>> I think this strategy is geared more toward fast stops on flat terrain
>> which transfers most of the weight of a lightly loaded vehicle onto the
>> front
>> tires, but less of a heavily loaded vehicle. In the absence of rapid
>> deceleration,
>> a rear cargo load could place a disproportionate burden on the rear brakes
>> with this system.
>> 
>> DeWitt Harrison
>> Boulder, CO
>> 88 5kcstq
>> 
>
>