I had to get to the end of this chain. Tyler is absolutely correct,
residual pressure valves were used in old drum brake system to maintain
pressure on the lip seal in the wheel cylinders. Drum brake systems could
get away with this as there are return springs on the brake shoes, in a disc
brake you would end up with a drag, wear, and probably fluid boil with
attendant loss of brakes in short order if you had a residual pressure
valve. Residual valves were mostly gone by mid 60s or so as wheel cylinder
seals (cups) were redesigned to include cup expanders, the spring and
stampings that go inside the wheel cylinder that maintained seal to push rod
contact.
A little history on passenger car and Light Truck braking systems.
Several types of valves became common with split hydraulic brake systems in
passenger cars and light trucks and subsequent disc drum systems. Initially
these valves were separate pieces, then integrate valves were designed, and
finally some designs were incorporated into master cylinders.
1). Proportioning valves which provide different pressures to the front
(disc) brake than the rear drum brake. These were required as the torque
output versus pressure of a drum brake is much higher than that of a disc
brake, a side note here is brake boosters (power brakes) became pretty much
standard as with Disc-drum systems.
2). Metering valve which again tries to balance a disc brake and a drum
brake. The metering valve allowed a small pressure build up in the disc
brake system to take up initial travel and then "held off" additional
pressure increase until the drum brake overcame\me its return springs
(typically 75 to 100 psi). At higher pressures the front pressure was
allowed to build up. In part this function helped (not much) the condition
of front wheels locked on very low mu, slippery, payment while the rear
tires were spinning at idle in Drive. This valve also plays a part in the
brake wear balance of the vehicle. Some of the readers may recall these
valves as having a pin to pull out or push in to bleed the brakes.
3). Failure warning light, which is really a spool valve that shuttles when
a pressure differential is applied across it. Early designs of split
hydraulic system brakes for [passenger cars and light trucks sometimes
required a lot of fiddling with while bleeding to turn the lamp off.
4). Fluid level devices which give an indication of the brake fluid level,
usually in the master cylinder. Not really a valve but a different design
concept manufacturers can use to meet Federal Motor Vehicle Safety Standards
in place of or in addition to the pressure differential switch.
Just couldn't resist expanding on Tyler's comments below.
Thomas, If you managed to read all the way through this there is one thing
in one of your notes I must comment on. You said you filled the system with
DOT 5 fluid, but the V-Max uses DOT 3, not sure about the R1 but suspect it
also uses dot 3 or 4. I would recommend against changing to DOT 5 unless
you change all the rubber parts in your hydraulic system. DOT 5 is typically
a silicone fluid and not compatible with the glycol ester based DOT 3 and 4.
While this should not contributor to your initial complaint, I just don't
think the DOT 5 is worth it unless you are road racing and really cooking
the brakes on a regular basis. I do highly recommend changing DOT 3 at an
interval of no more than two years.
Ronald Fisch V.M.O.A. 78
86 mostly stock, [EMAIL PROTECTED]
-----Original Message-----
From: Tyler Pennock [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, October 24, 2000 5:38 PM
To: V-MAX TECH LIST
Subject: check valve
Subject: Re: check valve
a residual pressure valve is only used in drum brake systems, when
converting auto from disc/drum combo to 4 wheel disc, you are to remove the
residual valve in the rear brake outlet port in the master cylinder, then
install proportioning valve in the rear main line to balance system,
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