rebuilding brake pressure reducing valves

[john 215]

Hi,

Inside the car you have a easy to reach line lock 'for playing' [:p]
i know how many turn to return it how i like it.

Cheers John


LIVE LIFE A QUARTER OF A MILE AT A TIME!

1976 Speke FHC Beauty

1979 3.5 FHC(STATUS PENDING!!)

1982 2.0 DHC NOW A 4.6,ON THE ROAD NOW KICKING AR5E !!!!

[tencate]

By the way, those of you with adjustable brake proportioning valves, what are you getting for stopping distances? My best braking time from 60 mph (100 kph) to 0 is

135 feet

on my original TR8 (G-Tech). Larry in Michigan got something like 125 ft with his 5 speed TR7. Stock system, everything working.

Important parameter: tires are 14 inchers on Superlite wheels.

Just curious Pretty respectable for a car without anti-lock brakes!

Jim (and maybe the moderators are going to get mad at me for starting a new topic so perhaps I'll just stop here...)

[Hasbeen]

It appears that no one is thinking of modifying the piston on a brake system, to suit the rubber components available. This may be suitable for this bit.

I have not stripped one of these, & the pistons do look small for machining in the photos, but when I had my suspension & brake place I often modified the metal bits to suit the neoprene stuff that had recently become available.

My centerless grinder was installed to machine the damaged shafts of McPherson struts, but I used it as often for rebuilding brake bits.

Tencate, you appear to have the wrong idea about anti-lock brakes. They are not designed to, nor do they reduce stopping distances. In fact they extend stopping distances over that achievable by a good driver, using an identical system with out the anti-lock.

What anti-lock does is make it possible to steer while braking very hard, without a lock up causing loss of traction, & thus control.

It may save your life in many situations, depending on your ability, but it sure won't stop you in a shorter distance.

Hasbeen

[tencate]

Ah, you might be right about the anti-lock although I've seen a couple of SAE papers a few years back which indicate that modern systems now can do better than a skilled person in most cases---although I confess I don't know what current state of the art is. I'll post a link to them if I can find them and you can read for yourselves and decide what you think.

I AM still interested in the stopping distances people have been able to get. The old press articles (Road and Track) quote ~170 ft for the TR8, less for the TR7s and those distances are with 185 70R13 tires.

Finally to get back on topic, I hadn't thought about re-machining the valve to work with new seals. Interesting! The first step though is to send the shuttle and seals in to Apple Hydraulics to see if indeed they CAN rebuild these. Stay tuned.

Jim

[Marko]

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by tencate</i>

Ah, you might be right about the anti-lock although I've seen a couple of SAE papers a few years back which indicate that modern systems now can do better than a skilled person in most cases---although I confess I don't know what current state of the art is. I'll post a link to them if I can find them and you can read for yourselves and decide what you think.
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Modern ABS's would be all 4 channel ones, old systems would be 3 channel (2 front wheels and 1 rear or diff).

Abs work great when you get a brain fart. And good portion of "drivers" , if you can call them that way because they have the license but they dont know how to drive, use their cars to get from point A to point B without using their brain too much.

You can't be 100% concentrated all the time to be able to outperform an (modern) ABS. Atleast most people arent.

As Hasbeen said bigger advantade of ABS is how it affects steerability and stability of a car under hard braking, wet tarmac, snow, ice, potholes, ever tried to brake while crossing a manhole or streetcar tracks, every situation where you have large difference in friction between tires and surface.



But if your main concenr is shortening the stopping distance.... get better tires...

Every single type of brakes, even the worst ones, can lock up the wheels atleast once, that means that they can generate enough braking torque to stop the car.

Its just up to the tires then to stop the car or lock up and slide.




To get back on topic.

Does anybody know whats the pressure ratio between front and rear brakes on a TR?

Why not just connect the front brakes directly to the front calipers, and rear with a brake pressure relieve valve to set rear brake pressure in a ratio to main brake cyilinder?

Main brake cylinder for front and rear are the same diameter so there's no difference there.

Advantage of having front brakes connected directly to master brake cylinder is there's no element to reduce the pressure in the front system. You then modulate the brake pressure with your foot, not some gizmo in the hydraulic circuit.

[tencate]

Judging by the three cars I've measured brake pressures on here, the best braking one (all on the same tires) is the TR8 DHC with about 1100 psi to the fronts (max) and 700 psi to the rears (max). The TR8 FHC in the fuzzy YouTube video had about 900 psi max going to the rears and that car locks up the rear wheels all the time in hard stops.

The brake proportioning valve (aka pressure reducing valve) doesn't give you a linear decrease in rear braking with pressure, it has a knee which approximates the roll off needed as the car rotates about its center of gravity during braking and unloads the rear tires.

Fascinating stuff. BTW, I've found Fred Puhn's Brake Handbook informative reading!
Jim

[Marko]

Drum brakes are not linear either.