Hackerbilt, I realize it is not a fix-all or "band-aid" as you stated. As stated earlier, the car runs and drives fine except in a panic stop. It will then skid the 185/75 R14 front tires. I don't like not being able to steer in that situation. I just thought putting the proportioning valve in the front line would give me some adjustment. The rear wheels (235/75 R15) NEVER skid in any situation, unless I adjust them up real close. I believe the rear wheel cyls. are near correct with 11" drum brakes. I believe the proportioning valve is NOT needed on the rears like ALL the books recommend to install them. I still attribute this to the "bigs and littles". Perhaps that is why they don't even put front brakes on dragsters. Thanks.
The bicycles I rode as a kid only had rear wheel braking called coaster brakes that applied when you pushed the pedals backwards. I rode them back and forth to school even in the winter on snow and ice. I had a paper rout that I rode 6 miles a day 7 days a week from the time I was 12 until I turned 16. We got very good at locking the rear brake up to do a controlled sideways slide melting the rubber off to leave nice black marks. When the multi speed narrow tire bicycles first came out, kids would forget which brake was which and hit the front brake, locking the wheel to the fork. If the tire has enough traction to keep the wheel turning, the bike rotates around the wheel and the rider goes head first into the ground. The go karts we ran only had rear wheel brakes. When we started riding motorcycles on dirt, the first thing we were taught is to forget you even have a front wheel brake. On icy roads, if the rear brakes lock up, you can steer out of it with the front wheels. If the front wheels lock up there is no steering.
You can't believe your wheel brakes into working. Take them apart and measure them. Adjust the rear brakes up real close. You should here the shoe on the drum. The volume and pressure relationship come into play. If the available volume goes into taking up slack then there's not enough volume left to develop enough pressure. Your fronts with 2" Pistons require significantly less volume to move than the 2.5" Pistons and certainly less than wheel cylinders , and the rest of the volume goes to developing pressure . Apparently so much more pressure than the rears that the fronts lock. Now do the fronts lock on panic stops or is it on sand gravel, grass and any low traction surface. With your bigs out back, a little bit of brake pressure will go a long way. How much pressure is out back? Get a guage and see
Updated with tire size. Ok, here's some specs for everyone. 1960 Studebaker Lark 4dr wagon with a V8 and auto trans. approx 3200lbs, 108.5 wheel base Front brake kit is: '95ish S10 4x4 caliper 63.5mm bore 1968 Mustang rotor 11.29" Rear end is: 1967ish Mustang 8" Shoe is 10 x 1.75 drum 10 x 1.75 wheel cyl 7/8" bore Tires: Front 215/65 R15 Rear 225/60 R15 I'm leaning towards trying bigger rear wheel cylinders and maybe wider shoes or even looking for a 11" setup. BTW a '68 Mustang runs the same rear brake parts with 60mm calipers and the same rotors. My thinking is that the caliper bore might be too big, I might be able to find different smaller bore calipers (not sure if I can find one to fit the caliper bracket).
Pressure is Pressure and Volume is Volume. [don't confuse the 2] The M/C is moving the same volume through it's system, and when it cant move any move volume [all clearances taken up] it develops pressure [a driver can feel this as the pedal gets hard] The pressure is equal throughout the whole system, It is where hydraulic pressure is converted into Clamping pressure that gets the Front /rear bias. This is calculated with fluid mechanics [similar to gear ratios] where a small piston = less Clamping pressure / small driven gear = less torque For the people running Big in Littles, If you cant reduce clamping pressure with Calliper sizes etc, consider using a tandem M/C from a BMW E36 [these have a staggered bore and a floating centre piston] Put the small bore end [furthest from the pedal] to the rears and the large bore to the front wheels I am totally against using a P/V in the front circuit [previous posts attribute that] Why? Because a P/V doesn't actually proportion pressure , it only limits maximum pressure. All you end you doing is dialling back maximum pressure so it doesn't lock-up on the grass. It only is fooling you into thinking you've fixed the problem. It gets dangerous when high speed panic stops are needed
I am (a "youthful") 72 years old. My adolescent experiences were similar to yours....paper routes for several years, etc. I built a pretty decent go kart when I was 14. I am very familiar with New Departure and Bendix coaster brakes, the latter were inferior in my view. The problem with the front brakes on "English" bicycles was not the brakes, but the skinny tires. My comments regard motorcycles assumed street (pavement) operation and are not theoretical.......the couple of times I 'dropped' a bike back in the day was rear wheel braking in emergency stops and/or wet pavement. I am not claiming the difference between primary front braking vs rear is day and night. I am saying primary front braking is more predictable and less likely to get one crossed up in a panic stop. Ray
Wow does that make me want to grab my sawzall and start removing things. That's some ugly work there.
1oldtimer, your quote above brought my attention to this thread, because my car also acts similar as stated through out this thread. I believe my brake set up is very close to correct for my car, except for one thing... I don't have a metering valve. Up until now, I've never heard of a metering valve to hold off front disc brakes. All of the diagrams I've ever seen for hot rod brake systems don't show a metering valve, just a proportioning valve and residual pressure valves... http://static.speedwaymotors.com/images/charts/Brake_System.jpg Another article says in referring to proportioning valves, "This device lets you adjust the front-to-rear braking balance by proportionally decreasing the rear (or in some cases the front) brake line pressure." http://www.speedwaymotors.com/Wilwood-260-8419-Knob-Style-Proportioning-Valve,6494.html According to this other article I found today, it looks like a lot of us may have been doing this wrong for years... http://auto.howstuffworks.com/auto-parts/brakes/brake-types/master-brake2.htm I know this doesn't answer your original question, but I learned something today! Thanks.
Learn something here http://stoptech.com/technical-support/technical-white-papers/proportioning-valves Most callipers use a square section O-ring on the piston. These deflect enough to pull the piston/pad off the disk [no metering valve is needed in the front]
I don't understand this. It seems like limiting max pressure is fine to me...in a T with big front brakes and very skinny tires. Not so much on a bigger car with regular tires...as I've said already. (and don't even bring race car stuff into this. A T built to anything close to road course spec will look and behave FAR different than mine. Not to mention, mine and most others will never be driven at 10/10ths...more like 3/10ths. These aren't "Locosts" we're driving here! ) If ...800#(?) of pressure locks my front wheels instantly then where is the problem with limiting its pressure to just before that? I can still stop on a dime and the car is very predictable and easy to modulate. That was definately NOT the case prior to installing the front PV into the system. My T drives and stops like a new car since I've done my brake and suspension upgrades. (downgrades? LoL) Track use? Never gonna happen so i don't see how track-ability is a point to aim for. My car and most T's will never make even remotely acceptable track cars. They were never designed with that thought.
Four things. First, the bicycle analogies aren't really germane because you keep a bicycle upright by countersteering. The reason you tend to fall over after locking up the front wheel on a bicycle is that you'll have lost the ability to countersteer. The situation is a bit different with non-single-track vehicles. Second, just to complicate matters further, two factors not yet mentioned in this thread are the braking moment arm length of the brakes and the tractive moment arm length of the tyres, i.e. the tyres' rolling radius versus the effective radius of the brakes. So, "little" front tyres' reduced traction due to narrow width is only half of it. They'll also have a smaller rolling radius and, hence, less torque the brakes need to overcome. Combine that with front brakes with a large effective radius, and over-powerful front brakes result, especially if you've got little brakes on tall rear "bigs". Third, brake feel is useful. Most non-ABS cars are set up to lock the front wheels first, to avoid the tail coming out, but it is true that thus losing steering is not a good thing. Good brake feel allows a decent driver to control that, by making the locking event perceptible. There is a recognized evasive manoeuvre which involves deliberately locking up the fronts while steering, then releasing the brakes at the critical moment, but that requires being able to feel when you lock up and when you unlock. Good brake feel means the braking force varies with how hard you push, not how far you move your foot. Fourth, though anti-dive etc. geometry only affects weight transfer during steady-state braking in so far as it effects a change in the height of the centre of gravity, it may set up a momentary rotational inertia about the pitch axis which can cause transient weight transfer. Some expert drivers these days (doubtless having grown up on a diet of fast fwd cars) are advocating an aggressive braking technique which begins with stabbing the brakes hard to plant the nose of the car momentarily and so prevent lock-up, then loosing up slightly as the transient weight transfer passes. Just something to think about.
I read that 2 days ago, didn't help my situation. The rear brakes are NOT locking up on my car. Only added to the confusion again.
It takes a shitload more braking power to stop at 0.6G[average Civic] than 0.2G[dithering around in a car park] It also takes more braking power to haul up extra weight.[more passengers],and more braking power to haul up from 70mph vs 20mph Where does this power come from....................The drivers foot. Unfortunately the extra power from the drivers foot doesn't get transfered into front brake torque because you have a "pressure limiting valve" blocking it. If you put your car on a rolling road measuring brake torque, you will discover that there is still a heavy front bias when you gently use the brakes. It is only when you are heavy footed does the PV limit the front brake torques, and if you get even more heavy footed all the extra line pressure goes to the rear brakes. Track use is comparable to emergency stopping [on the track we do it to win, in an emergency it is to avoid an accident] Serious , you need to fix it properly [ the knowledge is out there for free ]
Firstly is your rear brakes capable of locking up? Put 2 brake hose clamps on the front and give it a 30 yard test [it could have other issues like "Flap" in the rear brake hose or frozen cylinders] You don't need to better your 60ft times, just give it a push down the road/your driveway and also make sure you have a parkbrake Consider putting a BMW E36 Staggered bore M/C on your car This is an easy way to alter line pressures between the 2 circuits [you still might need to fine tune the bias as discussed before]
There is a lot of miss information being spread as gospel on this thread. A metering valve and a proportioning valve are two different devices that provide two completely different functions that may be contained together within the same housing known as as combination, three way or sometimes referred to as a proportioning valve. Driving a car with hose clamps on the front brake hoses could be downright dangerous if the rear brakes aren't working. I would suggest anyone trying to design to design or repair a brake system get a repair manual and learn how the system actually works. Posted using the Full Custom H.A.M.B. App!
I have the knowledge...but in all likelyhood next year I will be replacing the axle with a narrower 9" I have, so it's not sensible to change out the rear brake assemblies on the axle that are there now. I need larger diameter drums and potentially larger bore wheel cylinders to help the rear of the car do more work when stopping. By making those changes the PV can go away again. I'm not finding things as you say in bold above though. I'm not heavy footed in normal stopping. I've found that the PV has helped in normal, soft stops on crappy surfaces and is unnoticeable on pavement stops. On pavement the car has never had issues stopping...just on gravel/grass or the like. The front wheels would lock and the car would continue on its merry way, slowing gradually. I will admit I havent jammed on the brakes enough to make the tires lock up at any point on pavement. The car stops so fast on pavement its actually pretty impressive. With or without the PV.
IIRC, the earlier '64-67 Mustangs also used those same rear brakes but used four piston calipers rather than single piston. These calipers (if the 'net info I found is correct) used four 43mm pistons, for a total piston area of 5806 sq. mm. or not quite two times as much as the calipers you're using (180%). The difference between what you have and OEM '68 Mustang is only 13%, so I wouldn't think those are too big...
This is what I was alluding to when I mentioned tire/brake size further back (just didn't recall the technical terms). Hackerbuilt has a rather extreme case, not something you would normally find. If he has enough line pressure to lock or nearly lock the front brakes under a full panic situation, I don't see why 'limiting' pressure is a bad thing. Admittedly, he hasn't tested this but seems satisfied with his brake performance although for peace of mind I think I would test this...
That leaves brake torque force against the available traction on a 68 mustang compared to old timer and montana's rides. Weight to tire size to rotors of Old timers vs 68 mustang ? Still just 13% ? And then combination of the difference for net difference?
Well, the Stude is about the same weight or maybe a little lighter depending on the V8 engine and options selected for the Mustang, and tire size isn't that much different, I would think that he's get at least the same brake performance as the Mustang.
Well, this topic for sure wins the contest for most contested subject! This even beats radial vs. bias tires. My two bits based on general common principles: 1. Drum brakes take more time to actuate because they have "slack" in their system. 2. Drum brakes require less pressure to activate (because they're self-actuating) and they also have more friction surface area (measure area of shoes vs. pads and see). 3. Drum brakes are usually in the rear, with discs up front. 4. Generally you want your front wheels to do most of the braking. My conclusion is that you want your drum brakes to activate first, but you also want them to receive less braking force. The solution to my conclusion is a combination valve. Without one, you're basically activating the front brakes first and then letting the rear brakes do most of the braking which sounds to me like a recipe for weight shift and rear lockup. And, incidentally, I'd rather have a front lockup than a rear one. At least with a front lockup you can regain your steering by releasing your brakes. Let the fireworks continue.......
A little thought experiment. How about we take an example of a car with perfect brakes and start messing with it ?? The first thing we do is add a rubber rake - smaller fronts and bigger tears. What happens to the breaking ? The front are stopping the same weight/force with a smaller lever and the tears fight a longer lever. Brake bias is off right? The first change to correct - or back to equal is increasing the rear clamp force to combat that longer lever- right ? And decrease the front clamp force so the shorter lever can at least do something, right? Think away
It's a traction issue only for guys with cars who have a kattiewhompassed brake bias. Before you can have the traction issued you're gonna need both, that bad brake bias and rear brakes that don't work right. Where's the cart from that dead horse?
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