degins

The combo valve is a plumb and forget valve while the adjustable one requires abit of tuning. I'd use the combo type for street use.

I agree with your assessemnt that a proportioning valve is necessary. There are vendors that claim they are not needed. Then again, these same vendors sell "complete" kits that don't include master cylinders, hoses, proportioning valves, or dust shields.

Starfury

Thanks, Degins I don't mind a bit of tuning, but the car is a long way from being track-ready which is why I'm leaning towards the combo valve. Mostly I'm curious as to how well it works compared to an adjustable unit. Obviously the adjustable unit will allow you to fine tune the brake bias to whatever you want, but how is the brake bias with the combo valve?

JapanGT

The front is isolated from the rear, that is the reason for a split system, as mandated by law. If I allow air into the rear circuit it does not effect the front circuit and vice versa.

With the bleeder open you cannot have any pressure, partially closed maybe some pressure and closed, up to a thousand pounds of pressure.
The rear drums require much more fluid than do disks. So your assertion is simply wrong. Because even though the same volume of fluid ( not pressure )
is moved in both circuits, the fluid moves into a larger area in the rear circuit.

Wrong as pointed out above. It will vary from brake system to system, depending on components and condition. It is not something
that can be issued as a blanket statement.

JapanGT

I recommend testing the brake bias in a wet empty car park or empty dead end street
with little in the way of obstacles. If you car pulls up straight and without either end
locking up before the other, then I would not change the system. Usually I would check
emergency braking and also check the lock up point for front and back.

Jav

nassaubayman

What makes you think a combo unit isn't adjustable?



I think the upside to a combo unit far outweigh having a separate proportioning valve. You have less splices and flares to deal with. You have one less piece to worry about where to mount. The adjustment **** is in a handy spot. The only down side is it costs more.

Starfury

The CSRP kit comes with either a separate adjustable proportioning valve or the OE style combo valve. To my knowledge, SSBC is the only company that makes an adjustablecombo valve like that.

Starfury

I was trying to avoid giving a brake mechanics lesson here, but apparently it's necessary.

First of all, the FLUID is isolated between the front and rear braking systems, pressure is not. There are two pistons in the m/c. They are connected hydraulically, not mechanically. The pedal rod pushes on the rear piston which builds pressure in the front circuitwhich then pushes on the front piston to build pressure in therear circuit. It's stilla single closed fluid circuit. If you lose pressure in either circuit, you're losing pressure everywhere. Pascal's law: fluid pressure in a closed system remains the same at all points within the system. This is why the pedal drops to the floor if you openone bleeder screw. The drop in pressure is spreadacross the entire system.

If the two systems were completely isolated, you'd never know if you had a problem with either system until you noticed a drop in braking performance. The pedal would remain the same as long as one one system was working properly. Obviously this would be unsafe, which is why braking systems are not designed this way.

Second, wheel cylinders requiring more fluid doesn't change the fact that they require less pressure. This is why there's a metering valve, to make sure you have some risidual pressure in the rear to keep the shoes close to the drums so you don't have the fronts contacting the discslong before the shoes touch the drums. You're not building much pressure anywhere untilboth pads and shoes are contacting their respective friction surfaces. And like I explained, pressure is constant throughout the entire system, so without some form of proportioning valve and metering valve, the drums are doing far more work as pressure builds than the discs are.

Third, none of what I said is incorrect. I generally try to be fairly nice to people here and give them a chance to understand why they're wrong, but you're all making it very difficult. A lot of engineering goes into designing a vehicle's braking system. If you don't understand in detail how a hydraulic braking system works, you shouldn't be modifying your braking system outside of the factory design.

nassaubayman

I guess I'm confused..... I always thought "combo" meant "combination". Inthis case - a distribution block / proportioning valve combination.

I'm not familiar with the CSRP valve - what's "combo" about it?

Starfury

A combo valve is exactly that, a combination of distribution block and/or prop valve and/or metering valve. The CSRP combo valve is a repro of the OE valve. It looks similar to the 4-wheel drum distribution block, whichlooks likea block of brass. It's a non-adjustable unit, so the brake bias is set at factory spec.

The other option they offer is an adjustable in-line proportioning valve/metering valve combo which gets plumbed in-line with the rear brakes. It allows you the ability to fine tune the brakes but it can be more of a hassle because you do have to tune it, and as you said that's one more splice you have to deal with.

That SSBC valve is nice, but like you said, it's more expensive, and it may be overkill for me right now. However, what I might do is just get the OE style valve for now and consider upgrading to the SSBC valve later if I decide I need it. That's a lot easier than plumbing an in-line adjustable valve down the road.

silverblue66

Tad, I have a question for you. I always thought that the reason for the duel bowl mc is that the front and rear were isolated making them safer than the "fruit jar" single bown mc. But I have also noticed that when bleeding brakes and opening the bleeder screw the pedal goes straight to the floor, thus loosing all braking. Why then is the duel bowl mc safer?
Kip