1994 Camry w/ABS: Is this a brake proportioning valve?

[sanjays]

Hello Everyone,
I have a 1994 Camry LE 4-cyl with ABS and 4-wheel discs. I plan to change all the brake lines myself. When I rebuilt one of the calipers (it was sticking) I found quite a bit of rust sediment in the cylinder. Since the cylinder bore itself is in great shape, I can only assume the rust came from the brake lines.

In the 1993 Camry shop manual (page BR-3), there is a description of a brake part that lies behind the engine and mounted to the firewall. The description reads as "Proportioning Valve (w/o ABS) or 2-Way Union (W/ABS)." I interpreted this to imply that 3rd Gen. Camrys with ABS (which use 4-wheel discs) don't have proportioning valves. This makes sense since those valves are really only necessary with rear drum brakes.

However when I examined my Camry, I see that six brake lines are indeed going into some contraption mounted to the firewall. It consists of two parts that are both welded to a mounting bracket (the bracket is just a thin piece of sheet metal):
- One part is just a small, L-shaped two-way coupler that connects two pipes together: The output from the ABS to the R-Front brake.
It seems to serve no purpose. I plan to bypass this when I put in the new lines.

- A larger part (lies on top of the prior mentioned part) that sort of looks like two cylinders joined together side-by-side. On top of each cylinder is a brake line going to the rear calipers. On each of the two sides of the part is a pipe going to the (rear-brake outputs from the) ABS unit. So basically it has two pipes going in and two coming out.

It is my understanding that a "brake proportioning valve" uses a hydraulic pressure sensor to measure the FRONT brake pressure. Depending on the pressure, the rear brakes then have their pressure attenuated by the valve.

However the device in my vehicle only has the REAR brake lines going in and then out. The front brake lines do not connect anywhere on the part.

Can someone clarify as to what this device is called and if it actually serves any useful purpose. Can it cause rear brakes to drag?

note: Haven't finished putting the rebuilt calipers on. Hopefully the rebuild solves the rear-drag issue.

[73sport]

Does it have a wire attached to it at all?

Honestly I have done no research on this nor have I seen it. If it has a wire sometimes they use pressure differential valve to detect master cylinder failure.

That is, if the M/C is actuated (depressed), both of the systems (front and rear) should build pressure. If one does and one doesn't then the valve (piston) is moved off center tripping a switch indicating a hardware failure (because the piston no longer has near equal pressure on both sides, the valve moves triping the indicator).

Because yours does not connect to the front lines, it seems its only acting as distribution node. (just a guess from what you said)

I can't agree with removing it or that 4wd cars do not require a proportioning valve. The p/v is for bias. Even a car w/50-50 weight distribution encounters weight transfer during breaking. As the weight transfers forward, a system w/50-50 bias would now begin locking the rears as there is less weight on the rear tires for traction, thus they skid.
A car w/anti-locks may control this with the system or more likely encorporates the biasing valve into the anti-lock system.

Unless you have aluminum calipers (not just aluminum pistons in those calipers) it is likley that most of the rust came from the calipers but the lines could be jeopordized also.

*** Be VERY careful making modifications and please do more research on those parts and what they do within the braking system. ***