No conventional brake prop valves in any 88-91??

[1987cp]

Now this may sound silly, but what is meant here by "metering" as opposed to "proportioning"? I know a prop valve is what's used to limit pressure to the rear brakes, but what's the metering part mean?

[johnunit]

Metering seems to slow/stop the movement of fluid to the front brakes until the "slack" in the rear drums has been taken up. Proportioning continuously reduces pressure to the rear brakes, while metering momentarily reduces/stops it to the front.

[gadget73]

The metering valve puts no pressure to the front brakes until you exceed about 100 psi to the front brakes. From 101 psi on up, the front brakes have the same pressure as the master cylinder is producing. Its essentially a holdoff valve.

The proportioning valve reduces pressure by a percentage. Prop valves have a split and a slope figure, stock it splits at 300, and the slope is .36. What that means is that up to 300 psi, the rear brakes get the full pressure of the master cylinder. Past 300 psi, the rear brakes get a percentage of what the fronts get, in this case 36%. At 1000 psi from the master cylinder you'd have 300 + (.36 * 700) or 552 psi on the rear brakes, assuming the valves were dead nuts on published values. Wagons have a .46 slope figure, so they would have more pressure.

[91grandmarquis]

^ He seems to be a box of infinite knowledge. I learn something new from every one of his posts. Damn.

[gadget73]

success. I've fooled another unsuspecting victim into thinking I know what the hell I'm talking about.

[86VickyLX]

The existing stuff will not cause the brakes to lock up in the back. At worst, they're cutting the rear line pressure down a bit lower than ideal so the rear brakes aren't doing as much as they could. The front brakes are grabbing slightly later than they could, which also slightly reduces overall braking capacity. Basically you're not going to kill yourself with the stock valving and rear discs, but there could be an improvement in performance with some valving tweaks.

Markus: later model MC is probably what you want, some mid-90s model with 4 wheel discs and no ABS. The later style booster is a dual diaphragm one too. I don't know how much actual improvement in boost that gives you, but its smaller in diameter if you need more firewall clearance for something. I'm thinking if you've got stock fronts and rear discs, the ideal setup would be the 92-94 non-abs stuff since those front brakes are the same diameter as the box front brakes and the rear discs are also the same as the 97. Those have the prop valve threaded right into the side of the master cylinder between the MC and the line down to the frame. The existing frame mounted valve would have to go away and be replaced with L blocks or unions or something if you used that setup though. I don't know what sort of thread is at the master cylinder end though. If its standard double flare, thats easy. If its wierdo metric BS, I don't know what the trick is unless you use a metric to standard adapter, or get your hands on whatever sort of bubble flare thing is used with metric brake line fittings. Its a double bubble or some crap like that. Not exactly the same as the double flare that is usually seen.


I really wish it was warmer outside. I want to go junkyarding for research, but they're calling for some massive amount of snow this weekend. Boo.

I drove a '91 with that master cylinder and booster, and I stopped like instantly when I pressed the brake pedal even a bit, I crapped myself how fast it stopped. I also drove an '88 grand marquis with the same master cylinder and booster and it stopped just the same.

[87gtVIC]

The metering valve puts no pressure to the front brakes until you exceed about 100 psi to the front brakes.

Did you mean " The metering valve puts no pressure to the front brakes until you exceed about 100 psi to the rear brakes?"

[gadget73]

well, yes and no. The master cylinder puts the same pressure on both ports, so technically if you're at 98 psi from the rear brake port on the master cyl, you're at 98 psi on the front port as well. The metering valve is in the line between the front brake port (physically the rear one) on the master cylinder and the front calipers, so it really could care less what the rear brakes are doing. You could jam a pipe plug in the rear brake circuit for all it cares, and it would operate exactly the same.

[87gtVIC]

ahh I see now.

[yucatecd]

Dear Panthers,
A year ago in Tallahasee, rush hour traffic, the little car in front of my 89 CP dynamited her brakes and I did too but skidded into her. My front and rear disks didn't stop me as fast as a young lady's cheap newer rice burner. Insurance paid for it but I'm not looking forward to my next premium bill/

Next week I'm bringing the cruiser back to scott for more brake mods.

Donald McCaig

[Glen]

So after all the above, should I match the MC & booster to the rear disk? In my case 97, without anti lock.

[gadget73]

Its the proportioning thats somewhat more critical. The master cylinders are all the same bore. The later model booster will give you more assist and braking force though, and thats probably a useful thing to have.

[Glen]

Sounds good to me. When the booster goes I will get the newer year.

[1987cp]

Just revisited this thread now that I'm contemplating brake mods sooner than I'd intended.

What I'm getting out of the first posts is that an '88-'91 master cylinder has two outputs to the front brakes, and does not run the front brake lines through an external metering valve. This would seem to suggest that this master has something in the way of an integrated metering valve.

The metering part would be of primary importance. Of secondary importance would be rear-wheel proportioning, which would then be handled in the normal manner with external proportioning and residual pressure valves on the rear brake line.

Is my thinking correct, or have I gotten myself mentally up a creek without a paddle?

[gadget73]

The 88-91 master cylinders have one line out to the fronts as far as I've seen. They probably have a T block on the frame somewhere though. Never looked that close, but I know there is only one hole on the side of the thing for a front brake line. They also have some sort of a thingy threaded between the steel line and the master cyl itself. I'm guessing thats the metering valve, but without further investigation, I'm not positive.