Weak SLH brakes

[spiro440]

Just came back from the track. My brakes are not what they should be. I have the Caravan calipers, solid discs in the rear. The 7/8 MC and the proportioning valve of a 4 wheels disc car ( I think from a shadow) that's what i put on. My brake pads are R4 from porterfield. The fluid used is racing blue .
I am stomped. I had the 911 pads before and was even worse. I figure that they were glazed and got R4 to replace them. A few other racer's took my car for 15 min quick sessions and told me that I should take care of those brakes. Without me even mentionning it!!
The pedal is firm, but has no bite. The rear wheels also have a tendancy to lock up but never the front.
Any insight on this would be great.
Does the mc (1 1/8) from the dodge truck push more fluid or more pressure?

[Orangetona]

Whats your car? It sounds like you could have the wrong type of proportioning valve. Usually the back brakes lock up when you put the wrong ratio (for lack of a better term) valve in.

[ajakeski]

How about the rubber hoses? When they get old they break down inside and restrict flow. Sometimes completely.

You may need an adjustable proportioning valve too.

[Orangetona]

Also, are all the lines 3/16?

---------- Post added at 07:55 PM ---------- Previous post was at 07:53 PM ----------

How about the rubber hoses? When they get old they break down inside and restrict flow. Sometimes completely.

I thought that myself but taking into consideration that it would probably only be 1 hose thats bad, you should be able to feel the difference between sides etc

[cordes]

I would install the 24mm MC and see if that gives you what you need. There is no reason why it shouldn't lock up the fronts.

[spiro440]

I would install the 24mm MC and see if that gives you what you need. There is no reason why it shouldn't lock up the fronts.

Isn't the 7/8 MC the same as 24mm or was it the #1?

Also, are all the lines 3/16?[COLOR="Silver"
[/COLOR]

I thought that myself but taking into consideration that it would probably only be 1 hose thats bad, you should be able to feel the difference between sides etc

How about the rubber hoses? When they get old they break down inside and restrict flow. Sometimes completely.


You may need an adjustable proportioning valve too.

All stock sizes, All stainless braided lines

Whats your car? It sounds like you could have the wrong type of proportioning valve. Usually the back brakes lock up when you put the wrong ratio (for lack of a better term) valve in.

It's a GLH. I got the prop. valve that came with the doner car. (Shadow?)

[cordes]

Double check my math, but the 7/8" MC is probably the 21mm. It is certainly smaller than the 24.

[spiro440]

you are right. I will install the 1" one and see what happens. I have 2 of them just waiting. Will probably look for the 1 1/8.
How do I know which prop. valve I have?

[bakes]

Hold it Hold it are you saying you have not enough braking friction or are you saying after a few laps you getting bad brake fade ?

if your getting real bad brake fade 1st cut the front knuckle bearing retainers back to match the knuckles profile , these retainers can and do block the air flow to the rotor . 2nd if that is not enough make air ducts and flow them at the cailper and the rotor air intake.

[spiro440]

The pedal has the same feel after 30 min. as it has in the first few laps. That's why I am stumped. The R4 are racing pads. there friction coefficiency are higher than Hawks.

[bakes]

soulds like you over heating the pad and rotors

---------- Post added at 06:49 PM ---------- Previous post was at 06:48 PM ----------

or you gassing the pads

[Reaper1]

The proportioning valve isn't right. You also need the 24mm M/C. The larger one from the trucks will give a more firm pedal, but you will need more effort to get the same stopping power.

The prop valve you need has a yellow tag on it. That should solve your issue. If you are using the same pads front and rear and they are both Porterfields, I found that the are TOO effective when they get hot for our cars. I actually had to swap them out for crappy parts store pads in the back to get a good balance and prevent rear lock (which my car had a HUGE issue with!).

[Force Fed Mopar]

So it is firm feeling, not soft or squishy like there's air in it? I put my rear calipers on the wrong sides (ie upside down) which put the bleed screws on the bottom which won't let air out

If it's firm, but doesn't feel like its grabbing, could be the calipers sticking. Or maybe a bad prop valve.

[Orangetona]

The proportioning valve isn't right. You also need the 24mm M/C. The larger one from the trucks will give a more firm pedal, but you will need more effort to get the same stopping power.

The prop valve you need has a yellow tag on it. That should solve your issue. If you are using the same pads front and rear and they are both Porterfields, I found that the are TOO effective when they get hot for our cars. I actually had to swap them out for crappy parts store pads in the back to get a good balance and prevent rear lock (which my car had a HUGE issue with!).

My thoughts exactly. This doesnt only happen on our cars when we Frankenstein stock brake systems.

---------- Post added at 01:20 AM ---------- Previous post was at 01:18 AM ----------

So it is firm feeling, not soft or squishy like there's air in it? I put my rear calipers on the wrong sides (ie upside down) which put the bleed screws on the bottom which won't let air out

If it's firm, but doesn't feel like its grabbing, could be the calipers sticking. Or maybe a bad prop valve.

+1 on that also...they would never work right being installed with the bleeder on the bottom

[ShadowFromHell]

The 24mm/1" master is a MUST. The 21 does not move enough fluid for the big minivan calipers.

[shelbymonster]

spiro has a omni , ive read in many places that the stock proportioning valve would be enough , ive never drove my old charger on the track but i remember having real nice braking power , what year rear brake set-up you got in the back spiro ?

[Force Fed Mopar]

The 24mm/1" master is a MUST. The 21 does not move enough fluid for the big minivan calipers.

I dunno about that, seems like I used a 7/8 master on my GLHS when I did my minivan caliper/solid rear disc swap on my GLHS.

[Orangetona]

The 24mm/1" master is a MUST. The 21 does not move enough fluid for the big minivan calipers.

I dont think that the question is that the master is too small. Hes driving a car thats much lighter and the brake system is much more compact. He should be able to lock the front brakes up without a problem. Having ONLY the back brakes lock up is almost directly in line with the wrong prop valve.

Also to the OP, all lines are 3/16 yeah?

---------- Post added at 08:59 AM ---------- Previous post was at 08:58 AM ----------

spiro has a omni , ive read in many places that the stock proportioning valve would be enough , ive never drove my old charger on the track but i remember having real nice braking power , what year rear brake set-up you got in the back spiro ?

I would tend to agree with that too. Just because its the correct ratio for the application. I cant see why it wouldnt work.

[tryingbe]

Brake systems distribute the pressure from the master cylinder through a differential valve. These function by splitting the two master cylinder outputs between the left-front and right-rear brakes and vise versa. This way if one set fails, the other set can still stop the vehicle because the brakes are split diagonally from each other. In most cases, pressure to the rear brakes has to be reduced. This is accomplished through a proportioning differential valve. There are several different proportioning valves available, depending on the brake system combination your vehicle has. They function by reducing the amount of brake fluid pressure to the rear brakes after a certain input pressure point, called the split point. The ratio by which the rear brake pressure is reduced after the split point is called the proportioning slope. The lower the slope value, the more the pressure to the rear brakes is reduced. So, if you find that your rear brakes tend to lock up prematurely, then you need a valve with a lower slope and/or lower split point. A perfectly balanced brake system does not need a proportioning valve. Instead these use a basic differential valve that have no proportioning feature, and therefore have no split point and have a slope of 1. Stock proportioning valves are identified by the color of the indent tag. Below is a chart of available valve configurations.

http://minimopar.knizefamily.net/perf/brakes.html

[spiro440]

The proportioning valve isn't right. You also need the 24mm M/C. The larger one from the trucks will give a more firm pedal, but you will need more effort to get the same stopping power.

The prop valve you need has a yellow tag on it. That should solve your issue. If you are using the same pads front and rear and they are both Porterfields, I found that the are TOO effective when they get hot for our cars. I actually had to swap them out for crappy parts store pads in the back to get a good balance and prevent rear lock (which my car had a HUGE issue with!).

I also have regular pads in the back. Thinking to cut half the pads of in the rear.

I will swap the MC to the 1" one which should be like the 24mm and cross my fingers.

So it is firm feeling, not soft or squishy like there's air in it? I put my rear calipers on the wrong sides (ie upside down) which put the bleed screws on the bottom which won't let air out

If it's firm, but doesn't feel like its grabbing, could be the calipers sticking. Or maybe a bad prop valve.

spiro has a omni , ive read in many places that the stock proportioning valve would be enough , ive never drove my old charger on the track but i remember having real nice braking power , what year rear brake set-up you got in the back spiro ?

I can't verify at the moment if the yellow tag is there. (cars getting an alignment and getting the rocks out of tire/mag. Spun out yesterday!!!)
Can't recall having a tag. On my GLH prop. valve there is no tag!? Only a part number stamped.
Anybody else running the stock prop.valve in there omni with the slh set-up?

---------- Post added at 10:07 AM ---------- Previous post was at 10:01 AM ----------

Tag Color Function Material Split Point Slope
(none) Differential Brass - 1
Grey Differential-Proportioning Brass 500psi 0.27
Tan Differential-Proportioning Brass 600psi 0.43
White Differential-Proportioning Brass 750psi 0.43
Black Differential-Proportioning Brass 800psi 0.59

Got this off minimopar.: No mention of the yellow tag!