Help me stop!

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Ironmike

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Well, I guess this is a "revisited" post, sorta. Hope someone can finally help me sort this out.

4 years ago I did the Scarebird front conversion on my 71 Demon 340, which had the factory big drums up front. The conversion went on fine and thought I had no problems.....until a deer ran out in front of me. Just didn't stop well.

So....went through 2 master cyls, went from a disc/drum distribution block form a 73 dart, back to my drum/drum dist. block. Still the same results. Stops straight, but not very good.

My local dragstrip has a notoriously short shutdown and it's honestly a bit scary.
You couldn't lock up the brakes on this car if Hulk Hogan jammed 'em on, in his prime.

My thoughts are this: the Scarebird conversion uses discs from a Toyota minivan and calipers from a Chev Celebrity/Camaro, so they SHOULD stop this car pretty fast....I think.
I bought EBC Yellow stuff pads, all new lines, everything you could think of.

I wonder if the weak link is the dist block on these cars. I was thinking of completely eliminating it with straight couplings, but I just don't know.

This is a non powerbrake car, and the Scarebird rotors are 10", I think. Single piston caliper. Anyone see a weak link there?

I am planning on ordering the SSBC 4 piston set up, but really don't want to charge something I really cant afford.

I'm at my wits end. I don't want to have an accident from this....or are my expectations just too high? I know for a fact, in the late 70's I was driving a Dart and damn near hit a kid.........those brakes locked up and left 40 feet of rubber on the road. I remember like it was yesterday. I know this car CAN stop well without spending another grand. I just got to a brain "freeze" point now.
 
I am running a stock dist. block on my converted 69 dart.

I use a 1980 or so dodge mastercylinder and a adjustable proportioning valve on the line to the back brakes.

It has stock 74 disc brake set up off an a body and 11in rear drums and it stops very well
 
Ironmike said:
Well, I guess this is a "revisited" post, sorta. Hope someone can finally help me sort this out.

4 years ago I did the Scarebird front conversion on my 71 Demon 340, which had the factory big drums up front. The conversion went on fine and thought I had no problems.....until a deer ran out in front of me. Just didn't stop well.

So....went through 2 master cyls, went from a disc/drum distribution block form a 73 dart, back to my drum/drum dist. block. Still the same results. Stops straight, but not very good.

My local dragstrip has a notoriously short shutdown and it's honestly a bit scary.
You couldn't lock up the brakes on this car if Hulk Hogan jammed 'em on, in his prime.

My thoughts are this: the Scarebird conversion uses discs from a Toyota minivan and calipers from a Chev Celebrity/Camaro, so they SHOULD stop this car pretty fast....I think.
I bought EBC Yellow stuff pads, all new lines, everything you could think of.

I wonder if the weak link is the dist block on these cars. I was thinking of completely eliminating it with straight couplings, but I just don't know.

This is a non powerbrake car, and the Scarebird rotors are 10", I think. Single piston caliper. Anyone see a weak link there?

I am planning on ordering the SSBC 4 piston set up, but really don't want to charge something I really cant afford.

I'm at my wits end. I don't want to have an accident from this....or are my expectations just too high? I know for a fact, in the late 70's I was driving a Dart and damn near hit a kid.........those brakes locked up and left 40 feet of rubber on the road. I remember like it was yesterday. I know this car CAN stop well without spending another grand. I just got to a brain "freeze" point now.
Click to expand...


look into the master cylinder and proportioning valve setup. I have the scarebird stuff on a bunch of cars that I have done and only one gave me a bit of a problem. 3500 lbs car too!

it turned out that I had the incorrect master cylinder( too large a bore and I don't know how many times it was rebuilt) on it and didn't have the proportioning valve adjusted right. I did have to get a new distribution block due to age and it seemed that it just didn't flow correctly. once that was done it was good to "stop".

I changed to a 74 dart master with non-power disc/drum and adjusted the rear propoprtioning valve up a bit to work right. that car now stops better than my newer cars. I also went to non metallic pads for a better grab on the disc (just made me feel better when stopping than ceramic pads)
in effect I did this by going from 1" to 15/16" on the 73-74 model dart I chose to decrease the effort "Increasing MC bore will increase your pedal effort and decrease your pedal travel. Decreasing MC bore will decrease your pedal effort and increase your pedal travel."

I CAN lock em up(the rears) if I hit the pedal hard and the car does not try to swap ends when it happens Yeah I've had to panic stop (where I had all 4 lock up.. SCARY) a couple times due to grandmas thinking they can get out an itty - bitty gap in traffic and still go slow while everyone else is doing 50-60.

here is the link I use to determine what type of braking pressure I need/want
http://cysunnychang.tripod.com/personal/useful_information/effects.htm
 
x2 to the above. What is your MC diameter?

You should be able to use my setup information with compared with yours to get relative ratios;

My setup
Manual disc/drum

15/16 aluminum MC
73-76 abody 10" discs and slider calipers
15/16ths wheel cylinders 11x2.5" drums

I added a $40 willwood proportioning valve to dial out the rear brake bias. I could have also sourced smaller wheel cylinders and may eventually anyways.

it stops well with a very firm pedal. I can lock it up at autox with even with sticky hot tires. I will eventually use a higher friction pad rather than the $10 parts store ones that have been on it since I bought the car and adjust the prop valve back some.
 
A distribution block is just that. A Y-block. I suspect you mean, combination valve. The kind with 5 lines attached to it(2 in and 3 out).The combination valve is often called a brake proportioning valve. While it may be possible for that valve to make trouble,its hardly likely. The circuit that pertains to the front brakes is just like a Y-block;that is one line in and 2 lines out.Also bear in mind that this valve is a safety valve , in that if one end fails it turns on the dash warning lite.
-Bear in mind how brakes work. They convert the momentum of the vehicle into heat through friction at the pad/disc interface.Things go wrong when A) the pad cant do it, because it is too small, or wrong material,or B) the disc cant get rid of the heat to the surrounding air, or C) There is not enough clamping force coming from your leg,..EDIT.. or D) one or more of the parts are not functioning as designed.
-Its also possible for some of the brake force to be lost before it reaches the caliper. Lost to flexing of hoses or flexing of the caliper, or even the firewall.The flexing of things is easy to see or feel.The pedal ratio can be figured mathematically. The brake force can be computed once all the bore sizes are known.
-If your pedal is hard, Then the problem is not likely to be hydraulic.
-IIRC factory discs on A-bodys are all at or near to 11 inchers. And the caliper pistons are around 2.5inch.The pads are kinda middle of the road. Theyre adequate from 60mph.Just.
-If your parts are smaller than this,then you will need a pretty aggressive pad to also be adequate, just. Or a more powerful mechanical advantage through pedal-ratio. Or a power booster. Or a gym membership.
-Playing with M/C bore sizes is great to fine tune the system, and personalize it. It cannot, however, compensate for a poorly designed mechanical advantage or a too-small system.
-Im not disrespecting the Scarebird system.I know nothing about it.
-And theres a wild card; weight. If your trunk is full of concrete, your gonna need a whole lotta brakes.
My 3450 # A-body has 15/16 m/c,KH 4-piston caliper system, 10x 2.5 rear system, rear w/c are 7/8, and a booster from a 73 Dart. Its the best braking car Ive ever owned. No competition driving.
-Hope this helps.
 
Well, my car's pretty light. 3209 with me in it. I THINK my master has a 1 inch bore. It's a Raybestos #mc36406. It's the second one, so far. I do have a Russell prop valve to the rear. Also I think EBC's Yellow Stuff pads are NOT ceramic.

I have to get this sorted out. I just spent a buttload o' money on engine and it's gonna be a beast. It HAS to stop better.

I hear about a valve in the block that needs to be centered or something, but can't find any hard info. Thought about just ditching it and using a "T".

Do you guys think a smaller MC bore would help?

I'm completely puzzled. I'm certainly no brake rookie. That's why this is killing me.

Please keep the advice coming:coffee2:
 
-No, a smaller bore in the m/c will probably not cure your problem.It will decrease the effort slightly to produce the same braking force as now, while requiring slightly more travel to do so.Or looked at another way, it will increase the clamping force slightly for the same amount of pedal force. The numbers are small. Going from 1 inch to 15/16 would be 6 or 7 %. This not likely to be significant if your brakes are as lousy as you say.
-As to ceramic pads, Ive never felt the need for them. I have heard that they need to be warmed up before they really bite.Not the best set-up for a streeter.

-When you say you have a Russel prop valve to the rear, just how many valves do you have?
-The proportioning valve has no effect on the front brakes. It simply reduces rear pressure to prevent rear wheel lock-up which has a nasty side-effect.
- Do you also have a metering valve in the front line? That valve looks like a Y-block but has a little rod sticking out of it with a rubber bellows around it.This valve shuts off the complete flow of the brake fluid between 3 and 135 psi. This is so that the rear brake shoes get a little head start.It was only used on disc brake cars for a few years in the late 60s/early 70s. This valve is usually under the battery tray on the rail. Do not ditch it. It is highly unlikely to be the cause of your problem.
-Somewhere close to the m/c should be also a brake warning switch.
-With all the swapping you have been doing with zero results, Im leaning towards, a bad pedal-ratio, the calipers being too small, or not built sturdy enough, or the pads just arent biting.This assumes you have a hard pedal. Just what size are your pistons.
-By 73 we had the combination valve.
-If you have a combination valve, the 73up kind;there is a valve in there for proportioning to the rear and a brake warning sw.
-The switch in the block just turns on the brake warning lite. So,turn on the Ig.key,and pull on the park brake to prove the bulb works.Release the parkbrake to turn off the lite.Works Ok? Next go under the hood, pull that wire off the sw. and short it to ground. Lite on proves that part of the circuit works too.Put wire back on switch to turn lite off. Lite off?All is good,switch is centered.
-If the lite is on before you start, pull wire off sw. Lite goes off, means sw.needs centering.Lite doesnt go off, means park brake stuck on, so go yank wire off it. Come back, put wire back on sw.. Lite goes on means sw.needs centering. lite off means all good. go turn key off and fix park brake sw. put wire back on.Recheck lite still off with key on.
-Centering switch;another post.
 
I would have said that using racing brake pads might be part of the problem, but went to the link and they say (unlike typical racing pads), these work OK when cold:

"Unlike most racing pads, your EBC Yellow Stuff Brake Pads have a strong bite even in cold conditions. You won't need to run a couple of laps before you feel the full fury of these brake pads."

The distribution block from your 1965 is simply a "quad T", all open inside, so can't restrict the flow. The 1973 one you had before was a "combination valve". You do need a proportioning valve for your rear drums and adjustable ones are just $30, or you can go back to your 1973 combo valve and get a prop valve, plus imbalance switch (wire to a lamp) and front "metering valve" (avoids nose dive).

As suggested, try an MC w/ a smaller bore, say 7/8"D, and insure you get all air out of the system so the pedal doesn't travel too far. There is a reason almost all cars today (w/ front disks) have power MC's, but many here use a manual MC w/ disks. BTW, any brakes - drum, disk w/ any MC should be able to skid all tires. Silly people here keep saying that drum brakes can't stop a car, yet they can skid the tires which is as far as you can go, indeed too far, you should brake to just before they skid or pump the brakes when they do skid.
 
Thought I'd shoot you guys a pic of my dist. block and one of the whole set-up.
The rotors are 10". Piston diameter is 2 1/4. Pads seemed a bit odd. The outer pad is worn at least twice as much as inner. Seemed odd with only 3-4000 miles on them.

Also, it just seems like 10" rotors aren't quite enough to stop this thing properly. My distribution block DOES have "communication" between the front and rear. The warning light cylinder "thingy" is in between. I've had one apart before.

As said before I also have an adjustable proportioning valve in the rear.
One thing I never changed from the beginning is the rotors. Could they just be a bad material?

Pedal ratio shouldn't be an issue. Stock pedals. I'm wondering if I should buy a pressure valve, hook it to a caliper and see what kind of pressure I'm getting. I really need to find a "fix", or I'm going to have to pull the trigger on a whole new conversion. Man, that's a lot of green!

Come on AJ, Come on Bill....what are we overlooking?:prayer:
 

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Well That right there tells the story!
-That valve in the pic is just a brake warning sw. It has a shuttle valve inside that moves towards the side that has lost fluid pressure, thus turning on the light. Fluid is not supposed to migrate from one side to the other.If it does, the o-rings are shot.
-The caliper is large enough to do a great job
-The one worn pad is a symptom of a caliper not sliding on the slider ways or pistons stuck in their bores, depending on which side is the more worn.In your case, the outer pad is the stationary pad. Since its worn the most, it must be dragging continuously. The other side not being as worn, indicates that the piston-seals are retracting and allowing the pad to retract. So the question remains; what is preventing the stationary side from retracting? This is usually because the caliper is not sliding on the slider ways. or slider pins. Check it out, and fix it.
-Now if the caliper is dragging; it will heat up the rotor, and bake/glaze up the pad, possibly to the point of no longer providing any braking force. Since you said the car stops straight, that means the caliper on the other side must be doing the same thing. So, in effect 50% of your stopping ability may be gone

-Fix the sticking calipers, replace the pads, consider machining the rotors, problem solved.

-BTW; With the sizes of the various hydraulic, and mechanical, parts that you have, there is no real deficiency. Your brakes should be adequate for street duty.
 
I put the Scarebird setup on a freinds early Barracuda and it would lock up wheels easily and about squeeze your guts out against the seatbelt. You've got something amiss because I would definitely do the Scarebird on my cars if I hadn't already done the 73 & up on one and the K/H on the other before I had any experience with the Scarebird. We did go with the smaller master cylinder diameter on his to make the pedal feel easier but the larger one we used first would lock wheels easily, it just took more leg effort. His pads came from Rock Auto.
 
Decided to check and make sure my calipers were sliding ok and not getting hung up or anything. What I found is bothering me.

I took off the pads, reinstalled the caliper to check the range and ease of slide. A little rough, but not bad. Re installed the pads and found that installed and ready to run, the caliper is at it's MAXIMUM outward travel. So with the inner pads looking like new and outers 70% worn, my calipers cannot move outward. At all. Actually if you look in the front of the caliper, all you see is inner pad and rotor. I've never run across this.

I'm trying like crazy to wrap my brain around this, and I'm wondering if this is the whole problem. As far as wear, it looks like I'm not even using the inners. But then the piston IS applying the inners only, so again, it's confusing.

Am I wrong, or is this the problem?
 
Not 100% sure on your setup but on mine the instructions had me center the caliper on the rotor with shims that were provided in the kit. Sounds like that may be your issue.
 
-If the caliper cannot move outwards far enough to prevent the pads from dragging, you will need to figure out why and correct it. During the wearing of the pads, the caliper will move inboard. There has to be a system in the design to allow this.The calipers must be free on the guides. Not enough to rattle, but free non-the-less.I would rather mine rattle than stick.There is no mechanical way for the outboard pad to retract. You have to depend on the rotors to knock them back after every application, and seal retraction on the pistons to allow it, and the guide system must be free, not a little rough.I usually leave my wheel bearing adjustment a little on the loose side of the spec., to help.
-Like I said Im not familiar with the Scarebird system. They could have one of three common mounting systems. If,as a previous poster mentioned, they are shim-able, then thats part of your answer.Move them out to help center the loaded caliper on the rotor. But the "ways" have to be clear, and reasonably smooth.
-Perhaps a picture of the exploded assy would help. I will do some digging.
-Ok, so I went to their site and found that their set-up is pretty much the same as the GM system, in that the calipers slide on bushings. So yes they will require centering. First remove the pins and lubricate the o-rings with silicon o-ring lube.A little dab will do ya.Work the bushings back and forth.If theyre tight,it may be due to corrosion in the grooves so pop them out and have a look.Sometimes the bushings need to be polished. If the O-rings are swollen from a previous wrong grease, replace them.Next, push the piston back a bit. Reassemble everything, but just run the bolts in to seat every thing.Now go step on the brake to cinch everything up. Next grab the rotor and give it a spin. A no-spin means shimming is required. So back off each bolt 1/2 turn, pull/pry the caliper outboard,and retest. Repeat as often as may be necessary to near free-spin the rotor.Dont confuse outboard drag with inboard drag A little drag is permissible. Now,with a thin-bladed screwdriver, push those little bushings outboard away from the brackets. The gap you see is the minimum shim size.The MINIMUM. A little more is Ok.
-The caliper only needs to be moved outboard far enough to provide a small amount of clearance with new pads and to ensure the pin-bolt heads do not interfere with the caliper sliding motion.
-So after shimming, pump up the brakes, and release. Go back and check for a free turning rotor. A small amount of drag is permissible, and normal on this type of set-up. Just make sure that by pulling or prying the rotor outboardly, and releasing it, to withdraw the outboard pad, and allow seal retraction to work on the inboard side, it will free-spin.Check your wheel bearing adjustment.The spec on that is zero to .003 axial inch.Like I said I go to the loose side with slider calipers. It helps to knock back the outer pad, to reduce drag to a minimum,(saves pad wear, rotor heating,and fuel).If you dont like the slight extra pedal travel this sometimes allows, then tighten her up a bit. But honestly, the spec.IMHO is pretty tight. I run my slider calipers at up to .007. The KH system on my S is a fixed caliper and does not need the assistance, so I run it tighter. I Think I got this right.
Ok so, if you find your Scarebird instructions and shims, and its different from my helps, follow theirs/Ignore mine.Good luck.
 
AJ/FormS answered it all. We are all waiting for the outcome. Sounds like perhaps only one pad is touching the rotor, and dragging all the time so it becomes glazed. Other things equal, fixed calipers like the 4 piston K-H on 64-72 cars are better than "sliders" like yours. But most cars use sliders so they do work fine when maintained (pins greased, ...).
 
Dropped off my engine at the dyno place today, to get hooked up and ready to run tomorrow AM, so....I could give my entire focus to this problem.

After reading all your posts again and again, I took a look at things and I THINK I might have found it! I think.

The first pic is just a shot of everything installed, thru the caliper "inspection window". Can't even SEE the outer pad.

the second one is a shot of the huge diff in wear. The darn inner pads are like new.

So looking and looking, I find that the inner pad cannot move past the Scarebird bracket, to squeeze the rotor. So there's a little (1/8 inch) lip of the pad bed sticking out on both top and bottom edge, preventing any further inner movement. Not only that but I found a gouge in that "lip" where it was being pressed into a weld on the bracket. The next couple pics are the lip before and after, and a shot of the gouge. I ground everything nice and flush, and smooth... and now the pad can pass thru the bracket to the rotor, where it should be. Everything moves and slides very smooth.

So my thoughts are that as I brake the car, the inner pad could NOT move any further, pulling the outer pad against the rotor. This caused a ton of wear to outer pad only and gave me half the braking power I SHOULD have!

Put both sides back together and knocked on wood!

Man, I hope this is all good now. It sure makes sense in my head. I can't know forsure until I drive the thing, probably a month. It's all weather dependant. That and the hope my new bullet survives the dyno.

So AJ, Bill, what do YOU guys think? I GREATLY appreciate your help through this and I sure hope it's now solved. I'm no longer trying to scrape the dough together for a Wilwood or SSBC kit. I'm waiting til I drive it.

Man, if this was the problem I can't believe it evaded me for FOUR summers!
 

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