Hard peddle and pulls when braking

[Cudafever]

It's a 70 Grand Coupe Barracuda.

About 10 years ago i did the from disk brake swap.(73 Cuda spindles with all new part.) Bought a 73 master cyl(i don't remember if it was for manual or power brakes m/c) my car is manual braking car.

From all the reading on this "brake forum section" I'm guessing that i bought a power brake m/c.
Any one know what m/c, piston diameter, worked best for you?

As far as the pull goes, i replace the calipers several time with the most improvement, was the full loaded calipers, but still pulls under a hard braking situation.

It has been some 10 year now, and have just learned to live with it.

My 340 is coming out for a much more powerful 408 Stroker, with forged every thing.
I really need to fix this problem before the new motor slides into place.

Any help would be greatly appreciated.

 

[moparleo]

If the brake fluid has not been changed in the last couple of years, here is a good place to start. You can gravity bleed the brakes or do a manual bleed with new brake fluid. Start at the r/r and work your way forwards. Bleed/flush each wheel until clean, clear fluid comes out the bleeder. Use a length of vacuum hose pressed onto the bleeder screw and drain into a clear container so you can see the fluid condition as well as air bubbles.
Check the front brake lines. The flexible part. These lines fail similar to radiator hoses in that the inner plies separate from the outer covering causing blockage. Especially if you have ever clamped them closed when servicing the calipers.
To check line pressure up front , have someone pump the brake pedal a few times and hold the pedal while you crack the line loose from the caliper. Check both sides. The stream should be relatively even. With the front end raised on jack stands, check for caliper/hose drag by spinning each wheel with the bleeder cracked loose so there should be no pressure on the caliper piston.
Remove the rear brake drums and check for any broken hardware, leaks. Reassemble and readjust the rear brakes manually. A rear wheel out of adjustment can cause a pull during braking as there is more friction to one side.

 

[Cudafever]

It was flushed 10 years ago and it acts the same now as it did then...........But it is time for a flush to prevent other problems from developing.

You make a good point with the front flex lines. They look good on the outside but who know the condition on the inside.

One more bit of info that i didn't add, that you reminded me of, about brake pressure.

The right from brake has always dragged. pump the peddle up with the front tire off the ground. the left would turn fairly free. the right was vary stiff to turn but would free up after many turns. This is why i said i tried sever caliper. Was trying to get the right front to release.

There seems to be a few pound of pressure that hangs on. I can apply and release the brake peddle, then open the bleeder on the right caliper, wheel turn free.

When you do a front disc conversion, do you have to replace the proportion valve?

I still have the original drum brake one on my car..................

 

[ramenth]

As far as the prop valve goes, yes, you should replace it if you're doing a disk brake conversion. You're best bet is an adjustable one from a place like Summit or Jeg's. A few of our vendors on the right side of the page carry them also and some give discounts to FEBO members.

From the way you're describing it I'd almost bet, though, you have a hose gone bad as Leo suggested. Easy way to test is to put a screwdriver in the caliper "window" and pull back on the pads. If the piston pulls back then it's not the hose (fluid will be displaced back into the master at that point). If it doesn't pull back, open the bleeder on the caliper while you're pulling on the screwdriver. If it pulls back with the bleeder open then it's the hose, if still doesn't pull back then it's the caliper (highly unlikely since you've replaced it).

Another thing that can cause a drag like this is head space in the master. If the master is full up to the top of the caps, then there's no head space for fluid to return to. Make sure there's some space between the fluid and the caps.

Check your wheel bearings, too. Over tightened bearings can cause a drag on the car and be exacerbated by a push on the brakes. I usually tighten the bearings til there's a good drag on the rotors as I turn them (turn the rotor as you're tightening) then back it off until it spins "free."

 

[Cudafever]

if i force the caliper piston in the rotor/tire turns free.

I set my wheel bearing preload, the same as you.

 

[Chryco Psycho]

ok so the rotor doesn't turn freely until you force the piston back ? If so there is a problem with the fluid returning to the master , so there could be dirt in the caliper preventing the piston from retracting or a damaged hose locking some pressure in the caliper just opening the bleeder slightly should correct it , or you have a problem in the proportioning valve , or the pushrod is too long in the back of the master holding the brakes on slightly & limiting the fluid return

 

[Cudafever]

Chryco, the proportion valve was my next step, some 10 years ago, just never tried it.
With the eng out this will be a much easier task.

You have me thinking about the push rod length. although there is some free brake peddle..............I remember adj the cam like bushing under the dash so that i had max peddle............if that's been my problem all a long i will be sooo.............OK Went and looked at the rod/peddle assembly. the peddle has play before the rod moves. Was a grate idea.

 

[Chryco Psycho]

But if you have power brakes there is a pushrod out of the booster into the rear of the master , if it is too long the fluid cannot return properly , it is a 2 piece pushrod that is threaded so you can adjust the length of the rod , you will have to remove the master to get at it .

 

[moparleo]

Diagnosing a problem with any thing should mean checking all of the simple ,obvious things first. I have found that most problems are simple problems. Make a list of all the possible things that could be causing the problem and then check one thing at a time. don't assume that something is correct unless you personally check it your self. Don't overlook obvious things. This applies no matter what the problem is. Diagnosing a problem is a step by step process.

 

[Cudafever]

But if you have power brakes there is a pushrod out of the booster into the rear of the master , if it is too long the fluid cannot return properly , it is a 2 piece pushrod that is threaded so you can adjust the length of the rod , you will have to remove the master to get at it .

I agree, but mine are Manuel brakes (No Brake Booster)

 

[Cudafever]

Diagnosing a problem with any thing should mean checking all of the simple ,obvious things first. I have found that most problems are simple problems. Make a list of all the possible things that could be causing the problem and then check one thing at a time. don't assume that something is correct unless you personally check it your self. Don't overlook obvious things. This applies no matter what the problem is. Diagnosing a problem is a step by step process.

I agree, that's why i started this thread, there may be things that i haven't considered or over look in my plan.

Has any one converted to front disks and not replace the Proportion Valve ???

What is the difference between the two Proportion Valves????

I realize the bias may be different between all drum and a disc/drum combo. But that was never the problem in stopping. It's the pull on the steering wheel when i brake that is the problem.

Does any one know how to tell what piston diameter i have in my master cyl,....... with out disassemble? Is there a different casting # for each bore?

 

[moparleo]

The proportioning valve controls front to rear bias, not side to side. Too much rear pressure will cause the rear brakes to lock up before the front do. You were having a pulling problem. Lets fix that first. To eliminate the possible brake hose problem, go with S/S hoses front and rear( the one attached to the diff housing ) This will accomplish a few things like full fluid pressure through the hoses, Braided lines will not balloon under pressure , this give you a firmer pedal. They also look cool. Can't lose. Then inspect rear brakes for leaks and proper functioning hardware. If all is good with the rear, do a complete brake fluid flush. After you do this, if you still have the problem it will be a mechanical problem, not a hydraulic problem. Use a new bottle of high quality brake fluid. Also s/s brake lines are very reasonable so the total cost of the work described above shouldn't be much more than $100.00.

http://www.ebay.com/itm/STAINLESS-B...Parts_Accessories&hash=item4cf0750901&vxp=mtr

One other thing just came to mind. Check the front strut rods and bushings for wear. If one side bushing is worn and/or the bolt is loose, the car will pull hard to the side that is loose. A way to check this with out getting under the car is to stand beside the car and have some one go forward slowly and apply the brake. and then go in reverse slowly and apply the brakes again. Watch for the whole wheel assembly for movement back and forth. If it does, you are in need of some front end work. Good time to go through the whole front suspension if not already done recently We get a discount from P-S-T, which are one of our sponsors.

Let us know how it turns out.

 

[dfrazz]

Also, for a good front end kit Mancini Racing sells all Moog equipment which is made in the USA, unlike other vendors parts from Asia and poor quality, and a lot less mark up than some other vendors. I know this from personal experience..

 

[bc3j]

I have switched from an all drum brake car to front disc/rear drums and only use the stock distribution valve and no proportioning valve. I have however, replaced the rear brake cylinders with a 13/16" instead of the stock 15/16". I use the slider type front calipers with a 2.75" piston. I run manual brakes with a 1" bore master cylinder with the drum brake stock pushrod. This combination works for me as the rear brakes do not lock under a panic stop.

 

[Cudafever]

Moparleo, thank for the link!
To good of a deal bought the set.

The strut rod is a vary good idea, i can't start the car right now as my rocker arms are on my new motor, so i can set the rocker arm tip geometry corrected. but they will be back on the old motor, when the weather gets above 40F:icon_eyes:

When i did the disc brakes, all parts were replace with Moog part.
That don't mean that some of them are worn by now....

bc3j, thank for sharing you specs.
Wouldn't a smaller wheel cyl cause the brake to come on sooner?.......

Now that i have thought about it for a minute........."pound per Square inch" Smaller wheel cyl = less pressure on the brakes for the same line pressure. :icon_mrgreen:

 

[Chryco Psycho]

Check pricing at Rock Auto , they handle all the Moog parts & have reasonable pricing as well