Car pulls under braking, what gives?

[cecoen]

Ok, here is the deal. Older Unique kit with the "Deal?" master cylinders. It has "DEAL" written on the brake pedal so not sure if it is the pedal manufacturer or the master cylinder manufacturer, could be the "girling" units?

Anyway, it has two seperate master cylinders, one for the front and one for the rear brakes. They have small round reseviors with one brake line for the front and one brake line for the rear(they split to the left and right sides closer to the wheels).

The calipers are brand new(MGB units) with new rotors and pads(cheap soft pads). I have bled the front and rear by pulling the balance bar off and doing them seperately. I have pushed over 1 quart of fluid through them but it still pulls to the left(same symptom that started this whole brake rebuild) although it does stop much better than before it is still pulling and it will only lock up the front left? Any ideas? The only old parts left are the master cylinder and the lines. The master cylinders have only one line leaving the unit so how the heck could it be the master cylinder supplying more pressure to one side?

I have driven the car with the new brakes pretty easily for a few miles to break them in before I tried standing on the brakes. Under light braking it seemed to stop fine with little or no pulling? Although I did notice a slight pulling in the same direction from the alignment being off a little.

The car also "nose dives" pretty badly under braking. How do I get more braking from the rear?
Could the car be nose diving enough under braking for bump steer to be the pulling problem? It has the orig. MG front end and is very soft.

A lot of info here, what are you guys thoughts? Thanks for all the support you guys gave me with the rear brake questions already and thanks in advance for the help here.

Chad

[Rick Parker]

This may sound elementry but is it possible that there is any air in the line or in the caliper on the weak side preventing adequete clamping force . Or that there is a weak spring on that corner or the camber is different from the other side, air pressure too?

Just a few thoughts

..............Rick

[Bob Putnam]

Chad,

I suspect that "Deal" is "Neal" Performance Products.

A little primer on hydraulics:

Pressure in a closed hydraulic system will be equal everywhere.
There are some small transient variations and very small gravitational effects, but the bottom line is: The only way you can have different pressures is to have a blockage that separates a system into two parts. Air in the system will NOT create any pressure difference within the system, but will increase pedal travel required for a given pressure.

If you have pulling, it can only come from uneven forces due to sticking calipers, bad pads, defective rotors, suspension geometry or tire variations (in order of probability...).

Has the front/rear brake balance been checked? Generally, the best setup is to have the front brakes lock just a bit before the rear. Since you have an adjustable balance bar, you can adjust so that the rears lock first, and then reduce the rear pressure to optimal. Nose dive is a result of built-in geometry and spring rates. Once front-to-rear brake balance is set, it can't be changed without changing suspension bits.

[John 550]

Check (change ) the front hoses to the caliper , if they were " stretched " (the inside hose could snap ) and could collaps and fail under pressure . It's common trade practice for the mechanics to hang caliper by there hoses while changing pads . This applys to old suburbans

[Buzz]

The pulling may be the result of two things. If you are nose diving badly under hard braking, and one side of your front suspension is softer than the other, it may upset the geometry enough to cause a pull. This would not occur under lighter braking with less flexing of the suspension. The other is more obvious - If only one side is locking up you will definitely get a pull due to uneven stopping power side to side.
Bob, what if the air in the system is trapped right at the caliper itself? Could that "buffer" the hydraulic line pressure by compressing the air instead of moving the piston? Although - logic seems to dictate that whatever pressure is lost compressing the air would result in an equal drop throughout the entire system....

[Wayne Maybury]

I believe that air in the system will cause a "mushy" pedal which will travel more than a normal amount. The air will simply be compressed. I really doubt that air will cause pulling.

Wayne

[cecoen]

Thanks everyone. I will check the usuals like air pressure and such. I think you guys are telling me that air won't cause the problem so more bleeding isn't necessary. I have pushed an awefull lot of fluid through it so I would think there is no air left.

So that leaves the junction block with the two wires coming off of it(what is that anyway? It doesn't have a warning light on the dash that I know of, so why the two wires?) and the hard and soft lines. I will swap the soft lines from side to side to see if it pulls the other way. Other than that it, I guess, it could be a bad caliper from the factory. Wouldn't be the first time that has happened!

DUH! It somehow went right over my head about adjusting the BALANCE bar to get more rear brakes out of it! You would think that the name of the bar would trip that thought process! Jeesh, do I feel dumb now.

Thanks for all of the sugestions, you have been crucial in making this thing stop!

Chad

[excelguru]

Bob is right about the air. It's impossible for trapped air to cause the pulling in a closed pressure system (fluid dynamics). It would simply cause a spongy pedal feel. However, if the inner hose on one side is damaged (from "hanging" the calipers), it could cause a blockage or partial blockage which would definitley change the pressure from one side to the other.

Bob's checklist is correct and accurate (sticky calipers, bad pads, defective rotors, suspension geometry, tire variations). Most likely, it's sticky calipers.

Keith

[Excaliber]

It's been my experience, after bleeding etc. has been done, the problem is most likely a caliper. If it pulls to the left, then the RIGHT side caliper piston(s) are sticking in their bore.

Sometimes it is not as simple as "cleaning" the piston and bore and putting in a new "0" ring. More than once I've just had to buy BOTH calipers new or rebuilt to get even braking.

Ernie

[Chaplin]

I would bet on sticky calipers. When you changed the pads and pushed the pistons back in the calipers, did they move freely?? Both sides? Did you clean and grease the pins that the calipers slide on??

Also you may want to take off each caliper, one side at a time, have someone press the brake pedal and make sure that each piston moves freely- but be careful not to allow the piston to move too far out or it may pop out of the caliper.

If, after checking the above, you still have problems, I would check the items Bob Putnam listed.

Good luck.

[coyled]

I had the same problem after new r4 front brake pads. If there is air in the system, the pedal will pump up. I chased enough things around and then finally checked the pads in front. i pad was glazed. I later called porterfield and found out that I had 1 pad that was a different compound then the other 3 pads. It would stop straight until the pads warmed up and then a left turn. Check the pads.Good luck, scott.

[poorboy]

Chad;

The 2 wires are coming off of the stop lite switch. That car should have GM rotors & Chrysler calipers.

Poorboy

[cecoen]

Thanks to all for the great feedback. I'm a little ill right now so I haven't had a chance to get to the bottom of what I think is a blockage in a line or a sticky caliper causing the pulling. I will let y'all know what it turns out to be when I figure it out.

Poorboy,
Actually, the ENTIRE front end is MG stuff. Believe me, I tried to match up brake components for days telling the parts guy "I'm sure it is a 70 monte carlo rotor and chrysler calipers" The parts guy finally got tired of me telling him what I thought the parts were and matched the brake parts by some pictures and found out it is all from a '76 MGB.

I thought the brake pedal had a light switch on it. I didn't realize that the two wires were the brake lights. I thought wires coming off of the junction block were for some sort of warning lights or something? OH well, wouldn't be the first time I was wrong!

Chad

[Richard Hudgins]

cecoen,

Since you have MGB suspension components you may have a damper problem. If I recall correctly, the MGB used lever dampers as the upper a-arm. If this unit has gone bad, you will experience the behaviour you have stated.

You know, if the damper is bad, you will have less bump resistance and therefore more weight transfer to that corner.

Might be worth looking at.

[Excaliber]

...like I did on the Healey,,,just put some heavy oil in them (cheap skate that I am)........

I don't need to stop that fast,,,that big blue cloud of smoke that follows me around pretty well keeps the other cars back......lol.

Ernie

[RICK LAKE]

Hi Chad I have a couple of Ideas on your problem. Take the car to a place and have the system PRESSURE bled. They hook a machine up to the system and it pushs all the air out. Road test and see if this is any better. Your rebuilt calipers could be bad. There is a tester that Snap-on, matco, or mac sell for about 300.00$ that will test the clamping pressures of your calipers. You put the pressure sensors between the pads and press on the brakes. It give an reading on both calipers, or will tell you if 1 is hanging up in the bore. For your car nosing over I would fix the ride height first. Get a barbell set and put your wieght in the drivers seat that set the car up on a flat surface and measure from the ground to the bottom of the frame. I have my car 1/4 higher in the front end because of hard braking in autocross. Your springs may be too soft for your car? I hope this helps Rick Lake

[B. SMITH]

CHAD.

I HAD A UNIQUE WITH YOUR SYSTEM. THEY ARE FINE BRAKES FOR NON RACING DRIVING.

YOU PROBABLY NEED DE-GLAZING ON THE ROTORS. MORE GLAZING ON RIGHT, CAR WILL PULL LEFT AND VICE VERSA.

NEXT CHOICE IS THE STUCK AND OR LEAKING CALIPERS.

ALSO BE LOOKING FOR MISMATCHED OR FLUID CONTAMINATED PADS.

GOOD LUCK, B. SMITH

[Steve Vague]

Chad,
you should also try this, make sure both right and left calipers are shimmed correctly. If you have removed them you may have inadvertantly reinstalled with out proper centering. Not sure if the MGB is effected as much by this as is the MGA. It was also critical on my Aurora, (std ford).
Steve

[cecoen]

Hey all,
Great sounding advise. I was gone all weekend but will try out the advise this week. I'll keep y'all posted when I get to the bottom of this for future brake post searches. Thanks for all the responses.

Chad

[mr0077]

Chad, one other suggestion I didn't read above (though it was built into Bob Putnam's advise)...check your suspension bushings and tie rod ends. If you have a bad bushing or tie rod end, it will allow one wheel to toe out under braking, causing it to pull to that side. Sounds like you've already checked all the brake stuff...
Lotsa Luck, and let us know what you find.