front wheels still lock up after a good use! any ideas

so after changing the master cylinder, calipers, pads, i still notice the front wheels lock up, now im wondering where i can get the proportioning valve for front disc brakes, and rear drum brakes, could this be the problem also changing the hoses...any clues, checked the bearings and are good, Problems, cant seem to get rid of them.

 

Every time I've had that happen, it's been the hoses.

 

Could also be the pushrod in the booster is too long by just .010". Check this 1st.

 

what do you exactly mean by they lock up ?

....sensitive and lock up when always braking ?

check pin

or

...one caliper or both are not releasing when you let go of pedal ?

check brake hose


just in case ...if your always coming to a screeching halt make sure you didnt over adjust your rear brakes ..

also make sure your in the proper hole on the brake pedal arm ..one is for power brakes the other for manual ...I believe the bottom is for power brakes

 

I had one time on a conversion that only the right front would "Drag" after the car, or brakes in this case, warmed up. Turned out to be the pushrod was too long by just a bit. Maybe .010"-.020". Shortened the pushrod & all was now OK.

 

Ok, so heres what the problem is, i just took out the car once again after regreasing the bearings, when its cold it works great, i use the car for about 20 minutes, and after that i feel the car heavier, the car does move, i got home and lifted up both front wheels for the third time and they are both very heavy to move, as if someone would be braking. and as soon as it get cold i guess, it moves freely once again. i will get the hose today and see what happens, so the proportioning valve is out of the question of being the problem.

 

telriv.. question for you, how do you shorten the pushrod.also wouldnt that make the rear tires brake aswell.

 

so your saying when brakes are cold tire free spins with no brakes applied
and when you get back from a little cruising they will turn hard ...??




new calipers new pads ....are the rotors new also ?....

did you have to force the calipers with new pads on the rotor ?

how does your break pedal feel ....normal nice ??

the rims are super hot ?

 

If the pushrod is too long when things warm up they expand. Same for any other part on the vehicle. Even if you are not exactly sure that this is the problem shorting it up .020" won't hurt anything. It's worth a try, doesn't cost any $$$ & won't take long to accomplish & the brakes do not have to be bled once again. If this is not the problem it will have cost you only about 20 minutes worth of time. Remove the master from the booster by pulling it slightly forward, after removing the 2 nuts, & moving slightly to the side. Leave the lines connected. They will "Stretch" enough to be able to pull out the pushrod. Then you can shorten it slightly. Remember we're only talking about .020" here. Don't go overboard!!!!

 

Forgot to answer question for rear. The fronts need very little to apply the front discs. The rears need to overcome the pull back springs & the normal shoe adjustment space. So this will very seldom happen on the rear.

 

I think Tom is on the right track, it doesn't take much for the return port in the master to be partially blocked if the pushrod preloads the master slightly. It's a common issue with 1st gen f-bodies.

 

Something else you could try. Take it for a short ride again until you feel the car being held back. Jack it up & try to turn the front wheels again. If they are tight, loosen the bleeder screw & see if any fluid comes out that is still under pressure. If the wheel now frees up it's the master cylinder pushrod that is too long.

 

Great Idea..Tom..Thanks i never thought of that, ou: i went ahead and replaced the front hoses to be on the safe side, so how do you cut the pushrod for the booster..also why do you think it does it after a short drive.

 

I just went through this on my 67 Skylark. If you unbolt the master cylinder from the booster, and it pushes the master away from the booster with any force, the pushrod is too long. Mine was too long by about inch. If you marke where the pushrod sits in the power booster with a marker, and then insert it into the back of the master cylinder and mark it again. If there's a gap between the marks, that's the length of excess you need to cut off the pushrod. My brakes dragged after driving for 5 minutes. The brake pedal was stiff before I even pressed on it. My rotors were blue from the excessive heat.

-Josh

 

That's a good no cost approach Jason. Just for safety's sake I would back the nuts off a turn & lock another nut against the original nut before taking it for a ride. You will have a longer pedal travel but should still have plenty of braking. Drive carefully. If this works you now know what's wrong definitely.

 

Very very good info here, im thinking this will be the problem, i looked under the dash since i could not do anything else today and noticed it might have a nut where the pushrod pins up to the pedal, do you guys think this might have adjustment, i think i remember adjusting this...maybe thats my problem, i will try to adjust it if i can and see what it does, if it still remains the same, i will try cutting it..thanks ill keep you guys updated tomorrow..

 

so whent ahead and bled the brakes after installing new hoses, also while it was up i inspected the shaft on the booster, when i removed the master cylinder i noticed it had some pressure and was pushing it out, so i went under the dash and saw it had an adjustment nut...where you loosen it up and then with your fingerss you tighten up the shaft making it shorter, so i tried the car around the block, and then jacked it up, and moved the tire, it was not locking up anymore, i cannot celebrate yet, :rant: i will have to wait till i use the car a bit more, im taking advantage on working on the brakes so i will be replacing the back shoes aswell, see if i get better braking.. does not feel spongy but maybe i overdid it on the adjustment of the shafto No: but still brakes alright.. well thanks and ill keep you guys posted.

 

Just tried the car again after the lines, and still locks up.. i felt curious about the shaft and started to loosen up the master cylinder and bam, wheels started to move again freely..i can see the shaft is about a half inch longer and needs to be cut down..how do i take off the shaft, should i take off the booster, also which side needs to be cut..

 

I hope you're planning to cut the pushrod between the master cylinder and booster, and not the pushrod from the brake pedal to the booster. The Brake pedal rod adjusts the height of the brake pedal in the car, that's all. The pushrod between the master cylinder and booster needs to be shortened. It should be shaped like a bullet, with a rounded end on one side, and a flat end on the other. Trim the excedd from the flat end. The rounded end pushes against the plunger of the master cylinder.

-Josh