front discs locking up

-
D

dads75

Member
Joined
Nov 14, 2010
Messages
5
Reaction score
0
Location
saint john new brunswick
hey everyone. I got a 75 dart sport with manual disc breaks. after about 10-15 min of driving the front breaks start grabbing to the point the front end starts to shake and I have to pull over to let them cool down. Wait 10 mins and off I go. calipers pads and rotors were all replaced new a couple years ago but the car doesn't get driven much. I took the calipers off and the piston is moving fine. Could it be a flex hose failure???Any help would be greatly appreciated.

thanks
 
Is something holding brake pedal down. If master cyl plunger is not returning all way back it will hold some pressure and drag.
 
Check the "ways" that the pads and caliper slide on. Check both the fixed and floating components. With the pads out, slide the caliper assembly back and forth as to simulate use. If the caliper does not slide freely, there you have it. The caliper is heavy and the "ways" are not well machined, so do not expect them to slide like they were on ball or roller bearings.

If "ways" are nicked or rusted, the pads and caliper could hang. The piston would function normally w/o the pads and rotor. If the "ways" are nicked or rusted, a little work with a medium, followed by a fine flat file will bring them back. A Dremel tool with a sanding roll would work, just be careful not to stay in one spot tool long and leave a divot.
 
more info is needed to help. Are calipers free, do you have a power booster, does car have headers near brake lines, how much drag on the rotors before you take a ride ? This is an easy problem if you get all things are checked. make sure brake fluid is not contaminated. one strange problem can be the rubber line have an implosion (that means the fluid goes to the wheel from pedal pressure by your foot and it can't return at normal flow) this is a problem when the lines are ancient. Good Luck
 
try your flex hoses-- my son's 98 truck had this issue until both hoses were replaced-- since then no problems. Lawrence
 
tommytegg said:
more info is needed to help. Are calipers free, do you have a power booster, does car have headers near brake lines, how much drag on the rotors before you take a ride ? This is an easy problem if you get all things are checked. make sure brake fluid is not contaminated. one strange problem can be the rubber line have an implosion (that means the fluid goes to the wheel from pedal pressure by your foot and it can't return at normal flow) this is a problem when the lines are ancient. Good Luck
Click to expand...
both calipers are free and working fine, I can compress them easily and they seem to work fine. no power booster just manual breaks and no headers..yet. just the (as I call them over slung manifolds). gonna flush the system and change the flex hoses as everything else is new (at the wheel). there dosent seem to be any drag when they are cool. I was thinking the flex lines as well , they don't seem to be weather cracked but they are old (probably 6 - 8 years)

thanks everyone for the sugestions
 
I've been having the same problem with my K-H front discs, and would like to thank you all for your helpful replies. It did improve somewhat when I squirted the caliper, pads and rotor down with brake cleaner, but there's still too much drag as far as I am concerned. I think I am next going to try removing my calipers and cleaning the "ways", as 2 Darts suggested.
 
Flex hoses will collapse and act like "check valves". Also make sure that hoses aren't twisted when calipers were put on...seen that a few times in my shop..:banghead:
 
Your brake pedal pushrod going into the MC is too long or doesn't have enough play.
Adjust it with about 1/16" or 1/8" play and the problem will mostlikely be gone.
 
Check to make sure your fluid level isn't overfilled when the fluid gets hot it expands and if its overfull it has no where to go so it will apply the brakes. This is true with all cars and trucks and is the reason why its a bad idea to top off your brake fluid because if you have a clear master cylinder resivour you can look at it and know when your brakes are getting low and will prevent the brake lamp from coming on as well.
 
moparman3406bbl said:
check to make sure your fluid level isn't overfilled when the fluid gets hot it expands and if its overfull it has no where to go so it will apply the brakes. This is true with all cars and trucks and is the reason why its a bad idea to top off your brake fluid because if you have a clear master cylinder resivour you can look at it and know when your brakes are getting low and will prevent the brake lamp from coming on as well.
Click to expand...

??whut??
 
BigBlockMopar said:
Your brake pedal pushrod going into the MC is too long or doesn't have enough play.
Adjust it with about 1/16" or 1/8" play and the problem will mostlikely be gone.
Click to expand...

Good call there, and I was just getting ready to mention that this can happen if the rod is overadjusted.
(The fluid can't return because the piston does not come back far enough to let the fluid return, and when they start getting hot you have a hydraulic lockup)
 
I knew my brakes were dragging because my car just didn't coast like it used to. At first I spent a lot of time adjusting the rear drum brakes because for some reason I thought it was the rear brakes that were dragging. Finally I realized it was the front K-H discs, on both sides. Then I read this thread and learned more about how the system works. I was then able to cure the problem by removing my brake light switch. The problem was caused by all the lost motion in the pedal and pushrod assembly. Due to that slop, it was necessary to get the brake light switch too close to the pedal in order to actuate it, so the body of the switch was then preventing the master cylinder from returning to its normal position. I've removed the pedal assembly and am re-sizing both holes.
 
Did this on my '73 Duster. I adjusted my brake light switch too tight. Readjusted, just fine.
 
You must log in or register to reply here.
-

Back
Top