dragging front brakes
Thread Starter
Instructor
Joined: Apr 2005
Posts: 138
Likes: 0
From: 86 Convertible 4+3 Coronado, CA
dragging front brakes
I'm looking for advice on my first steps troubleshooting dragging front brakes. Although I'm getting pretty good at wrenching on my Corvette, my brake experience is limited to replacing master cylinder and flushing & bleeding brake lines.
I pulled both front wheels to refinish rims and noticed slight dragging on both front brakes as I spun the wheels while up on the jackstands. I did some searches on the forum; after a highway test drive of ten miles, I pulled over and put my hand on the calipers...they were not hot to the touch, so the dragging is a minor problem (at this point!)
The rotors and hoses are original (20 years, 122k miles)...the pads were replace 9 years ago (about 25k miles).
My question: should I jump right into a caliper overhaul, replacing hoses while I'm at it, or is there something else I should check first? FSM suggests brake booster may be a problem, but other than the slight drag, brakes are working fine.
Thanks in advance for any advice!
I pulled both front wheels to refinish rims and noticed slight dragging on both front brakes as I spun the wheels while up on the jackstands. I did some searches on the forum; after a highway test drive of ten miles, I pulled over and put my hand on the calipers...they were not hot to the touch, so the dragging is a minor problem (at this point!)
The rotors and hoses are original (20 years, 122k miles)...the pads were replace 9 years ago (about 25k miles).
My question: should I jump right into a caliper overhaul, replacing hoses while I'm at it, or is there something else I should check first? FSM suggests brake booster may be a problem, but other than the slight drag, brakes are working fine.
Thanks in advance for any advice!
Cruising
Joined: Apr 2005
Posts: 11
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I had a similar problem with my rear brakes only it got a lot worse. I added speed bleeders and flushed the system this weekend (14 yr old fluid looked like old motor oil). It seems to have fixed the dragging issue. A GM mechanic said "that from living on the coast,Santa Cruz area, I probably had a lot moisture in the system" Good Luck.
Thread Starter
Instructor
Joined: Apr 2005
Posts: 138
Likes: 0
From: 86 Convertible 4+3 Coronado, CA
Thanks for ideas so far...I flushed entire system when I replaced master cylinder two months ago. No leaks and the fluid is remaining bright and clean.
Any other thoughts?
Any other thoughts?
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
These are all nice things to do for your brake system. I believe the problem might be that the actuator rod or push rod coming out of the booster is a little to long holding pressure on the piston for the master cylinder.
Un-bolt the master but leave lines connected and pull forward. Check the wheels on jack stands again, if they are free then proceed. The little nut on the end of the shaft may need to be screwed in to the shaft. You can have some one push the pedal down slightly to have it come out some so you can have better accessibility. Hold the shaft with pliers or vice grip (easy) and turn the screw in maybe about 2 turns (a guess). Re-bolt master and check wheels again. If 2 turns are to much, pedal might be to low. A re-adjustment might be necessary, you will have to figure that out. Best of luck.
Un-bolt the master but leave lines connected and pull forward. Check the wheels on jack stands again, if they are free then proceed. The little nut on the end of the shaft may need to be screwed in to the shaft. You can have some one push the pedal down slightly to have it come out some so you can have better accessibility. Hold the shaft with pliers or vice grip (easy) and turn the screw in maybe about 2 turns (a guess). Re-bolt master and check wheels again. If 2 turns are to much, pedal might be to low. A re-adjustment might be necessary, you will have to figure that out. Best of luck.
Melting Slicks
Joined: Jun 2004
Posts: 3,253
Likes: 2
From: Castro Valley CA
I agree with the caliper rebuild and fluid flush. I race my 94 LT1 and frequently experience stuck pistons. It will typically occur when the pads are well worn and the piston sticks out farther. Small tears on the seal(which may not result in fluid leakage or braking performance degradation) will prevent the piston(s) from retracting fully when you let off the brakes. I would spend another $50 for 4 speedbleeders, that way you will get a good flush and a hard pedal.
Thread Starter
Instructor
Joined: Apr 2005
Posts: 138
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From: 86 Convertible 4+3 Coronado, CA
Thanks for the advice. I've already got SpeedBleeders and agree with your comments on how they simplify brake bleeding.
Before I tear into a caliper rebuild, I'll give the booster adjustment a shot. However, given the age of the components, I suspect I'll need that rebuild, too!
Thanks again for the suggestions on troubleshooting!
Before I tear into a caliper rebuild, I'll give the booster adjustment a shot. However, given the age of the components, I suspect I'll need that rebuild, too!
Thanks again for the suggestions on troubleshooting!
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Very slight dragging while spinning by hand is fine. It's more than likely just the surface rust and dirt dragging, not enough to kick the pads back further into the calipers. The pads do not retract on their own.
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Melting Slicks
Joined: Jun 2004
Posts: 3,253
Likes: 2
From: Castro Valley CA
The release of hydralic pressure will indeed cause the pistons to retract(float, move, piston kickback, etc., call it what you like.) There is zero dimensional clearance between the pad and the rotor when your foot is on the brake, when you release them there is an air gap(i.e. clearance.) I agree that we are not talking about much movement, perhap .020 on each side, but it is not zero, at least not on my J55's when they are working properly.
Melting Slicks
Joined: Jul 2006
Posts: 3,356
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From: Chesapeake Va
Originally Posted by CentralCoaster
Very slight dragging while spinning by hand is fine. It's more than likely just the surface rust and dirt dragging, not enough to kick the pads back further into the calipers. The pads do not retract on their own.
Some drag is normal. If you believe the master/booster is applying pressure when it shouldnt be, thats easy to diag. With the wheels off, have someone press the brake pedal and release it. Try to turn the rotor. If it feels like its dragging open the bleeder and see if it makes a difference in the way it feels. hope this helps!!
Thread Starter
Instructor
Joined: Apr 2005
Posts: 138
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From: 86 Convertible 4+3 Coronado, CA
It sounds like I'm not too far off the mark...very slight drag, with no detectable heating after a high speed drive.
I'll the "open bleeder" check as well...it makes sense. As stated earlier, I have no experience with the way the brakes should be riding without any pedal application...thanks again for the forum's experience!
I'll the "open bleeder" check as well...it makes sense. As stated earlier, I have no experience with the way the brakes should be riding without any pedal application...thanks again for the forum's experience!
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
Originally Posted by pcolt94
These are all nice things to do for your brake system. I believe the problem might be that the actuator rod or push rod coming out of the booster is a little to long holding pressure on the piston for the master cylinder.
PColt is on the right track, but there's a real easy way to check the adjustment of your power booster push rod:
1. Take the cap off of your master cylinder.
2. With the engine off, gently push down on the brake pedal.
3. Watch the surface of the brake fluid for a little squirt of fluid from the small hole in the bottom of the reservoir. You should see this squirt just as the brake pedal moves. If you don't see the squirt, your push rod is too long, and the piston doesn't open this port when you take your foot off the brake. This WILL cause the brakes to drag.
If you have to push the pedal down more than about 3/8 inch to see the squirt, your push rod is too short, and this will give you a low brake pedal.
This is such an easy test, everyone should do it! Who knows how much better your brakes might be!
To fix these problems, see PColts procedure.
S.T.W.
Team Owner
Joined: May 2002
Posts: 24,337
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Originally Posted by Hot Rod Roy
PColt is on the right track, but there's a real easy way to check the adjustment of your power booster push rod:
1. Take the cap off of your master cylinder.
2. With the engine off, gently push down on the brake pedal.
3. Watch the surface of the brake fluid for a little squirt of fluid from the small hole in the bottom of the reservoir. You should see this squirt just as the brake pedal moves. If you don't see the squirt, your push rod is too long, and the piston doesn't open this port when you take your foot off the brake. This WILL cause the brakes to drag.
If you have to push the pedal down more than about 3/8 inch to see the squirt, your push rod is too short, and this will give you a low brake pedal.
This is such an easy test, everyone should do it! Who knows how much better your brakes might be!
To fix these problems, see PColts procedure.
S.T.W.
1. Take the cap off of your master cylinder.
2. With the engine off, gently push down on the brake pedal.
3. Watch the surface of the brake fluid for a little squirt of fluid from the small hole in the bottom of the reservoir. You should see this squirt just as the brake pedal moves. If you don't see the squirt, your push rod is too long, and the piston doesn't open this port when you take your foot off the brake. This WILL cause the brakes to drag.
If you have to push the pedal down more than about 3/8 inch to see the squirt, your push rod is too short, and this will give you a low brake pedal.
This is such an easy test, everyone should do it! Who knows how much better your brakes might be!
To fix these problems, see PColts procedure.
S.T.W. Good test. Just don't put your eye close to it... it can easily squirt out of the reservoir.
Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
As a side note...as you posted, your rubber lines are 20 yrs old. It is possible that the inner rubber has weakened or deteriorated over the years. That will reduce the id of the line on application causing fluid retention in the caliper below the restriction.
