Hanging brakes - help needed

[lutronjim]

Couldn't find old post so starting new.

C10 disk front/drum back with booster. Master cylinder and proportioning valve less than 3 years old via disk brake kit. Booster old from junk yard for power drums.

Quick stops - brakes wont fully release. Figured its triggered by high pressure.

Got wheels off ground. Engine off - I pushed on pedal as hard as I could. Three tries and no hanging front or back.

Cranked engine - pushed hard on pedal - front brakes hung - rears free.
Pulled vac hose from booster - fronts still hung. (One time on road before pulling hose released them.) Quick light pumping of pedal freed them.

Replaced vac hose - pushed hard on pedal - front brakes hung - rears free.
Quick pumping of pedal by hand freed them.

Just fronts hanging sounds like proportioning value. But why does it only hang when booster active?

Help would be greatly appreciated.

[p0508]

If you have them bled properly and you have the correct proportioning valve for Front disc rear drum I can think of 3 things.

Check Master Cylinder to Booster side: Ensure the nipple going into the master cylinder from the booster is just resting on the master cylinder flange and not pushing on it whatsoever.

Check Booster to Pedal rod. Make sure you have the correct pedal ratio. Make sure your rod adjustment is allowing the master cylinder to move throughout its FULL travel. If you have the rod adjusted to far toward the booster and it doesn't fully release the master cylinder then it will always retain residual pressure that will get worse as you use the brakes.

My guess is its in your rod adjustment. Free it up a bit and see if it helps. You can always remove plate under your dash (the one with the rubber dimples that stop the pedals) to give your pedal a little more travel and see if that solves your issue, If it does your pedal adjustment is off. I think you are getting a tiny bit of preload on your booster.

3rd thing is a bad booster.

[saxart]

How old are the calipers? Up here in the north it can be common for calipers to lock up internally from rust at the rubber piston seal.

[Sheepdip]

Originally Posted by saxart

How old are the calipers? Up here in the north it can be common for calipers to lock up internally from rust at the rubber piston seal.

^^^^^^^^^^^^^What he said^^^^^^^^^^^^^^^^^^

[lutronjim]

Thanks for come backs.

The calipers were part of the conversion package - < 3 yrs.

I will check adjustments.

A question - if either were too long, wouldn't it show up on a trip from things bouncing around? I can run around town for a month and then drive the 230 miles to see granddaughter and back with no trouble if don't have a quick stop.

[p0508]

By quick stop I'm assuming you mean hard stop? Did you ever follow any bed in procedures? If you didn't and you think your adjustments are correct, go out and try to bed the brakes in and see if that takes care of your hang up problem.

_____________________________________________________________________

Bedding allows your brakes to reach their full potential. Until they are bedded, brakes simply do not work as well as they can. If you've installed a big brake kit, changed pads and rotors, or even purchased a new car, you should set aside time to bed the brakes per the instructions below. Proper bedding improves pedal feel, reduces or eliminates brake squeal, prevents (and often cures) brake judder, reduces brake dust, and extends the life of pads and rotors. For more details on the theory of bedding, please refer to this article: Pad and Rotor Bed-In Theory, Definitions and Procedures

Caution: Immediately after installing new pads, rotors or a big brake kit, the first few applications of the brakes will result in very little braking power. Gently use the brakes a few times at low speed to build up some grip before blasting down the road at high speed. Otherwise, you may be in for a nasty surprise the first time you hit the brakes at 60 mph.

If you just installed rotors with zinc plating or if the rotors have an anti-corrosion phosphate coating, you should postpone bedding until normal driving has allowed your pads to polish the rotors clean and removed all traces of the plating or coating. If your new brake rotors have an oily anti-corrosion coating, clean this off thoroughly with brake cleaning spray and/or hot soapy water before installation.

Read and understand these instructions completely before starting. If you have questions, give us a call or email. Do not substitute higher speeds for the 60mph called for. The heat in brakes goes up exponentially as you increase the speed from which you brake. Repeated stops from 80 or 90mph with street pads will overheat the brakes and you may end up having to replace pads and rotors.

When following these instructions, avoid other vehicles. Bedding is best done when traffic is light, as other drivers will have no idea what you are up to and may respond in a variety of ways ranging from fear to curiosity to aggression. A police officer will probably not sympathize when you try to explain why you were driving erratically! Zeckhausen Racing does not endorse speeding on public roads and takes no responsibility for injuries or tickets you may receive while following these instructions. Use common sense!

From 60mph, gently apply the brakes a couple of times to bring them up to operating temperature. This prevents you from thermally shocking the rotors and pads in the next steps.

Make eight to ten near-stops from 60mph to about 20 mph. Do it HARD by pressing the brakes firmly, but do not lock the wheels or engage ABS. At the end of each slowdown, immediately accelerate back to 60mph, then apply the brakes again. DO NOT COME TO A COMPLETE STOP! If you stop completely, with your foot on the brake pedal, pad material will be imprinted onto the hot rotors, which could lead to vibration and uneven braking.

The brakes may begin to fade after the 7th or 8th near-stop. This fade will stabilize, but not completely go away until the brakes have fully cooled. A strong smell from the brakes, and even some smoke, is normal.

After the last near-stop, accelerate back up to speed and cruise for a few minutes, using the brakes as little as possible to allow them to cool down. Try not to become trapped in traffic or come to a complete stop while the brakes are still hot.

If full race pads, such as Hawk DTC-70 or Performance Friction PFC11 are being used, add four near-stops from 80 to 20 mph.

After the break-in cycle, there should be a slight blue tint and a light gray film on each rotor face. The blue tint tells you the rotor has reached break-in temperature and the gray film is pad material starting to transfer onto the rotor face. This is what you are looking for. The best braking occurs when there is an even layer of of pad material deposited across the rotors. This minimizes squealing, increases braking torque, and maximizes pad and rotor life.

After the first break in cycle shown above, the brakes may still not be fully broken in. A second bed-in cycle, AFTER the brakes have cooled down fully from the first cycle, may be necessary before the brakes really start to perform well. This is especially true if you have installed new pads on old rotors, since the pads need some usage to conform to the rotor wear pattern. If you've just installed a big brake kit, pedal travel may not feel as firm as you expected. After the second bedding cycle, the pedal will become noticeably firmer. If necessary, bleed the brakes to improve pedal firmness.

[lutronjim]

Guess I didn't make myself very clear. The brakes are over 2 years old. They work and stop fine - except for hangup.

Haven't had a chance to get to truck. Wife has Alzheimer's and I get very little free time.

[p0508]

I was under the impression this was a new setup, my bad. In that case you need to look into something getting worn and rusted as stated above. Calipers, booster.

[saxart]

Originally Posted by lutronjim

They work and stop fine - except for hangup.

I'm assuming this hang-up hasn't always been an issue, meaning, at one point earlier this system worked fine. If that is true, then you can rule out any issues with booster push rod length. (Unless a jam nut has come loose or something)

Since there isn't anything definitive in the suggestions, I would start by replacing what is easiest and cheapest. Calipers. Your description still sounds to me like you have calipers that have developed rust internally. Being that they are the lowest point in the braking system and subject to the most "weather" they are always the first thing I would suspect.


If this were my truck, I would put a set of calipers and pads in it, purging the brake lines with fresh fluid after disconnecting the lines from the calipers. If the fluid looks dark and old, I'd probably start by purging fresh fluid all the way through the back brakes, working my way to the front as I installed the new calipers.

Once you have done this first step, the only thing left is the booster and master cylinder, but if this first step doesn't fix it, you can cross calipers off the list.

[Ironangel]

I'd check for debris in the MC. Also make sure the return spring is returning the piston within the MC, that it is pushing the piston far enough to reveal the return hole in the MC itself. Hence, a maladjusted pedal to booster rod? If hydraulic pressure is not being released, the MC piston is not returning fully to expose the return/relief port or something like a particle of rubber hose is blocking the port...

[AussieinNC]

1/ Suggest you unbolt the master cylinder from the booster and place one 1/16" flat washer on each stud, then replace master cylinder. This will space the master a little further away from the booster...

2/ Were the front rubber hoses replaced with the disk install? These hoses have a bad habit of failing internally and not allowing fluid to return correctly...

3/ The booster is listed as second hand and is the week link in this scenario...if first two suggestions dont cure the issue, replace the booster....

[RichardJ]

saxart
>>at one point earlier this system worked fine. If that is true, then you can rule out any issues with booster push rod length.<<

Aussieinnc
>>1/ Suggest you unbolt the master cylinder from the booster and place one 1/16" flat washer on each stud,<<


I think there is some possibility that it is the booster rod length causing this problem, but there may be a secondary issue.
About 3 months back, I had a problem with my C4 Vette that may be the same problem you have described.
At lights, I always take manual transmissions out of gear with my foot off the clutch and if possible my foot off the brake. The Vette rolls very easily and is sensitive to any uneven ground, more so than other vehicles.

Out of the blue, it stopped rolling at traffic lights and I could sense a difference in brake feel when coming to a stop in stop-n-go traffic.

The only thing that had been touched in years was a new booster about 3 years ago.
This issue would only start after being driven in traffic for awhile and the brakes heated, but not necessarily with any hard braking.

My Vette manual covered the usual brake dragging problems, but also mentioned a problem with the element of heat added.

Old, contaminated brake fluid heats up more and expands more than clean new fluid.

I had decided to check booster rod length and in the process I discovered the Rubber reservoir cover on the MC had a large crack and the fluid was near black.

The booster rod clearance was under by about .002" when it should be over by .010 - .020"

I always check pin length and I attribute it having changed to the cheap aftermarket steel booster. Original C4 Plastic boosters don't hold up well in the high underhood temperatures of the C4 Vette. I have replaced the Plastic three times in 20 years and decided there wouldn't be a fourth. They're just a couple inches from the headers and fail on a regular basis. Probably the same reason the reservoir cap failed.

I adjusted the booster pin, flushed the brake system, replaced the cap and the brakes are perfect.

[AussieinNC]

Originally Posted by RichardJ

saxart
>>at one point earlier this system worked fine. If that is true, then you can rule out any issues with booster push rod length.<<

Aussieinnc
>>1/ Suggest you unbolt the master cylinder from the booster and place one 1/16" flat washer on each stud,<<


I think there is some possibility that it is the booster rod length causing this problem, but there may be a secondary issue.
About 3 months back, I had a problem with my C4 Vette that may be the same problem you have described.
At lights, I always take manual transmissions out of gear with my foot off the clutch and if possible my foot off the brake. The Vette rolls very easily and is sensitive to any uneven ground, more so than other vehicles.

Out of the blue, it stopped rolling at traffic lights and I could sense a difference in brake feel when coming to a stop in stop-n-go traffic.

The only thing that had been touched in years was a new booster about 3 years ago.
This issue would only start after being driven in traffic for awhile and the brakes heated, but not necessarily with any hard braking.

My Vette manual covered the usual brake dragging problems, but also mentioned a problem with the element of heat added.

Old, contaminated brake fluid heats up more and expands more than clean new fluid.

I had decided to check booster rod length and in the process I discovered the Rubber reservoir cover on the MC had a large crack and the fluid was near black.

The booster rod clearance was under by about .002" when it should be over by .010 - .020"

I always check pin length and I attribute it having changed to the cheap aftermarket steel booster. Original C4 Plastic boosters don't hold up well in the high underhood temperatures of the C4 Vette. I have replaced the Plastic three times in 20 years and decided there wouldn't be a fourth. They're just a couple inches from the headers and fail on a regular basis. Probably the same reason the reservoir cap failed.

I adjusted the booster pin, flushed the brake system, replaced the cap and the brakes are perfect.

Wrap the headers in heat wrap, 2 layers...then add heat wrap on the side of the booster that is closest to the headers....no more issues....at least on both of my C4's....

[saxart]

Lots going on in this thread. Make sure you keep us posted once you resolve this. Threads like this are very helpful to hear the fix!

[lutronjim]

The brakes have worked OK in past couple of years. Don't remember exactly when they started to not release fully.

The disk kit came with new stuff, master cylinder, proportioning valve, hoses, spindles, rotors, calipers, etc. I used the used booster that was on truck to upgrade to power.

Used DOT4 fluid and bled until all old fluid was out of system.

Today I had a little time and put the washers between booster and master cylinder - still didn't release.

I was going to take out bump stop but noticed that I had a good 3/8" petal travel before feeling rod engagement.

I will try later this week to replace booster.

[lutronjim]

Ordered booster from O'Reilly's and got it home today. Box was beat up but didn't pay too much attention.

When I got booster out of box to check MC push rod length, I found that the booster has been installed before. Clear evidence where finish was missing were it bolts on.

If someone took the trouble to install and then take it back off to return, I canda figured its defective.

Went to Napa and know waiting till another delivery.

[S_Gibson]

I had issues with old brake hoses. When I pushed the brakes it would stop the truck, but it took about 30 seconds to release. On some occasions it would release as it should, but it continued to get worse. Brake hoses are cheap and easy to change. If you don't know the age of the hoses or know they are old it doesn't hurt to replace them. The ones on my truck had swollen so bad internally I'm surprised fluid moved in either directions.

[jkeady]

I second replacing hoses. I have had so many oddities pop out from old hoses on vehicles that I have made it a matter of habit to replace the hoses when I replace calipers / wheel cylinders and suspect the hoses are more than 15 or 20 years old.

[lutronjim]

I replaced the rear hose before I found that the fronts were hanging. The front hoses were new with the front brake kit.

[saxart]

My vote still says the calipers are seized up...

[lutronjim]

Problem resolved - I hope. Finally has time to replace the booster with unit from NAPA. I also replaced firewall seal that I got from GMCPauls.

By pulling mounting bracket to replace seal I got to check linkage with no pressure on it to make sure nothing was binding there. It was easy to move.

I really don't see how booster would cause this but I can now stand on brakes real hard and let up and coast. Here's hopping it stays that way.

I appreciate all the feedback.