Author Topic: Can simply bleeding the brakes make them not drag and work correctly?  (Read 816 times)

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Offline DeadStang

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So, out of the blue, my '65 Coupe started reeking of brakes while driving home the other day.  The rear wheels were HOT to the touch and the wheels seemed to be dragging a bit (hard to tell on the ground in the driveway).  It was real -- I am always paranoid about stuff and I sniff my car(s) for gas and antifreeze smells, etc. all the time -- but I made the husband sniff the back of the car and he agreed with me.  So I got to work on it and literally could find nothing wrong with anything.  Everything is fresh, thick, and seems to function as it should.  So I bled literally 2/3 of a gallon of fresh brake fluid thru the lines before it finally came thru clean (even went back to repeat the rears after finishing up the fronts -- got a little more dirty fluid!).  The fluid was brownish, some came thru emulsified-looking, and there was some precipitate of solid flecky material; the fluid settled in the milk jug and even separated like boiled chicken fat as well.  So, obviously, the fluid was 300 years old and the system needed flushing.  I finally finished up last night too late to go out, but could the problem have just been the fluid?  Or am I missing something? 

Offline gte428cj

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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #1 on: September 29, 2018, 12:19:43 am »
I had this same problem. It was not a problem with bleeding the brakes. The problem was the hydraulic pressure not being released from the rear brakes.

My car has front disk brakes. Cars with front disk brakes have a proportioning valve in the rear brake line. This valve will maintain 10 pounds of  pressure to the rear brakes when you are not pressing the brake petal. When this valve fails, it can hold the rear brakes on all the time, causing overheating brakes. This can completely destroy the brakes including the shoes, wheel cylinder and drums.

You didn't say it you have front disk brakes, but if you do this is the problem. The fix is to replace or rebuild the proportioning valve. You will then have to bleed the brakes.

Mike

Offline Vcode

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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #2 on: September 29, 2018, 07:30:07 am »
Scott did a article on rebuilding the valve.

https://www.musclecarresearch.com/valve-rebuild-wagner
'69 Mach 1 SCJ

Offline redscj

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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #3 on: September 29, 2018, 08:22:37 am »
     Is the emergency brake fully releasing? Sometimes crud builds up inside the cable sheath. Then the spring is either slow to retract the shoes or just can't retract them at all. Might want to visually make sure that one of the springs hasn't broken a coil or more off. Old horses just go lame on occasion.  ;)
Grant
69 Mach 1 Dearborn SCJ 4.30 4spd 6/17/69 Candy Apple Red
69 Sportsroof Metuchen SCJ 4.30 C6 5/28/69 Acapulco Blue

Offline sah62

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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #4 on: September 29, 2018, 09:09:37 am »
Scott did a article on rebuilding the valve.

https://www.musclecarresearch.com/valve-rebuild-wagner

Thanks, but the '65 uses a very different valve. I believe both a rebuild kit and a reproduction of the valve is available from places like NPD.
Scott Hollenbeck
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Offline rockhouse66

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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #5 on: September 29, 2018, 10:44:49 am »
My first guess would be that the master cylinder is sticking, maybe because you loosened up some crud in there by bleeding the brakes (full stroke on the pedal).  Second guess would be a bad rear brake hose that is collapsed and behaving like a check valve - pressure forces fluid through but won't allow it to return.  Even a hose that looks good on the outside can be collapsed inside.
Jim

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Offline DeadStang

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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #6 on: September 29, 2018, 06:18:15 pm »
I was hoping I'd get off lightly with just the bleed, lol.  It does have front disc brakes and the proportioning valve wasn't something I thought about.  And I also wondered about the M/C as a whole lot of really nasty fluid was mixed up inside after I started bleeding them -- so much that I sucked about 4 ounces directly out of the M/C with a syringe and tossed it twice before/while continuing to bleed. 

Offline geraldt52

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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #7 on: September 29, 2018, 07:39:13 pm »
If the master cylinder were sticking I would think both front and rear brakes would be dragging, as that car should have a "single" master cylinder.  If the rear wheel cylinders were the culprit, it'd be unusual for both sides to have the same problem at the same time.

I'd guess the rear brake hose.  You could probably verify that by trying to bleed the rear with a MityVac, instead of pumping the pedal...but it probably wouldn't be conclusive, and changing the rear brake hose is easy/cheap. 

Offline crossboss

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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #8 on: September 29, 2018, 08:13:04 pm »
Since you mentioned the fluid was 'dirty' and it separated like water and oil, quite possibly someone added DOT 3, and DOT 4/5 and contaminated the fluid. DOT 3 is notorious for absorbing water and as a result will have rust in the system. DOT 3 and DOT 5 are not compatible. Also, you might have a brake prop rod issue. Check for proper length. Too short can cause no pedal pressure, and too long can heat/lock/drag up the brakes.
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Current lifelong project: 1969 Mustang Fastback/FOX chassis, Powered by a modern Can-Am 494 (Boss 429), Kaase headed, Autolite 1425 cfm 'B' Inline carb, 6 speed, 4 wheel discs, ala Trans-Am style--Whew!

Offline DeadStang

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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #9 on: September 29, 2018, 11:04:32 pm »
I've been driving this thing for the past couple of years with no brake issues until the other day.  I think the fluid is just nasty and rusty and full of water from age -- I've had that before in some of the old hulks I've drug home.  Interestingly, the M/C with DOT 5 in the SCJ Coupe, that I have not touched in 10 years, is spotlessly clean (this job in the '65 is going to make me bleed those brakes now, just for maintenance). 

It rained torrentially today so I didn't get it out for a test drive, but I think that's the next step to see if the rear wheels heat up again.  If they do, I am not sure what more I can do diagnostically, so I think I'll throw a brake line at it and look into the proportioning valve as well.  I went and looked at it and the proportioning valve is very different from a '69, but it appears to be SO much easier to access and replace.  Remind me why I like Cobra Jets again?!

Offline rockhouse66

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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #10 on: September 30, 2018, 08:58:37 am »
  I went and looked at it and the proportioning valve is very different from a '69, but it appears to be SO much easier to access and replace.  Remind me why I like Cobra Jets again?!

You will soon find that the '65 disc brake prop valve is priced like a Cobra Jet part though  ::)
Jim

'69 Grande CJ

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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #11 on: October 01, 2018, 03:53:44 am »
Your brake situation is likely to have been normal since both rears were similar in temperature and it was the smell that alerted you to look into the brakes and not a swerving or otherwise a drivability issue. 

The proportioning valve, accumulator or any other hydraulic component which could cause the brakes to drag is not impossible in these times of fake parts.

My guess is that you braked a little harder than usual and didn't think about it and exploited a flaw in the brake hardware.  The secondary shoe has a weaker spring than the primary shoe and therefore performs more work by a multiplier of it's larger size.  Your primary shoe has a flawed weak spring or it broke and released the shoe to early jamming the brake assembly and causing a drag.  Did you notice a pop the next time you hit the brakes in reverse?


Offline DeadStang

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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #12 on: October 01, 2018, 10:20:09 am »
Your brake situation is likely to have been normal since both rears were similar in temperature and it was the smell that alerted you to look into the brakes and not a swerving or otherwise a drivability issue. 

The proportioning valve, accumulator or any other hydraulic component which could cause the brakes to drag is not impossible in these times of fake parts.

My guess is that you braked a little harder than usual and didn't think about it and exploited a flaw in the brake hardware.  The secondary shoe has a weaker spring than the primary shoe and therefore performs more work by a multiplier of it's larger size.  Your primary shoe has a flawed weak spring or it broke and released the shoe to early jamming the brake assembly and causing a drag.  Did you notice a pop the next time you hit the brakes in reverse?

No pop before I did the bleeding.  I took it out yesterday and drove all around my area.  I even got out and pushed the car 2-3 times on flat ground and it rolled easily.  I did brake kind of hard pulling off the highway onto my road and there was a loud pop or thunk from the passenger side of the vehicle I couldn't identify or reproduce.  After all that driving, the wheels were cool but the drums were a little warm, with maybe the driver's side being a little warmer.  It seemed normal and what I would expect.  An aside, in a fairly hard brake, towards the end of the stop, the car pulls slightly to the driver's side.  I had never noticed this and would not had I not been driving around, trying to get my brakes to repeat what happened.

Offline Brian Conway

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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #13 on: October 01, 2018, 02:54:55 pm »
Something you can take a look at real quick is how many threads are left exposed on your proportioning valve.  Most discussions involving this disc/drum set up usually state 11 threads exposed as a common adjustment similarity.  My 65 and I suppose Jim's 66 have the same disc/drum brakes.  Happy to help out if I can.  Brian
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69 9T02R 4 spd  SCJ Built 9/19/68
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Re: Can simply bleeding the brakes make them not drag and work correctly?
« Reply #14 on: October 09, 2018, 07:16:33 am »
I was trained by a career brake man that was considered the best drum brake man in the business. He did vintage race cars and 6000 pound caddys which had drum brakes and when he was done they would stop so well you would assume it had disc brakes.I met him and his son and grandson at the brake shop buying parts and stuck around to learn.  He had a rolls of asbestos brake linings and the first time he arced a set of 8 shoes I was shocked at how much lining he removed.  He took the arced shoes to the drum and showed me the brake action and of course he was right. 

Using a contrasting color, fog a coat of paint on the rear shoes.  Use just enough paint so the witness to the shoe/drum contact surface area will be visible.  Next drive the car under 35 and perform soft slow stops and pull the drums and look at the witness.  Reassemble and take it up to 70 and do a couple of cow in the road panic stops and look at the witness.  You will find that the brake shoes that are causing the swerve will have less drum contact than the other side.

Improper arcing, a partially crushed or restricted steel or rubber fluid line, a wheel cylinder binding, bad springs or bent shoes could cause your swerve. 

I just rebuilt a set of Kelsey Hayes 4 piston calipers and did nothing to the rear brakes other than check them out on a 65 GT fastback with a Shelby drop.  The pedal goes almost to the floor with the manual master cylinder because you do not need or want the rears to come on too soon so they are adjusted out or away from the drum.  That car stops on a dime from 60 and I can modulate all four brakes right to the tires slipping point.  During my test program of panic stops from 30 40 50 60 70 and 80 to zero the car hops on all four wheels as they are brought right up to the slip point then the brake pedal is slightly released to keep them turning and chirping.  That level of control is referred to as proper braking modulation.

The time to learn how your car performs in a panic stop is not the first time.  Remove one drum and have an assistant ever so slowly depress the pedal and watch the action.  The primary shoe should not move, only the secondary.  Observe the clearance of the shoe against the backdrop of the backing plate for a reference and notice how the shoe angle changes with relation to the back plate as the shoe moves further out.  Arc the linings to accommodate that geometry.

Brake fluid is hygroscopic and absorbs water, new fluid is about 1 percent water and the maximum saturation is about 7 or 8 percent. The water settles to the lowest point in the hydraulic system which is the seals.  The resulting corrosion is kept in check when the parts move through the seals, imagine a wiper blade working in the rain.  The corrosion is pushed back and the system is working without issue.  When brake fluid is changed, especially the pedal pumping variety, jets of new fluid blast the formerly harmless chunks of rust in the cylinder right up to the seal, where else can it go. When the car returns to service the brakes will likely start to leak in a year or two.  A 66 mustang that we decided to sell has 15K original miles and original brakes and fluid.  The master blew it's seals so I re-sleeved it and devised a method to install the master and get the air out without touching the fluid in the 4 drum brakes. The wheel cylinders must as bad or worse than the master but there no leaks yet.
« Last Edit: October 12, 2018, 12:19:13 am by 69cobrajetrugae2 »