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  #1 (permalink)  
Old 09-20-2017, 08:41 AM
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Default Brake system issue...

I have a B&B cobra with a 4 piston Wilwood front system and the GM calipers with E brakes on the rear. I have a new 1-1/32" bore master cylinder. The issue I'm having is that the pedal will go about half way to the floor on the first press and then will be 2" to 3" higher on subsequent presses. The pedal feels spongy as well. The pedal will stay high until 10 seconds or longer elapse and then the first press again will result in the lower pedal. I've bled the brakes several times with no air bubbles apparent. When I apply the E brake, the pedal becomes super firm and high, suggesting my problem is with the rear. Maybe not? I've replaced all the rubber lines with new SS braided lines, hopefully eliminating any hose flex issues. The rear calipers are in good condition and the E brake levers on the calipers are in proper adjustment. I also installed a new 2lb residual valve in the rear line. I currently have the master cylinder configured with the front brakes connected to the port closest to the end and the back brakes connected to the port closest to the pedal. I have a proportioning valve installed in the rear line, but no adjustments on it affect the pedal issue. Any ideas about what could be causing this issue?

Last edited by Akimbeau; 09-20-2017 at 08:43 AM..
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Old 09-20-2017, 09:15 AM
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How close are the master cylinder and brake lines to the header and exhaust? You could be boiling the fluid in the lines and master cylinder and that could result in what you are seeing. If they are close you could add some heat reflective tape to protect them.

Would not hurt to bleed the brakes again as well, it is amazing how long after you bled them that you can come up with air bubbles again.
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Old 09-20-2017, 09:29 AM
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The brake pedal has the issue with the car cold. I have been driving the car for over a year with the issue. The brakes stop the car fine, but the pedal feels funny. I'm looking to sell the car and don't want this to be a point of concern for the new buyer. I just tried bleeding them again with no change in symptoms.
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Old 09-20-2017, 12:45 PM
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Hi Akimbeau,
I had a similar problem when I upgraded to the wilwood dynalite front brake kit. I also replaced my master cylinder. I was surprised that my brake pedal was soft and I did the same as you I bled them again but to no avail. The problem was that I had an older style proportion valve and with the larger upgraded rotor my proportioning valve was insufficient. I had to replace the proportioning valve with a wilwood adjustable proportioning valve. Summit Racing (Wilwood Brake Proportioning Valves 260-11179). This cured my soft brake pedal.
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Old 09-20-2017, 01:59 PM
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Thanks for your reply, Leecbr. I had a chat with Wilwood and the tech guy said the proportioning valve I was using was sufficient, as was the bore size of the new master cylinder. He suggested I bench bleed the master cylinder again, which I did, no improvement. On a follow-up call to Wilwood, the tech guy thought it was still air in the line and that I should do a hand bleed to get full throw of the master cylinder piston while in the car thru the brake line system. Sounds rather difficult given the size of the foot box.

He did say that some people have needed to shim the GM Metric calipers with a brake pad shim to get proper operation. Has anyone needed to do this that has these types of calipers?
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Old 09-20-2017, 04:47 PM
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Quote:
Originally Posted by Akimbeau View Post
I currently have the master cylinder configured with the front brakes connected to the port closest to the end and the back brakes connected to the port closest to the pedal.
They s/b the other way around. Not intuitive, but port on MC closest to pedal goes to front brakes. Forward port goes to rear brakes. Ignore the drum brake reference in the illustration, the port assignment is the same for rear discs.


EDIT: That's how mine is set up, but further reading indicates different MCs may be set up differently. The simple guidance is the larger chamber / reservoir s/b plumbed to the front brakes. If they're the same size it doesn't matter. Most diagrams show the brakes connected like mine - the reverse of yours. END EDIT

Also, the GM brakes have a special caliper adjusting procedure - did you follow that exactly?

From the installation manual:
After the cables are installed, you need to adjust the system. Engage and release the emergency brake lever several times to activate the self-adjustment mechanism built into the calipers. You’ll know you’ve got it when emergency brake is fully engaged and the rear wheels will no longer turn by hand. If your rear caliper pistons do not ratchet out by use of the e-brake arm on the caliper follow this procedure to get the piston to extend the brake pads to the rotor surface. Remove the spring and the e-brake arm from the caliper. Turn the threaded bolt extending from the body of the caliper by hand or with the aid of a wrench. Continue to turn the bolt until the brake pads come in contact with the rotor. After the desired adjustment is achieved reattach the e-brake arm and the spring onto the caliper. Continue with the bleeding procedure.
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Last edited by cycleguy55; 09-20-2017 at 04:56 PM..
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Old 09-20-2017, 04:56 PM
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Check the brake hoses, make sure they are not expanding during operation.
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Old 09-21-2017, 05:55 AM
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Cycleguy55, The reservoirs are the same size on this master cylinder. I switched ports and there was no difference in the symptoms. Also, I replaced all flex hoses with steel braided hoses so hose flex is not the issue.

Snapier, I have become an expert at adjusting the GM E brakes, so I know that is not the problem.

I re-bled the brakes, operating the master cylinder a few times by hand in the car to fully depress the piston and then completing the bleeding normally, no change in symptoms.

I should buy stock in brake fluid...I'm going thru it like crazy!



Keep the ideas coming, I appreciate them all!

Last edited by Akimbeau; 09-21-2017 at 06:00 AM..
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Old 09-21-2017, 06:42 AM
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If it is still an air bubble issue, this may help? When bleeding my slave I had issues. After research, I decided to reverse bleed, air bubbles rising made sense. I also liked the syringe technique found on motorcycle blogs, worked very well for me. First time, lots of air release, firm pedal, done. Then when I upgraded to Wilwoods recently, I used the same technique on both front and back, just as effectively.

Given my three masters in the footbox, and the fact I wasn't having luck with push and pull pressure methods, the syringe reverse bleed became my one person method, it's so simple and effective on mine. A 10 cc syringe is easy to reach in with one hand to the masters and lift the plunger with thumb to remove fluid. Then used a 30 cc syringe to add fluid from the bleeder using short tubing from Lowe's and adapters from my pressure/vac kit. Very controllable and good in tighter spaces. Brent
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Old 09-21-2017, 08:37 AM
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FWIW, I was having no end of challenges bleeding my brakes (same as you - 4 piston Wilwood in front and GM brakes rear).

I finally gave in and put speed bleeders in all my calipers. Problem solved. Highly recommended.
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Old 09-21-2017, 08:40 AM
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Perhaps a dumb question, but one that needs answering. Did you accidentally use a silicone brake fluid and mix it with a non synthetic brake fluid? They don't play well together and will wreak havoc on lines and seals.
Just a thought.
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Old 09-21-2017, 01:33 PM
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From what you described in your original post, it sure seems as though the rear brakes are out of adjustment. The GM calipers use a ratchet mchanism and sometimes, you can just be on the edge of it clicking, which will move the pad closer to the rotor and your pedal will be high. I have literally done a hundred brake jobs with these style calipers and probably half of them end up with the situation you describe. This is of course assuming there is no air in the system .
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Old 09-21-2017, 01:35 PM
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Quote:
Originally Posted by cycleguy55 View Post
FWIW, I was having no end of challenges bleeding my brakes (same as you - 4 piston Wilwood in front and GM brakes rear).

I finally gave in and put speed bleeders in all my calipers. Problem solved. Highly recommended.
Cycleguy55,
Question on the speed bleeders. I had bought multiple bleeder sets for my rear Girlings. Non check valve version for use in reverse bleeding/flushing if/when needed and check valve speed bleeders left in afterward for regular maintenance.

On my new front Wilwoods I didn't install bleeders there (yet, wanted to) with concerns of others on the web having issues damaging the threads/seal with speed bleeders on their Wilwoods.

I don't believe Wilwood sells them (maybe?), but do you have a brand you like or any specific advice/cautions in that regard? Maybe the others were just not careful to really ensure the right bleeder dimensions (easy to figure)?

Those like myself, and perhaps the OP, could benefit from any thoughts there. Thanks, Brent
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Old 09-21-2017, 02:29 PM
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Quote:
Originally Posted by joyridin' View Post
From what you described in your original post, it sure seems as though the rear brakes are out of adjustment. The GM calipers use a ratchet mchanism and sometimes, you can just be on the edge of it clicking, which will move the pad closer to the rotor and your pedal will be high. I have literally done a hundred brake jobs with these style calipers and probably half of them end up with the situation you describe. This is of course assuming there is no air in the system .
I'm following a GM guide for adjusting the e brake lever. What I end up with is the lever will have about 1/4" gap between the stop and when the e brake is locked up. The pads end up tight to the rotor when the e brake lever is on the stop.
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Old 09-21-2017, 02:42 PM
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Quote:
Originally Posted by jhv48 View Post
Perhaps a dumb question, but one that needs answering. Did you accidentally use a silicone brake fluid and mix it with a non synthetic brake fluid? They don't play well together and will wreak havoc on lines and seals.
Just a thought.
All the same synthetic brake fluid
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Old 09-21-2017, 03:50 PM
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Quote:
Originally Posted by Akimbeau View Post
All the same synthetic brake fluid
Next question. Did you buy the car from someone or are you the first owner? When you got the car, did the brakes work correctly? What type of brake fluid did it have in it? Most come with DOT 3 or 4, though some have 5.1. If the car was setup for racing, it might have used DOT 5 fluid, a silicone based fluid that works better in higher temps but doesn't hold water in suspension.
DOT 3, 4 and 5.1 are polyethylene glycol based. DOT 5 is silicone-based and does not mix with the polyethylene glycol based fluids.

If the car had either synthetic or silicone and someone accidentally mixed the two, the seals in both the calipers and the master cylinder would slowly be destroyed and need rebuilding. To boot, in order to change from one type of brake fluid to the other requires a thorough flushing of all lines and cylinders before adding the new fluid.

Seems like you've tried everything else. This is the only thing left.
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Old 09-21-2017, 07:52 PM
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If you had air still in the system, the pedal would not get firm on the second pump. It sounds like you have bled the system adequately.

A residual pressure valve is made to cure the problem you are describing, and you have added one to the rear brake line. Either you have installed it backwards, or the one you have is leaking. Either condition will allow your rear pistons to retract too much and give you more pedal travel on the first pump. Since the second pump is firm (the rear pistons have not had time to retract) my guess is your residual pressure valve is leaking/faulty.

I would try a new residual pressure valve. My 2 cents. Good luck.
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Old 09-22-2017, 05:56 AM
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Quote:
Originally Posted by Akimbeau View Post
I'm following a GM guide for adjusting the e brake lever. What I end up with is the lever will have about 1/4" gap between the stop and when the e brake is locked up. The pads end up tight to the rotor when the e brake lever is on the stop.
You are talking about adjusting the e-brake lever. I am talking about adjusting the rear brakes to give yourself a brake pedal. The 2 are different.

What you would need to do is back off the e-brake until the lever on the caliper is as far back as it can go, then hit the brake pedal while pulling on the lever.

As stated, there is a ratchet mechanism in the caliper piston that is used to adjust the brake pedal feel. When you crank up the e-brake handle, you are bypassing this mechanism.
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Old 09-22-2017, 07:47 AM
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Quote:
Originally Posted by jhv48 View Post
Next question. Did you buy the car from someone or are you the first owner? When you got the car, did the brakes work correctly? What type of brake fluid did it have in it? Most come with DOT 3 or 4, though some have 5.1. If the car was setup for racing, it might have used DOT 5 fluid, a silicone based fluid that works better in higher temps but doesn't hold water in suspension.
DOT 3, 4 and 5.1 are polyethylene glycol based. DOT 5 is silicone-based and does not mix with the polyethylene glycol based fluids.

If the car had either synthetic or silicone and someone accidentally mixed the two, the seals in both the calipers and the master cylinder would slowly be destroyed and need rebuilding. To boot, in order to change from one type of brake fluid to the other requires a thorough flushing of all lines and cylinders before adding the new fluid.

Seems like you've tried everything else. This is the only thing left.
The brakes have been totally rebuilt and all fluid has been changed. I have always used Dot 4 synthetic.
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Old 09-22-2017, 07:52 AM
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Quote:
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If you had air still in the system, the pedal would not get firm on the second pump. It sounds like you have bled the system adequately.

A residual pressure valve is made to cure the problem you are describing, and you have added one to the rear brake line. Either you have installed it backwards, or the one you have is leaking. Either condition will allow your rear pistons to retract too much and give you more pedal travel on the first pump. Since the second pump is firm (the rear pistons have not had time to retract) my guess is your residual pressure valve is leaking/faulty.

I would try a new residual pressure valve. My 2 cents. Good luck.
I have considered this possiblity. The residual valve is new and I checked for proper direction installation. The thing is my master cylinder is above my calipers so it shouldn't need a residua valve, unless these e brake calipers do? I might try a new valve and see what happens.
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