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JLPurcell

Brake Problems (still)!

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I need some help on my brake system. I will start our with the history. The brakes were working fine. I sourced and installed a vented MK63 front brake upgrade. Upon completion I had a hard pedal and poor braking situation. I took off the brake booster and sent it out, it tested good. I put the original stock front brake /rotors and calipers. Still hard pedal. I have bleed the brakes repeatedly, today I started the car and felt for vacuum has vacuum in houses to the brake booster and holds vacuum after engine is turned off. Any suggestions? I am my end on this problem. Thanks for any help!

  

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32 minutes ago, Patcon said:

How old are the flexible lines?

Fronts for the MK63 calipers recently sourced, Stock and rear NOS.

 

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Sounds exactly like the symptoms of a missing reaction disc in the master vac. Did you replace the brake master cylinder when you did the front upgrade?

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Hard pedal or excessive pressure to stop the car?

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You mentioned you pulled the booster off to have it tested. Like Diseazd says that reaction disc can fall off the plunger and end up inside the booster shell. 

Plagued me for a while, Once I fixed that everything worked fine. It is worth a second look to eliminate that as the problem. 

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18 minutes ago, Patcon said:

Hard pedal or excessive pressure to stop the car?

Hard pedal with very little stopping power. The booster checks out ok. I started after the MK63 upgrade and remained when I changed back to the stock brake system. I sent out the booster and it checked out ok. 

 

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2 hours ago, Diseazd said:

Sounds exactly like the symptoms of a missing reaction disc in the master vac. Did you replace the brake master cylinder when you did the front upgrade?

No, I did not do anything with the booster or the brake master until the change of the front calipers at which time the problem emerged. I then sent out the brake booster for inspection. 

 

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I would also suspect reaction disc or bad/hard pads on the brakes. If you need a reaction disc and can't find one. I have one sitting on the bench right now.

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2 hours ago, Patcon said:

I would also suspect reaction disc or bad/hard pads on the brakes. If you need a reaction disc and can't find one. I have one sitting on the bench right now.

How much for the disc? I need to get it coming just in case, I have an event for the car in early April. Thanks Charles.

 

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4 minutes ago, JLPurcell said:

How much for the disc? I need to get it coming just in case, I have an event for the car in early April. Thanks Charles.

 

PM me an address. I will send it to you for free.

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You don’t have to disconnect the steel lines from the master cylinder to install the disc. Just take off the two nuts holding the m/c to the master vac and carefully pull it away from the master vac. Pull out the plunger/adjuster shaft. Super glue the disc to the back of the plunger/adjuster shaft and reinstall in reverse order. 

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6 minutes ago, Diseazd said:

You don’t have to disconnect the steel lines from the master cylinder to install the disc. Just take off the two nuts holding the m/c to the master vac and carefully pull it away from the master vac. Pull out the plunger/adjuster shaft. Super glue the disc to the back of the plunger/adjuster shaft and reinstall in reverse order. 

I plan to pull this apart tonight to see if the disc is missing. Since getting feedback on this thread I have watched a couple of videos on the purpose of the disc. I still don't understand how it could have been lost without my having initially worked on the booster or master cylinder, but I have looked at every other aspect of the brake system. Thanks for enlightening me to this possibility. Jerry Purcell

Edited by JLPurcell

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Once you take the plunger pressure off the disc, they sometimes just fall into the body of the booster.

If you see it is not where it should be you might try pulling the booster off again shake it a bit and if you hear something bouncing around in there you can usually bounce it toward the opening and get it out. 

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Charles is sending him another......a lot easier to just use that one. A loose reaction disc won’t hurt anything if it just stays in the booster IMO.

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4 minutes ago, Diseazd said:

Charles is sending him another......a lot easier to just use that one. A loose reaction disc won’t hurt anything if it just stays in the booster IMO.

I did not intend to imply it would affect anything. Just a plausible answer as to where they typically end up. 

 

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2 hours ago, Terrapin Z said:

I did not intend to imply it would affect anything. Just a plausible answer as to where they typically end up. 

 

Charles, thank your for your input. Together members of this site are the brain trust on Z cars. I used to think that I was an expert on these cars, but sometimes the members of this site make me feel wanting for Z knowledge. I just hope that I can share something from time to time that helps someone. JLP

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21 hours ago, JLPurcell said:

No, I did not do anything with the booster or the brake master until the change of the front calipers at which time the problem emerged. I then sent out the brake booster for inspection. 

Since this is the case I would rule out the reaction disc from the initial installation. Also in my case the missing reaction disc caused the opposite brake condition.

My brakes became very touchy and want to grab with little pressure on the pedal. The normal modulation was gone.

See what you can find. I do have another suspicion based on what you describe as well.

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10 minutes ago, Lumens said:

Since this is the case I would rule out the reaction disc from the initial installation. Also in my case the missing reaction disc caused the opposite brake condition.

My brakes became very touchy and want to grab with little pressure on the pedal. The normal modulation was gone.

See what you can find. I do have another suspicion based on what you describe as well.

I am all ears, I have removed the brake master cylinder and taken it apart. I have removed the booster and there is a black rubber disc on the front of the plunger, ( am still looking forward to comparing it to the one Charles is sending). So at this point I am still searching and thinking of a total run through of the remaining system. Ideas?

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On 3/9/2019 at 10:47 AM, JLPurcell said:

today I started the car and felt for vacuum has vacuum in houses to the brake booster and holds vacuum after engine is turned off. Any suggestions? I am my end on this problem. Thanks for any help!  

Can't tell where you checked for vacuum.  Is it possible that the check valve is in backwards, or that something is blacking vacuum from the booster body?  Or maybe something is bound up in the booster itself, not letting the vacuum do its thing.

 

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Wow.....Sorry Jerry.....just seemed like the symptoms I had with a reaction disc. Pedal hard as a rock but had to stand on the pedal with both feet to stop. 

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Did you bleed the lines while doing all of this by pumping on the master cylinder?

Have you checked that the master is still functioning properly?

Could it be that your master has failed?

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42 minutes ago, Diseazd said:

Wow.....Sorry Jerry.....just seemed like the symptoms I had with a reaction disc. Pedal hard as a rock but had to stand on the pedal with both feet to stop. 

I am at wits end at this point. There are only a couple of components in the system at this point. Brake warning light switch and valve in rear brake system. I don't believe that it can be the rear brake components they have not been touched since working, and The front is back together with all of the original parts at this point. Just leaves me scratching my head. I was so hoping that the disc was the problem. JLP 

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Have you checked the direction of the booster check valve as suggested above?

I am scratching my head as to how the problem could be anything other than the booster or vacuum feeding the booster. In my experience, pretty much every other negative situation in the brakes leads to a soft, spongy, whatever, pedal. I suppose if a wheel cylinder were frozen solid the result would be a harder pedal but...

If you block the booster vacuum entirely, does anything symptomatically change in the way the pedal feels? 

Definitely check the direction of the check valve. If it is backwards, it will feel like no booster...thus hard pedal.

Even though the pedal is hard, does the car stop as it should...assuming you give enough leg effort?

 

 

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Pulled the rear brake proportioning valve off this evening and took it apart. The lower seal was full of some kind of sandy material. Does anyone have one of these Sumitomo valves they would be willing to sell? I am in the process of going through each component of the brake system. "One bite at a time". JLP

 

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