The D**n P15 Brakes

[MattWalker]

I'm having a problem now where my brakes lock after about 15-20 miles of driving. The brake pedal gets stuck all the way up hard. I can feel it getting higher and higher as a drive until the car just gets stuck. After about 45 minutes sitting, it releases.

I've read several threads and it seems the likely culprit is the master cylinder relief port being clogged or perhaps the wrong piston length in the rebuilt master?

Are there any other possibilities? I'm thinking it is heat since it slowly goes away as it sits which I would attribute to the system cooling off.

[RobertKB]

All symptoms would point to the relief port.

[Guest P15-D24]

relief port.

[Plymouthy Adams]

ensure the pedal adjustemnt is correct to allow proper return for the relief port to do its job..

[suntennis]

When the brake pedal is correctly adjusted, there will be 1/2 to one inch free play till when there is pressure applied to the master cylinder. That free play is when the only pedal resistance is from the brake pedal return spring.

[T120]

Also ensure your brake fluid is not contaminated.The brake fluid you collect when bleeding the cylinders at all 4 wheels should be as clear as the new brake fluid you are adding to top up the master cylinder.

Edited August 27, 2012 by Ralph D25cpe

[greg g]

remember to leave some space at the top of the reservoir for expansion and for fluid to flow back when the brake is released. There should be two holes in the floor of the reservoir visible withthe cap removed. one is larger than the other, the small one allows for the return of cluid to the res. Some mechanics wire will find it and clear it of debris.

Also assure you have about 1 inch of free play at the top of the pedal stroke. this will also lessen the problem.

[rumble48]

I had this same problem, the fluid was clear enough to look in and see the relief hole......

that said, when I rebuilt the master I found it plugged and the piston area full of crud.... problem solved...

[greg g]

So three or four suggestions, and the OP disapears without so much as a fare thee well.

Whats so hard about taking off the cap, and using a flashlight to see if there are two visible holes inthe reservoir and making ure they are clear.

Edited August 30, 2012 by greg g

[Plymouthy Adams]

proper set up the right amout of ffree paly..lid off..careful slow push of the brake..and if proepr and clear..the fluid would be seen rip[p[ing the reservor as it return from the cylinders..quick and easy..and yes many suggestion are made to help folks and never any feedback if tried or the real answer to the problem when found..forum is not benefitting from the possible knowledge base it is designed to build..

[MattWalker]

Sorry, don't have much of one other than none of that worked. The hole was clear, the fluid did come back in, there is alot of free play, also master was rebuilt within the last year. I was about to replace the master with a raybestos but decided to go with a dual chamber upgrade with a wilwood remote resevoir master. Im not doing it myself but will let u guys see the results.

Thanks for the help.

[40P10touring sedan]

My 40 did the very same thing...the more you hit the brakes, the more that pedal would pump up and stay there...unless you let it sit for a while. My relief port was fine...sounds like yours is too...my problem was the PO set the rebuilt MC with no play between the rod and the MC piston...should be 1/4" to 3/8"...remove the floorboard or come at it from undernieth and pull the rubber boot off of the MC...use a good light and see if there's any movement of the piston when the rod off of the brake pedal is moved alittle bit...you'll need two wrenches for your friend to readjust the rod length...make sure thye're tight when your done....heck, could be loose now?!

If it isn't the MC or the freeplay of the rod, start looking for the wheel{s} that lock up, maybe a bas brake line is collapsed internally and restricting the flow back to the MC...happened to a guy here and the hose in question wasn't that old{a few months I think...just made bad or went bad}.

[BobT-47P15]

My standard question pertains to the condition of the brake line

rubber hoses. In my case, the little hose at the rear axle looked

perfectly good on the outside. But, on the inside it was collapsing,

preventing the fluid from returning to the MC and locking up the

rear brakes after a quick-ish stop. If left to sit for a while, the

fluid would work its way back to the MC and you could go again.

To relieve the pressure immediately, I would open the bleeders, let out a

little fluid and allow the brakes to back off some. Replaced the hose &

all was well again.

The other advice above is good also.

[T120]

When your brake pedal is hard at the top of it's travel with no freeplay,does your brake light stay on?

[MattWalker]

in response to the brake lines - yes mine are brand new, I have never heard that new ones as well can act that way, I had assumed if they were not old that couldn't be the cause... hmmmm.

To the brake light question, yes they do and that starts very soon even before they lock up.

Well I pulled the trigger on the mechanic doing the dual chamber conversion. He's mounting it behind the current mc and making a longer push rod. I don't know if anybody has used this mc for this purpose on a p15 - he is using this one I believe - http://www.summitracing.com/parts/WIL-260-7563/.

has a 1" instead of a 1.125" but we're thinking it should be ok. Would be a bummer if it still happens after the upgrade but it will be a good move either way for safety.

[T120]

You know I'd still be supicious that somehow the fluid in the brake system is either incorrect or contaminated.I would drain the fluid in the brake system and replace with new DOT3 brake fluid.Just my thoughts

Edited August 31, 2012 by Ralph D25cpe

[MattWalker]

the brake fluid has been changed, not kidding, 4 times in the past year. When I changed all the cylinders, once. Changed the front hoses, twice. Rebuild the master, three times, changed the rear hoses and brake lines, 4th time. The only original brake parts now are the mc housing and the front steel brake lines.

[T120]

Sounds like you covered all the bases.A mystery to be sure,a guess on my part.If something other than approved brake fluid is inadvertantly added to the master cylinder it will cause problems.I hope the new master cylinder is the answer to your problem.

[K_Jordan]

I recently had the same problem and had to adjust the length of the push rod to the mc. In my case the push rod was to long, but when I shortened it the brakes where perfectly fine.

[MattWalker]

After talking with the mechanic, the push rod adjustment might have been the problem. It seems the bore in the first part of the piston was too large and not pushing much fluid until the latter part of the stroke, to compensate he adjusted the rod longer so the pedal was further in the stroke when fully up but in the better part of the cylinder. This was probably causing the relief port to not be hit most or all of the time. However to adjust it with enough play the pedal is much too soft and scary to drive because of the cylinder being worn out....at least this is my interpretation of what he said...... anyways it seems like a new MC was in the cards and it looks like this will resolve the problem.

I can't wait til its done I just want to drive the stupid thing!! I've had it for a year and driven it 200 miles. The electrical is the next thing to go I'm sure, I'm already seeing signs. Anybody ever have a new wiring harness installed professionally? What was the cost?

[Plymouthy Adams]

you start the thread with "I am having" but in the end it was a mechanic that doing all the work...seems post 4 feel on deaf ears...one would think it would be best just to give the mechanic the address for the forum, when it is apparent they do not know what they are doing..

[MattWalker]

We I suppose would be the correct pronoun as I have many, many hours on this car and these brakes as well but in frustration I took it to a mechanic. He's actually a great mechanic but had never done Plymouths before. I misunderstood what he was telling me about the relief port, it was working after he tool slack off the push rod which gels with everybody's posts here.

[Plymouthy Adams]

as long as you were there and helping and hopefully learning about your car so you can take of the maintenance in the future..gotta start somewhere for sure..anyway..it is up and running and that is good

[40P10touring sedan]

The relief port comes into play at the very back end of the release stroke, so rod end play is critical...as you can tell.

BTW- I like that MC on summit, if you go with that one let us{me} know how it works out...looks really slim and for my '40 I need that.

[MattWalker]

I have learned quite a bit about cars working on this p15, I have enjoyed it at times and been more frustrated than ever at others.

He's installing the new MCon tuesday, he showed me the plan and it looks pretty cool. The bracket bolts to the existing bolt holes so it is completely reversible. I was against it at first cuz I wanted to keep the car all original configuration but it does seem alot safer. I already lost brakes completely in this car once, I don't want to experience that again.

Anybody got any cool ideas for a reservoir? The ones it comes with are these white plastic ugly things. I was thinking a Plymouth gin bottle or some kind of cool mason jar? I know some cars back then had a jar for washer fluid right?