Leaky master brake cylinder

[1948Matt]

I had my brake go out on me while driving down a hill . I got the car stopped and home. When I tore it apart, the master cylinder was leaking from the front boot and there was no pedal pressure at all. I found a rebuilt replacement online and after a heck of a time getting it all worked out and installed... it is still leaking?!?! This is a completely different MC. What is leaking at the boot? Please help...I am ready to sell this thing over some stupid brakes!

Thanks,

Matt

[Norm's Coupe]

Your rebuilt MC is probably bad too. Just because something is rebuilt by a professional or is new, it doesn't always mean it's good. I'd call the place you bought the rebuilt MC from and ask to return it for a replacement. If it was bought on ebay and no returns, that's another reason for not shopping ebay.

I would either buy a rebuild kit locally and rebuild it myself or have it done by a local shop. That way you have more recourse.

[BobT-47P15]

Your rebuilt MC is probably bad too. Just because something is rebuilt by a professional or is new' date=' it doesn't always mean it's good. I'd call the place you bought the rebuilt MC from and ask to return it for a replacement. If it was bought on ebay and no returns, that's another reason for not shopping ebay.

I would either buy a rebuild kit locally and rebuild it myself or have it done by a local shop. That way you have more recourse.[/quote']

Norm has a good point. Wonder how long ago that master was rebuilt.

Even if it was rebuilt lately, they may have used old rubber parts.

Don't get discouraged......that sort of thing is just one of the many

challenges of having an old car.

The brakes on the 1949 P15 coupe I recently bought don't work at all. I filled the master cyl one day

and 3 or 4 weeks later it was empty, and I can't see where the fluid went. Refilled it, and get

no pedal. So, when the weather gets warmer, will work on that.

Took a bit to get it running in the first place, but that was only

half of the stop & go equation.

###P.S. Went over to the car this afternoon, looked in the master cyl---dry again. Didn't

have time to look under to try and find where it went.

[1948Matt]

Thanks for the replies everyone... Yes, I bought it on Ebay, so hopefully the guy I bought it from will make it right. I will look into the rebuild kit.

Let me clairify the whole "selling it" thing. You see my first time driving this car was the day the brakes failed and I have been working on them for the last couple of weeks (an hour at a time) to get it back on the road. Also, this was sold to me in "daily driver" condition and so I am sharing a car with the wife while I get these issues resolved. I hope this explains a little of my frusterations.

BTW, does anyone have an exploded view or diagram of a master cylinder that I can look at?

Matt

[BobT-47P15]

Here's one pic from an earlier post on the subject.

You might do a forum search on the topic to see if some previous

info comes up.

In fact, here's a link to a recent discussion: http://www430.pair.com/p15d24/mopar_forum/showthread.php?t=13344

[GeorgeLeonard]

Did you buy the car on Ebay too? Ive bought several cars on Ebay "sight unseen" and for the life of me, I cant figure out why I havent learned better by now!

[oldmopar]

You really should do the entire brake system if the master failed the other parts may also have problems. With a single cylinder mc if any part fails you will have no brakes. I recommend in addition to the mc you rebuild or replace all 6 wheel cylinders (fronts have 2 each) also the 3 brake hoses and if the steel brake lines are in bad shape they also should be replaced and condition of shoes checked and replaced if necessary. If you do the work your self parts should run around $300.00 not sure what it cost to have it done by a repair shop but still cheaper then a accident.

Not trying to discourage you for keeping the car just trying to keep you safe

Ed

[Norm's Coupe]

Let me clairify the whole "selling it" thing. You see my first time driving this car was the day the brakes failed and I have been working on them for the last couple of weeks (an hour at a time) to get it back on the road. Also, this was sold to me in "daily driver" condition and so I am sharing a car with the wife while I get these issues resolved. I hope this explains a little of my frusterations.

Matt

That sheds a whole different light on things, especially if you have to rely on the car to get yourself to work and back. When an old car like ours is used as a daily driver, it's about the same as buying any used car off the lot, or private party. Never know what you are getting, until you drive it for a couple of weeks or more. That goes double for buying a car as old as ours.

Personally, I only look at our old cars as a hobby car and don't rely on it as a daily driver. In fact, I think most of us look at them that way.

That said, if you like the car and enjoy having an old car to tool around in, it can be a daily driver. However, just like any modern used car, our old cars are going to require some type of maintenance to keep them going. Once you get all the bugs out, the car will be just as good as any other though. It's just a process of elimination until you get all that's wrong now fixed. Then it's just a matter of upkeep.

For example, my daily driver is a 95 Lumina APV. I really like the car. So........instead of trading it in when something happens to it, I get it fixed. Since the car has long been paid for, I look at the repair bills as a car payment each year or compare those bills to the cost of buying a new car. Either way, it's a lot cheaper to fix the old Lumina. Reading the paper and listing to the ads, a new car like it would cost at least around $35,000, or about $300 to $400 per month in car payments. So far I haven't put any money into it other than normal maintenace except, an alternator, circuit board for the wipers, hatch lock, door handles, TCC Control Valve Switch for the tranny, heater/A/C motor, and new electric window motor. That's all over a period of the last 5 to 6 years. So...........I'm a long way from the cost of a new car even with all those things replaced.

So........I'd either rebuild the MC again, or buy a new one. NAPA not only has the rebuild kits, but they also have new master cylinders for our cars. I bought one of their rebuild kits years ago, but then could not get the master cylinder off the car. So........I drove it to the service garage and had it installed. Total bill, about $20 for the kit, and about $85 to have the shop rebuild it and put it back on. That was in 1995 and haven't had a problem with it since.

[1948Matt]

Hey Guys,

I found the culprit... It looks like when the cylinder was rebuilt, the rubber from the plunger got caught on the lip and then pinched when it was bolted on. When I pressed the pedal, it ripped the rubber, hence the leak. So, I pick up a new rebuid kit tomorrow morning. I will keep you posted.

Matt

BTW... the ebay seller is working with me and I may get some $$ back for the rebuild kit

[RobertKB]

Good luck with the rebuild and I hope it cures your problem. Good advice given about rebuilding the whole system if not recently done. Sounds like your ebay seller is maybe going to be decent about things as well.

[1948Matt]

Well... here we go again. Just to make things difficult, it looks like the master cylinder that I have is not for a Plymouth, but a Desoto. Not a big deal, except that the bore in the Plymouth cylinder is 1 1/8" and the bore for the Desoto is 1". Therefore, the rebuid kit does not fit. To make things worse, it is much harder to find a Desoto rebuid kit... so on the search I go again. Any suggestions? Also, does the Desoto MC look almost exactly the same as the Plymouth? It must right?

[Norm's Coupe]

I believe they all look alike except for the bore inside.

That said, the fact that you have two different size bores on your car is a big deal. For the brakes to operate correctly the bore for all wheel cylinders and the master cylinder should be the same size. So.........I'd buy a whole new master cylinder with the 1 1/8th inch bore.

Sorry for the bad news.

[Don Coatney]

I was just thinking earlier today that it would be a good idea for all cars that

are parked for long periods of time to give the brake pedal a pump or two

every week. This will exersize the rubber and perhaps help move around any

moisture that is trapped in the system. The moisture sitting in one spot is

what causes the oxidation and pitting.

the bore in the Plymouth cylinder is 1 1/8" and the bore for the Desoto is 1".

Therefore, the rebuid kit does not fit.

The silver master cylinder pictured below came off my P-15 and it has a 1"

bore. The other two cylinders are also for a Plymouth and have a 1 1/8"

bore. Both sizes will work on your Plymouth. The 1" bore will actually give

you a quicker response on the pedal. You should be able to get 1" rubber

at any good auto parts store. The rubber needs to match the size of the

bore but does not have to be Desoto or Plymouth specific.

For the brakes to operate correctly the

bore for all wheel cylinders and the master cylinder should be the same

size.

Are you sure? I have never heard tell of that before. Do your disc brake

calipers have a 1 1/8" bore?

[oldmopar]

I would be interested the answer to the bore size vs wheel cylinder I have a mc with a 1" bore that looks new or in great condition but never used it on my Plymouths because I thought the size had to be 1 1/8.

[Norm's Coupe]

Don,

I believe I read that someplace about the bore size. Also when I bought the NOS master cylinder with the optional hole for remote filling a few years ago, I mentioned it to my mechanic friend. His first response was, "is the bore the same as on my coupe". Told him I did not know. The master cylinder was a NAPA one, so gave him the part number off the box. He looked it up and said it was.

So........like you I'm no auto mechanic, but that's where I got that info from. Now as far as our disc calipers go, maybe that's another reason we need those residual valves with our master cylinders.

[krodaddy]

A smaller bore in the master cylinder will require the brake pedal to be pushed farther down to displace the same amount of brake fluid as a larger bore. This results in a softer feeling pedal and improved braking control because of more feedback thru the pedal.

We did this with the front brakes on our BMW road racing motorcycles a few years ago and it worked great. I don't see why the same principle wouldn't apply to our cars.

Barry

[Norm's Coupe]

I guess if one wants to modify anything on our cars, we can always find a way to do it. And, whatever that modification might be, we are happy if we make it work. However, that doesn't mean it's correct or that it's the safest thing to do.

When it comes to brakes, we hold our lives and the lives of others on the road in our hands. Therefore, since I'm not a mechanical automotive engineer I'll go with what they say about keeping everything even.

Yes, I did modify my brakes to disc brakes on the front of my coupe. However, I did not design or dream up the modification. The system was made by some automotive engineer, and I followed their instructions to the "T" when I installed the system. I'm not one to reinvent the wheel when it comes to brakes or other safety items on the car.

[Don Coatney]

Who is to say using a 1" master cylinder is a modification? My car had one on it when I bought it.

[Norm's Coupe]

Don,

On the other hand, who's to say someone did not change your master cylinder over the last 60 years?

[1948Matt]

Any idea where I can get a rebuild kit for the 1" bore MC? I have a couple local (national chains) looking into it for me, but is there another route that I can go?

[grey beard]

There are many vehicles reunning around safely with the original master cylinder and disc brakes on the front. Many of you have these.

Conversely, there are many vehicles that have been retrofitted with dual chamber master cylinders that actuate stock brake systems. These work safely, as well. That ms bore size must match wheel cylinder size is a load of old bunny, IMHO.

I keep hoping and praying that someone among our group of wise parts men with parts book experience will come up with a dual reservoir ms that is short enough to fit into the stock pedal configuration and space allowed to fit Pilothouse trucks and MoPar cars. If we had such an animal available to us, we would all be driving more safely with our old rides. Early Mustangs had the same problem and there are likely a blue million work-around dual ms replacements available, but of course those units had all the room in the world, hanging out there on the firewall, as they did. This one single question has been asked more often than most on this forum, and I have yet to learn of a satisfactory answer that does not require moving the steering box or the pedal linkage.

Someone could still make my day with this info.

[Norm's Coupe]

Any idea where I can get a rebuild kit for the 1" bore MC? I have a couple local (national chains) looking into it for me, but is there another route that I can go?

Are you sure NAPA doesn't have a rebuild kit for you in the 1" size? The reason I ask is they do sell both master cylinders, the 1 1/8th" and the 1" size according to NAPA parts book my mechanic friend checked. If they sell the master cylinder they should have a rebuild kit for their own products, which would also fit yours. The stores don't have all the parts books a lot of times, or they simply don't want to look things up in a cross reference book to find it. I would find and go to the NAPA warehouse for your city, in person and ask for one, not call them. You can tell them the same master cylinder is used in other Mopar cars through 1954. The 1 1/8th inch NAPA master cylinder I bought a few years ago (as mentioned below) is listed in their book to fit Plymouth and Chrysler 1946 through 1954. So........it doesn't have to be a master cylinder for Plymouth only.

[Don Coatney]

That ms bore size must match wheel cylinder size is a load of old bunny, IMHO.

I also thought so. Thanks for your opinion on this subject.

[Don Coatney]

Any idea where I can get a rebuild kit for the 1" bore MC? I have a couple local (national chains) looking into it for me, but is there another route that I can go?

As I said, "You should be able to get 1" rubber

at any good auto parts store. The rubber needs to match the size of the

bore but does not have to be Desoto or Plymouth specific"

You dont need a full "kit". You just need the rubber parts.

[Norm's Coupe]

Originally Posted by grey beard View Post

That ms bore size must match wheel cylinder size is a load of old bunny, IMHO.

Personally, I don't care if someone uses a different size. I was simply repeating what I had read somewhere and was told by a mechanic.

But........if it is a load of old bunny, then why do they make two different sizes? Must be some reason, other than the fact someone got out of bed one morning and said, lets now change the bore size from 1 1/8 to 1".