Brakes locking down

My 63 Avanti has a problem with the brakes. I'm getting backpressure into the master cylinder. Enough to turn the brake lights on. After a short drive, the lights will stay on for about 5 minutes, then go off. I thought I had it fixed when I rebuilt the master cylinder. But it's back. I know there is a pressure relief somewhere but where is it and how do I fix it. It's the original single line master cylinder. I was told to replace the rear flexable brake line, but I don't think that would cause backpressure on the mstr. cyl..

63 R2 Avanti

[Mike]

Probably, you have no freeplay, in the pedal; and the master isn't releasing enough to unmask the very small, (less than .040"), port in the bottom of the reservoir. It may be blocked, too. It's toward the rear of the car, from the larger,( 3/16"?), port. It's adjusted by changing the length of the push rod.
Stude's very precise about setting this clearance, in the manual. You need some. You don't want much!
Mike M.

[charley norton]

I don't think it's freeplay, Mike. I measured the rod coming out of the booster and it was dead on spec.. The brake pedal when I first start driving feels normal, but after the brakes are used a few times, it gets hard as a rock. It goes back to normal abuot the same time the tail lights go out. I think it may be blocked liked you suggested. You think I can stick a pin in that port and unblock it? Or should I take the master cylinder off?

63 R2 Avanti

[Sonny]

quote:Originally posted by charley norton

My 63 Avanti has a problem with the brakes. I'm getting backpressure into the master cylinder. Enough to turn the brake lights on. After a short drive, the lights will stay on for about 5 minutes, then go off. I thought I had it fixed when I rebuilt the master cylinder. But it's back. I know there is a pressure relief somewhere but where is it and how do I fix it. It's the original single line master cylinder. I was told to replace the rear flexable brake line, but I don't think that would cause backpressure on the mstr. cyl..

63 R2 Avanti

It very well could be a hose that's delaminating on the inside, especially with the single line setup Charley. I had the same thing on my brother's '50. I had rebuilt the master cylinder AND the dam hill holder. It turned out to be the right hand, front wheel hose. We just changed them all, problem solved.

Sonny

http://RacingStudebakers.com

[Mike]

I had the positions of the two ports switched, sorry.
There are two ports in the bottom of the master cylinder reservoir. The one that releases the last bit of pressure in the master, is about a quarter of an inch to the rear of the boss for the bolt that holds the cap on. It's at the bottom of a 3/16" drilling; and is about .030" in diameter. It goes through to the cylinder bore. A straight pin, (.024"), will drop right in there; and be hard to retrieve! A small paper clip, (.034"), is too big.
The second hole is a half an inch further to the rear. It's 3/16" all the way through. It's the main way that fluid gets to the piston.
With the cap off, you should see a small fountain of fluid at the .030" hole as the brake pedal is released. Watch out for splashes.
If the hole is clear, and there is no fountain, probably there isn't any free play in the pedal.
If you installed only the parts shown in the Avanti manual, inside the cylinder, you don't have a residual pressure valve. It wouldn't be strong enough to keep the brake lights on, anyway.
You're holding pressure at the switch; so I doubt it's a line. A blocked hose or line might hold pressure at the wheel. But, for safety's sake, replace lines and hoses that are questionable. I did all of mine.
Mike M.

[charley norton]

I talked to the previous owner. Before the car was put in storage, He raplaced all the lines(both flexable and hard). He also replaced the wheel cyl., calipers, master cyl. and booster. He thinks it may be a defective booster and suggested I replace it with the one on the parts car. Could it be a booster prob.? Like I said, the pedal has a lot of pressure on it when this happens.

63 R2 Avanti

[Guest]

I have had a similar problem with my 49 Commander, I can't get the little hole clear, I have decided to just get a new master cylinder, I also wonder if the parts in the rebuild kit were just a bit different than NOS. The little fountain of fluid from the small hole is critical, and no mater what I have done I don't see that. My other theory is that I had to hone too much out of the master cylinder to clean it up, the book talks about a go/no-go gauge, that may allow the piston to slide sideways and bind in the cylinder? When you apply the brakes the pressure is quite high in the master cylinder. Also if it has set a year or two without the brakes being used there is most likely some crud that has formed in the master cylinder. I know from experience that the brake system cruds up quickly if not used frequently.

Restore it, don't replace it.Keep the Studebaker reproduction industry going

[Sonny]

quote:Originally posted by charley norton

I talked to the previous owner. Before the car was put in storage, He raplaced all the lines(both flexable and hard). He also replaced the wheel cyl., calipers, master cyl. and booster. He thinks it may be a defective booster and suggested I replace it with the one on the parts car. Could it be a booster prob.? Like I said, the pedal has a lot of pressure on it when this happens.

63 R2 Avanti

In a word, absolutely! I'd forgotten about that funky booster system..... Have you "hit the book" on this yet? There's a real good diagnosis section concerning brakes. From what I see, the book says it very well can be in the power brake/booster system.

Sonny

http://RacingStudebakers.com

[charley norton]

Thanks Sonny, I think I'll swap the booster and master cyl. out this weekend if I get a chance.

63 R2 Avanti

[Sonny]

quote:Originally posted by charley norton

Thanks Sonny, I think I'll swap the booster and master cyl. out this weekend if I get a chance.

63 R2 Avanti

You're very welcome Charlie. Good luck on that.

Sonny

http://RacingStudebakers.com

[MikeW]

Charley, are you filling the MC all the way to the top? If you are then try leaving about half an inch of air at the top. I don't know about Avantis but for the older Studes if you fill the MC to the top it will react as you describe. The Shop Manual calls for an half inch from the top fill. That leaves an air cushion so the fluid can expand as it heats up from use.

Mike

https://www.packardhawk.com

[charley norton]

Hey Mike,
I checked the fluid level in the Master cyl this morn. and it is pretty full. The bowl sits off level (or my garage sits off level). One side is about 1/8" from the top and the other is maybe a tad over 1/4" from the top. It's a small resevoir for such a big car, isn't it? Tommorrow after work,I'll pull some off the top and take it out for a run. I'll let you know how that works.

63 R2 Avanti

[wagone]

Charley: I went back here at your suggestion from today on the other forum. My brakes have not exhibited your problem and I don't fill my reservoir closer than 1/2 inch from top. Your problem could be that simple or it could be a bad booster or one of the other items mentioned. But in my car (the previous owner replaced the original MC and booster with one from a late '60's Avanti 11) on this brake unit the underside of the MC cap has a little "bladder" attached to it and hence the unit cannot be filled too close to the top (as yours is--1/4") or fluid will push out the reservoir when I go to reinstall the cap. So unfortunately I can't be of help to you on this. Good luck, but it shouldn't be too hard to correct.
Wagone in Iowa PS--I'm going to the other forum tonight with an added thought or two on Avantis and hood insulators--catch you soon.

[charley norton]

Mike: Fianally got a chance to check the master cyl. The hole nearest the boss that has a big bore but a small hole is completely stopped up. I used one of my micro screw drivers to clean it out but is no use. Does the hole (port) go straight through or does it enter a channel. If it doesn't go straight through, I probably just made the problem worse and will need to get another master cyl.. If it goes straight through, I may try drilling it out. What do you think??

63 R2 Avanti

[Mike]

Is the screwdriver you are probing with smaller than paper clip wire?
If the piston isn't returning all the way, it could be blocking the port. If the cylinder ever worked, it must have been drilled. Maybe it's blocked by rust. It's about .030", drilled straight down to the cylinder bore. No special precision is required. I have drilled mine to .040". It just makes a bigger fountain, when the brake pedal is released. You really should remove the master and take it apart; so there is no chance of damaging the seals.
Mike M.