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charley norton
05-16-2005, 05:35 AM
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
05-16-2005, 05:50 AM
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
05-16-2005, 12:12 PM
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
05-16-2005, 01:22 PM
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
05-16-2005, 03:17 PM
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
05-18-2005, 07:09 AM
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

1949commander
05-18-2005, 08:21 AM
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
05-18-2005, 08:34 AM
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
05-18-2005, 05:03 PM
Thanks Sonny, I think I'll swap the booster and master cyl. out this weekend if I get a chance.

63 R2 Avanti

Sonny
05-18-2005, 06:46 PM
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
05-18-2005, 09:00 PM
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
www.packardhawk.com

charley norton
05-20-2005, 06:14 AM
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
05-20-2005, 08:05 PM
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
05-22-2005, 05:37 PM
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
05-23-2005, 05:36 AM
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.

1949commander
05-23-2005, 09:42 AM
I fixed my brakes this Saturday with a NEW master cylinder. I thought that rebuilding my old one was a safe bet but I think I may have discovered the problem. It seems that the parts in the rebuild kit which were new from Wagner may not be the same as the original. With the rebuild kit the piston cannot return far enough to clear the by pass hole even with the rod adjusted way short. I am going to dissassemble my old one this weekend to verify this problem. I tried everything to clean the hole out and nothing would go through it. I even bought a welding tip cleaner which has some very small wires and none would go through. But if the piston is blocking the hole that would explain the problem. I know know that from day one the rebuilt one never worked like the new one. I guess from now on I will have to measure everything I get if its new production.[:0]

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

charley norton
05-23-2005, 03:12 PM
Mike, I removed the piston and spring before I started messing with it. The port is really stopped up. The screwdriver I have is slightly less than .030". I'm going to look for a .040" bit. I think the kit I used is a good one as it is from old stock, but 49c.... may be right in just replacing it.

63 R2 Avanti

Mike
05-23-2005, 03:54 PM
Sounds like you're home free; just clear the port. If you are buying a bit, .030" is correct.
The small holes in the new tandem master I'm using were never drilled at the facory; just the 3/16" countersink. Brake lights stayed on and brakes dragged, in the garage. The smallest bit I had was .040".
Remember, there should be very slight free play, between the push rod and piston, when you install the master.
Mike M.

charley norton
05-27-2005, 05:47 PM
I ended up buying a torch head drill bit set. The biggest bit was 1\8". It worked perfectly! No more pressure on the brakes. Thanks for everyones help

63 R2 Avanti

64V19816
08-22-2006, 08:12 AM
THANK YOU!!!!!!!!!!!! This post has solved a problem Ive had since putting the Cruiser back in service after a 15 year layup. One tiny hole......so much problem with plugged up. A quick zip with the dremel and the tiny drill bit and problem solved. I was ready to start buying brake cylinders!