Need booster replacement help for my disk brake 1962.

[62 driver]

My drum brakes were working well and dumb me wanted to install disk brake for safety!  Now I need a bigger booster to back up the new disk brakes.  I don’t want a aftermarket one.  So I am looking for a GM one that’s larger then my 7” and will bolt on.  Will a 1966 Cadillac work? Will a 1968 work? I don’t want to enlarge the 4 firewall holes.   Dave

[russ austin]

Just use your original booster. I works for me on my 63. I put together my own front disk brake system.

[62 driver]

I would but the Bendix setup that has been restored by Karps will not lock up the front disk brakes.  I am down to replacing the booster to get the pressure high enough to really stop the car.  It takes 10 car length to stop from 35 MPH. It act just like the booster is not working. It’s been well bled with all new parts including rubber hoses.  Matt has the same set up in his 61 with stock Delco M/C and booster.  His stops good! My drum brakes worked well the day I installed the disk.  I am going to use a stock Delco M/C and I wanted to pair it with a newer disk brake booster that bolts on without altering the fire wall.   

[Matt 12861]

Right, I am curious how do this.  The more I look at booster and cylinders the more confusing it is.

[TJ Hopland]

I question if the booster is your problem.   You should be able to lock up the brakes without the booster working at all.  It may take planning and both feet but should be possible.

What bleeding techniques have you used?    Can you post photos of what the caliper looks like especially the location of the bleeder?   Did you change anything else in the system?  Prop valve?   Did these use a pressure switch for the brake lights or was it a normal electrical switch on the pedal?

[62 driver]

Thanks for your questions.  The caliper are marked right and left. I have used the pressure tank to bleed the brakes. I don’t think there’s air in the lines. On a dirt the front disk brakes lock up but not on the road at 35mph. You have to press hard to stop the car. I ran new 3/8 line and all new parts. My son has a 61 with the same setup as me that I installed 4 years ago. His is Delco and mine is Bendix. I will compare my calipers with his tomorrow and report back. Dave

[Omarine]

Hello Dave,

you mention 3/8 brake line - are you sure that's correct for your disc brake setup? i ask because it's usually 3/16 steel line on 1 piston calipers...that would definitely affect pressure at the pedal.  also the bore of the MC must match, most commonly 1" bore; but if it's mismatched, you can stand on the pedal and still want for more power...

cheers
oscar

[Dave Shepherd]

Good advice Oscar, 3/8 line is way too big.  Plus the brake pedal lever ratio is much less with power brakes and with discs that are not properly boosted, it would require high pedal pressures.  The master cylinder design and bore size are critical here. the larger bore size requires less pedal pressure but has a softer feel, smaller bore is a firmer pedal but requires higher pedal pressures. So getting it right requires the right combination of parts.

[62 driver]

Thanks to all!  Yes I meant 3/16. I just went out to look at the position of the bleed valves. They are down and wrong compared to my son 61. His are on the top and disk brake conversion works well. I don’t understand how this could happen.  They are marked right and left! I will try to swap side and see if the bleed valve is on top. I might have the wrong calipers! This will take a few days and I will report back. Old age must be setting in!

[Omarine]

good catch Dave, that would definitely keep the brake from purging out all the air - keep us posted...

[TJ Hopland]

That's why I was asking about the bleeders, seen it many times on either poorly designed conversions or just mistakes where the bleeders end up in the wrong position.    It's likely that the L and R markings are for the original application but this being a conversion needs them reversed which sounds like the case here.    Too bad they are not like a lot of the medium duty trucks are where the holes for the bleeder and the hose are the same so it doesn't matter which side you need you just screw the hose in the bottom and the bleeder in the top.

Doesn't sound like the case here but I have also seen it where if the system uses a fluid pressure switch for the brake lights that you need to bleed that too.  Those are often in a T fitting sort of a thing and you get air trapped in the passage leading to the switch you end up with 2 issues,  soft brakes and no brake lights.  They usually don't have a bleeder so you have to unscrew the switch as if it was the bleeder.    Its amazing how little air it takes to screw up hydraulic brakes.     

[62 driver]

I found time to flip the calipers around today. They are marked right and left.  I had the right on the passenger side and left on the driver side. I now have the right on the driver side and left on passenger side. My brakes now work well. I always thought the passenger side was right. O well problem solved. Thanks to all who give me ideas. Dave

[mario]

I always thought the passenger side was right. 

It is!!!
Ciao,
Mario Caimotto

[TJ Hopland]

Maybe Bruce wrote the directions?  I'm sure he will be along soon to tell us the passenger side of his cars is on the left and that is right.  Wait, who's on first? 

And while I'm asking questions was that a world wide thing and how old do you have to be to know what that means?   I assume the 'kids' today don't know Abbot and Costello.

[Matt 12861]

Dave, Could you post a couple pictures of your master cylinder/booster in your '62?
Thanks.

[Cadman-iac]

One thing that a lot of people don't think about is the original position of the calipers. They could be what I would refer to as forward or rearward calipers.  Meaning that if it was designed to sit towards the rear of the spindle centerline it would be a rearward position caliper. And if it's designed to sit forward of the spindle centerline it would of course be a forward caliper.
If your new caliper brackets place the caliper opposite of the position the caliper was designed to sit in,  then the bleeder screws will be on the wrong end.
I hope I explained that well enough. Think of it this way, if the caliper was originally positioned behind the vertical centerline of the spindle but above the horizontal centerline, or if you look at it like a clock, it's in the 12 to 3 o'clock position, but your aftermarket bracket places it in the 9 to 12 o'clock position, then your basically upside down. The correction for this is to swap them side to side as you apparently have done in order to fix it.
Now that I have thoroughly confused everyone, are there any questions?
I hope this helps explain what I think happened.

Rick