Hey guys,
ok so I have a problem and am in desperate need of your expertise..
i have a 1955 Oldsmobile Super 88 Holiday 4 door with drum brakes front/back. I have upgraded the brakes to a modern day booster, master cylinder and proportioning valve. I bought a universal kit off ebay that fits my car and also came with new brake pedal. I installed it and the first master cylinder was weeping fluid from one of the block off ports. I got a new one.
Over the weekend I bench blead the new MC and got the air out. i installed and blead all the brakes starting in back right and working forward. I adjusted all the shoes so there is a slight drag on each corner too. After everything was blead I still have a very soft pedal and little stopping power. What should I check/look for...? Please any help be greatly appreciated as this problem is driving me nuts

 

A soft pedal as its going almost to the floor or a soft squishy pedal with little travel?

 

Soft pedal going to the floor.

 

Something is bypassing fluid. Likely the master is bad out of the box(internally or externally leaking).
Pull it and look at the rear seal for evidence of fluid. If it leaked into the booster send it all back.
Are these parts offshore?

 

Make sure that the push pin for the booster actuator matches the plunger in the master cylinder. You need remove the master cylinder from the booster, no need to remove the lines just move it forward.

 

This is the kit that I purchased. I have already received a replacement for the master cylinder and proportioning valve. Could I have gotten another defective kit??

 

So clearly not an "upgrade"...

First, your selected M/C is for DISC BRAKE cars. Second, a prop valve is NOT used for four wheel drum cars except in VERY LIMITED instances (the nose heavy early Toronados were one of the few exceptions). Third, the system in the photo you posted appears to be one of those worthless 7" or 8" single diaphragm boosters. You're now 0-for-3. Why did you even select that setup?

 

Ok Joe, sp clearly I guess it is not a upgrade. Over the factory I thought it was. When purchasing the lit the seller asks if you are running drums or discs and gives parts based on that. I have never done a conversion so forgive me for not knowing. I thought it was a good kit thats why I purchased it!

 

Most aftermarket brake vendors are clueless and will foist off on you whatever they can make fit, right or wrong. What is the bore on the M/C that you got? What is the diameter of the booster diaphragm? And are you REALLY running a proportioning valve, or did you mean a distribution block? Photos of the actual parts and not the ad would be useful.

 

Booster is a 9”

 

What is the bore of the M/C? And that IS a disc brake combo valve, which should NOT be used for a four wheel drum system. If the seller told you that you needed that, I have little confidence in anything else he told you.

 

So shld i eliminate the valve?

 

Stock M/C was a 1" bore. I would replace that 1 1/8" M/C with a 1" M/C. And again, you do NOT want to use a combo valve on a four wheel drum car. You simply plumb the rear brakes to the rear port on the M/C. Tee the front brakes and plumb that to the front port. Done.

 

Ok thanks

 

Soft pedal, goes to the floor.
Probably not a problem with having a large-bore master cylinder. In fact, that should make the pedal even firmer.

Wild guess: You still have a bunch of air trapped in the system.
Second wild guess: Need to tighten up the shoe adjustment some more.
Third wild guess: You've got FOUR ports on that master cylinder, and you're only using two of them. Still have the plastic plugs in the other two? They'll have to be replaced with inverted-flare plugs, typically brass but sometimes steel.

 

Good call on the 4 port. I didnt catch it.

 

i have never had a vehicle with drum brakes in front and back. Should the brakes feel like they do on a modern vehicle? Right now the only time brakes come on is when the pedal is bottomed out

 

The pedal should be firm and not on the floor, doesn’t matter if it’s drum or disc. Pior to the mid 60s when disc brakes became more common, people managed just fine with 4 wheel drums. Contrary to popular belief, all things being equal, drums will stop better than disc simply due to greater surface area of friction against the metal. The problem with drums is they don’t dissipate heat as well as discs. There is a reason big trucks still use drum brakes.

Having said all that, drums also take a little more maintenance. Drums need to be adjusted evenly to stop straight, if you have a little more shoe to drum clearance on one side over the other, the brakes will want to pull. So, driving with drums might take a little getting use to.

If the pedal is mushy and goes to the floor, I’m betting you still have lots of air in the lines.

 

Unfortunately, all things are never equal. The piston area, contact area, and effective lever arm are all different. Since brake shoes are physically larger than pads, they deflect during application, which means that the friction surfaces are not loaded equally across the entire surface of the shoe. The self-energizing nature of drum brakes also contributes to this uneven loading (which is why the secondary shoe is longer than the primary shoe). The effective coefficient of friction also varies due to gas buildup between the pads/shoes and the disk/drum. And finally, as drum brakes heat up, the drum expands away from the shoes, which is what causes brake fade. When disks heat up, they expand towards the pads.

Of course, none of this is related to the OP's pedal problem.

 

I stand corrected. All things START equal, until all the variables are factored in. Theoretical equal and reality equal, with real world equal somewhere in the middle. 😁

 

Fine. That just means that if there's any air in the system, it is trapped.

BEFORE or AFTER you applied the brakes a time or two, to align the shoes? If you haven't checked the adjustment AFTER applying the brakes, you need to check that again.

You are adjusting the brakes at the star-wheels, NOT at the park-brake adjuster...right?

Was the front of the master cylinder tipped "downward" at a slight angle during bench bleeding? Most master cylinders are mounted to the booster/firewall with the front tipped "upward"; air gets trapped in the front of the cylinder and will NEVER bleed out. Either raise the back of the car so the master is tilted downward, or remove the master cylinder from the booster/firewall WITHOUT disconnecting the brake tubing and tilt it down in front. Then tickle the pedal, or the primary piston directly--the trapped air will bubble back into the reservoir.

Disc or Drum, rule-of-thumb, not applicable in every possible circumstance but generally true:

When braking normally (yeah, what's "normal"?) the brake pedal should still be higher than the gas pedal at-rest (curb idle) position.

When braking hard, the brake pedal might be level with the gas pedal.

If the brake pedal is lower than the gas pedal, you're panic-braking or something is wrong. (Which could mean that the gas pedal is too high, but that's not at all typical,)

Yes, there are other possibilities, such as a defective master cylinder, the brake pushrod connected to the wrong hole in the brake pedal, (Does that apply to a '50s vehicle? It sure did in the middle-60s and newer) or the wrong pushrod between booster and master cylinder. (Some master cylinders have a deep recess in the primary piston for the pushrod, some have a shallow recess. Deep recess needs a longer pushrod)

A problem I see occasionally is someone using low-drag front calipers without a Quick-Take-Up master cylinder--but as you don't have front discs, this wouldn't apply to you.




Do you still have RUBBER brake hoses? (NOT TEFLON UNDER STEEL-BRAID!!!) If so, take a Vice-Grip or brake-hose clamping tool, and GENTLY clamp the rear hose. You want to clamp the hose so no fluid can flow, but not crush the livin' bejesus out of it. If the brake pedal becomes firm while the hose is clamped, the problem is in the rear drums. If the pedal doesn't change much, the problem is ahead of the clamp.

Do the same for the front brakes (takes two clamps, one on each hose). Again, if the pedal firms up, the problem is in the front wheel cylinders or front brake adjustment. If the pedal doesn't firm up much, the problem is between the clamps and the pedal.

With the rear hose clamped, or both front hoses clamped, the pedal should be "high and hard".

IF you've got aftermarket steel-braid-over-Teflon (PTFE) brake hoses, DO NOT CLAMP THEM.

 

Thank you to everyone for giving me good info to help me finally solve my braking problems. I can finally say that my braking problem has been resolved. After doing a gravity bleed and a pressure bleed the air is finally out of my brake lines! i also adjusted the clevis clip so that I have no more slop in my brake pedal!