Better master cylinder?

[Steve-o81]

Hi, I have a 1981 Silverado half ton that originally had a 305 I put a 350 in it out of a 1970s bread truck and it takes forever to come to a complete stop. I want to get a beefier master cylinder to combat the problem. I have rear drum brakes disc fronts. I’m not changing that so is there a beefier master cylinder I can swap in that’s a direct fit?

 

[GXPWeasel]

I don't know that a different / bigger / better master brake cylinder is going to solver your problem. Or at least, it may not be the easiest way to solve it. What do you have for brakes now? I mean, pad material? I'm a FIRM believer in ceramic pads, but they have to be bedded correctly to get their full potential out of them. I'm guessing since it was originally a 305 truck that you do have the 11" rotors up front, and 2" wide drums / shoes out back. Those are the standard brakes, and they do offer an HD brake package with 11.25" rotors up front, and 2.756" drums/shoes out back, but I'm not sure what it involves to change them over.

If I were you, I'd start by doing a complete brake fluid flush, and making sure you're getting braking power from all 4 corners. It sounds to me like maybe you're not getting your full potential out of the brakes you do have, which is not likely the fault of the Master (unless it's leaking). I've not heard others on this forum complain of the lack of braking ability with just the standard brakes, so again, I'd check that everything is working correctly first.

 

[Steve-o81]

Stock cheaper brakes on it I believe all around. This truck has 110k original miles on it so I assume you are correct it’s not the master cylinder I’ll check other things thanks!

 

[WebMonkey]

are your rear brakes operating correctly?

i know an unloaded truck will 'use the fronts' for the bulk of the 'stopping power' but i noticed a difference after rebuilding my rear drum setup.

and as above, i'd check my front 'pad' material for slicking.
compromised flexible lines etc.

good luck!

 

[Octane]

The braking bite is in the pads and rotors and maybe some steel braided hoses.

 

[jake wells]

Nbs body style master swap you can find info on the web it applies more pressure though the lines.

 

[Shorty81]

are your rear brakes operating correctly?

i know an unloaded truck will 'use the fronts' for the bulk of the 'stopping power' but i noticed a difference after rebuilding my rear drum setup.

and as above, i'd check my front 'pad' material for slicking.
compromised flexible lines etc.

good luck!

Like Chris says, change out your rubber hoses. They tend to collapse.

 

[bucket]

Brakes are a balanced system and there's more to an upgrade than just using a different master cylinder, unless it is to overcome less than stellar factory engineering. But I suspect that in this case, the current brake system is not at peak performance.

Nbs body style master swap you can find info on the web it applies more pressure though the lines.

Eh, it's not quite cut and dry like that. With the pedal ratio as a constant, the only way line pressure can be increased is by downsizing the master cylinder bore, and that will be at the expense of greater pedal travel. There's a whole lot to it and every single application can be different from another.

 

[SirRobyn0]

Brakes are a balanced system and there's more to an upgrade than just using a different master cylinder, unless it is to overcome less than stellar factory engineering. But I suspect that in this case, the current brake system is not at peak performance.

Eh, it's not quite cut and dry like that. With the pedal ratio as a constant, the only way line pressure can be increased is by downsizing the master cylinder bore, and that will be at the expense of greater pedal travel. There's a whole lot to it and every single application can be different from another.

Bucket is talking about brake science here and that info is spot on. The only way you will put more pressure down the lines with less pedal effort is with a master and booster kit, but I can't recommend doing that to 40 year old factory equipment at the wheels.

I have done lots of brake conversions at work, from full disk kits to just master kits produced by companies for the purpose. The standalone master cylinders / booster kit are always the hardest to do because you have to try to get them to work properly with the original equipment at the wheels. And if you are looking for more modern brake feel you'll want a 4 way kit with disk all the way around with master cylinder AND booster anyway.

Rear drums out of adjustment will equal low soft pedal, bad axle seals leaking gear oil on the shoes, usually will cause grabbing but sometimes just ineffective braking. Bad or restricted rubber hoses, proportioning valve, calipers and wheel cylinders. Somewhere in there most likely lies the problem. Unless you have a hard pedal in which case it could be a brake master cylinder or lack of vacuum to the booster.

We have debated a few times in the past on which pad types, ceramic, semi-metal, or organic are best. These trucks all rolled out of the factory with asbestos based organics, since those are no longer available the next closest is NAO organics. Some folks may not agree with me but I have had my best luck with NAO organics for brake pedal feel and initial stopping power on squares, however they make the most dust and have a relatively short life span compared to semi-met and ceramics which will net you longer pad life, and reduced brake fade. If nothing else is found wrong try switching pad types one way or another which could make a difference. That's the best advice I can give.

 

[Turbo4whl]

Bucket is talking about brake science here and that info is spot on. The only way you will put more pressure down the lines with less pedal effort is with a master and booster kit, but I can't recommend doing that to 40 year old factory equipment at the wheels.

I have done lots of brake conversions at work, from full disk kits to just master kits produced by companies for the purpose. The standalone master cylinders / booster kit are always the hardest to do because you have to try to get them to work properly with the original equipment at the wheels. And if you are looking for more modern brake feel you'll want a 4 way kit with disk all the way around with master cylinder AND booster anyway.

Rear drums out of adjustment will equal low soft pedal, bad axle seals leaking gear oil on the shoes, usually will cause grabbing but sometimes just ineffective braking. Bad or restricted rubber hoses, proportioning valve, calipers and wheel cylinders. Somewhere in there most likely lies the problem. Unless you have a hard pedal in which case it could be a brake master cylinder or lack of vacuum to the booster.

We have debated a few times in the past on which pad types, ceramic, semi-metal, or organic are best. These trucks all rolled out of the factory with asbestos based organics, since those are no longer available the next closest is NAO organics. Some folks may not agree with me but I have had my best luck with NAO organics for brake pedal feel and initial stopping power on squares, however they make the most dust and have a relatively short life span compared to semi-met and ceramics which will net you longer pad life, and reduced brake fade. If nothing else is found wrong try switching pad types one way or another which could make a difference. That's the best advice I can give.

This paragraph says it all:

"Rear drums out of adjustment will equal low soft pedal, bad axle seals leaking gear oil on the shoes, usually will cause grabbing but sometimes just ineffective braking. Bad or restricted rubber hoses, proportioning valve, calipers and wheel cylinders. Somewhere in there most likely lies the problem. Unless you have a hard pedal in which case it could be a brake master cylinder or lack of vacuum to the booster." -Rob

The duel piston master cylinder GM has used for years requires that the rear brakes be adjusted correctly.

 

[rpcraft]

One thing I would consider is a system flush but only after checking all the other parts. Firstly take your front calipers and inspect what is going on behind the pistons in the calipers and see what the bores look like. You might have accumulated too much water or copper in your brake lines over time and that severely affects line pressure and pedal feel. Will probably be worth checking and or rebuilding the calipers and then grease up the slider pins well and do a proper front brake job, and just clean anything that can affect smooth operation. So many people do pad slaps and never pay attention to other components. It's criminally negligent sometimes to see what people do compared to what should be done on brakes.

Once you check your front pop off your rear drums, do a visual inspection for leaks and proper operation of the brake cylinders (and rear axle seals). The brake cylinders can often times get trash in them that stops both pistons from extending properly and then you will only have one part of the drum pad working. Once you do that check all your hardware is good and the drum adjusters are working properly and lubricated too. Once you get finished put the drums back on and adjust them properly and then flush the brake system out with a good brand of brake fluid. I imagine it might cost a 150 bucks for some consumable parts and a way to flush the system HF has a air operated bleeder/flush tool that is worth the money and so far has allowed me to flush everything I own multiple times over. Doing all this may sound like a lot of work but it will really go a long way in giving you some positive feedback at the pedal and ensuring your rig is safe to drive.

 

[80BrownK10]

I am pretty sure the factory master can lock up even over sized tires with factory brake stuff.

As others suggest, I would get all new clean fluid in it, replace ALL the rubber lines if not done in the last 5 years or so . Rubber deteriorates, and yours is 40 years old! Then make sure the wheel cylinders and calioers are free. Then make sure pads and shoes are in good condition, heck as cheap as they are for these things I'd just replace them unless you did it in the last few years. Parts are so cheap for this truck I would almost bet all new shoes, pads, wheel cylinders, rubber hoses and fluid can be done for under $100 easy, and that's buying some decent brakes I would think. Rock Auto has great prices and ships FAST!

 

[Raider L]

A lot of the right things have been said, but many times the simplest thing turns out to solve a host of other problems. I was doing a brake overhaul one time, and I discovered I had been stopping on the front brakes for a very long time and had similar weak braking. I would suggest the adjustment of the rear drums with that star adjuster in there. Get the tool, don't do it with a screw driver. And if your drums are missing the rubber hole plugs, get them, they're cheap insurance.

I discovered that the rubber brake hose over the differential has collapsed inside and the rear brakes weren't even working, hince the weak braking. When I got a new one I couldn't believe the difference it made.

A lot of times if one up front is collapsing you can tell because the truck will pull to the stronger side. But the rear is less noticeable because both sides are tied into the same line and you don't notice it as much.