Write-Up: Brake Master Cylinder - Install & Bench Bleed

I have been noticing my brake peddle sometimes gets soft while sitting at a stop light. not every time but on rare occasions i will keep pressing it down and it gets very spongy and goes to the floor. lift up and its good with plenty of pressure. i plan on bleeding the brakes tomorrow to eliminate air in one of the calipers but if that does not fix this i'm thinking i need a new MC.
This has only ever happen at the stop light, i have no peddle vibration and the car stops HARD! so hard the speedo will sometimes still be dropping after i have come to a stop when i light them up from 90mph+

install seems pretty straight forward with drain, unbolt, bench bleed, reinstall and re-bleed.

my question is which one will perform the best? i am looking at the ones on rockauto and the prices vary from $40 to $300. i would like one with a resovoir, so the options i am seeing are either cast iron or aluminum and 6-7/8" or 9" versions. which one is better? why?

also wanted to add i never have any fluid loss so i can only assume the internal seals are leaking fluid causing a loss in pressure. i am very hard on my brakes and plan on doing some auto-X soon so i need a MC that will hold up and may even work better with the f-body calipers.

Classic case of MC seal allowing fluid to leak past the piston. I've had this same experience on other (older) cars, but never on the Riviera. If I were swapping mine, I'd look for another ATE brand like OEM. It's amazing how long they can last!

the one made by bendix say ATE, and goes for $74
the one by acdelco (same part as gmpartsdirect) can be found for $211.
big price difference for the "same" thing.
also anyone know why they have 2 different sizes? i guess i need to measure mine...

THe 2 sizes will work, but just match yours and don't worry about it.

When I replaced my MC I got a new one with reservoir from NAPA. It works fine although the receptacle for the wire for the low fluid sensor - well, it fits but not 100% right - although it's been fine for 2+years now.

I would get any 'name' (bendix, wagner) MC, or a Cardone A-1 rebuild (they do a ery good job of it now). I would also look at the wheel cylinders, the soft lines, and the hard lines for wee[ing.

Albertj

I wonder how similar a Camaro MC is to ours? For 2-piston calipers, I'd imagine the piston would be larger, but not sure.

it shows the same size bore as ours (1") but i would be worried that b/c the fbody is RWD the pressure proportion is different than ours.
i may get it in to find the rear brakes keep locking up b/c the front port was designed for the front on ours but the rear on theirs. IDK but i dont think it would be an improvement since the bore is the same

The proportion is determined by the valves under our car, not the Master cylinder. The only thing you may notice a difference in is the volume in the reservoir and how that is split from front to rear.
Such as, the reservoir for the front has more fluid than the rear. Which is the way most older master cylinders were set up because your front braking system (calipers and hoses) hold more fluid and require more to operate.
But again, the pressure to each is determined by the proportioning valve's which are separate from the MC.
If the bores are the same then you should just get the one recommended for our car and you won't have any issues with your strut tower brace hitting the MC.
If the Camaro with the Dual Piston Caliper uses the same 1" bore as ours then that at least that tells us that we are using the correct MC for the F-Body front brakes.

I think there's something different about the Camaro MC design - because of the slight delay when the pedal is first applied, compared to the old single piston caliper, it was near instantaneous. I've never tried the brakes in a Camaro to see how they feel, but I'd guess that delay wouldn't be there.

If the Camaro MC is a similar size, and if it can bolt up, might be interesting to find out what the differences are.

The difference is merely because of the additional amount of fluid being moved in the system. If the F-body master has a larger bore (assuming not too much larger), it might offer a more responsive system.

Though, even with the larger bore, you could compensate with a manual prop valve piggybacked into the system before the actual rear prop valve.

I've thought about messing around with some of the various small screw in prop valves that GM used through the years. I've yet to find a reliable source for their bias per part#.

I've not noticed any delay when going from the stock front calipers to the F-body calipers with the stainless braided hose.
I have instant braking. I'm not sure what you are referring to actually.
I've never experienced it. If anything, I have a much firmer and completely compliant brake feel with no delay.
I did install stainless hoses front and back, but I don't think that would be an explanation for the difference in reaction time to braking.!!

I've actually found through trial and error on making custom brake systems for completely custom motorcycles where there is no manufacture's template to use, is that if you reduce the piston / bore size while maintaining the volume of fluid in your reservoir when going to a double caliper front end compared to a master cylinder designed for a single caliper front end you will get better braking action, not worse.
Seems counter- intuitive , but once the system is filled with fluid and the Master cylinder is matched for that amount of fluid, too large of a bore will cause a weaker brake action. A smaller bore with the correct size reservoir will provide the best front brakes.
It took a little (a lot ) of experimentation and a bunch of head scratching to figure it out..
But I must also say there is a point where a second master cylinder is required.
We made one bike once with a rear wheel that had a string of continuous 2 cylinder calipers that were run circumferentially around the whole rear disc, hooked in series with fluid lines. I forget now how many caliper's we were able to use, but it required that we use two master cylinders mounted in parallel to provide enough fluid and pressure to handle all those calipers.
Completely for show obviously as the rear brakes had a tendency to lock up very easily.
But you would be surprised what people are willing to pay for to have something different and "Cool"

maybe delay isnt the right word. it's like there is about 1/2 inch of play in the peddle before you actually start getting stopping power. many people refer to it as a lower peddle after the fbody upgrade. (i have SS lines too)


so anyone know if the 6" or 9" MC is better???

I'd say it's due to the incorrect rod in the booster, might need a slightly longer one.

I don't have the play. So I still don't know what you all are referring to.
I touch my brake pedal and feel instant fluid pressure, no play at all.
I did all 4 wheels with stainless hose's did you also.?

I'm sorry, I don't know if the 9 " long bore will be more beneficial than a 6".
Unless someone has tried it before, there won't be any way to know.
unless of course you have a degree in such things, but I think even then it would be easier to just try one and then another and see what the results are.
It happens like that all the time in R&D labs. Your expecting the engineer to go back to his office and do a bunch of calculations and come back to tell you what is the best way to go.
When you suggest something as foolish as that they say, "Fuck That", it's cheaper if we just try the other one in the test cell. And so you move on.
Been there, done that. Maybe you will have to be the first if you feel like trying.

I think there is some induced delay when swapping to F-Body calipers (makes sense, as the dual piston reservoirs require a larger fluid capacity than the single OEMs), but the amount is small, and the perception is based on who's driving. Some may find it acceptable, some might think it's annoying, some won't notice at all - based on the driver's personal expectations and tolerances. Most people say they notice but don't mind it, and I would agree.

Try this, Rick. At night, watch the 3rd brake light in the rear view mirror while driving. Apply the brake pedal slightly until the brake light illuminates, but no harder. You will notice there is no braking force. Now notice how much further you must push the pedal before the car starts to slow down. Like Matt said, it's about 1/2-3/4" more pedal, then with very sudden and firm action, the car stops very well. I noticed this difference the day I put the F-Bodies on, compared to the OEM calipers, which started braking almost immediately when the brake lights went on.

However, in practice, I compensate for this by hitting the brake pedal a little harder than I used to. This doesn't bother me, nor do I find it unsafe or less effective for braking. Once it engages, the result is worth the slight wait. But I do know there's a difference (on my car), because any time I get into any other vehicle, I always apply the brakes a bit too hard at first. This is because I've been conditioned by the slight delay in my F-Body modded Riv.

Just out of curiosity, did you install stainless braided hoses on all four wheels.?
I will check and experiment with what you have suggested to see if maybe I've just become so used to it i don't notice it.

No, front wheels only.

BrianEsser wrote:

I'd say it's due to the incorrect rod in the booster, might need a slightly longer one.

The rod's used to be adjustable as well. Are they still adjustable to take up the play.?
The manufacturer's used to call out about 1/2" play IIRC for master brake cylinder and booster replacements.
It was meant to allow for expansion and contraction as well as proper actuation of the brake switch just prior to the brakes actually being applied.
Sounds a little like what we are talking about, doesn't it.
Might be worth looking in the FSM and see if there is any mention of adjustable rod's.
I had become used to hearing the brake light switch "click" before the actual application of hydraulic pressure in my older cars and trucks.
Nowadays you just expect everything to be silent and not noticeable.

Rick, your use of the stainless braided lines is absolutely a very big portion of your change in pedal feel. It happens all the time.

AA wrote:

I think there is some induced delay when swapping to F-Body calipers (makes sense, as the dual piston reservoirs require a larger fluid capacity than the single OEMs), but the amount is small, and the perception is based on who's driving. Some may find it acceptable, some might think it's annoying, some won't notice at all - based on the driver's personal expectations and tolerances. Most people say they notice but don't mind it, and I would agree.

Try this, Rick. At night, watch the 3rd brake light in the rear view mirror while driving. Apply the brake pedal slightly until the brake light illuminates, but no harder. You will notice there is no braking force. Now notice how much further you must push the pedal before the car starts to slow down. Like Matt said, it's about 1/2-3/4" more pedal, then with very sudden and firm action, the car stops very well. I noticed this difference the day I put the F-Bodies on, compared to the OEM calipers, which started braking almost immediately when the brake lights went on.

However, in practice, I compensate for this by hitting the brake pedal a little harder than I used to. This doesn't bother me, nor do I find it unsafe or less effective for braking. Once it engages, the result is worth the slight wait. But I do know there's a difference (on my car), because any time I get into any other vehicle, I always apply the brakes a bit too hard at first. This is because I've been conditioned by the slight delay in my F-Body modded Riv.

I go between driving my car car and very occasionally my G/F's car without missing a beat.
Either you guys are just over analyzing things to a degree or I'm not experiencing anything of what your talking about.
I don't compensate for anything by hitting the brake pedal harder until i feel pressure or engagement and i certainly don't have a problem getting into anyone else's car and using the brakes with some unnecessary prerequisite learning curve.
I just don't have the same issue. Sorry.

Rick, you are not the only one who has said they didn't notice, but enough people have noticed that I think it's a real phenomena. And it's very common to use braided SS lines with this mod - almost everyone does because you can't use the OEM rubber from the Camaro (too short). Mine are also very, very firm, after a slight delay. Rubber lines can feel spongy, but I would not think they would cause what I'm feeling here. I went from rubber F/R hoses to SS fronts, and larger calipers. Keeping the OEM rear hoses would not suddenly cause the extra pedal travel (delay).

Maybe there's another factor we're not considering. Do you still have the original MC?

im pretty sure its the MC but want a second opinion to make sure its not the booster. when i brake from a good amount of speed. pedal is alil soft goes down about halfway and car stops. now when i let up alil and let the idle move me. press back on the pedal and it goes to the floor. if i let up and brake quick and hard i have pressure again and car stops. started this about two days ago. fluid level has not changed.

sounds similar to what mine is doing. i just bought a new MC and plan on replacing it this friday. i'll report back and let you know if it fixed the problem.
With mine though the peddle slowly sinks to the floor when at a light then if i let off it's fine and at normal height. no leaks.

ya sounds the same. but mines getting pretty bad. almost rolled into someone( wasn't watching, my bad) i will probably end up changing it tomorrow though. got the time and money on hand so y not.

Definitely sounds like a Master Cylinder, if you are loosing NO fluid.

k thanks. if i change it tomorrow. will post back and let yall know.