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Hard pedal - stealth brake metering rod the cause?

8K views 70 replies 14 participants last post by  tayto 
#1 ·
Ever since I bought the car years ago, the brake pedal pressure has been hard. I've replaced damn near everything including the booster and master cylinder. I know the car has both the stealth brake mods done, so I am wondering if these are the cause of the high pedal pressure. Any ideas? Its kind of the last thing to try....

TIA
 
#2 ·
I think we once talked about master cylinders before. There are 2 flavors. A large bore cylinder will give a hard pedal and a small bore. First time I drove a friend's 94 9C1, i thought her car lost the power assist. I run one now in the 91 with both brake mods and it's a stiff pedal. The mods wouldn't make it stiffer by themselves. If I didn't have a grippy set of FF pads, I suspect it be pretty hard stopping the car. So my suggestion would be try the other master cylinder or try a set of pads with an FF rating or higher. It would still be a firm pedal but you wouldn't have to push as hard to get it to stop. I'm using the Bendix Fleet Metlok. Great pad if you don't mind all the brake dust.
 
#3 ·
Other variables to throw in the mix could be:
the Kore brakes
froze rear pins (if used)
other PM

Without knowing more, I'd just go through and check that all 'manual' operation and cycling works/looks right, then eyeball for bent-jammed SYHK underneath from roadkill or shrapnel. Then a one-time grande 4-side bleed job.

I had the rear bolt mod only on my FWB, but it worked like a charm.
 
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#4 ·
Among the things I replaced were both front calipers.... I may have to try (another) master cylinder and swap out the pads. I am currently running ceramics on all 4 corners.
 
#5 ·
For those of us that are not familiar with what brake parts you have front and back could you please post this info. Kits might change and some people mix and match.

For the beginners: To test brake system boost While parked with the engine off press the pedal to the floor several times the second or third press should feel different, it should feel hard. Keep your foot on the brake pedal and start the car. The pedal should go down with out any extra force and feel soft.

Have a look at this post:


What I get from it is that there may be differences between pedal geometry of: 9C1, Impala, Caprice, Wagon, ect. This and the different MC bore will cause different feel. Change the volume of the calipers and things change again. Miss match caliper volume ratios front to back will also change things.

If I understand correctly a smaller bore MC will give you more pedal travel. If short pedal travel means firm to you a smaller bore will help. IF firm means you are unhappy with excessive pedal force to stop you may be able to lower the pedal force by finding pads that have more friction. Usually soft, fast wearing, and shed dust.
 
#6 ·
The catch is that I can't stop the car quickly. Like in a panic-stop situation, it would end poorly. I am not sure what to do here other than try a different proportioning block. Barring that, the entire kit may have to come off and be replaced.
 
#7 ·
I purchased the Wildwood proportioning valve since the OEM one is NLA. Hopefully, this will bring my brakes back. If not, the entire Kore3 kit is going in the bin and will be replaced with the Wildwood set
 
#9 ·
If it's going in the bin, i'll pay shipping for it :) Seriously though, is this the 325mm set up with corvette calipers? If so and you haven't changed the master cylinder to match them, you're significantly applying less pressure to the pads. This that would explain your problem after reviewing the various bore diameters.
 
#8 ·
I swapped in a hydroboost brake booster. The one from a 07 Tahoe with the flat plate from a 94 or earlier Astrovan is an easy install (you can get of the plates on ebay for $25). The only mod is to cut the eye off, and weld the one from the original vacuum booster on at 6 3/8 on center. I have that on my 91, and it works great. Hoses are bolt in from a mid 80s diesel, and T the return line. You can use the original MC.
 
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#12 ·
I've read attention being paid to all the components except no word noticed yet about the vacuum circuit. Is there a way to disconnect / remove maybe the MC to make sure free cycle of pedal mechanical assy to rule out mech. bind?
 
#15 · (Edited)
I appreciate your brain-power here, for sure. However, I find it very hard to believe that out of the hundreds? Thousands? of people that have installed kits like mine, nobody has mentioned the conversion making the car borderline unsafe to drive. Navy Lifer says that he's running the exact same system as mine and his brakes are acceptable. Logically, if this is 'par for the course' when doing a bbk, one would expect to find many threads with this same concern. That is not the case.

The pedal feels like it just stops and that's all the movement you're going to get. It travels a certain distance and then it feels like you're pushing against a wall.

Your data above is interesting and it brings up the question of why anyone would go to the 'vette bbk if the Caprice calipers are larger. That's big-brain stuff, and I lack the computational power.

I am fully prepared to eat my share of crow if the Widlwood proportioning valve doesn't fix the issue. I'm currently eyeballing the Corvette MC at Advance... $70 and I have a credit so it may be worth a shot to install at the same time as the proportioning valve.

96 Black, all the vac lines are new and the draw is 100% to spec. I also made sure nothing is actually stopping the pedal travel (good suggestion, btw!) and everything is good.
 
#18 ·
No worries. I just go where the math takes me. How far does the pedal travel before the hard stop? You might be bottoming out the MC if there's an air pocket somewhere.
IF you should try the vette MC at some point, looking at an 05, looks like you'd have to reflare one line as the vette has two identical sized ports assuming the bolt hole spacing is the same as a caprice's.
 
#16 ·
Dan, Did this happen before you took your car to the body shop or is it since? I read all your past posts since I joined here, and never saw where you mentioned this prior. (That I recall) You have had troubles with that shop. Not being a conspiracy theorist, it's the cop in me. I have to wonder about the possibility.

Mark: Snowman-33
 
#17 ·
The stiff pedal has been an issue since I got the car. It's just now become more of an annoyance than I am willing to deal with. I believe I have posted about it before, but may not have.

I just ordered the C5 master cylinder and will install it at the same time as the proportioning valve. I suspect that between the two, I'll get the brakes I need
 
#22 ·
91ss Thank you for post #13 with actual part information and math.

Navy Lifer says that he's running the exact same system as mine and his brakes are acceptable.
Post#15

In post #5 when I suggested a smaller bore MC I referred to this thread:


In post #10 Navy Lifer says this:
My own SS, with the same front & rear calipers, uses a 1" MC which was supplied by Baer WAY back when I bought the original Baer GT system in 1999>2000 time frame (their version of the C5 front caliper setup as offered by KORE3). If I had held off on changing the MC during the original brake install, I think I would be happier, but my current combination still works pretty good.
I think I have been through this tread several times and still do not know which MC you are using. Which one is in the car now?

Then in post #10 Navy Lifer says this:
Bottom line, if you have a 1-1/8" MC, you might consider going to a 1-1/4" MC--the pedal will be firmer
So he specifically states a larger bore stiffens the system. Just as several other people have said.
 
#23 ·
Navy Lifer says that he's running the exact same system as mine and his brakes are acceptable.
Post#15
Again please clarify with a quote from him or refer to a PM where he says his system is the same as yours. You saying yours is the same as his is different.

Looking at the parts book:

18029976 Brake Booster JM4 front disk, rear drum Wagon and sedan 9" or 11" drum

18029981 Brake Booster JL9 front disk, rear disk police and Impala

Navy Lifer is referring to a Impala with a factory four disk brake booster and you are referring to a wagon which came with a factory front disk rear drum booster.

The brake boost force may be why he thought 1.125 MC was OK.
 
#24 ·
Couple things Navy Lifer didn't have quite right in the post back in 2013 and may have since clarified. I'm sure he's got it all right and just some times hard to translate into words what you're thinking. I'm guilty of that many times too.
One regarding MC bore size and confusion. There are 2 sizes 1.125 and 1.25. The ones that mention a 40mm bore are the 1.125. The 40mm piston is at the very back and is part of the design they called 'quick take up' It's sole purpose was to push a lot of fluid to start moving calipers and more so the shoes to contact point, then the 1.125 bore takes over. My 91 FSM has good description and cross section diagram of how that MC works. The 1.25 does not have (or need) that piston since it's already displacing more volume. The other thing was his stating you need more volume as pads where down.

"Fluid volume requirements are largely based on pad volume--the total fluid displacement change from 100% new pads and rotors compared to pads and rotors at minimum thickness. The example to present here is the difference in 94-96 Impala SS (RPO JB9) and 9C1 (RPO JA9)--the thicker front pads on the JA9 system were considered to be enough of a volume requirement change to use the 1.25" bore MC to provide desired pedal travel. From the brake engineer's standpoint, using the 1.125" MC would have resulted in greater pedal travel that came too close to the MC piston travel limits at max wear conditions."

That's not quite correct either. Or phrased incorrectly as the next paragraph has it right. The first sentence is right in regards to MC reservoir fluid. The MC bores/piston only have to move the pistons from their resting place. That will be the same whether new or old pads. What is need with worn pads is more starting volume in the calipers. That's taken care of by MC reservoir not bore size. It's the 'auto adjustment' for volume. If he meant 'Fluid requirements..." as in reservoir. then correct. It can be true that one can not have enough volume in the MC bore to apply full pressure to the caliper if it's too small for a given large caliper. But in our caprices, with it's large calipers, both MC's have enough volume. Going to a smaller vette caliper would require even less volume.

Another thing is the operation of the proportioning valve. Took me a while to get it straight too :) It does not delay pressure build up. The meter function delays and only affects the front brakes. A proportioning valve reduces pressure. The pressure reduction is controlled by the spring inside pushing a piston against the inlet orifice. The math works out roughtly to: Pressure in = spring pressure + pressure out. The piston shape at the orifice can affect the net force i suppose. The IN pressure has to overcome the spring first and the remaining pressure is what goes to the OUT. So the stiffer the spring, the less pressure out. Hence why removing it in the stealth mod gives you all the pressure to the out. The adjustable ones like Wildwood just use a screw to vary the preload on the spring.
 
#26 ·
@Z09B4U and @91ss - its cool. We're all friends here. Seems like feathers are getting ruffled. If I misread the original thread, no offense meant so...yeah. I have the .125, but I have the 'vette MC coming so my guess is that this is the issue. I have contacted Tobin at Kore3 and he advises against going to the vette mc due to the "21% increase in pedal travel" due to the way the MC takes-up. He seems to think the issue is within the block, but once I get all the parts and start installing them - we will know for sure.
 
#29 ·
Didn't see any ruffling. Just sharing our knowledge. Keep on going!
91ss +2
I would like to thank 91ss for another well written post.

Still frustrated with not knowing what is being used on the back brakes.

Atlantadan there should be a lot of acknowledgment for you fighting for your car after a accident, and your problems with the body shop. You have a vision for what you want. Many people do not know the time involved.

In post#5 I thought if all parts were listed someone would spot the problem quick and easy.

Before you try the new MC you might want to quantify where the brake system is now. The FSM lists this for a STOCK system. It would be great to know how your current system compares.

With ignition off and vacuum depleted: Brake pedal travel is 2.25 inches with 100Lb force. The force is hard to measure but if you have a lack of travel the smaller MC bore may work for you.
My B4U should be very close to a stock wagon(same front and back brakes). I can not test mine now but with boost the 2.25" seems correct. For me the Caprice is the most "hair trigger" brake system I have. My newest is 1996 so I have no current comparison.

I have contacted Tobin at Kore3 and he advises against going to the vette mc due to the "21% increase in pedal travel" due to the way the MC takes-up.
You might ask him about brake boosters. I have had cars that passed testing but did not have the feel of an identical car or a new booster.
 
#30 ·
There are also under dash ratio differences in the cars.
95wagon
https://www.impalassforum.com/threads/master-cyl-upgrades-brake-line-questions.318666/#post-3185322

10205029 Brake pedal with bracket JM4 front disk, rear drum Wagon and sedan 9" or 11" drum

10205031 Brake pedal with bracket JL9 front disk, rear disk police and Impala

18029976 Brake Booster JM4 front disk, rear drum Wagon and sedan 9" or 11" drum

18029981 Brake Booster JL9 front disk, rear disk police and Impala

So you may be running a different booster with a different pedal geometry.

When the parts are all correct the system should work. I had to drive a 1981 dodge van with manual steering, four on the floor, and manual brakes. Even it could do a emergency stop in traffic. Any semi tractor I have driven was easier to steer and clutch than that van and it did require more pedal force than anything I have ever driven,
 
#31 ·
#33 ·
I will have to crawl under my dash to check which lever I have ,
Pretty sure is the lower mounting and non offset pushrod (this equates to less travel, more effort)
I have the original 1.125 quick take up
44mm-36mm front calipers
This equates to 3.9 square inch roughly.
Rears are 30-28 = 2.86
I will say with a gutted combination valve ( only bias warning light) I never have any complaints about hard pedal and tough to stop.
All the following pads, the braking has been fine.
Textar
Pagid
Hawk Ceramic

The production combo valve does control the maximum rear pressure, even as the pressure before it rises above that threshold
 
#34 · (Edited)
Installed the Corvette MC. Edit: The pedal travel has increased a pretty good amount, but so has the non-panic braking power. I took it for a drive and just cruising around, the brakes are much improved. It stops how I thought it always should have, given the brake setup. However, in a panic stop situation - its like pushing against a brick wall. Very, very stiff pedal and low braking power.

Looking at the Wildwood proportioning block, the threads on the inlets/outlets are different from the OEM stuff. OEM has one fine thread, and one coarse. The Widlwood block is all fine. So it may be a minute before I install that due to having to get new raw hard-line and fittings and making up my own lines.
 
#35 ·
Dan....while I know its double bleeding, you won't know if it was the proportioning valve or MC that is your issue if you swap both at same time....But with that said if it fixes it than all is good but you won't know what part did fix it

Have not seen Bill Harper jump in or if he even visits the forum anymore but a email to him may bring his comments to your problem
 
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