Greg I see Wilwood recalled their 7/8yths bore MC. I think I am done with Wilwood do you have a suggestion with another MC? Thanks

I am going to guess the issue is the bore, not the fact it is Wilwood. This is not voodoo. You can calculate your bore. Details in this thread:

http://www.pro-touring.com/threads/1...Tobin-of-KORE3

Caliper specs are here:

http://lukeskaff.com/projects/car/th...-measurements/

Don

Yes they did --- certain codes on them --- not every one they ever built - but close! Had one on the Mustang track car!

Baer makes a real trick looking billet model.... if you're looking for "fancy" under the hood.... and I used a Tilton in the '33 (although it was dual singles with a balance bar).... AP Racing also has MANY styles of M/C and all kinds of mount options.


http://baer.com/Remaster.html


http://tiltonracing.com/product-cate...ter-cylinders/


https://www.apracing.com/products/ra...ted_types.aspx

TOTALLY AGREE!!


Lots of people get the bore, and or, pedal ratio wrong..... using a power brake pedal ratio on a manual master cylinder is a very common "mistake". But so too, is the wrong bore diameter.

The std bore on a regular MC for the 71 corvette was 1 inch. I spoke with Wilwood many many times before going with 15/16ths since I had C-4 calibers and they used a 3/4 bore. The ratio is just shy of 6:1. I took it up to 45mph today, it stops but the brakes do not lock and its all pedal. Need to have good brakes before letting her loose, but the LS-3 427 is going to be sweet. This is crazy, I never had an issue before on my other builds. Thanks

Interesting info I will peel it back but it showed a bore of 1.25 front and 1 inch rear. So if mine is 15/16 assuming it is not enough would that be a possible issue? Soft pedal not enough fluid going to the calibers?

Do the math.... :)

Don

I think you are confusing caliper bore with master cylinder bore. You use your caliper bore and pedal ratio etc to calculate the required master cylinder bore.

Don

I was referring to the thread for MC which had a larger bore. Going through the thread for the math formula. Thanks

THere is also a BEDDING procedure with brand new rotors and pads.....

I've just gone through something similar for different reasons. Booster died. replaced it and wow. I think in the 5 years I've owned the car the booster never worked right, as the new booster has the pedal so soft it's crazy and then when it does brake it locks em up.

Didn't have a prop valve it does now.

For me the soft brake pedal is that the car originally had manual brakes, not assisted. The pedal ratio is 6:1 which is not ideal for a boosted application. A 4:1 or 5:1 ratio is what's required.

Assume from reading that article this is something you've also considered. I'm looking for a new pedal now

No need for a new pedal!! Just remove it -- it's simple to take out -- and drill a new hole in it for the proper ratio (move it down toward the bottom of the pedal about an 1" or 2"). DONE.

Greg, I was looking at that, my question is angle. I have to take the pedal out tomorrow to measure. I know it's 6:1 as that's what the chassis manual says (car only had manual brakes from factory, no power assist). I'm concerned new hole will result in too great an angle and may result in a "sticking" situation. Guess I will find out more tomorrow when I remove it. I agree it probably only needs a 1" move on the hole.

*Only For Advanced Fabricators*
 

This post is only for advanced fabricators that have the skill, knowledge, and experience to do this properly (!).

If you cannot relocate the pedal rod connection point without causing a linkage bind condition, there IS one more alternate option that some do not consider in these discussions, and that is to cut the pedal and lengthen it. This should only be done with a very powerful TIG / Stick welder and very experienced welding skills...

This can effectively increase the mechanical brake pedal ratio considerably, but will make the pad of the pedal lower which poses some limitations as to how far you can go.

:cheers:

I spoke with Tobin (Kore 3) and he normally uses a 7/8ths bore on his C5 setup which has a larger area contact. After he spent a few minutes he believes my pedal should be a lot firmer so I will re-bleed them one more time. He suggested removing the lines one more time and plug one so I bleed them one at a time. I will try this weekend and see what happens. Thanks for your help. :waveflag:

I used a 7/8 master with C5 brakes and I found braking to be OK but not what I was hoping for. Went to a more aggressive pad compound if I remember right.

Don

7/8th MC is just about all I've ever used... and the brakes have always been stellar! I've put on Baers - Wilwoods - and any number of other combinations.

Did you check the Wilwood MC to see if it's one of their recalled versions??

I will call them tomorrow. So what I am hearing is 7/8ths more pressure than 15/16ths but softer pedal?

I'd stick with the 15/16t until you verify it's not a math problem or air. I personally didn't like the 7/8 due to pedal travel.

After I bled the MC I put caps in and checked for air. I could not push the pedal and it did not move after holding it for a while so I feel pretty darn sure the MC is bled correctly. I might re-bleed the system one more time. From what I have learned dropping down to 7/8ths the pedal would be softer.

Anyone heard that the E-brake should be engaged before bleeding the rear brakes. On the C4 it is just using the piston vice a rear drum unit.

I seem to recall that it needs to be properly adjusted. When they use that style caliper on some swaps you have to unbolt the caliper and rotate it so the bleeder is at the top to get all the air out. Not sure if that applies here.

Don

Just went Tobin (Kore3) suggestion and bought the CPP 15/16ths MC to fit my car then I might go with it boosted if this is not enough which should be fine. Std setup for manual is 1 inch bore. Thanks for all your help, I will let you know how it goes. This retired Marine has had enough.

Hope you have better luck with CPP masters than I have. I just had two that leaked badly through the plugged ports on the passenger side. Complete waste of time. Now waiting for a third that is supposedly using a different casting. I wanted to go with an AC Delco but the car owner is insisting on another CPP master.

Don

The attraction to CPP MC is it comes in 15/16ths. This is my second Wilwood MC at $200. Tobin has a great reputation so we will give this a try.

It might be a dumb theory, but I get the sense that adjustable proportioning valves make effective bleeding much more difficult, especially if the valve is set to close off one end of the system when you're bleeding. I say this because I've only had problems bleeding systems that have adjustable proportioning valves. With my current system (mostly new steel lines/bends/masters/pedal), which has no adjustable valve (dual masters with balance bar instead), basic gravity bleeding actually worked the first time (as far as I can tell at this point). I was so happy to avoid that stupid compressor suction setup . . .

Low cost OEM MC's for bore size test purposes
 

FYI - I see people spending all kinds of money on expensive master cylinders, swapping them out for different bore sizes for test purposes to see what / if any improvements are to be had (brake feel tuning purposes). Here are some super low cost OE GM MC's that you should be aware of to use for initial bore size swap out test purposes:

7/8" bore manual brake: RAYBESTOS MC39027
(1977 Chevy Monza)
WARNING: This MC does NOT have the deep MC pushrod hole. You CAN drill the piston for a deeper pushrod hole, use a rubber boot to make sure the brake pedal rod doesn't accidentally fall out, or rig up a brake pedal rod retainer of sorts.

http://piratejack.net/master-cylinder-manual-rod-boot/

Here you can see how www.mpbrakes.com (Master Power Brake Company) takes late model MC's that are equipped with the short rod / shallow MC pushrod and then drills them for the deep pushrod hole for manual brake usage:

https://www.mpbrakes.com/images/MC39...earM-Large.jpg

BTW - You are looking at a 2000 +/- model year US S-10 MC that has been drilled for manual brake usage in the image link above.

15/16" bore manual brake: CARDONE SELECT 131639
(1977 Chevy Malibu - deep MC pushrod hole)
(Baer used to supply these with their braking systems years ago)

1" bore manual brake: CARDONE SELECT 131371
(1968 - 1976 C3 Corvette - deep MC pushrod hole)

Once you prove out what MC bore size you may like best, THEN spend the money on a "bling" MC if desired.

Oh, and the general rule with GM MC's is the 1/2" port is for the front brakes, and the 9/16" port is for the rear brakes (mentioning this because some MC's are reversed from others as far as which port is which). There are some exceptions...

If I keep the push rod in the manual position vice pwr on the stock pedal it will just make the brakes very sensitive correct? So 5.7:1 vice 3.5/4:1?

Pedal rod angularity warning
 

Note that the brake pedal rod MUST enter the master cylinder dead on straight in a manual brake scenario. Discussions of drilling different holes in the brake pedal in efforts to alter brake pedal ratios are not valid because the brake pedal rod will then enter the backside of the MC at an inappropriate angle causing linkage bind, MC failure from extreme side loading of the pistons, and even possible complete failure of the brake pedal rod linkage entirely.

Summary? You MUST keep your brake rod connection in the factory manual brake top hole - no if's, and's, or but's about it.

:drive:

Funny.... when you buy a 1969 Camaro Brake pedal assembly - it has two holes from the factory -- Manual -- and Power....

It's only about a 1 inch difference and the angle of the pushrod is hardly an issue. The pushrod swings thru an arc regardless - it doesn't go straight in and out. The pedal pivots thru an arc....

The difference between a power booster and a manual is taken up in the ANGLE of the mounting at the other side of the firewall.... the power booster is usually tilted back (at the top) slightly due to the LOWER hole in the brake pedal being used (less ratio).... and the manual is usually mounted flat - and uses the "upper" hole (more pedal ratio).

Factory vacuum booster angle
 

The 1st gen F car factory vacuum booster is angled upward at whopping 17 degrees. Go crawl under the dash of a 1st gen F body and try to force the manual brake rod into the lower power brake pedal hole and see how that goes for you - it flat out isn't going to happen. If you somehow do actually manage to force it to happen, you are definitely going to get into linkage bind and extreme MC piston side loading leading to direct failure. Sooooo..... unless you angle your manual brake MC upwards by whatever means imaginable (to accommodate a 17 degree angle as bolted to the firewall), you are causing trouble talking about moving the brake pedal rod connection point from the upper manual brake pedal point to the lower power brake point in a manual brake equipped 1st gen F car.

Thanks it is in the manual position now but switching to power and like Greg said the power location is about an inch lower. Thanks for the comments to both of you.

I'm not sure you're tracking here. There are two holes in the pedal -- changing ratio - depending on if you have power or manual....

If the cars pedal only has the power brake hole -- but is being used as a manual car... then of course the ratio is messed up (4:1 vs 6:1) and the pushrod position and angle would be in the wrong location.

What I stated is that the MANUAL hole - if missing - needs to be added to the pedal to correct the ratio. When corrected - the pushrod would then be in the proper position for the manual master cylinder - and the ratio would also be corrected.

You're trying to inject a different issue -- which is to try to use the wrong position. The lower hole (closer to the floor) is there for POWER brakes - and the booster is at an angle so the rod and arc etc work correctly. The Manual brake position is about 1 inch higher -- making it a straighter "angle" -- and the factory manual master is mounted as such -- flat to the firewall.

I will use the lower hole in the 71 corvette pedal for the power brake setup thanks

Just clarifying issues for our constituency
 

Rest assured that I am certainly not trying to cause any trouble. In fact, I'm only making it certain that "under discussed" issues are crystal clear for some of our members / readers.

:cheers:

No issues here thanks for all your help guys. Once it is set up I will get back and close this out.

So you are going to power brakes?

YES, booster came today

C3 Steering column support structure
 

Have you attempted to install your vacuum booster yet? If not, be warned that the C3 Vette steering column support bracket is different than the power brake support. I have no earthly idea why Chevrolet did that. Besides having to cut a different hole lower down in the fiberglass firewall for the vacuum brake booster location, you will also find that the bolt pattern isn't anywhere near what you need for the bottom two mounting points. The top two MC mounting studs can be extracted, which then at least places the top two vacuum booster mounting points in the correct location, but then you find that the lower two mounting points will not correlate properly with the manual brake spec steering column support structure (which is what the C3 Vette vacuum boosters essentially bolt to) (besides the fiberglass). I checked out a bit of your build thread and see that you are a competent fabricator. I recommend you pull the manual brake steering support structure out and weld in some further material at the bottom of the bolt pattern to properly support the bottom two fastener points of your vacuum booster, OR swap in a factory C3 power brake spec steering column support bracket.

This why we developed a special direct bolt in C3 manual brake spec conversion system that accommodates the different manual brake firewall and the different manual brake spec steering column support bracket:

http://www.hydratechbraking.com/C3Co...920161312A1BD0

Rest assured that I am not sales pitching you on a hydraulic brake assist system, just covering the bases on converting a factory manual brake C3 Vette to a power brake (bizarre why Chevrolet did that)...

:lateral:

Wilwood MC's versus C3 Vette MC's
 

As another interesting and pertinent side note, (that some do not know or consider in their builds), be aware that the Wilwood MC's are specifically designed to provide a 75/25 output (75% to the front, but only 25% to the rear). By direct comparison, the factory C3 MC's are designed to provide approximately a 65/35 (65% to the front and a larger output of 35%+ to the rear). You have been mentioning that your front brakes are behaving, but can't quite get your rear brakes to bite down properly. Soooo.... The output difference between the Wilwood MC and the C3 Vette MC's are indeed different - the C3 MC's put out more volume to the rear brakes by design (it's the location of the comp ports inside the fluid wells of the MC fluid bowls that makes the difference).

:secret: