Fine tuning pedal feel

[Railing68]

Quote: 70LS1-"Another thing you can do to adjust the sensitivity of your pedal is to alter the pedal ratio. By lowering the attachment point on the pedal you can lower the leverage assist built into it."

Is this a good idea, meaning couldn't this overstroke the piston creating brake drag?

I would like the pedal feel to initially be more firm and sensitive. It seems on a quick stab especially, that modulation isn't perfect by any means. I read in another post that several guys have run LS1 F body brakes and done some tweaking, after several searches this is all I could find. My car stops fairly well but I think it should be considerably stronger.

15/16 MC? Is there one that excepts standard fittings? I don't really want to change it since 98-02 came with 1".

I am using vac assist and 1" MC with pump and canister, any suggestions would be greatly appreciated. I am not short of vacuum. Hydraboost really isn't an option for me so any other relevant info please. Thanks, SS

[70 LS1]

How would that overstroke the piston? Different cars are built with different pedal ratios. All you are doing is adjusting the leverage from the pedal. The piston is only going to move so far based mostly by the pressure on the other side. Once the desired pressure is reached, you modulate the pedal to maintain that pressure and stop the car efficiently. With a higher pedal ratio, you have to push less hard on the pedal to get the same line pressure.

Maybe I am not understanding your question.

[Railing68]

I appreciate the response, the pamphlet that came with the master talked about the adjusting the clevis rod length, and that if it was too long the piston of the MC could be overstroked and create drag? By moving the location to the higher point this will increase mech advantage correct? If I understand your response, the desired pedal travel will be reduced and obviously I would not continue to push the pedal further than needed. Thereby increasing sensitivity, reducing travel and firmness...seems logical did you use the upper hole with your application and was it power vac-assist?

I presume the upper location will dictate shortening the rod accordingly too eliminate drag?

Currently it seems that the pedal needs to be depressed too far for the given result.

I had asked this question on another board and was told to only use the lower for power, and upper for manual. Hopefully this is the ticket for a firmer pedal etc, since I am running canton power steering pulleys and cooler, I don't think that hydraboost is an option.
Thanks again, SS.

[70 LS1]

You definitely don't want to switch to the upper hole with power. That would change the pedal ratio too much. You would need to drill a different hole. As you move the clevis up the pedal, you will have to push less hard for the same braking, however, you have to push the pedal farther.

So let me see if I have this right.

You have to push the pedal harder than you want to give the desired braking? Is this all the time or only when you jump on the brakes?
And
You have to push the pedal farther than you want?


I have C5 master, rotors and calipers front and rear on my 1970 Corvette. My pedal ratio is approx 6.25:1 and I run manual brakes. The C5 master is between 13/16 and 7/8".

Are you sure there is no air in the system and no leaks?

[Railing68]

Yes, when I jump on the brakes I have to push farther and harder than I would like. A slightly slower gradual pressure yields good results, but that isn't good for emergency situations. Pedal travel seems a little long and a bit soft under boost, compared to my old beater 1978 truck w/power brakes that is very responsive and almost too touchy. I am hoping to achieve a slightly firmer pedal that yields stronger braking with less effort ( if that makes sense)?

I also noticed that the backs don't lock easily even with major adjustment to the porportioning valve. With the old original style 1.125 bore MC and stock fronts the rear pbrs felt strong, I am not so sure currently. I have dialed more rear bias in according to valve position and they don't feel as strong there either.

I don't want to give the wrong idea that the brakes don't work, but I think they should be stronger under less effort!

I think that first gen fbody is the same pedal ratio as your vette, I don't know how it differs from 4th gen LS1 fbody.

I am 99.9% sure there is no air within the lines, I have bled multiple times and used vacu-bleeder in addition. It is hard to explain but it seems that the pedal feels almost better after an application or at partial pressure. They will lock but, the quick stab is not where I am happy and needs a lot of pedal pressure to lock. To be honest they are inconsistent somewhat. Without boost they are way to hard to use, if this gives any insight to a bore size change.

Is a bore size change in order? If so I might just go manual 15/16 however, the 1" mc and booster are brand new, kinda a waste. To use the c5 master did you have to alter it with a lathe to get it to bolt up? What did you have to do for adapters for brake lines?
thanks, SS

[70 LS1]

What are you using for calipers front and rear? And if you know the piston size that would help.

It could be your booster. I know with my Tahoe the brakes feel ok when I am using them normally and feel squishy when I have to stab them. That is one of the reasons I went with manual brakes.

[Railing68]

2000 camaro dual piston in front and 93-7 single in rear, both PBR. I don't know the diameter currently but I could probably find out via GM parts direct etc?

What is the formula for the correct bore size for said piston diameter?

The 98-02 camaro used 1" bore and vac assist however, pedal ratio, mc, and booster all differ from mine. That swap is another possibility, not sure though. mounting holes and clevis issues for starters with a late model swap. SS

[70 LS1]

What are you using for a master and booster? I thought the 4th Gen Camaro master was smaller than 1". Where did you get that from?

[Railing68]

I might have stated that somewhat confusingly(is that a word) anyway, I am using 67-76 corvette 1" mc and stock style 67-9 camaro 68-74 nova style booster. All my research shows that the 98-02 camaro is 1" bore, hence the reason I used the same. I was not able to find a reasonable replacement 15/16 bore other than s10 88-93 etc..

I had the parts guy confirm the size or 4th gen via his Cardone book, probably a good Idea to reverify. Another member from camaros.net also shared info with me and stated the same thing 1".

This has Got me wondering if there was a error or metric conversion that was misinterpreted. I am going to try to get all the relevant info today, piston size for calipers etc and will repost.

I found this on a private site however, I think that info vs C5 piston diameter is incorrect!

98+ CAMARO BRAKES “LS1”:
Rotor Size: 12 inches
Rotor Thickness: 1.25 inches
-Caliper specs
Piston size: 1.75 inch outer diameter
Total pistons surface area: 9.62 square inches
Material type: Cast Aluminum via gravity cast

C5 BRAKES:
Rotor size: 12.75 inches
Rotor thickness: 1.25 inches
-Caliper specs
Piston size: Somewhere close to 1.75 inch outer diameter
Total pistons surface area: around 9.62 square inches
Material type: Cast Aluminum via pressure cast (stronger)


Thanks for the help, SS.

[70 LS1]

The Camaro pistons are 44mm and the C5 pistons are 40mm.

If you are wanting to go with manual brakes, I wouldn't use the 15/16 master. You might try a C5 master. They are between 13/16 and 7/8". That is what I use with a manual setup and I am happy with it. Stock C3 vette uses 1 1/8" for power and 1" for manual. So if you install the 15/16 manual, your brakes would actually be worse requiring more pedal effort. The only reason I like manual better is I have never driven a power brake car that didn't feel a little squishy when you stab the pedal.

[Railing68]

I spoke with L. Torres at Precision Brakes and he was very helpful. To relay what I learned the MC bore size I am currently running is correct for the LS1 setup w/power. I could also drill a hole in the pedal assembly to increase advantage as stated by 70 LS1, which was confirmed by L Torres.

Also If I was to do it again, the Wilwood kit sold through precision w/ Forged Dynalite Calipers seems like a really good deal with plain rotors. Something I might look into after some test time on my current setup. Thanks for the help, SS.

[Railing68]

Even though this post is basically dead I will post some new info here rather than a starting a new one.

I replaced the used calipers I had with reman cardone units and some new longer flex lines. The Brakes are now what I expected them to be, much stronger and pedal feel is more firm. Whether it was the lines leaking or old calipers that someone had tryed to modify to fit smaller wheels is hard to tell. But I am happy with the results. SS:jump:

[70 LS1]

Glad it worked out for you.

[protour_chevelle]

How would that overstroke the piston? Different cars are built with different pedal ratios. All you are doing is adjusting the leverage from the pedal. The piston is only going to move so far based mostly by the pressure on the other side. Once the desired pressure is reached, you modulate the pedal to maintain that pressure and stop the car efficiently. With a higher pedal ratio, you have to push less hard on the pedal to get the same line pressure.

Maybe I am not understanding your question.

Yes you can overstroke a piston. We just had a thread in this section about a guy that was not able to bleed his brakes... Problem turned out the hydrboost rod was pushing the MS piston too far in causing improper bleeding.

Paul from Hydrotech can attest to this.

-Matt

[David Pozzi]

I would recomend changing MC bore size before changing pedal ratio. The pedal ratio is factory designed to have the proper geometry. A small change in location might not hurt but I'd do it as a last resort only.

The power brake (lower hole) position is less sensitive to change but a very small change on the upper manual brake hole does a lot more to the ratio. I wouldn't move the upper hole location more than 3/8" or 1/2".

[70 LS1]

I wouldn't move the upper hole location more than 3/8" or 1/2".

I agree completely.

[Railing68]

I don't think I need to, based on last test drive. But If I were going to I was thinking of splitting the difference between the upper and lower since it is a power set-up. I also adjusted the clevis rod and made it a bit longer when I did the last part changes.

I followed the directions of the mc and removed the cap and pressed the pedal fairly slowly to see fluid movement at 3/8-1" of pedal movement. To be honest it seems like the pedal really travels a bit farther than that but it is close. If the ports were blocked ie. overstroked piston etc.. most likely will get no fluid movement (visable that is) in the MC with the depression test. Or the booster would possibly groan. I actually could adjust the clevis further but will probably leave well enough alone until I can put several more miles on it. Darn Winter weather! SS

[David Pozzi]

I threw in my comment because it looked like this post was going to end soon and it will remain in the archives for a long time. I though if someone finds it by searching I wanted my comment to be in it as a warning to not get carried away moving holes on the pedal. The pedal geometry is set up to push straight on the master cyl and moving it off-center might put side forces on the MC piston reducing it's life, or other problems.

By the way, if switching from manual to power brakes, set the brake pedal height about 1.5" to 2" lower than a manual brake pedal. All GM power brake pedals are set lower since the lower pedal ratio can still fully stroke the master cyl before hitting the floor, even when set lower.