Monza - about 2200 at race weight.

Multiple issues but the one I want to look at for now is the brakes.

I need to measure and get the pedal ratio.

We have Aerospace 4-piston disc kit on the front and it is installed per the instructions.

I have a conversion kit on the rear using single puck calipers (mid 70's GM). Think the discs are 11".

Main issue (I think) is line pressure, pushing on burn outs, pushing on staging, and I don't dare think about the first turn out. I usually let it coast out to the last turn out.

I have a Wilwood tandem master and it's a 1.062 bore. Whatever the issue is, I'm not sure it's right for this combination of gear.

I had a collapse rubber flex line going to rearend on my car cause brake issues a while back.
I could put the car on jack stands and couldn’t get motor over 2000 rpms in gear before wheels started turning.

I have a gauge like this permanantly installed in my front brake circuit.

https://www.speedwaymotors.com...ssure-Gauge,592.html

It has been a very helpful educational and diagnostic tool for me.

Let us know please what your brake pedal ratio is.
What is your brake pedal effort? How about the brake pedal travel distance?

You probably already know that disc brakes require far more effort than drum brakes, which I reckon is why power boosters became so common in factory setups when disc brakes came out.

What composition of brake pads are you using? Some have better cold 'bite' than others; I think that organic pads are supposed to be the best.
Do you drag your brakes at all going up the staging lanes, to warm them up a bit?

Are the brakes brand new, or broken in a little?

This message has been edited. Last edited by: Bad Nusz,

I have had the same problem on a flex hose that Green 1 had.

Bad Nusz asks some good questions.

Here is another - Does your pedal go to the floor, (or close to it)? If not, does it feel a bit spongy, or "go solid", (lots of pedal effort, but just feels like there is no friction between pads and rotors)?

Couple more thoughts, issues I have run into:
Bleeding of entire system, including master cyl.
Some cars/brake lines are just darn near impossible to bleed all the air out of. Especially if the lines have a high spot or arch in them and the volume of fluid expelled in one brake pump during the bleed, is not enough to push the air bubbles completely beyond the high spot. As soon as you close the bleeder valve, the air rises back up to the high point again. Pressure bleeding is sometimes the only option.
Double check those rear GM-style calipers - I have received incorrectly boxed reman units from auto parts stores. Lefts instead of rights, & vice-versa. the GM calipers always had a large L or R cast into the back side of them, but they will bolt right in place on either side. The only other major visual difference, (and an easy check), is the bleeder valve should always be at the top when installed. Sounds simple enough, but I've had more than one guy bring a car to me that he could not get the brakes to bleed properly after replacing calipers, and that was exactly what I found.

Going to try to answer the questions but for some I do not know the answers.

The system itself is well bled, with a solid pedal - normal moving around the pits, putting it in the trailer is fine with no issues. There's about 1 1/2" to 1 5/8" pedal movement, I have about an 1/8" or less free play in the pedal before it starts engaging the m/c and I can probably get another 1/2" of movement if I stand on the pedal as hard as I can. I do not know the composition of the front pads, they are whatever was provided in the kit from Aerospace. The rear pads are cheap, generic pads from Advance Auto.

Then we get to the pedal ratio and that's a problem. The overall length of my pedal from the top pivot point to the center of the foot pad is 12" dead on. From the top pivot point to the connection point of the M/C rod is a touch over 4". Doing the math, I am out in the boonies here. This ****pit is tight to start with so options are a bit limited. I believe I can lengthen the pedal about an inch making it 13". I can also move the connection point up maybe another inch. This will help but still only gives me about a 4.3:1 ratio. I don't really see given the current layout (and being able to drive it) that I can come up with much more. Would a change to a larger cylinder bore M/C help any?

Larger master cylinder bore will give you less pressure and more volume. Smaller bore increases pressure but less volume so a lower pedal.
From what you've posted I assume it's a firewall mounted MC. The best bet would be to move the MC up so you could move the attaching point up and increase ratio. I know they came with manual brakes and I would have thought they had a better pedal ratio despite the fact they had tiny calipers and drums.

This is a 2x3 chassis under a Monza body shell. I would need to re-work the mounting, firewall and a few other pieces. Starting to look like an off-season project now.

Aye, there's the rub. Not enough mechanical advantage on the brake pedal it seems.

My '82 S-10 came with power brakes. The stock pedal ratio was I believe 3.5:1.

S-10s of that generation could be had with manual brakes; there is an additional hole in the brake arm drilled further up for that option.

Using that hole, I got a pedal ratio of 6:1 when I converted to manual brakes, which I am told by some sources that is the ideal ratio for manual brakes. Other sources claim 7:1.

Your Monza is different, of course.
You may need to raise up the master cylinder as Eman suggested, but maybe you could move up the pushrod without introducing too much angle?

You may need to redrill the brake arm. Indeed, I understand on newer generations of S-10 trucks, which were never available with manual brakes, you must re-drill the brake arms, so it's not unheard of to do that.
Heck, a brake arm from an older S-10, with the extra hole, may even work.

One good guy to chat with is "Malibu Dave"; he's very knowledgeable about S-10, G-body and F-body brakes. I bet he knows something about Monza brakes as well. He sells some nice conversion parts.
https://www.manualbrakes.com/

As Eman suggested too, a smaller brake master cylinder would give you more pressure, but longer pedal travel.

Larger pistons on the brakes would put more pressure on the pads too, but take a bit more fluid volume and pedal travel.

Would you know the piston diameter of your calipers?

As an aside, on my S10 race truck the brake master cylinder is a stock, GM aluminum unit. I believe it has a piston diameter of 1", and I 'think' it was made for a disc/disc brake system.

My front calipers are stock-type 'metric' calipers with 2.5" bores, common on S-10 trucks, G and F-bodies in the 1980s.

My rear calipers are Wilwood metric-style calipers with 2" bores.

Overall, I'm pretty happy with my brakes, although I could maybe have used 2.5"-piston calipers on the back as well, considering the big slicks and all the ballast.

This message has been edited. Last edited by: Bad Nusz,

It's taken some thinking and measuring but it looks like the easy thing to do (relatively) is moving the pivot point of the brake arm closer to the connection point of the M/C. I can get pretty close to a 6:1 ratio by doing so. And while it sounds like a no brainer it took me a bit to realize it. A chunk of metal and some welding tomorrow will get it done.

Cool; I hope that plan works for you.

Just a reminder if I may that welding on the brake arm itself could possibly fatigue the metal. Use care.
T.

Thanks. I just cut one small bracket back off the brake pedal itself and nothing else. The hanger bracket is where I did all of the re-work. Hard to believe that moving the pivot point about 2" closer to the M/C point made that much of a difference but it's a huge change. Of course I haven't had a chance to try it out, hopefully this weekend if the weather around here squares away.

A couple of things to look at. Be sure that the pushrod can bottom in the master cylinder and not bind going in due to changing the angle. If it can't go deep enough it kind of defeats having a dual MC if a line broke.
Next thing is to be sure the rod cannot pull out of the MC no matter what. I welded a plate with a hole that the pushrod passes throug so no matter what the rod cannot drop if for some reason the pedal got pulled up, like catching your foot under it. It was a year or 2 ago a racer had this happen. Car had been built for years and had a lot of passes on it. I'd say of all he remembers that 1 pass!

The push rod is dead level with the M/C and there is only about a 1/8" play before the rod pushes the M/C piston. Overall this deal worked out a lot better than I thought it would the other day. I figured I was going to have to tear everything apart and start from scratch. Now on to the next issue!

Ah, a success story! Let us know please how your car worked at the track this weekend.