Better Brakes

[tomhornak]

To anyone with ideas:
I have am Everett Morrison Cobra with Corvette suspension, I first built it with manual brakes as per the kit, I found it did not stop faster than 70' from 10mph. I contacted EM and they said I should buy thier Power booster, so I did, I installed it and put on very "sticky" brake pads, they were supposed to really stop a Corvette very well in race applications and street applications. My 632cid big block has a big cam and therefore does not develope enough vacuum, so I installed an electric vacuum pump to gets down to 24" with an automatic switch set to 21" of mercury. I have this connected via check valve to a 1+ gallon vacuum reservoir. I know I have plenty of vacuum and the reservoir is plenty large (as the pump kicks on after 10+ stops). But I still can not lock up the wheels, even with full foot pressure on the pedal. Although the stopping distance is MUCH better, I suspect that if I can replace my two piston calipers with 4 piston versions, I'll get better hydrolic leverage due to more piston area, I already have the smallest diameter Master Cylinder possible. Anyone else have a similar problem with Corvette brakes on a Cobra? or experience with the EM Corvette suspension kits not stopping well? Anyone know of after market 4 piston calipers ? Thank you. Tom

[relaxinrob]

Tom,

The first thing I would do in your situation is to bleed/flush your brake system thoroughly. This will accomplish two things: 1. It will get out any air that's in the system and; 2. It will give you new brake fluid.

You will be amazed how much this can improve your braking. You should be able to lock up the brakes anytime, unless your system has ABS from the corvette.

[tomhornak]

Thank you for the response. When I put in the booster and new master cylinder, I replaced all the brake fluid (even thought the original only had less than 10 miles on it). Now I have about 100 miles on this fluid and all the system has been bled numours times, even with a pressure bleeder. There is no "mush" in the pedal. When I step on it, I get a hard pedal response with no pedal climbing if I pump the pedal. To me this implies that there truely is no air in the lines and the fluid is perfectly clean and new. But, I agree with you that the wheels SHOULD lock up, I can only think that due to my tire size (295 front and 315 rear), there is just too much tire to skid ? But then the braking distance should be better, it just still does not seem/feel safe. I do not have any ABS in the system, the lines run direct except for an adjustable proportioning valve in series with the rears. I adjusted that at 75% per EMs recommendation, but until I can lock either the front or rear, I cannot tune it further. Tom

[Ant]

Tom,

I am not a brake expert so here is some recommendations.


Workout your pedal ratio that is pivot point, length of pedal, down or up from that, and where the pushrod comes off pedal, either above pivot of below.
Measure your pistons on each circuit (if you have dual master cylinders one for the back and front)
Wilwood have a graph on their website that you can work out your piston area!

Brake material should be the same front and rear, dont run a competition pad on the front and standard OEM on the rear like a lot of people do!

Email Wilwood or any brake tech guys and tell them what you have, and say you would like to know what they recommend of their products for your application, I have wilwood brakes and find they are excellent.
You should be able to compare the piston sizes to what you have and master cylinder sizing to see if you are in the Ball park!
Most big outfits like Wilwood etc are happy to help as its in their own interest to promote their products.

Hope that makes a bit of sense!

[tomhornak]

AJ,
Thank you I will do that on Monday. Good idea, thank you again.

Tom

[Hotfingrs]

One thing I did on mine, was go to a smaller bore master cylinder. When I bought the car, I believe it had a 1" and a 7/8" and I put on 2 5/8" ones. The smaller bore increases pedal travel, but also increases line pressure. I have non-power brakes. If you have the room, I'd also try to increase your pedal ratio.

[Ira4th]

I absolutely love my Morrison kit, with one issue and exception. I have never been happy with the brakes.

This vehicle has full corvette suspension and brakes, but to my understanding, a manual pedal assembly, unfortunately, there is no room for a traditional Chevrolet booster.

1. I have little or NO pedal travel at all
2. No room for a boosters
3. Car has the brake pedal setup with separated front and rear master, and hydraulic clutch.

Does anyone have similar issues or solutions. I don't drive the car for one reason, Doesn't stop well.

[Tommy]

I have a mid-90's vintage EM with brakes and suspension from a 1987 Corvette. I have had my car on the track numerous times and worked the manual brakes hard from speeds as high as 140 MPH. They have always worked great. They should because they were designed to stop a car that weighs about a thousand pounds more than mine. ... If you cannot lock the brakes on your car in a practice emergency stop from about 30 MPH, something is not setup right. ... Send me a PM if you'd like to talk about your situation.

[Tommy]

Ira,
Regarding our conversation: Here are some photos of my brake pedal assembly.

[john chesnut]

I've built a number of cars using C4 Corvette suspension, stock calipers and used large wheels and tires. The brakes have been great, even on the track. Like Tommy says, they should be great in our light cars.

I've never have had power brakes in the cars that I have built. I use a pedal assembly with a 6:1 ratio. I can lock the brakes up easily.

My Wilwood pedal is set up with twin 3/4 inch MC's. I take the time to make sure that the balance bar is set up correctly. In general I run 100#'s more front line pressure than rear.

I just use the better quality brake pads that I can buy from a quality parts store. It's obviously important to make sure that the the system is bleed properly. It's important to make sure that the discs are cleaned completely when installing them. They come coated with a rust inhibitor. Use break cleaner and a good clean rag to remove the coating.

it's most important to "bed" in the pads. If you don't do this your brakes will never work to their potential. The first time you drive the car after installing the brakes you should make several hard stops from moderate speeds. Don't lock the brakes up. But hit them hard enough to really heat them up. Brake hard until you come almost to a stop. Then accelerate quickly to a moderate speed and hit them again. Repeat this several times until you can smell the brakes getting good and hot. Then park and let them cool down completely. Your rotors should have lost all of their shine. Dust from the pads should become embedded into the pores of the rotor. This 1 step will make a huge difference in braking performance.

If everything is set and working properly the car should stop straight and true. You will want the front brakes to lock before the rear.

I hope that you get the brakes sorted out. They should work fine for your application.

[Tommy]

John,
I spoke briefly with Ira and he thinks the problem stems from an improperly installed balance bar assembly. That's why I posted the photos.

Ira,
It is possible to purchase a new balance bar kit if your brake pedal is set up to accept it. Here' s an example: click here.