I've tried several evolutions of brake setups for my C4... eventually getting the bigger brake pieces available on the late models and eventually going to what I thought would be a "better-than-stock" solution. Boy was that a mistake!

What I found out after irreversable cutting/welding was that my aftermarket "dual-master-cyld-balance-bar-footpedal-six piston-racing brakes" wouldn't stop the car. I nurtured these along with lots of tech help from Willwood with mixed results. However, the brakes have always been the weak link since... they simply required too much driver effort to stop the car.

I am now trying to go back to an OEM style firewall/footpedal assy and am going back to using a vaccum booster. The car is non-ABS. No e-brake is needed.

Parts at my disposal: I have a set of GN-III with appropriate rotors/hats. I also have a set of the OEM heavy duty (thicker) front calipers/rotors from a '96. For the rear I have stock OEM rears calipers/rotors and also have a conversion mount to mount front---->rears which are mated to another set of OEM HD 96 front calipers/rotors. I have at least a dozen sets of racing pads. I've also got a whole shelf of Willwood master cylds in various sizes and at least two different lengths of pedal assy's (that I'd like to throw off a tall bridge).

Can anyone who's had some success please guide me in the proper parts selection for a roadracing car? ... I'd like to get it right this time.

 

Craig, if I remember correctly, you are in the Oregon/Washington area. Shoot me a PM with your number and I'll see what I can do.

 

If it helps any I am using the C5 caliper in front, C5 rotors, Carbotech pads, and brake ducts. This has been working wonderfully at Road America and didn't cost much. Misc parts, brake bias spring, high temp fluid, speedbleeders, braided lines and Jeffvette adapter plates. Have fun out there!

 

I have GN3's on the front and J55 front calipers on the rear of my '96.

I currently run a DRM master cylider which has a slightly larger bore than stock (I think it's a modified MC off of a Tahoe or something). I'm also running a Wilwood bias valve. The pedel effort is very nice (firm but responsive) and brake feel is great.

I ran it for a while with the stock master cylinder, which worked OK, but the pedel was a little soft for my taste.

I have a bunch of pics and would be happy to chat about the setup if you'd like. Just PM me and I'll give you my contact details.

There are also several guys in the ZR1 section of the forum running similar setups with much success.

 

It almost sounds like there is "some other" issue at work. If you'll indulge me ... a few questions:

Can you be more specific with:
was the braking distance too far?

what were those results?

pedal travel too far or was the pedal too hard?

Did you remove the abs or did it come that way?

The 12" C4 brakes aren't that hot, the J55s are better and the C5 brakes are supposed to be better than the J55s. However, you should have leapfrogged all that with a 6 piston Wilwood caliper.

 

Thank you for your assistance guys.

Jeff: I'd like to talk to you about your set-up as I know you've been successful.

Aardwolf: I do have a set of calipers/rotors left from an old C5 that I used to run. You've got these plugged into your stock master cyld?

Astoc: The problem now is that braking simply reqiures too much pedal effort. I can slow down, but I cannot push hard enough, for exhample, to skid the tires... this makes it hard to come close to threshold braking.

Willwood worked with me to tune the hydrolics, gradually using smaller and smaller bore masters. But, there is a limit to how small you can go. At some point the master cyld volume gets too small to feed the 6-pistons in the calipers.

Non-ABS and the hardlines appear adequete to handle the volume of fluid.

More history: I originally changed from the OEM booster/master cyld set-up as a "fix" for a "low booster vaccum problem" that I was experiencing. The motor doesn't pull enough vaccum to run the booster very long, unless you also downshift... this causing an erradic hard pedal (usually when going your fastest and in close traffic). Specifically, I was having trouble at the T10-11-12 transition at PIR. You come off the backstraight at top speed, brake to about 90mph then turn-in without downshifting, you sometimes need to break again at the T10-11 transition if in traffic... an you definatly need to break at the T11-12 cute... occasionally, the downshifting wouldn't co-inside with your braking... and the brakes would not be there for as expected (at the expected pedal effort). Of course, the dual master cyld did away with the booster.

Mark: I'd like to find out more about your Doug Rippie master cyld, as I'm considering junking my current set-up for something more "tried and true." Unfortunatly, I've got a lot of firewall work to revise, headers to trim and steering column to "re"-reposition to get back to anything near an OEM fittment. What are j55 front calipers? are these the OEM HD calipers + 1 1/8" wide rotors that are found on the late model C4's?

 

Yes, J55 is the option code for that whole package.

 

So, am I right to assume that I need to get rid of the dual master cyld set up and get back a booster to have adequate brakes?

If you click on my profile pics, you'll see that this is gonna take alot of revising. For one, the engine will have to be moved back to the stock location (it's currently 6" lower and 8" rearward) in order to put in the stock firewall. Then the hood will have to be cut to accomodate the manifold/carb. I think that the crossover headers will have to be replaced with a more conventional style and the exhaust revised out of the passenger compartment. I can adjust the linkage on the Jerico rearward, but I'll need a longer driveline... do you see how it all just snowballs? Woops, now I'm just whining

Maybe my question is: Has anyone out there made a dual master cyld system work on one of our cars?

If not, then it looks like I'll need to do some serious refabrication to get back to near stock... and at that point I would like to copy a tried and true set up (Jeffvette/DRM or ?)

 

What Wilwood parts are you using? I ask for two reasons: 1) To help figure out what is going on and 2) I might be interested in buying your Wilwood stuff. I am currently designing the brake system for my track car based on using Wilwood pedal, masters, and calipers.

Thanks
Ken

 

You don't want any of my stuff... it's jinxed

... and Willwood has later d/ced these mastercylds due to a design flaw. The resiover cap seals are very hard to keep in place when the lid is secured... and if they do leak, then the brake fluid spills out on the corners creating a fire hazard if it splashes on your headers and possible brake failure if you run out of fluid. One more reason to stay with "tried and true".

 

OK, but will you tell us what size master, pedal ratio, and the caliper piston diameters? Like I said, I am designing my system, and I would like to see how your components compare to what I am coming up with.

Thanks
Ken

 

Hi Brian,

Yep, the J55's are the OEM hd calipers.

I got my MC used from a forum member, but it was orignally purchased from DRM. I was told it's a modified Chevy Tahoe unit. It works with the factory vacuum booster. It doesn't have an internal bias spring, so I use and external wilwood bias valve to regulate rear pressure.

Since you were having problem maintaining consistent vacuum, you could go with a vacuum canister, which would stabilize the vacuum to get rid of the peaks as well as keeping you from having to downshift as much (theoretically).

Theoretically, you should be able to keep your current dual MC setup, but since it's not boosted, you'll need to be able to change the leverage point of the pedel to allow you to apply more line pressure. Pedel travel will be longer, though.

 

Craig, these are the brake line pressures I measured on my 85 C4. This is as hard as I could push on the pedal.

With power booster at idle: 1300/900 psi (front/rear)
Without power booster: 400/400 psi

Does that answer your question? Obviously you'd need a vacuum pump to get near the pressure I get on a stock motor.

Also I'm running 6-piston C5 Wilwood SL6 calipers up front and stock 85 brakes in back and have no problem with fluid capacity on the stock m/c. Now, an 84 master cylinder would be trick (if it fit), since it's got the small bore available.

Sometime around 88 GM changed the m/c and reversed the front and rear reservoirs, but other than a minor rerouting of the rear brake line, they seem interchangeable, comparing them on the bench.

 

Central coaster: Thank you. I'm only able to get about 700# with firm pressure. I've always wondered what the stock baseline pressures were.

Ken: Sure, I'll be happy to get you more info on my brake parts, pedal ratio and master cylds that I've tried. I'll have to get home and look in my parts bin and get back to you. There's no sence in someone repeating my poor product selections.

Mark brought up using a vaccum canister, another brought up using an electric booster... now I've never heard of an electric booster(?) Good ideas if I need to go back to using a booster. And, I really don't remember if Wilwood offered a longer pedal as an option. I'll measure what I've got now... a really basic factor that I may have missed altogether.

 

My pressures aren't stock baseline, but should be within reason. I put a 110# bias spring in there to minimize the rear pressure reduction as much as possible. Because otherwise putting monster rotors on the front magnifies the front braking so much the rears become useless.

With just the larger front rotors/calipers my 60-0 braking distance increased from 130 to about 150! Now I'm back down around 120 ft. I assume you've got your bias dialed in. The needed pressures can be deceiving when you consider the weight transfer and the rotor/piston sizing.

At 1-G decelleration the C4 can use up to 35% rear braking in a straight line (because of the low CG and good weight distribution). Obviously using all 35% in back doesn't give you any leftover for turning or downshifting, but it gets you in the ballpark. Then just divide by your rotor diameter and piston area front and rear and that's the pressure bias you should be close to.

 

Ken: While I couldn't get all the info that you wanted as the M/C sizes are stamped on the sides of the M/C... and these are mounted too close together to see all the #'s. Please at least know that I did in fact have to stand on my head to measure the pedal ratio... in a rainstorm to boot

The front M/C is 7/8" The rear is sandwiched in too close to tell, but if I remember right it's a little smaller. The clutch master is 3/4". These are Willwood "composite" M/C and I would recommend staying clear of them. The pedal set have a pedal length of 11.5 inches from the pivot to the end of the pedal. The M/C rod attaches at 1.5 inches from the pivot (making the pedal length 10" form the M/C attachment). I have Willwood GNIII fronts and apearantly J55's on the rear. When I push on the pedal with very firm pressure, my brake pressures are about 700" front/600 rear.

I have some pics if you'd like me to e-mail you, or if you'd like to host for the other forum members (my internet connection is as wimpy as my brakes... only dial up available in my area).

 

Thanks for taking the time to measure that stuff. I will put it in my Excel sheet and see what I find. I'll let you know what I come up with.

Thanks again.
Ken