Ever since I did my swap, I have noticed that my brakes have been real mushy. it didn't ever really bother me that much until I was out racing about 2 weeks ago and hit the brakes real good and it felt like they weren't doing anything.

I have LS1 brakes on front and rear, before the swap they would stop the car on a dime, and the pedal feel was very firm. Now it's "mushy".

I have a pretty decent size cam, i'm running an actual 4th gen vacuum hose from the booster to the back of the LS6 intake, there's no leak that I'm aware of. I've bled the brake system with a mity-vac as well as by hand with a wrench...what gives?

I never replaced the proportioning valve when upgrading brakes because i was told that the '91 Z28's had 4 wheel disc valves even if the car was equipped with drums in the rear, like mine was. Plus, before the swap, as I mentioned, they felt fine.

So what is going on? Anyone else having this problem?

 

what are you cam specs? define mushy .... if its the cam overlap or lack of vacuum it should be more hard than mushy.

with my current cam its not even noticeable. I have just enough overlap where you can tell with no doubt I have cam but not enough to make the car drive like crap


my old sbc had brakes after a drive where I had enough rpm change (high rpm then throttle closed) I could pull into a parking lot and had about 3 pumps of the brakes until they were hard as a rock


if you cam is that big you may look into a vacuum pump or some people go to hydro boost

 

I don't know anything about brake systems other than changing pads so take this with a grain of salt. I throw this out only to spur conversation. So.... Wouldn't the vacuum assist effect only pedal effort? And wouldn't mushy pedal be feedback that the hyrdaulic pressure isn't building correctly in the brake system? Reasons being air in lines, water in fluid, old rubber lines buldging, leak?

 

You've got a problem in the system, vacuum isnt the issue

Big cams drop manifold vacuum, so the booster cant do its job. In that case the pedal is rock hard, not mushy

 

look just below the master cylinder on the booster, and see if the paint is peeling or bubbling.

 

Yea I HAD (past tense) a leak from the reservoir due to the rubber gasket not being sealed correctly and the lid couldn't snap on all the way. I figured that out and put it on correctly but now that i think about it, I don't know if I've bled the brakes since then. I suppose it's possible that air got in the lines at some point. I've bled the system twice already and it had no effect.

The cam specs are 239/242 .64x/.64x 111LSA. I don't think this is the problem though if the mushy effect wouldn't be caused by cam overlap.

 

Youre fluid could most definitely be contaminated. You need to bleed the brakes to the point youve bled the whole system. Every ounce of fluid in that master needs to come out and be replaced with new fresh fluid.

If the reservoir cap wasnt secured properly for any longer then say, even an hour...then all the moisture in the air has contaminated the brake fluid. Remember, the DOT ratings are to represent the fluids ability to retain water/moisture and it doesnt take much to contaminate the entire system.

 

Crap, I forgot about that. I'll do that over the winter then I suppose. It's a good reason to break open the system to install my 4th gen master cylinder/reservoir lol

 

big cam = rock hard pedal. Mushy is bad master or air/contamination

 

I'm glad I read this thread, I have a mushy brake pedal and now that you mentioned it, my brake booster hose is disconnected lol!

 

if that hose was disconnected then the pedal should be very firm, not mushy. You also have issues with your brake lines having air in them

 

I disconnected my booster vac before. It actually wasnt that bad. DEF required some leg, but the braking performance was still fantastic with good pedal feel.

My suggestion...and this is mostly just opinion based on my experience. Ditch the prop valve. Run the fronts at 100%. And run an adjustable willwood valve for the rears. Ive run this set up on my Jeeps, and my TA for years with zero issues, and the best braking Ive ever experienced.

But Ill agree others. You have a hydraulic issue somewhere. Ive never experienced fluid that was exposed to air causing any noticable issues, but I guess thats certainly a valid concern. There is no reason you shouldnt be able to make it work with the factory prop valve...ditching it isnt the only solution, just the way i like to set up my brakes.

Good luck!

J.