Nova1978

As the title states, I have a C5/LS1 brake setup on my 1978 Nova. It's the 2 piston front calipers on the 12.8" rotors and single piston rear with 12" rotors. I have bled and bled and bled the system and get no air from any caliper. The pedal when the car is off is firm, it moves maybe 1" before I can't push it anymore. When I start the car, the pedal will drop about 1/2 way down with little to no force - feels like it's spongy. The brakes stop the car, but it doesn't seem to have a firm pedal until you reach that 1/2 pedal stroke or more. I have also never been able to lock up the wheels/tires with this setup.



My master cylinder is a 1999+ S10 master cylinder (LHD application, not the RHD application one). I have the stock style 11" booster, and my 6.0L LS shows 60-62kPa MAP at idle (roughly 10-11 inches of vacuum). I am using a disc/disc proportioning valve. Rear port on the master is plumbed to the front brakes and front port is plumbed to the rear brakes.

Is this problem indicative of air still in the system somewhere, an over-boosted system, incorrect master cylinder / too small bore (it's a 1" bore master) or a different issue that I'm not thinking of? I have measured the pushrod to master cylinder clearance and found it to be about 0.030". I have also checked the proportioning valve to make sure I didn't "trip" the system by checking for continuity between the prop valve sensor and ground and it shows an open circuit so it isn't tripped.

ryeguy2006a

iTrader: (27)

You should definitely be able to lock up the wheels with this setup. Maybe try bleeding the brakes with the motor running? Or possibly try a Mityvac.

Nova1978

I figured this setup should be able to lock up the wheels as I was able to lock up the fronts with the smaller stock discs when the brakes were still stock. The C5/LS1 brakes have larger rotors and bigger calipers so it should stop the car better in theory...

I've been using a motive products power bleeder for this. When I first installed the system, I gravity bled the entire system and then used the power bleeder. Today I picked up a master cylinder bleeder kit to see if I had any air bubbles trapped in the master and honestly I can't remember if I bench bled this master when I got it 8+ years ago. I did get quite a few bubbles out of the front port on the master and a few out of the rear port. I tired a combination of fast and slow as well as waiting a while between strokes to try and dislodge any bubbles that may be present. I took about an hour bleeding the master to make sure there was no air left. I also completely flushed the brake fluid with new as the existing fluid is going on 8+ years old. I won't be able to test out if this made a difference or not for a few days though - rain, rain and more rain....

LS1 TJ

Might not make any difference but I would replace the stock prop valve with an adjustable prop valve.
I've used the C5 brakes on a number of LS swaps hot rods and they have worked very well.
I have both the motive pressure bleeder and a Mity Vac. I just seem to have better luck with the Mity Vac for brake bleeding.

Nova1978

I was thinking about going to something like the wilwood adjustable valve, but if I go that far, I might as well incorporate a line lock....





Anyways, I got a long enough break in the rain to where the roads dried out and got a chance to test on the brakes some more. No change after bench bleeding the master and flushing the system. I'm wondering if I should just get rid of the S10 master and go with a master that was designed for these brakes - a C5/6 master cylinder. Same bore diameter, but maybe something is wrong with the S10 master I have. I would also change to the corvette style 9" dual diaphragm booster as I think that looks better and would give me some more clearance to the valve cover.

I also picked up an Allstar one person bleeder kit to try out. I've heard good things about this from the 6th Gen Camaro guys. It has a check valve in it so you can cycle the pedal without sucking air back into the system.

LS1 TJ

Pics aren't the best but I always go with the C5 booster and 2002 fbody master. I use the Wilwood prop valve with the single outlet for the front brakes and then use a "tee" mounted on the cross member running to left and right front brake lines.
I like the fbody master because it has the outlets on the right side of the master. DSE has a mount for the C5 booster.

Nova1978

What bore is the 2002 F-body master cylinder? I was going to try a C6 master since it had outlets on the driver side and they were both the same size/thread pitch. Also, maybe I’m expecting too much from this setup - how is your pedal travel with this setup? Mine feels like I have to push about 1/4 of the way before it even starts to do anything, and then about 1/2 way down to stop the car. I feel like as soon as I start pushing the pedal, I should feel resistance and I should get some deceleration of the car, not after 1/4 of the pedal travel.

Also, that is a clean setup you have, I may have to borrow some inspiration from you on that brake setup.

LS1 TJ

I'm not sure about the fbody master bore size. The brake pedal needs some free play. On my 68 C10 I had no trouble locking up the brakes. The linkage did have a threaded adjustment. The C5 master has the outlets on the drivers side. The bummer thing about the fbody and C5 masters is that the outlet line nuts are an odd ball size. I go junk yard diving to cut the lines off just for the nuts.

Nova1978

Right - the bubble flair is an issue. The nice thing about the C6 master is both outlets are the more common M10 size instead of the staggered M10 and M11 sizes. Plus DSE makes some adapter to go from M10 bubble flair to the easier to deal with double flair. That’s what made the C6 master more attractive, but your setup is very clean looking. I’d like to get the pedal feel to where it starts doing something as soon as I start pressing the brake. My 22 Camaro 1LE has me spoiled with that. I basically breathe on the brake pedal and it comes to a stop in a hurry.