View Full Version : Help with brake issue
robm-951
09-30-2016, 06:37 PM
I have a 68 firebird that's running the CPP big brake kit that uses the Silverado front calipers with the Lincoln rears. I'm using all the factory hard lines up to the factory 4 wheel drum distribution block. I running a 7" dual diaphragm booster with an ACDelco 18M974 (S10) master cylinder with the front port plumbed to the rear brakes.
The issue I have is the pedal seems to have a lot of travel. With the engine off the brake pedal is firm and high, buts sinks quite a bit with the engine on. also when braking while driving, the pedal stroke is a lot and it starts braking then keeps going down. Braking performance seems good for the limited time I've driven it.
I am wondering if I need a larger bore master than the 1". Any advise or things I should look into?
minendrews68
10-01-2016, 12:37 PM
I know it's a stupid question, but, could there be air in the lines? Sounds like it..
robm-951
10-01-2016, 02:42 PM
Not a stupid question at all. I wondered the same thing but I thought I had it bled completely. I guess I'll get another stab at it when I put it back together
Did you bleed the master cylinder too?
robm-951
10-01-2016, 06:26 PM
Did you bleed the master cylinder too?
I did.
ClosNova805
10-01-2016, 09:13 PM
What hole do you have it set to on the pedal ?
robm-951
10-02-2016, 05:27 AM
What hole do you have it set to on the pedal ?
I thought I had the booster clevis mounted in the lower hole on the brake pedal, but am now second guessing that. I went and double checked and since I have the parallel brackets it looks like the booster would line up with the upper hole. I just ordered a set of the angled brackets so I can be sure I'm using the lower hole.
Thanks.
Dark Pursuit
10-02-2016, 06:00 AM
a larger bore master cylinder should give you a SOFTER pedal.
robm-951
10-02-2016, 11:13 AM
a larger bore master cylinder should give you a SOFTER pedal.
Yeah, but it will also shorten the stroke.
I think CosNova805 nailed it. When I first did the suspension and brakes on the car I took it for a drive and thought the braking wasn't quite right and that it probably still had some air in the system. Not long after that I pulled the motor for an LS swap. While the car was apart, I cut and welded the angled brackets I had to make the booster and master parallel with the firewall. When I put it back together I used the upper hole without any thought to the ratio change. After quite a while when I first drove the car again, I remembered only thinking the brakes had a pedal feel issue previously and that it was worst than I remembered. I going to try it again with a new set of angled mounting brackets, the lower hole on the pedal, and a complete bleed job. Hopefully that will take care of it.
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