Chebby disc brakes not stopping well

[Blue71]

Previous owner put the Chebby conversion on this 71, with BC Bronco Booster. It has 33" tires. Checked booster and seems to be working fine. The initial stopping power seems good and I can tell the booster is doing its job, but if you wanna stop quickly, it takes a ton of pedal to get it stopped. It almost feels like stock manual brakes nearing the end of the stop. Today I tackled part of it by grinding even more off the back of the knuckles to where my clearance is at least 1/2". Put new $35.00 pads on and cleaned everything. Test drove it but still doesn't have nearly the same stopping power as the 77 I had with 33's and factory Ford discs up front. Any ideas? I don't wanna go hydro boost or anything for now. I feel like three must be another problem.

THanks,

BLUE71

 

[DirtDonk]

Was going to suggest pad material issues, but you said you changed pads. So that's less likely now.
What about engine vacuum? How much do you have, and how big is the booster?
I wonder if the booster could have a leak that only shows up after the pedal is pushed, so that it works fine initially, but looses it's ooomph after a moment of pressing open on the back valves?

The piston is larger on the GM type calipers than on the stock Ford units, so what's the pedal feel like? Hard with short travel? Or a bit soft-ish with longer travel?
When you start losing some of it's overall strength, does the pedal keep going down, or does it stop dead?

Paul

 

[Broncobowsher]

I was going to suggest caliper clearance, but it sounds like you have that taken care of.
Are the pads the same material as what you had or something different?
And follow with Dirt's advise, it's good.

 

[Pa PITT]

.... Wow that one stumps me also... When I read the title .. My thought was get some clearance .. Next was get new pad.. You done that as well. I'll say go get the cheapest pads you can find . But I think you have booster issues.. So I really say swap over to a Hydro Boost system.

 

[treihesse]

Bad master cylinder.

 

[Blue71]

I will double check booster. Pedal is easy and slows Bronco initially for the first 1" of pedal travel and feels correct at that point. . Then if u feel you need to emergency stop or really stop fast...you still feel the brakes working fine on that first 1" of pedal travel and the pedal gets hard for the next 1" or 2" which puts the pedal getting hard at about half way to the floor. You can push as hard as you want, but vehicle eases to a stop. Pedal remains hard that whole time while pushing as hard as I can. Feels like it takes about 4x as long to cruise to a stop, instead of actually getting good stopping power.

Hope that makes sense.

Thanks,

Andy

Was going to suggest pad material issues, but you said you changed pads. So that's less likely now.
What about engine vacuum? How much do you have, and how big is the booster?
I wonder if the booster could have a leak that only shows up after the pedal is pushed, so that it works fine initially, but looses it's ooomph after a moment of pressing open on the back valves?

The piston is larger on the GM type calipers than on the stock Ford units, so what's the pedal feel like? Hard with short travel? Or a bit soft-ish with longer travel?
When you start losing some of it's overall strength, does the pedal keep going down, or does it stop dead?

Paul