K10 disc brakes on my 65 swb K10

[K10-BB*65]

Trying to get some information. I converted to disc brakes and larger rear drums using the front and rears from a 76 K10 along with the master cylinder, and proportion valve. I used a smaller booster from a sixties impala since I didn't like the big truck one and the big bracket that makes it stick out from the firewall. Problem is the brakes take a lot of pedal pressure to stop. It doesn't seem any better than the stock 4 wheel drums. Any ideas? Maybe need a different booster? The discs and calipers are new as well as the master and wheel cylinders.
Thanks

[Captainfab]

It sounds like you may have a defective booster, or maybe not enough vacuum for the size and style of booster.

I make booster brackets that keep the booster close to the firewall and use all factory holes. There are many, many compatible boosters. See the link in my sig line \/ \/ \/

Some guys have better luck with drilling a hole in the brake pedal 1" lower than the original hole.

[murdoc]

I agree with Captainfab. I have the same issue with my c-10 when I converted to disc brakes. Although I have yet to remedy the issue, everything points to my used brake booster and/or not enough vacuum.

I also installed new brake lines, hoses, calipers, and master. Look into the booster and see what recommended vacuum is for the booster, see also what your engine is producing at the hose.

[K10-BB*65]

Thanks guys. I have a new later model booster to try and it sounds like that low profile bracket may be just the thing I need to swap it in. I was also concerned about the push rod going into the booster as well. Is there a formula to use as far as the length required to get the correct travel for the booster / master cylinder? When I did the original swap I tried to duplicate what I had with the original master but it may not be correct for the 76 K10 dual master cyl.
Thanks again.

[K10-BB*65]

I do have a lot of cam in this motor so the vacuum could be an issue too.

[Captainfab]

Drilling the hole 1" lower on the pedal gets you close to the same pedal ratio as the '76 would be. If your engine is low on vacuum, you will want to consider at least a dual diaphram vacuum booster or a hydroboost.