Frank84C4

84 C4. All new brake parts. Calipers, hoses, metal lines, master, booster. Hawk HPS pads. No leaks, bled properly. Car stops but brakes will not lock up. Any suggestions?

billschroeder5842

So, let me understand this; your car stops (properly I assume) but the brakes will not "Lock up" where the wheels stop spinning thereby causing a potentially uncontrollable skid?

Sounds like you have a safe operating system?

Frank84C4

Benny42

There is probably a few things going on here. New pads probably aren't bedded yet. What size and condition are your tires? It is hard to lock up a sticky new 275/40/17 but a worn out old 245/50/16 can lock up fairly easily.. What road surface were you testing on? All that said, you do not want to "lock them up" in a panic stop. That gives longer stopping distances and can end up in a crash or a ditch.

Churchkey

Need to bed the brake pads in the procedure should be on Google.

HPS pads are cold blooded & do not have good initial bite they need some heat in them to work well.
If street driven & not a track car consider standard brake pads.

Good luck

Frank84C4

Thank you. I have brand new 255/50-16. I understand what you saying about locking up the wheels, but I am uncomfortable with the stopping distance. I am going to change to stock pads

VikingTrad3r

have you ruled out the obvious: air in system, failing bake booster, bulging brake lines?

Dt86

I replaced stock pads with hawk street pads and there was an improvement in braking. Somethings wrong. Did you bed them in as per their instructions? How did you bleed the lines? Did you bench bleed the master cylinder?

gerardvg

Hi
The car should easily lock the brakes, even with cold hp plus brake pads (my 85 does)...
Yes I agree its dangerous if the brakes are not effective.
Check the vacuum supply to booster, does the engine provide good vacuum?
Jack each front wheel up, get a friend to spin each tire and confirm even with engine off the tire stops easily.
For the back you need to have both tires of the ground, check each rear tire stops easily you will need engine running.
Don't forget if you have an auto trans put brake on before putting it back in park, there is only a small rod that locks the trans.

Check the booster to master cylinder rod, it should be adjusted correctly.
Hopefully someone can post the measurement specs.

Good Luck

farmer661

I have the same situation, 84 with Hawk pads, new brake booster. I have changed fluid and bled per the manual a few times. It has a good hard feel, just doesn't stop with any authority. I have adjusted the master cylinder rod a few times, but no substantial improvement. It will not come close to locking the tires. I have thought about buying a brake pressure gauge and seeing if that gives me some hints. I will watch this thread with interest!

Ken

East Texas

gerardvg

Wow that's real bad, i have always had great brakes on my 85.
Even when they were the standard setup, very much in feel and minimal effort required like a modern car.
The only difference is a 13/16 bore master cylinder for 84 to 7/8 bore master cylinder for 85, I think the 84 uses a metal booster compared to plastic for 85.
Same discs and calipers, should be minimal difference in braking.

It should come down to Engine Vacuum or Booster assistance....and brake pad friction compound.
I use hawk HP Plus and they bite real good, i suppose measuring the caliper pressure between caliper and piston and actual booster assistance will be the next step.

My brakes have always inspired confidence high speed Track use and around town, minimal effort required at any speed.
It needs serious attention before using the back of another car to stop you, remember C4s will go under and lift most cars over the hood to windshield ....

Hope someone with an 84 with excellent brakes will comment, is it a known 84 corvette issue or just bad new parts ? affecting pedal effort.

I went from 255 55 16 to 275 40 17 mainly due to lack of availability with wide and better grip tires, i went to 88-96 J55 13 inch front discs and dual piston calipers a while back but was mainly for high speed track work. Nothing wrong with the standard brakes on the road.
Have owned my 85 for 20 years now,

Cruisinfanatic

you don't need to bleed lines just to change pads

Frank84C4

Dt86

Thank you for telling me something that I already know. Perhaps reading the thread before commenting would be appropriate in this instance.

pcolt94

I think you actually know what you mean as I had a similar condition when I got my 94 in 03. I changed everything multiple times, pads rotors flex lines, ABS the whole works and this went on for a long time. I could stand on the brakes and just could not get enough stopping action.I even upgraded to the 13" J55 system which helped but still was never right or could get the ABS to activate.

This was until my booster went bad and leaked, (a normal repair) the only part that was never changed because it was not bad and had no symptoms. With the replacement of the brake booster it was a world of difference. I could lock the wheels up, activate the ABS as all worked as you thought it should.

I can't completely explain it and if had suspected the booster I would have replaced it. All I know is the new (AZ) booster was the missing piece in the puzzle that made it all right. Just my experience, not opinion.

Cruisinfanatic

Glad for ya. I read it just fine. Maybe you didn't as the OP said in the first post that they were bled properly.

Frank84C4

I am installing factory pads next. If that doesn't do it then I am going to replace the booster. I changed out the original with all the othet parts.

Dt86

Uh ok... you make no sense. From your last post, why would he bleed brakes if he was just changing pads??

VikingTrad3r

aklim

Question. What do you have for the hose going from the metal lines to the calipers?