Brakes will NOT lock up
#1
Navigator
Thread Starter
Brakes will NOT lock up
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?
#3
Navigator
Thread Starter
It feels to me the stopping distance is excessive
and unsafe. In a panic stop shouldn't the brakes lock up?
#4
Drifting
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.
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Frank84C4 (07-05-2018)
#5
Melting Slicks
Member Since: Sep 2008
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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
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
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Frank84C4 (07-05-2018)
#6
Navigator
Thread Starter
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
#7
have you ruled out the obvious: air in system, failing bake booster, bulging brake lines?
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Frank84C4 (07-05-2018)
#8
Safety Car
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?
Last edited by Dt86; 07-04-2018 at 06:28 PM.
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Frank84C4 (07-05-2018)
#9
Melting Slicks
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
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Frank84C4 (07-05-2018)
#10
Intermediate
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
Ken
East Texas
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Frank84C4 (07-05-2018)
#11
Melting Slicks
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
Ken
East Texas
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,
Last edited by gerardvg; 07-05-2018 at 06:20 AM.
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Frank84C4 (07-05-2018)
#13
Navigator
Thread Starter
Thank you all
I am going over the whole system again. I have ordered stock pads. If anyone has the booster adjustments specs that would be very helpful.
Thanks again
Thanks again
#14
Safety Car
Originally Posted by Cruisinfanatic
you don't need to bleed lines just to change pads
Thank you for telling me something that I already know. Perhaps reading the thread before commenting would be appropriate in this instance.
#15
Le Mans Master
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.
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farmer661 (07-06-2018)
#16
Le Mans Master
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.
Last edited by Cruisinfanatic; 07-06-2018 at 10:53 PM.
#17
Navigator
Thread Starter
Thank you
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.
#18
Safety Car
Originally Posted by 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.
#19
you will get it!!
i had multiple issues going on with my 86 brakes when i got it. took a while to sort out. they are awesome now. notwithstanding my abs wires are still cut by the po. brakes work very good though.
#20
Team Owner
Question. What do you have for the hose going from the metal lines to the calipers?